Provided by: libdbix-recordset-perl_0.26-3_all 
NAME
DBIx::Intrors - Embperl and DBIx::Recordset
Embperl and DBIx::Recordset
This introduction gives an overview how to use DBIx::Recordset together with
HTML::Embperl. Since there are only a few Embperl specific things herein, it should be
also useful for non Embperl users.
Overview
It is often very difficult to layout and design the output of normal CGI scripts, because
you are dealing with HTML-sourcecode which spans multiple prints, and it isn't possible
to use some sort of HTML-editor. Embperl takes a different approach to this problem.
With Embperl, you can build your HTML-pages with any tool you like, and you can embed
fragments of code directly in the page. This makes it much easier for non-programmers to
use, because they are able to use their usual tools and they see the fragments of code as
normal text. This indroduction will deal with the Perl Modules HTML::Embperl and
DBIx::Recordset, with a focus on database access.
Embperl
In brief, the purpose of Embperl is to execute code that is embedded in HTML-pages as the
page is requested from the server. There are two ways to do this with Embperl. The first
way is to embed the code between [- and -] tags. This will cause Embperl to execute the
code and remove it from the source before sending the page. The second way is to use [+
and +] as the delimiter, in which case the code will be executed and the result of the
execution is send to the browser in place of the code. All database access is done via
the module DBIx::Recordset, which simplifies a lot of common tasks when accessing a
database via DBI.
Basic Example
The following example shows the basic functions of both modules. It shows the contents of
a table whose name is passed as a parameter:
<body>
<h1>Contents of table "[+ $fdat{'!Table'} +]"</h1>
[-
use DBIx::Recordset ;
$fdat{'!DataSource'} = 'dbi:mysql:test' ;
*set = DBIx::Recordset -> Search(\%fdat) ;
$names = $set -> Names ;
-]
<table>
<tr>
<th>[+ $names -> [$col] +]</th>
</tr>
<tr>
[- $rec = $set[$row] -]
<td>[+ $rec -> {$names->[$col]} +]</td>
</tr>
</table>
</body>
To show the contents of the table "address" you may call it with:
http://www.domain.com/path/to/example1.htm?!Table=address
All query parameters are placed in the hash %fdat by Embperl. In our example,
$fdat{'!Table'} would contain the value "address". Additionally, Embperl replaces the
code between "[+" and "+]" with the result, so the headline of the page would be 'Contents
of table "address"'.
The following [- -] block will be executed by Embperl. No trace of it will show up in the
page that is sent to the browser. The first line sets the database which should be
accessed. The syntax is the same as for the DBI connect call. If you omit the line, you
must additionally send the databasename as a query parameter - but for security reasons,
that isn't a very good idea.
Search
Next we call the method "Search" of DBIx::Recordset, where we have the choice between the
object and the class-method. This applies to a lot of other methods as well. When we call
it as a class method, as we do in our example, it constructs a new DBIx::Recordset object
and uses the passed parameters to query the database. It's also possible to divide these
two steps and call "Setup" to first construct the object and then "Search" with this
object to execute the Search. In the example above, we do not pass any query parameters --
so "Search" will return the contents of the whole table. (DBIx::Recordset converts the
call internally to the SQL statement "SELECT * FROM address").
The last line of the [- -] block retrieves the fieldnames of the table. Here we can see a
special feature of DBIx::Recordset, which we will discuss in detail later on. The
constructor returns a typeglob (*set), but the call to "Names" uses a scalar ($set). By
returning a typeglob, DBIx::Recordset is able to return a scalar, an array and a hash at
the same time. (If you don't like the idea of using typeglobs, you can also construct all
three with different methods).
Display the table
At first glance, the following might appear to be a simple HTML-table. But Embperl expands
it, so that the full contents of the database table is shown. Let us first look at the
header, which should show the fieldnames of the database-table: $names contains a
reference to an array which contains the fieldnames. Embperl gives us the magical variable
$col. $col will be automatically incremented as long as the result of the expression which
contains $col doesn't return undefined. At the same time, Embperl repeats the surrounding
"<th"> or "<td"> tags. If we have a table with the three columns "name", "firstname" and
"town", the output would look like this:
<th>name</th><th>firstname</th><th>town</th>
Now the header is ready and we can start to output the contents. Here we use the array
part of the typeglob that is returned by "Search". Access to the results of the SQL-query
is done via the array @set, and every row of the array "contains" one row of the database-
table. It does not really contain the row, but DBIx::Recordset will fetch the row from the
databases for you if you access the corresponding array row. The rows are stored as a
hash, where the fieldnames are the hashkeys. This is the same mechanism that helped us to
expand the columns of the header, but it's at work here in a two-dimensional manner. $row
contains the row-count and $col contains the column-count.
Supplying query parameters
But our small example can do even more: If we supply more query parameters in our request,
we can decide which parts of the table should be selected (and therefor, shown). If we
request the page with
http://wwww.domain.com/path/to/example1.htm?!Table=address&town=Berlin
Embperl will not only place "!""T""able" in the hash %fdat, but also "town". Since "town"
corresponds to a fieldname in our table, DBIx::Recordset interprets it as a parameter for
the "WHERE" part of the "SELECT" command. DBIx::Recordset will generate the following SQL-
query:
SELECT * FROM address WHERE town='Berlin' ;
The programmer doesn't have to pay attention to datatypes or quoting, this is done
automatically by DBIx::Recordset.
Also, complex queries are easy to implement: if, for example, the user wants to be able
to search for a name or for a town, it would be possible to use the following form:
<form action="/path/to/example1.htm" method=GET >
<input type=text name="+name|town">
<input type=hidden name="!Table" value="address">
<input type=submit>
</form>
If the user enters "Richter" to the input field and presses the submit button, the
following SQL-query will be generated:
SELECT * FROM address WHERE name='Richter' OR town='Richter' ;
Just by varying the parameters, it is possible to create simple or complex queries. In
this way, you can use the same page with different parameters to create different sorts of
queries.
Multiple tables
Until now, we only have worked with one table. In real life, you often have to deal with
mulitple tables. For this reason, DBIx::Recordset helps you to reduce the expense
associated with dealing with multiple tables. The simplest way to do this is to use the
parameters "!TabJoin" and "!TabRelation" to tell DBIx::Recordset to create an SQL-join
between two or more tables. This will link the tables together and the result looks just
like one great table.
More interesting is the possibility to create "links". As an example, we'll take the same
table we used above and divide it into two tables: one table for the names and one table
for the towns. As a link we add an id-field. If the fields are following some naming
convention, DBIx::Recordset is able to find this link automatically. If fields are named
in another way, you have to tell DBIx::Recordset manually how the tables belong together.
Table name: firstname, name, town_id
Table town: id, town
Here, every name has exactly one town and every town has a number of names assigned. With
a simple modification of our first example, we could get the same result as above (except
that we are now dealing with two tables instead of one):
[-
use DBIx::Recordset ;
$db = DBIx::Database -> new ('dbi:mysql:test') ;
$db -> TableAttr ('town', '!NameField', 'town') ;
$fdat{'!DataSource'} = $db ;
$fdat{'!LinkName'} = 3 ;
*set = DBIx::Recordset -> Search(\%fdat) ;
$names = $set -> Names ;
-]
And the request would be:
http://www.domain.com/path/to/example2.htm?!Table=name
DBIx::Database
The new thing here is the "DBIx::Database" object. It gathers meta-information about the
database and stores it for later use. Because of the names of the fields the object can
detect that the field "town_id" in the table "name" points to field "id" in the table
"town". Additionally, we tell the "DBIx::Database" object which column(s) contain the
human-readable name of the table "town". These initialisations only have to be executed
once. If you use mod_perl, for example, you should be able to move these lines into a
common startup file.
Also new is the parameter "!LinkName". It tells DBIx::Recordset to return the human-
readable name (in our example, "town") instead of the field which links the two tables
together ("town_id" in our example). Internally, DBIx::Recordset generates an SQL-join, so
there is only one "SELECT" command necessary and the result is just the same as in the
last example.
Sub-Objects
But what to do if we have the "id" of a town and want to display all the names that
belongs to it? An Embperl-page that does this job might look something like this:
<body>
[-
use DBIx::Recordset ;
$fdat{'!DataSource'} = 'dbi:mysql:test' ;
$fdat{'!Table'} = 'town' ;
*set = DBIx::Recordset -> Search(\%fdat) ;
-]
town: [+ $set{town} +]<br>
<table>
<tr>
<th>name</th><th>firstname</th>
</tr>
<tr>
[- $rec = $set{-name}[$row] -]
<td>[+ $rec -> {name} +]</td><td>[+ $rec -> {firstname} +]</td>
</tr>
</table>
</body>
A request to that page might look like this:
http://www.domain.com/path/to/example3.htm?id=5
In this example, we specify the name of the table directly inside the page, so it can't be
overwritten from outside. The call to "Search" returns the town for the given query
parameters. In our example, it will select the town with the "id" 5. The command "[+
$set{town} +]" shows the value of the field town in the current record. After the call to
"Search", this is the first selected record. Next, we need to display all the names. This
is very easy using the special field "-name". "-name" contains a sub-object for the table
"name". The query parameters for this sub-object are set by DBIx::Recordset in such a way
that it contains all names which meet the link-condition. We just wrap it in a table and
we are already done.
Modify the Database
Up to this point, we have only discussed the retrieval and display of data. But of course
it's also possible to modify data. The simplest way to do this is to assign new values to
the result of a "Search" call. For example, you may write "$set{town} = 'Frankfurt'" to
change the name of the town. DBIx::Recordset converts this into a vaild SQL-Update-
command.
While this is very useful in normal Perl scripts, you probably won't use it very often in
a cgi script. The methods "Insert"/"Update"/"Delete" will probably prove more useful.
Just like "Search", these directly accept query parameters posted to the page. The method
"Execute" combines all four of these together, making it possible to control the type of
action via the CGI-parameters.
Here is an example:
<html> <head> <title>Database Access with HTML::Embperl and DBIx::Recordset</title>
</head> <body>
[-
### Database-parameter ###
use DBIx::Recordset ;
$fdat{'!DataSource'} = 'dbi:mysql:test' ;
$fdat{'!Table'} ||= 'town' ;
$fdat{'!PrimKey'} = 'id' ;
$fdat{'$max'} = 10 ;
### Execute action according to the query parameters ###
*set = DBIx::Recordset -> Execute (\%fdat) ;
-]
[$if $DBI::errstr $]
<h1>Database Error [+ $DBI::errstr +]</h1>
[$else$]
[-$names = $set -> AllNames ; -]
[$if $set[0] && $set -> MoreRecords $]
[### We found more then one record ###]
[### -> display as a table ###]
<table>
<tr> [### Display header ###]
<th>[+ ucfirst ($names -> [$col]) +]</th>
</tr>
<tr> [### Display record -> Table will be expanded by Embperl ###]
[- $rec = $set[$row] -]
<td>
[- $name = $names -> [$col] -]
[$if $name eq $fdat{'!PrimKey'} $]
[### Generate HTML link to edit this record ###]
<a href="example4.htm?!Table=[+ $fdat{'!Table'} +]&[+ $fdat{'!PrimKey'} +]=[+ $rec ->{$fdat{'!PrimKey'}} +]">[+ $rec -> {$name} +]</a>
[$elsif $set -> Link4Field($name) $]
[### Link to other table -> generate HTML link ###]
[- $link = $set -> Link($set -> Link4Field($name)) -]
<a href="example4.htm?!Table=[+ $link -> {'!Table'} +]&[+ $link -> {'!LinkedField'} +]=[+ $rec -> {$link -> {'!MainField'}} +]">[+$rec -> {$name}+]</a>
[$else$]
[### Display contents of field ###]
[+ $rec -> {$names->[$col]} +]
[$endif$]
</td>
</tr>
</table>
[+ $set -> PrevNextForm ('\<\<Prev', 'Next\>\>', \%fdat) +]
<hr>
<a href="example4.htm?!Table=[+ $fdat{'!Table'} +]&%3dempty=1">Search</a> record in table '[+ $fdat{'!Table'} +]'
[$else$]
[### We found no/one record(s) ###]
[### -> Display form ###]
<form>
<table>
<tr>
[- $name = $names -> [$row] -]
<td> [### Display fieldname ###]
[+ ucfirst ($name) +]
</td>
<td> [### Display content of field ###]
<input type=text name="[+ $name +]" value="[+ $set{$name} +]">
[$if $set -> Link4Field($name) $]
[### Link to other table -> generate HTML link ###]
[- $link = $set -> Link($set -> Link4Field($name)) -]
<a href="example4.htm?!Table=[+ $link -> {'!Table'} +]&[+ $link -> {'!LinkedField'} +]=[+ $set{$link -> {'!MainField'}} +]">Show record from table '[+ $link -> {'!Table'} +]'</a>
[$endif$]
</td>
</tr>
</table>
[### Buttons for the different actions, the "name" attribute determinates ###]
[### which action should be taken ###]
<input type=submit name="=search" value="Search">
<input type=submit name="=empty" value="New">
<input type=submit name="=insert" value="Add">
<input type=submit name="=update" value="Update">
<input type=submit name="=delete" value="Delete">
<input type=hidden name="!Table" value="[+ $fdat{'!Table'} +]">
</form>
[$endif$]
[$endif$]
</body>
</html>
When you first request this page, it will show the contents of the preset table.
Alternatively, you can supply a tablename with the parameter "!T""able". The link, which
is shown at the bottom of the page, leads you to an imput form. There, you can fill in one
or more fields and press the Search button. This invokes the page itself and "Execute"
will be instructed by the parameter "=s""earch" (Name of the button "Search") to retrieve
all records which match the entered values.
If the query finds more then one record, a table with all records found will be shown. If
there are more records than specified by the parameter $max, only $max records are
displayed. If this is the case, the "PrevNextForm" method adds a "Previous" and a "Next"
button to the page, allowing you to browse through the whole table. In the example above,
we assume that every table has a primary key, which is passed to DBIx::Recordset by the
line "$fdat{'!PrimKey'} = 'id' ;". The column which contains this primary key will be
displayed as an HTML link containing the parameters to execute a search for just this
record. As you can see in example4.htm, this can be used to display a form which includes
some of the data from the found record (see below). Columns which are links to other
tables will also be shown with an HTML-link. A click on that link will open the linked
table or record.
If the search only selects one record, the same form is shown, but with the data from the
record filled in. Now it's possible to change the content. The changes are written to the
database when you press the button Update (parameter "=update"). A new, empty form could
be shown with the button New (parameter "=empty") and if you have written data into this
empty form, you can add it as a new record with the Add button (parameter "=insert"). Last
but not least, there is a Delete button (parameter "=delete"). In all of these cases, the
content of the form is sent to the page itself, and the "Execute" method at the start of
the page executes the desired action.
More comments can be found inside the source ([# #] blocks).