#32190: Support for model relationships defined pre-save
-------------------------------------+-------------------------------------
Reporter: Ryan | Owner: nobody
Vinzent |
Type: New | Status: new
feature |
Component: Database | Version: 3.1
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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There are many situations where it is optimal to define a bunch of
objects, and then later commit them in bulk. When the objects define a FK
relationship, this strategy requires a bit of hacking that I would prefer
not to do. Take the following example:
{{{#!python
class Parent(models.Model):
name = models.TextField()
class Child(models.Model):
name = models.TextField()
parent = models.ForeignKey(Parent, on_delete=models.RESTRICT)
}}}
Now if we have some function that defines a bunch of these objects to
later commit them in bulk:
{{{#!python
def build_objects(parent_child_mapping):
parents = []
children = []
# {"father": ["son", "daughter"], ...}
for parent_name, child_names in parent_child_mapping.items():
parent = Parent(name=parent_name)
parents.append(parent)
children.extend(Child(parent=parent, name=child_name) for
child_name in child_names)
# now commit all objects in bulk
Parent.objects.bulk_create(parents)
# fails with IntegrityError: parent_id is not nullable
Child.objects.bulk_create(children)
}}}
I would expect the above to work fine, given the parent ID's are known
when inserting the children, however this would throw an `IntegrityError`
because `parent_id` on the `Child` objects is still `None`.
Adding a simple hack to the function will let it work fine, but it's
annoying to do this ''everywhere'' where this pattern of creating objects
is followed.
{{{#!python
def build_objects(parent_child_mapping):
parents = []
children = []
for parent_name, child_names in parent_child_mapping.items():
parent = Parent(name=parent_name)
parents.append(parent)
children.extend(Child(parent=parent, name=child_name) for
child_name in child_names)
# now commit all objects in bulk
Parent.objects.bulk_create(parents)
# add hack to make sure object IDs are properly assigned
for child in children:
child.parent_id = child.parent.id
# now this call can succeed
Child.objects.bulk_create(children)
}}}
This seems like something that should be supported by Django, and I
believe this would make the ORM more consistent overall.
Thanks.
--
Ticket URL: <https://code.djangoproject.com/ticket/32190>
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