NAME¶
UR::Context::ObjectFabricator - Track closures used to fabricate objects from
data sources
DESCRIPTION¶
Object Fabricators are closures that accept listrefs of data returned by data
source iterators, take slices out of them, and construct UR objects out of the
results. They also handle updating the query cache and merging changed DB data
with previously cached objects.
UR::Context::ObjectFabricator objects are used internally by UR::Context, and
not intended to be used directly.
METHODS¶
- create_for_loading_template
-
my $fab = UR::Context::ObjectFabricator->create_for_loading_template(
$context, $loading_tmpl_hashref, $template_data,
$rule, $rule_template, $values, $dsx);
Returns an object fabricator instance that is able to construct objects of
the rule's target class from rows of data returned by data source
iterators. Object fabricators are used a part of the object loading
process, and are called by
UR::Context::get_objects_for_class_and_rule() to transform a row of
data returned by a data source iterator into a UR object.
For each class involved in a get request, the system prepares a loading
template that describes which columns of the data source data are to be
used to construct an instance of that class. For example, in the case
where a get() is done on a child class, and the parent and child
classes store data in separate tables linked by a
relation-property/foreign-key, then the query against the data source will
involve and SQL join (for RDBMS data sources). That join will produce a
result set that includes data from both tables.
The $loading_tmpl_hashref will have information about which columns of that
result set map to which properties of each involved class. The heart of
the fabricator closure is a list slice extracting the data for that class
and assigning it to a hash slice of properties to fill in the initial
object data for its class. The remainder of the closure is bookkeeping to
keep the object cache ($UR::Context::all_objects_loaded) and query cache
($UR::Context::all_params_loaded) consistent.
The interaction of the object fabricator, the query cache, object cache
pruner and object loading iterators that may or may not have loaded all
their data requires that the object fabricators keep a list of changes
they plan to make to the query cache instead of applying them directly.
When the Underlying Context Loading iterator has loaded the last row from
the Data Source Iterator, it calls "finalize()" on the object
fabricator to tell it to go ahead and apply its changes; essentially
treating that data as a transaction.
- all_object_fabricators
-
my @fabs = UR::Context::ObjectFabricator->all_object_fabricators();
Returns a list of all object fabricators that have not yet been
finalized
- fabricate
-
my $ur_object = $fab->fabricate([columns,from,data,source]);
Given a listref of data pulled from a data source iterator, it slices out
the appropriate columns from the list and constructs a single object to
return.
- is_loading_in_progress_for_boolexpr
-
my $bool = $fab->is_loading_in_progress_for_boolexpr($boolexpr);
Given a UR::BoolExpr instance, it returns true if the given fabricator is
prepared to construct objects matching this boolexpr. This is used by
UR::Context to know if other iterators are still pulling in objects that
could match another iterator's boolexpr, and it should therefore not trust
that the object cache is conplete.
- finalize
-
$fab->finalize();
Indicates to the iterator that the caller is done using it for constructing
objects, probably because the data source has no more data or the iterator
that was using this fabricator has gone out of scope.
- apply_all_params_loaded
-
$fab->apply_all_params_loaded();
As the fabricator constructs objects, it buffers changes to
all_params_loaded (the Context's query cache) to maintain consistency if
multiple iterators are working concurrently. At the appripriate time, call
apply_all_params_loaded() to take those changes and apply them to
the current Context's all_params_loaded.