I’m experimenting with the Doctrine ORM (v1.2) for PHP. I have defined a class “liquor”, with two child classes “gin” and “whiskey”. I am using concrete inheritance (class table inheritance in most literature) to map the classes to three seperate database tables.
I am attempting to execute the following:
$liquor_table = Doctrine_Core::getTable('liquor');
$liquors = $liquor_table->findAll();
Initially, I expected $liquors to be a Doctrine_Collection containing all liquors, whether they be whiskey or gin. But when I execute the code, I get a empty collection, despite having several rows in the whiskey and gin database tables. Based on the generated SQL, I understand why: the ORM is querying the “liquor” table, and not the whiskey/gin tables where the actual data is stored.
Note that the code works perfectly when I switch the inheritance type to column aggregation (simple table inheritance).
What’s the best way to obtain a Doctrine_Collection containing all liquors?
Update
After some more research, it looks like I’m expecting Doctrine to be performing a SQL UNION operation behind the scenes to combine the result sets from the “whiskey” and “gin” tables.
This is known as a polymorphic query.
According to this ticket, this functionality is not available in Doctrine 1.x. It is destined for the 2.0 release. (also see Doctrine 2.0 docs for CTI).
So in light of this information, what would be the cleanest, most efficient way to work around this deficiency? Switch to single table inheritance? Perform two DQL queries and manually merge the resulting Doctrine_Collections?
the only stable and useful inheritence mode of Doctrine for the moment is column_aggregation. I have tried the others in different projects. With column_aggregation you can imitate polymorphic queries.
Inheritance in general is something that is a bit buggy in Doctrine (1.x). With 2.x this will change, so we may have better options in the future.