Failing test case to show that habtm join table contents are removed when a model is destroyed but the destruction is blocked by a before_destroy.

The test fails on PostgreSQL when trying to load the records as
the comments_count field is not included in the GROUP BY clause.

[#5829 state:resolved]
Signed-off-by: NAndrew White <andyw@pixeltrix.co.uk>

Fix tests under postgres - we should always put conditions in the WHERE part not in ON constraints because postgres requires that the table has been joined before the condition references it.

Rename Reflection#through_reflection_chain and #through_options to Reflection#chain and Reflection#options as they now no longer relate solely to through associations.

Referencing a table via the ON condition in a join should force that table to be eager-loaded via a JOIN rather than via subsequent queries.

Referencing a table via the ON condition in a join should force that table to be eager-loaded via a JOIN rather than via subsequent queries.

Push source_type and polymorphic conditions out of ThroughAssociation and JoinDependency::JoinAssociation and into the reflection instead.

Add a test for STI on the through where the through is nested, and change the code which support this

implements ActiveRecord::Base.connection_config to be able to check the configuration of the current connection at runtime

When preloading has_and_belongs_to_many associations, we should only instantiate one AR object per actual record in the database. (Even when IM is off.)

When preloading has_and_belongs_to_many associations, we should only instantiate one AR object per actual record in the database. (Even when IM is off.)

observers leak across tests, so rather than modify the object, we should just count the number of times the observer was called

Use proper objects to do the work to build the associations (adding methods, callbacks etc) rather than calling a whole bunch of methods with rather long names.

Remove test which was broken on 1.8. This test is now irrelevant since singular associations no longer return a proxy object.