oracular (3) UR::DataSource.3pm.gz
NAME
UR::DataSource - manage the the relationship between objects and a specific storage system
SYNOPSIS
package MyApp::DataSource::DB;
class MyApp::DataSource::DB {
is => ['UR::DataSource::Oracle','UR::Singleton'],
};
sub server { 'main_db_server' }
sub login { 'db_user' }
sub auth { 'db_passwd' }
sub owner { 'db_owner' }
1;
DESCRIPTION
Data source instances represent a logical source of data to the application. Most of them are likely to
be some kind of relational database, but not all are. UR::DataSource is an abstract base class inherited
by other data sources.
In normal use, your data sources will probably inherit from an abstract data source class such as
UR::DataSource::Oracle or UR::DataSource::File, as well as UR::Singleton. This makes it easy to link
classes to this data source, since the class name will be the same as its ID, and the module autoloader
will instantiate it automatically.
INHERITANCE
UR::Object
Methods
User applications will seldom interact with data sources directly.
autogenerate_new_object_id_for_class_name_and_rule
my $id = $datasource->autogenerate_new_object_id_for_class_name_and_rule($class,$boolexpr);
UR::Object::Type calls this when the application calls create() on a class to create a new instance,
but does not specify a value for the ID property. The default implementation throws an exception
with "die", but UR::DataSource::RDBMS is able to query a sequence in the database to generate unique
IDs. A developer implementing a new data source will need to override this method and provide a
sensible implementation.
next_dummy_autogenerated_id
my $int = $datasource->next_dummy_autogenerated_id()
In a testing situation, is often preferable to avoid using the database's sequence for ID
autogeneration but still make ID values that are unique. UR::DataSource::RDBMS calls this method if
the "use_dummy_autogenerated_ids" (see below) flag is true. The IDs generated by this method are
unique during the life of the process. In addition, objects with dummy-generated IDs will never be
saved to a real data source during UR::Context::commit().
use_dummy_autogenerated_ids
$bool = $datasource->use_dummy_autogenerated_ids();
$datasource->use_dummy_autogenerated_ids($bool);
Get or set a flag controlling how object IDs are autogenerated. Data source child classes should
look at the value of this flag inside their implementation of
"autogenerate_new_object_id_for_class_name_and_rule". If true, they should call
"next_dummy_autogenerated_id" and return that value instead of attempting to generate an ID on their
own. This flag is also tied to the UR_USE_DUMMY_AUTOGENERATED_IDS environment variable.
resolve_data_sources_for_rule
$possibly_other_data_source = $data_source->resolve_data_sources_for_rule($boolexpr);
When UR::Context is determining which data source to use to process a get() request, it looks at the
class metadata for its data source, and then calls "resolve_data_sources_for_rule" to give that data
source a chance to defer to another data source.
create_iterator_closure_for_rule_template_and_values
$subref = $datasource->create_iterator_closure_for_rule_template_and_values(
$boolexpr_tmpl,
@values
);
A front-end for the more widely used "create_iterator_closure_for_rule"
create_iterator_closure_for_rule
$subref = $datasource->create_iterator_closure_for_rule($boolexpr);
This is the main entry point UR::Context uses to get data from its underlying data sources. There is
no default implementation; each subclass implementing specific data source types must supply its own
code.
The method must accept a UR::BoolExpr $boolexpr (rule), and return a subref. Each time the subref is
called it must return one arrayref of data satisfying the rule, and undef when there is no more data
to return.
_sync_database
$bool = $datasource->_sync_database(changed_objects => $listref);
Called by UR::Context commit(). $listref will contain all the changed objects that should be saved
to that data source. The default implementation prints a warning message and returns true without
saving anything. UR::DataSource::RDBMS has a functioning _sync_database() capable of generating SQL
to update, insert and delete rows from the database's tables.
The data source should return true if all the changes were successfully made, false if there were
problems.
commit
$bool = $datasource->commit()
Called by UR::Context commit(). After all data sources return true from _sync_database(), "commit"
must make those changes permanent. For RDBMS-type data sources, this commits the transaction.
Return true if the commit is successful, false otherwise.
rollback
$bool = $datasource->rollback()
Called by "commit" in UR::Context if any data sources has problems during _sync_database or commit.
It is also called by "rollback" in UR::Context. Data sources should reverse any changes applied
during a prior "_sync_database" that has not been made permanent by "commit".
get_default_handle
$scalar = $datasource->get_default_handle();
Should return the "handle" associated with any underlying logical data. For an RDBMS data source,
this is the DBI database handle. For a file-based data source, this is the <IO::File> file handle.
create_from_inline_class_data
$datasource = $data_source_class_name->create_from_inline_class_data(
$class_data_hashref,
$datasource_data_hashref
);
Called by the class initializer when a class definition contains an in-line data source definition.
See "Inline Data Sources" in UR::Object::Type::Initializer.
_ignore_table
$bool = $datasource->_ignore_table($table_name);
Used to indicate whether the "ur update classes" command should create a class for the named table or
not. If _ignore_table() returns true, then it will not create a class.
Internal API Methods
_get_class_data_for_loading
_generate_class_data_for_loading
$hashref = $datasource->_resolve_query_plan($class_meta);
These two methods are called by UR::Context as part of the object loading process.
"_generate_class_data_for_loading" collects information about a class and its metadata, such as
property names, subclassing information and tables connected to the class, and stores that data
inside the class's metadata object.
"_get_class_data_for_loading" is the main entry point; it calls "_generate_class_data_for_loading" if
the data has not been generated and cached yet, and caches the data in the class metadata object.
_resolve_query_plan
_generate_template_data_for_loading
$hashref = $datasource->_resolve_query_plan($boolexpr_tmpl);
These two methods are called by UR::Context as part of the object loading process.
"_generate_template_data_for_loading" collects information from the UR::BoolExpr::Template
$boolexpr_tmpl (rule template) and returns a hashref used later by the data source. This hashref
includes hints about what classes will be involved in loading the resulting data, how those classes
are joined together and how columns in the underlying query against the data source will map to
properties of the class.
"_resolve_query_plan" is the main entry point; it calls "_generate_template_data_for_loading" if the
data has not been generated and cached yet, and caches the data in the rule template object.
_generate_loading_templates_arrayref
my $listref = $datasource->_generate_loading_templates_arrayref($listref);
Called by _generate_template_data_for_loading(). The input is a listref of listrefs about properties
involved in a query. The second-level data is sets of quads:
1. The class object for this property
2. The property metadata object
3. The database table name the data will come from
4 The "object number", starting with 0. This is used in inheritance or delegation where a table join
will be required.
It returns a listref of hashrefs, one hashref for every class involved in the request; usually just
1, but can be more than one if inheritance or delegation is involved. The data includes information
about the class's properties, ID properties, and which columns of the result set the values will be
found.
MetaDB
Each Namespace created through "ur define namespace" will have a data source called the MetaDB. For
example, the MyApp namespace's MetaDB is called MyApp::DataSource::Meta. The MetaDB is used to store
information about the schemas of other data sources in the database. UR itself has a MetaDB with
information about the MetaDB's schema, called UR::DataSource::Meta.
SEE ALSO
UR::DataSource::RDBMS
The base class for relational database Data Sources, such as UR::DataSource::Oracle,
UR::DataSoure::Pg, UR::DataSource::MySQL and UR::DataSource::SQLite
UR::DataSource::File,
The base class for comma/tab delimited files
UR::DataSource::FileMux
The base class for file multiplexor data sources.
UR::Context, UR::DataSource::Meta