Provided by: sqitch_0.9996-1_all bug

Name

       sqitchtutorial-sqlite - A tutorial introduction to Sqitch change management on SQLite

Synopsis

         sqitch *

Description

       This tutorial explains how to create a sqitch-enabled SQLite project, use a VCS for
       deployment planning, and work with other developers to make sure changes remain in sync
       and in the proper order.

       We'll start by creating new project from scratch, a fictional antisocial networking site
       called Flipr. All examples use Git <http://git-scm.com/> as the VCS and SQLite
       <http://www.sqlite.org/> as the storage engine.

       If you'd like to manage an PostgreSQL database, see sqitchtutorial.

       If you'd like to manage an Oracle database, see sqitchtutorial-oracle.

       If you'd like to manage an MySQL database, see sqitchtutorial-mysql.

       If you'd like to manage an Firebird database, see sqitchtutorial-firebird.

       If you'd like to manage an Vertica database, see sqitchtutorial-vertica.

Starting a New Project

       Usually the first thing to do when starting a new project is to create a source code
       repository. So let's do that with Git:

         > mkdir flipr
         > cd flipr
         > git init .
         Initialized empty Git repository in /flipr/.git/
         > touch README.md
         > git add .
         > git commit -m 'Initialize project, add README.'
         [master (root-commit) 253542e] Initialize project, add README.
          1 file changed, 37 insertions(+)
          create mode 100644 README.md

       If you're a Git user and want to follow along the history, the repository used in these
       examples is on GitHub <https://github.com/theory/sqitch-sqlite-intro>.

       Now that we have a repository, let's get started with Sqitch. Every Sqitch project must
       have a name associated with it, and, optionally, a unique URI. We recommend including the
       URI, as it increases the uniqueness of object identifiers internally, so let's specify one
       when we initialize Sqitch:

         > sqitch init flipr --uri https://github.com/theory/sqitch-sqlite-intro/ --engine sqlite
         Created sqitch.conf
         Created sqitch.plan
         Created deploy/
         Created revert/
         Created verify/

       Let's have a look at sqitch.conf:

         > cat sqitch.conf
         [core]
               engine = sqlite
               # plan_file = sqitch.plan
               # top_dir = .
         # [engine "sqlite"]
               # target = db:sqlite:
               # registry = sqitch
               # client = sqlite3

       Good, it picked up on the fact that we're creating changes for the SQLite engine, thanks
       to the "-engine sqlite" option, and saved it to the file.  Furthermore, it wrote a
       commented-out "[engine "sqlite"]" section with all the available SQLite engine-specific
       settings commented out and ready to be edited as appropriate.

       By default, Sqitch will read sqitch.conf in the current directory for settings. But it
       will also read ~/.sqitch/sqitch.conf for user-specific settings. Since SQLite's "sqlite3"
       client is not in the path on my system, let's go ahead an tell it where to find the client
       on our computer.

         > sqitch config --user engine.sqlite.client /opt/local/bin/sqlite3

       And let's also tell it who we are, since this data will be used in all of our projects:

         > sqitch config --user user.name 'Marge N. OXVera'
         > sqitch config --user user.email 'marge@example.com'

       Have a look at ~/.sqitch/sqitch.conf and you'll see this:

         > cat ~/.sqitch/sqitch.conf
         [engine "sqlite"]
               client = /opt/local/bin/sqlite3
         [user]
               name = Marge N. OXVera
               email = marge@example.com

       Which means that Sqitch should be able to find "sqlite3" for any project, and that it will
       always properly identify us when planning and committing changes.

       Back to the repository. Have a look at the plan file, sqitch.plan:

         > cat sqitch.plan
         %syntax-version=1.0.0
         %project=flipr
         %uri=https://github.com/theory/sqitch-sqlite-intro/

       Note that it has picked up on the name and URI of the app we're building.  Sqitch uses
       this data to manage cross-project dependencies. The "%syntax-version" pragma is always set
       by Sqitch, so that it always knows how to parse the plan, even if the format changes in
       the future.

       Let's commit these changes and start creating the database changes.

         > git add .
         > git commit -m 'Initialize Sqitch configuration.'
         [master 91e2f0d] Initialize Sqitch configuration.
          2 files changed, 19 insertions(+)
          create mode 100644 sqitch.conf
          create mode 100644 sqitch.plan

Our First Change

       Let's create a table. Our app will need users, of course, so we'll create a table for
       them. Run this command:

         > sqitch add users -n 'Creates table to track our users.'
         Created deploy/users.sql
         Created revert/users.sql
         Created verify/users.sql
         Added "users" to sqitch.plan

       The "add" command adds a database change to the plan and writes deploy, revert, and verify
       scripts that represent the change. Now we edit these files. The "deploy" script's job is
       to create the table. By default, the deploy/users.sql file looks like this:

         -- Deploy flipr:users to sqlite

         BEGIN;

         -- XXX Add DDLs here.

         COMMIT;

       What we want to do is to replace the "XXX" comment with the "CREATE TABLE" statement, like
       so:

         -- Deploy flipr:users to sqlite

         BEGIN;

         CREATE TABLE users (
                 nickname  TEXT      PRIMARY KEY,
                 password  TEXT      NOT NULL,
                 fullname  TEXT      NOT NULL,
                 twitter   TEXT      NOT NULL,
                 timestamp DATETIME  NOT NULL DEFAULT CURRENT_TIMESTAMP
         );

         COMMIT;

       The "revert" script's job is to precisely revert the change to the deploy script, so we
       edit this to revert/users.sql to look like this:

         -- Revert flipr:users from sqlite

         BEGIN;

         DROP TABLE users;

         COMMIT;

       Now we can try deploying this change:

         > sqitch deploy db:sqlite:flipr_test.db
         Adding registry tables to db:sqlite:sqitch.db
         Deploying changes to db:sqlite:flipr_test.db
           + users .. ok

       First Sqitch created the registry database and tables used to track database changes. The
       registry is separate from the database to which the "users" change was deployed; by
       default, its name is "sqitch.$suffix", where $suffix is the same as the suffix on the
       target database, if any. It lives in the same directory as the target database. This will
       be useful if you use the SQLite "ATTACHDATABASE" <http://www.sqlite.org/lang_attach.html>
       command to manage multiple database files in a single project. In that case, you will want
       to use the same file for all the databases. Keep them all in the same directory with the
       same suffix and you get just that with the default sqitch database.

       If you'd like it to have a different name for the registry database, use "sqitch engine
       add sqlite $name" to configure it (or via the "target" command; more below). This will be
       useful if you don't want to use the same registry database to manage multiple databases,
       or if you do, but they live in different directories.

       Next, Sqitch deploys changes to the target database, which we specified on the command-
       line. We only have one so far; the "+" reinforces the idea that the change is being added
       to the database.

       With this change deployed, if you connect to the database, you'll be able to see the
       schema:

               > sqlite3 flipr_test.db '.tables'
               users

   Trust, But Verify
       But that's too much work. do you really want to do something like that after every deploy?

       Here's where the "verify" script comes in. Its job is to test that the deploy did was it
       was supposed to. It should do so without regard to any data that might be in the database,
       and should throw an error if the deploy was not successful. The easiest way to do that
       with a table is to simply "SELECT" from it. Put this query into verify/users.sql:

         SELECT nickname, password, fullname, twitter
               FROM users
          WHERE 0;

       Now you can run the "verify" script with the "verify" command:

         > sqitch verify db:sqlite:flipr_test.db
         Verifying db:sqlite:flipr_test.db
               * users .. ok
         Verify successful

       Looks good! If you want to make sure that the verify script correctly dies if the table
       doesn't exist, temporarily change the table name in the script to something that doesn't
       exist, something like:

         SELECT nickname, password, timestamp
               FROM users_nonesuch
          WHERE 0;

       Then "verify" again:

         > sqitch verify db:sqlite:flipr_test.db
         Verifying db:sqlite:flipr_test.db
           * users .. Error: near line 5: no such table: users_nonesuch
         # Verify script "verify/users.sql" failed.
         not ok

         Verify Summary Report
         ---------------------
         Changes: 1
         Errors:  1
         Verify failed

       SQLite is kind enough to tell us what the problem is. Don't forget to change the table
       name back before continuing!

   Status, Revert, Log, Repeat
       For purely informational purposes, we can always see how a deployment was recorded via the
       "status" command, which reads the tables from the registry database:

         > sqitch status db:sqlite:flipr_test.db
         # On database db:sqlite:flipr_test.db
         # Project:  flipr
         # Change:   f30fe47f5f99501fb8d481e910d9112c5ac0a676
         # Name:     users
         # Deployed: 2013-12-31 10:26:59 -0800
         # By:       Marge N. OXVera <marge@example.com>
         #
         Nothing to deploy (up-to-date)

       Let's make sure that we can revert the change:

         > sqitch  revert db:sqlite:flipr_test.db
         Revert all changes from db:sqlite:flipr_test.db? [Yes]
               - users .. ok

       The "revert" command first prompts to make sure that we really do want to revert. This is
       to prevent unnecessary accidents. You can pass the "-y" option to disable the prompt.
       Also, notice the "-" before the change name in the output, which reinforces that the
       change is being removed from the database. And now the schema should be gone:

               > sqlite3 flipr_test.db '.tables'

       And the status message should reflect as much:

         > sqitch status db:sqlite:flipr_test.db
         # On database db:sqlite:flipr_test.db
         No changes deployed

       Of course, since nothing is deployed, the "verify" command has nothing to verify:

         > sqitch verify db:sqlite:flipr_test.db
         Verifying db:sqlite:flipr_test.db
         No changes deployed

       However, we still have a record that the change happened, visible via the "log" command:

         > sqitch log db:sqlite:flipr_test.db
         On database db:sqlite:flipr_test.db
         Revert f30fe47f5f99501fb8d481e910d9112c5ac0a676
         Name:      users
         Committer: Marge N. OXVera <marge@example.com>
         Date:      2013-12-31 10:53:25 -0800

             Creates table to track our users.

         Deploy f30fe47f5f99501fb8d481e910d9112c5ac0a676
         Name:      users
         Committer: Marge N. OXVera <marge@example.com>
         Date:      2013-12-31 10:26:59 -0800

             Creates table to track our users.

       Note that the actions we took are shown in reverse chronological order, with the revert
       first and then the deploy.

       Cool. Let's tell Git to ignore *.db files and then commit it.

         > echo '*.db' > .gitignore
         > git add .
         > git commit -m 'Add users table.'
         [master 6725454] Add users table.
          5 files changed, 31 insertions(+)
          create mode 100644 .gitignore
          create mode 100644 deploy/users.sql
          create mode 100644 revert/users.sql
          create mode 100644 verify/users.sql

       And then deploy again. This time, let's use the "--verify" option, so that the "verify"
       script is applied when the change is deployed:

         > sqitch deploy db:sqlite:flipr_test.db --verify
         Deploying changes to db:sqlite:flipr_test.db
               + users .. ok

       And now the "users" table should be back:

         > sqlite3 flipr_test.db '.tables'
         users

       When we look at the status, the deployment will be there:

         > sqitch status db:sqlite:flipr_test.db
         # On database db:sqlite:flipr_test.db
         # Project:  flipr
         # Change:   f30fe47f5f99501fb8d481e910d9112c5ac0a676
         # Name:     users
         # Deployed: 2013-12-31 10:57:55 -0800
         # By:       Marge N. OXVera <marge@example.com>
         #
         Nothing to deploy (up-to-date)

On Target

       I'm getting a little tired of always having to type "db:sqlite:flipr_test.db", aren't you?
       This database connection URI <https://github.com/theory/uri-db/> tells Sqitch how to
       connect to the deployment target, but we don't have to keep using the URI.  We can name
       the target:

         > sqitch target add flipr_test db:sqlite:flipr_test.db

       The "target" command, inspired by "git-remote" <http://git-scm.com/docs/git-remote>,
       allows management of one or more named deployment targets. We've just added a target named
       "flipr_test", which means we can use the string "flipr_test" for the target, rather than
       the URI. But since we're doing so much testing, we can also tell Sqitch to deploy to the
       "flipr_test" target by default:

         > sqitch engine add sqlite flipr_test

       Now we can omit the target argument altogether, unless we need to deploy to another
       database. Which we will, eventually, but at least our examples will be simpler from here
       on in, e.g.:

         > sqitch status
         # On database flipr_test
         # Project:  flipr
         # Change:   f30fe47f5f99501fb8d481e910d9112c5ac0a676
         # Name:     users
         # Deployed: 2013-12-31 10:57:55 -0800
         # By:       Marge N. OXVera <marge@example.com>
         #
         Nothing to deploy (up-to-date)

       Yay, that allows things to be a little more concise. Let's also make sure that changes are
       verified after deploying them:

         > sqitch config --bool deploy.verify true
         > sqitch config --bool rebase.verify true

       We'll see the "rebase" command a bit later. In the meantime, let's commit the new
       configuration and and make some more changes!

         > git commit -am 'Set default target and always verify.'
         [master 5fb57ec] Set default target and always verify.
          1 file changed, 8 insertions(+)

Deploy with Dependency

       Let's add another change. Our app will need to store status messages from users. Let's
       call them -- and the table to store them -- "flips". First, add the new change:

         > sqitch add flips --requires users -n 'Adds table for storing flips.'
         Created deploy/flips.sql
         Created revert/flips.sql
         Created verify/flips.sql
         Added "flips [users]" to sqitch.plan

       Note that we're requiring the "users" change as a dependency of the new "flips" change.
       Although that change has already been added to the plan and therefore should always be
       applied before the "flips" change, it's a good idea to be explicit about dependencies.

       Now edit the scripts. When you're done, deploy/flips.sql should look like this:

         -- Deploy flipr:flips to sqlite
         -- requires: users

         BEGIN;

         CREATE TABLE flips (
                 id        INTEGER   PRIMARY KEY AUTOINCREMENT,
                 nickname  TEXT      NOT NULL REFERENCES users(nickname),
                 body      TEXT      NOT NULL DEFAULT '' CHECK ( length(body) <= 180 ),
                 timestamp DATETIME  NOT NULL DEFAULT CURRENT_TIMESTAMP
         );

         COMMIT;

       A couple things to notice here. On the second line, the dependence on the "users" change
       has been listed. This doesn't do anything, but the default "deploy" template lists it here
       for your reference while editing the file.  Useful, right?

       The "users.nickname" column references the "users" table. This is why we need to require
       the "users" change.

       Now for the verify script. Again, all we need to do is "SELECT" from the table. I
       recommend selecting each column by name, too, to be sure that no column is missing. Here's
       the verify/flips.sql:

         -- Verify flipr:flips on sqlite

         BEGIN;

         SELECT id, nickname, body, timestamp
               FROM flips
          WHERE 0;

         ROLLBACK;

       Now for the revert script: all we have to do is drop the table. Add this to
       revert/flips.sql:

         -- Revert flipr:flips from sqlite

         BEGIN;

         DROP TABLE flips;

         COMMIT;

       Couldn't be much simpler, right? Let's deploy this bad boy:

         > sqitch deploy
         Deploying changes to flipr_test
               + flips .. ok

       We know, since verification is enabled, that the table must have been created.  But for
       the purposes of visibility, let's have a quick look:

         > sqlite3 flipr_test.db '.tables'
         flips  users

       We can also verify all currently deployed changes with the "verify" command:

         > sqitch verify
         Verifying flipr_test
               * users .. ok
               * flips .. ok
         Verify successful

       Now have a look at the status:

         > sqitch status
         # On database flipr_test
         # Project:  flipr
         # Change:   32ee57069c0d7fec52b6f86f453dc0c16bc1090a
         # Name:     flips
         # Deployed: 2013-12-31 11:02:51 -0800
         # By:       Marge N. OXVera <marge@example.com>
         #
         Nothing to deploy (up-to-date)

       Success! Let's make sure we can revert the change, as well:

         > sqitch revert --to @HEAD^ -y
         Reverting changes to users from flipr_test
           - flips .. ok

       Note that we've used the "--to" option to specify the change to revert to.  And what do we
       revert to? The symbolic tag @HEAD, when passed to "revert", always refers to the last
       change deployed to the database. (For other commands, it refers to the last change in the
       plan.)  Appending the caret ("^") tells Sqitch to select the change prior to the last
       deployed change. So we revert to "users", the penultimate change. The other potentially
       useful symbolic tag is @ROOT, which refers to the first change deployed to the database
       (or in the plan, depending on the command).

       Back to the database. The "flips" table should be gone but the "users" table should still
       be around:

         > sqlite3 flipr_test.db '.tables'
         users

       The "status" command politely informs us that we have undeployed changes:

         > sqitch status
         # On database flipr_test
         # Project:  flipr
         # Change:   f30fe47f5f99501fb8d481e910d9112c5ac0a676
         # Name:     users
         # Deployed: 2013-12-31 10:57:55 -0800
         # By:       Marge N. OXVera <marge@example.com>
         #
         Undeployed change:
           * flips

       As does the "verify" command:

         > sqitch verify
         Verifying flipr_test
           * users .. ok
         Undeployed change:
           * flips
         Verify successful

       Note that the verify is successful, because all currently-deployed changes are verified.
       The list of undeployed changes (just "flips" here) reminds us about the current state.

       Okay, let's commit and deploy again:

         > git add .
         > git commit -am 'Add flips table.'
         [master 21cba95] Add flips table.
          4 files changed, 30 insertions(+)
          create mode 100644 deploy/flips.sql
          create mode 100644 revert/flips.sql
          create mode 100644 verify/flips.sql
         > sqitch deploy
         Deploying changes to flipr_test
           + flips .. ok

       Looks good. Check the status:

         > sqitch status
         # On database flipr_test
         # Project:  flipr
         # Change:   32ee57069c0d7fec52b6f86f453dc0c16bc1090a
         # Name:     flips
         # Deployed: 2013-12-31 11:05:44 -0800
         # By:       Marge N. OXVera <marge@example.com>
         #
         Nothing to deploy (up-to-date)

View to a Thrill

       One more thing to add before we are ready to ship a first beta release. Let's create a
       view that lists user names with their flips.

         > sqitch add userflips --requires users --requires flips \
               -n 'Creates the userflips view.'
         Created deploy/userflips.sql
         Created revert/userflips.sql
         Created verify/userflips.sql
         Added "userflips [users flips]" to sqitch.plan

       Now add this SQL to deploy/userflips.sql:

         CREATE VIEW userflips AS
         SELECT f.id, u.nickname, u.fullname, f.body, f.timestamp
               FROM users u
               JOIN flips f ON u.nickname = f.nickname;

       Add this SQL to verify/userflips.sql

         SELECT id, nickname, fullname, body, timestamp
               FROM userflips
          WHERE 0;

       And add the "DROP VIEW" statement to revert/userflips.sql:

         DROP VIEW userflips;

       Now Try it out!

         > sqitch deploy
         Deploying changes to flipr_test
           + userflips .. ok
         > sqitch revert -y
         Reverting all changes from flipr_test
           - userflips .. ok
           - flips ...... ok
           - users ...... ok
         > sqitch deploy
         Deploying changes to flipr_test
           + users ...... ok
           + flips ...... ok
           + userflips .. ok

       Looks good! Commit it.

         > git add .
         > git commit -m 'Add the userflips view.'
         [master c74bfb4] Add the userflips view.
          4 files changed, 29 insertions(+)
          create mode 100644 deploy/userflips.sql
          create mode 100644 revert/userflips.sql
          create mode 100644 verify/userflips.sql

Ship It!

       Now we're ready for the first development release of our app. Let's call it "1.0.0-dev1"
       Since we want to have it go out with deployments tied to the release, let's tag it:

         > sqitch tag v1.0.0-dev1 -n 'Tag v1.0.0-dev1.'
         Tagged "userflips" with @v1.0.0-dev1
         > git commit -am 'Tag the database with v1.0.0-dev1.'
         [master 7a479fd] Tag the database with v1.0.0-dev1.
          1 file changed, 1 insertion(+)
         > git tag v1.0.0-dev1 -am 'Tag v1.0.0-dev1'

       We can try deploying to make sure the tag gets picked up like so:

         > mkdir dev
         > sqitch deploy db:sqlite:dev/flipr.db
         Adding registry tables to db:sqlite:dev/sqitch.db
         Deploying changes to db:sqlite:dev/flipr.db
           + users ................... ok
           + flips ................... ok

       Great, both changes were deployed and "userflips" was tagged with "@v1.0.0-dev1". Let's
       have a look at the status:

         > sqitch status db:sqlite:dev/flipr_dev.db
         # On database db:sqlite:dev/flipr_dev.db
         # Project:  flipr
         # Change:   60ee3aba0445bf3287f9dc1dd97b1877523fa139
         # Name:     userflips
         # Tag:      @v1.0.0-dev1
         # Deployed: 2013-12-31 11:19:15 -0800
         # By:       Marge N. OXVera <marge@example.com>
         #
         Nothing to deploy (up-to-date)

       Note the listing of the tag as part of the status message. Now let's bundle everything up
       for release:

         > rm -rf dev
         > sqitch bundle
         Bundling into bundle
         Writing config
         Writing plan
         Writing scripts
               + users
               + flips
               + userflips @v1.0.0-dev1

       Now we can package the bundle directory and distribute it. When it gets installed
       somewhere, users can use Sqitch to deploy to the database. Let's try deploying it:

         > cd bundle
         > sqitch deploy db:sqlite:flipr_prod.db
         Adding registry tables to db:sqlite:sqitch.db
         Deploying changes to db:sqlite:flipr_prod.db
           + users ................... ok
           + flips ................... ok
           + userflips @v1.0.0-dev1 .. ok

       Looks much the same as before, eh? Package it up and ship it!

         > rm *.db
         > cd ..
         > mv bundle flipr-v1.0.0-dev1
         > tar -czf flipr-v1.0.0-dev1.tgz flipr-v1.0.0-dev1

Making a Hash of Things

       Now that we've got the basics of the app done, let's add a feature. Gotta track the
       hashtags associated with flips, right? Let's add a table for them.  But since other folks
       are working on other tasks in the repository, we'll work on a branch, so we can all stay
       out of each other's way. So let's branch:

         > git checkout -b hashtags
         Switched to a new branch 'hashtags'

       Now we can add a new change to create a table for hashtags.

         > sqitch add hashtags --requires flips -n 'Adds table for storing hashtags.'
         Created deploy/hashtags.sql
         Created revert/hashtags.sql
         Created verify/hashtags.sql
         Added "hashtags [flips]" to sqitch.plan

       You know the drill by now. Add this to deploy/hashtags.sql

         CREATE TABLE hashtags (
                 flip_id   INTEGER   NOT NULL REFERENCES flips(id),
                 hashtag   TEXT      NOT NULL CHECK ( length(hashtag) > 0 ),
                 PRIMARY KEY (flip_id, hashtag)
         );

       Again, select from the table in verify/hashtags.sql:

         SELECT flip_id, hashtag FROM hashtags WHERE 0;

       And drop it in revert/hashtags.sql

         DROP TABLE hashtags;

       And give it a whirl:

         > sqitch deploy
         Deploying changes to flipr_test
               + hashtags .. ok

       Look good?

         > sqitch status --show-tags
         # On database flipr_test
         # Project:  flipr
         # Change:   1352464e8b5f3d5eeac76a1986379f07de43bffd
         # Name:     hashtags
         # Deployed: 2013-12-31 11:30:53 -0800
         # By:       Marge N. OXVera <marge@example.com>
         #
         # Tag:
         #   @v1.0.0-dev1 - 2013-12-31 11:13:49 -0800 - Marge N. OXVera <marge@example.com>
         #
         Nothing to deploy (up-to-date)

       Note the use of "--show tags" to show all the deployed tags. Make sure we can revert, too:

         > sqitch revert --to @HEAD^ -y
         Reverting changes to userflips @v1.0.0-dev1 from flipr_test
           - hashtags .. ok
         > sqitch deploy
         Deploying changes to flipr_test
               + hashtags .. ok

       Great! Now make it so:

         > git add .
         > git commit -m 'Add hashtags table.'
         [hashtags 94f02b8] Add hashtags table.
          4 files changed, 28 insertions(+)
          create mode 100644 deploy/hashtags.sql
          create mode 100644 revert/hashtags.sql
          create mode 100644 verify/hashtags.sql

       Good, we've finished this feature. Time to merge back into "master".

   Emergency
       Let's do it:

         > git checkout master
         Switched to branch 'master'
         > git pull
         Updating 7a479fd..47a4107
         Fast-forward
          deploy/lists.sql | 13 +++++++++++++
          revert/lists.sql |  7 +++++++
          sqitch.plan      |  2 ++
          verify/lists.sql |  9 +++++++++
          4 files changed, 31 insertions(+)
          create mode 100644 deploy/lists.sql
          create mode 100644 revert/lists.sql
          create mode 100644 verify/lists.sql

       Hrm, that's interesting. Looks like someone made some changes to "master".  They added
       list support. Well, let's see what happens when we merge our changes.

         > git merge --no-ff hashtags
         Auto-merging sqitch.plan
         CONFLICT (content): Merge conflict in sqitch.plan
         Automatic merge failed; fix conflicts and then commit the result.

       Oh, a conflict in sqitch.plan. Not too surprising, since both the merged "lists" branch
       and our "hashtags" branch added changes to the plan. Let's try a different approach.

       The truth is, we got lazy. Those changes when we pulled master from the origin should have
       raised a red flag. It's considered a bad practice not to look at what's changed in
       "master" before merging in a branch. What one should do is either:

       •   Rebase the hashtags branch from master before merging. This "rewinds" the branch
           changes, pulls from "master", and then replays the changes back on top of the pulled
           changes.

       •   Create a patch and apply that to master. This is the sort of thing you might have to
           do if you're sending changes to another user, especially if the VCS is not Git.

       So let's restore things to how they were at master:

         > git reset --hard HEAD
         HEAD is now at 47a4107 Merge branch 'lists'

       That throws out our botched merge. Now let's go back to our branch and rebase it on
       "master":

         > git checkout hashtags
         Switched to branch 'hashtags'
         > git rebase master
         First, rewinding head to replay your work on top of it...
         Applying: Add hashtags table.
         Using index info to reconstruct a base tree...
         M     sqitch.plan
         Falling back to patching base and 3-way merge...
         Auto-merging sqitch.plan
         CONFLICT (content): Merge conflict in sqitch.plan
         Failed to merge in the changes.
         Patch failed at 0001 Add hashtags table.
         The copy of the patch that failed is found in:
            .git/rebase-apply/patch

         When you have resolved this problem, run "git rebase --continue".
         If you prefer to skip this patch, run "git rebase --skip" instead.
         To check out the original branch and stop rebasing, run "git rebase --abort".

       Oy, that's kind of a pain. It seems like no matter what we do, we'll need to resolve
       conflicts in that file. Except in Git. Fortunately for us, we can tell Git to resolve
       conflicts in sqitch.plan differently. Because we only ever append lines to the file, we
       can have it use the "union" merge driver, which, according to its docs <http://git-
       scm.com/docs/gitattributes#_built-in_merge_drivers>:

           Run 3-way file level merge for text files, but take lines from both versions, instead
           of leaving conflict markers. This tends to leave the added lines in the resulting file
           in random order and the user should verify the result. Do not use this if you do not
           understand the implications.

       This has the effect of appending lines from all the merging files, which is exactly what
       we need. So let's give it a try. First, back out the botched rebase:

         > git rebase --abort

       Now add the union merge driver to .gitattributes for sqitch.plan and rebase again:

         > echo sqitch.plan merge=union > .gitattributes
         > git rebase master
         First, rewinding head to replay your work on top of it...
         Applying: Add hashtags table.
         Using index info to reconstruct a base tree...
         M     sqitch.plan
         Falling back to patching base and 3-way merge...
         Auto-merging sqitch.plan

       Ah, that looks a bit better. Let's have a look at the plan:

         > cat sqitch.plan
         %syntax-version=1.0.0
         %project=flipr
         %uri=https://github.com/theory/sqitch-sqlite-intro/

         users 2013-12-31T18:06:04Z Marge N. OXVera <marge@example.com> # Creates table to track our users.
         flips [users] 2013-12-31T19:01:40Z Marge N. OXVera <marge@example.com> # Adds table for storing flips.
         userflips [users flips] 2013-12-31T19:11:11Z Marge N. OXVera <marge@example.com> # Creates the userflips view.
         @v1.0.0-dev1 2013-12-31T19:13:02Z Marge N. OXVera <marge@example.com> # Tag v1.0.0-dev1.

         lists [users] 2013-12-31T19:28:05Z Marge N. OXVera <marge@example.com> # Adds table for storing lists.
         hashtags [flips] 2013-12-31T19:30:13Z Marge N. OXVera <marge@example.com> # Adds table for storing hashtags.

       Note that it has appended the changes from the merged "lists" branch, and then merged the
       changes from our "hashtags" branch. Test it to make sure it works as expected:

         > sqitch rebase -y
         Reverting all changes from flipr_test
           - hashtags ................ ok
           - userflips @v1.0.0-dev1 .. ok
           - flips ................... ok
           - users ................... ok
         Deploying changes to flipr_test
           + users ................... ok
           + flips ................... ok
           + userflips @v1.0.0-dev1 .. ok
           + lists ................... ok
           + hashtags ................ ok

       Note the use of "rebase", which combines a "revert" and a "deploy" into a single command.
       Handy, right? It correctly reverted our changes, and then deployed them all again in the
       proper order. So let's commit .gitattributes; seems worthwhile to keep that change:

         > git add .
         > git commit -m 'Add `.gitattributes` with union merge for `sqitch.plan`.'
         [hashtags 4f93ac4] Add `.gitattributes` with union merge for `sqitch.plan`.
          1 file changed, 1 insertion(+)
          create mode 100644 .gitattributes

   Merges Mastered
       And now, finally, we can merge into "master":

         > git checkout master
         Switched to branch 'master'
         > git merge --no-ff hashtags -m "Merge branch 'hashtags'"
         Merge made by the 'recursive' strategy.
          .gitattributes      |  1 +
          deploy/hashtags.sql | 12 ++++++++++++
          revert/hashtags.sql |  7 +++++++
          sqitch.plan         |  1 +
          verify/hashtags.sql |  7 +++++++
          5 files changed, 28 insertions(+)
          create mode 100644 .gitattributes
          create mode 100644 deploy/hashtags.sql
          create mode 100644 revert/hashtags.sql
          create mode 100644 verify/hashtags.sql

       And double-check our work:

         > cat sqitch.plan
         %syntax-version=1.0.0
         %project=flipr
         %uri=https://github.com/theory/sqitch-sqlite-intro/

         users 2013-12-31T18:06:04Z Marge N. OXVera <marge@example.com> # Creates table to track our users.
         flips [users] 2013-12-31T19:01:40Z Marge N. OXVera <marge@example.com> # Adds table for storing flips.
         userflips [users flips] 2013-12-31T19:11:11Z Marge N. OXVera <marge@example.com> # Creates the userflips view.
         @v1.0.0-dev1 2013-12-31T19:13:02Z Marge N. OXVera <marge@example.com> # Tag v1.0.0-dev1.

         lists [users] 2013-12-31T19:28:05Z Marge N. OXVera <marge@example.com> # Adds table for storing lists.
         hashtags [flips] 2013-12-31T19:30:13Z Marge N. OXVera <marge@example.com> # Adds table for storing hashtags.

       Much much better, a nice clean master now. And because it is now identical to the
       "hashtags" branch, we can just carry on. Go ahead and tag it, bundle, and release:

         > sqitch tag v1.0.0-dev2 -n 'Tag v1.0.0-dev2.'
         Tagged "hashtags" with @v1.0.0-dev2
         > git commit -am 'Tag the database with v1.0.0-dev2.'
         [master 7abfd9b] Tag the database with v1.0.0-dev2.
          1 file changed, 1 insertion(+)
         > git tag v1.0.0-dev2 -am 'Tag v1.0.0-dev2'
         > sqitch bundle --dest-dir flipr-1.0.0-dev2
         Bundling into flipr-1.0.0-dev2
         Writing config
         Writing plan
         Writing scripts
           + users
           + flips
           + userflips @v1.0.0-dev1
           + lists
           + hashtags @v1.0.0-dev2

       Note the use of the "--dest-dir" option to "sqitch bundle". Just a nicer way to create the
       top-level directory name so we don't have to rename it from bundle.

In Place Changes

       Well, some folks have been testing the "1.0.0-dev2" release and have demanded that Twitter
       user links be added to Flipr pages. Why anyone would want to include social network links
       in an anti-social networking app is beyond us programmers, but we're just the plumbers,
       right? Gotta go with what Product demands. The upshot is that we need to update the
       "userflips" view, which is used for the feature in question, to include the Twitter user
       names.

       Normally, modifying views in database changes is a PITA
       <http://www.urbandictionary.com/define.php?term=pita>. You have to make changes like
       these:

       1.  Copy deploy/userflips.sql to deploy/userflips_twitter.sql.

       2.  Edit deploy/userflips_twitter.sql to drop and re-create the view with the "twitter"
           column to the view.

       3.  Copy deploy/userflips.sql to revert/userflips_twitter.sql.  Yes, copy the original
           change script to the new revert change.

       4.  Add a "DROP VIEW" statement to revert/userflips_twitter.sql.

       5.  Copy verify/userflips.sql to verify/userflips_twitter.sql.

       6.  Modify verify/userflips_twitter.sql to include a check for the "twiter" column.

       7.  Test the changes to make sure you can deploy and revert the "userflips_twitter"
           change.

       But you can have Sqitch do most of the work for you. The only requirement is that a tag
       appear between the two instances of a change we want to modify. In general, you're going
       to make a change like this after a release, which you've tagged anyway, right? Well we
       have, with "@v1.0.0-dev2" added in the previous section. With that, we can let Sqitch do
       most of the hard work for us, thanks to the "rework" command, which is similar to "add":

         > sqitch rework userflips -n 'Adds userflips.twitter.'
         Added "userflips [userflips@v1.0.0-dev2]" to sqitch.plan.
         Modify these files as appropriate:
               * deploy/userflips.sql
               * revert/userflips.sql
               * verify/userflips.sql

       Oh, so we can edit those files in place. Nice! How does Sqitch do it? Well, in point of
       fact, it has copied the files to stand in for the previous instance of the "userflips"
       change, which we can see via "git status":

         > git status
         # On branch master
         # Your branch is ahead of 'origin/master' by 4 commits.
         #   (use "git push" to publish your local commits)
         #
         # Changes not staged for commit:
         #   (use "git add <file>..." to update what will be committed)
         #   (use "git checkout -- <file>..." to discard changes in working directory)
         #
         #     modified:   revert/userflips.sql
         #     modified:   sqitch.plan
         #
         # Untracked files:
         #   (use "git add <file>..." to include in what will be committed)
         #
         #     deploy/userflips@v1.0.0-dev2.sql
         #     revert/userflips@v1.0.0-dev2.sql
         #     verify/userflips@v1.0.0-dev2.sql
         no changes added to commit (use "git add" and/or "git commit -a")

       The "untracked files" part of the output is the first thing to notice. They are all named
       "userflips@v1.0.0-dev2.sql". What that means is: "the "userflips" change as it was
       implemented as of the "@v1.0.0-dev2" tag."  These are copies of the original scripts, and
       thereafter Sqitch will find them when it needs to run scripts for the first instance of
       the "userflips" change. As such, it's important not to change them again. But hey, if
       you're reworking the change, you shouldn't need to.

       The other thing to notice is that revert/userflips.sql has changed. Sqitch replaced it
       with the original deploy script. As of now, deploy/userflips.sql and revert/userflips.sql
       are identical. This is on the assumption that the deploy script will be changed (we're
       reworking it, remember?), and that the revert script should actually change things back to
       how they were before. Of course, the original deploy script won't be idempotent
       <http://en.wikipedia.org/wiki/Idempotence> -- that is, able to be applied multiple times
       without changing the result beyond the initial application. It could be if SQLite
       supported "CREATE OR REPLACE VIEW", but since it doesn't, we will have to edit the script
       to drop the view before creating it. Or, more simply, it needs to be updated to revert
       changes back to how they were as-of the deployment of deploy/userflips@v1.0.0-dev2.sql.

       Modify deploy/userflips.sql to add the "twitter" column; in fact, let's also add a "DROP
       VIEW IF EXISTS" statement, in case we need to rework this change again in the future:

         @@ -4,8 +4,9 @@

          BEGIN;

         +DROP VIEW IF EXISTS userflips;
          CREATE VIEW userflips AS
         -SELECT f.id, u.nickname, u.fullname, f.body, f.timestamp
         +SELECT f.id, u.nickname, u.fullname, u.twitter, f.body, f.timestamp
            FROM users u
            JOIN flips f ON u.nickname = f.nickname;

       Next, modify verify/userflips.sql to check for the "twitter" column.  Here's the diff:

         @@ -2,7 +2,7 @@

          BEGIN;

         -SELECT id, nickname, fullname, body, timestamp
         +SELECT id, nickname, fullname, twitter, body, timestamp
            FROM userflips
           WHERE 0;

       And finally, modify revert/userflips@v1.0.0-dev2.sql to drop the view before creating it:

         @@ -4,6 +4,7 @@

          BEGIN;

         +DROP VIEW IF EXISTS userflips;
          CREATE VIEW userflips AS
          SELECT f.id, u.nickname, u.fullname, f.body, f.timestamp
            FROM users u

       Note that if we had included that statement when we originally created the "userflips"
       change, we wouldn't have to change this file at all.

       Now try a deployment:

         > sqitch deploy
         Deploying changes to flipr_test
               + userflips .. ok

       So, are the changes deployed?

         > sqlite3 flipr_test.db '.schema userflips'
         CREATE VIEW userflips AS
         SELECT f.id, u.nickname, u.fullname, u.twitter, f.body, f.timestamp
           FROM users u
           JOIN flips f ON u.nickname = f.nickname;

       Awesome, the view now includes the "twitter" column. But can we revert?

         > sqitch revert --to @HEAD^ -y
         Reverting changes to hashtags @v1.0.0-dev2 from flipr_test
               - userflips .. ok

       Did that work, is the "twitter" column gone?

         > sqlite3 flipr_test.db '.schema userflips'
         CREATE VIEW userflips AS
         SELECT f.id, u.nickname, u.fullname, f.body, f.timestamp
               FROM users u
               JOIN flips f ON u.nickname = f.nickname;

       Yes, it works! Sqitch properly finds the original instances of these changes in the new
       script files that include tags.

       Excellent. Let's go ahead and commit these changes:

         > git add .
         > git commit -m 'Add the twitter column to the userflips view.'
         [master 3eb96d9] Add the twitter column to the userflips view.
          7 files changed, 40 insertions(+), 4 deletions(-)
          create mode 100644 deploy/userflips@v1.0.0-dev2.sql
          create mode 100644 revert/userflips@v1.0.0-dev2.sql
          create mode 100644 verify/userflips@v1.0.0-dev2.sql

More to Come

       Sqitch is a work in progress. Better integration with version control systems is planned
       to make managing idempotent reworkings even easier. Stay tuned.

Author

       David E. Wheeler <david@justatheory.com>

License

       Copyright (c) 2012-2015 iovation Inc.

       Permission is hereby granted, free of charge, to any person obtaining a copy of this
       software and associated documentation files (the "Software"), to deal in the Software
       without restriction, including without limitation the rights to use, copy, modify, merge,
       publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
       to whom the Software is furnished to do so, subject to the following conditions:

       The above copyright notice and this permission notice shall be included in all copies or
       substantial portions of the Software.

       THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
       INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
       PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
       FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
       OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
       DEALINGS IN THE SOFTWARE.