Hi all,
I have a database table that defines polymorphism and another table
that has a foreign key to the original.
And in formallity:
## defines the ResourceDB, and it's polymorphism speicfic kind FileDB
mapper
(ResourceDB,_resources_table,polymorphic_on=_resources_table.c.type,properties=
{
})
mapper(FileDB,_files_table,properties={
}, inherits=ResourceDB, polymorphic_identity="file")
## defines ObjectMarkingDB, that has an external foreign key pointing
to ResourceDB
mapper(ObjectMarkingDB,_object_markings_table,
properties={
"imageResourceId":_object_markings_table.c.image_resource_id,
"imageResource":relation
(ResourceDB,None,foreign_keys=_object_markings_table.c.image_resource_id,primaryjoin=_object_markings_table.c.image_resource_id==_resources_table.c.id,viewonly=True,uselist=False),#single_parent=True),
)
All is rather simple so far, the problem arises when i perform a query
with eager loading, for example:
session.query(ObjectMarkingDB).<filtering and so on>.options(eagerload
("imageResource"))
The sql query to perform the eager loading is horrible, more horrible
than anything i can imagine.
I managed to write my own sql statement that takes a fraction of the
time, the question is:
Lets say i have a collection of ResourceDB objects, how do i
internally connect them to the ObjectMarkingDB instances?
Or in other words: how do i implement my own eager loading for this
specific purpse?
And in formallity, lets say i have a collection of ResourceDBs and i
collection of ObjectMarkingDBs. how do i:
for every ResourceDb in ResourceDBs: connect ResourceDB to relevant
ObjectMarkingDB
Thanks in advance,
Mati
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