I'm dynamically storing information in the database depending on the request:
// table, id and column are provided by the request
table_obj = getattr(models, table)
record = table_obj.objects.get(pk=id)
setattr(record, column, request.POST['value'])
The problem is that request.POST['value'] sometimes contains a foreign record's primary key (i.e. an integer) whereas Django expects the column's value to be an object of type ForeignModel:
Cannot assign "u'122'": "ModelA.b" must be a "ModelB" instance.
Now, is there an elegant way to dynamically check whether b is a column containing foreign keys and what model these keys are linked to? (So that I can load the foreign record by it's primary key and assign it to ModelA?) Or doesn't Django provide information like this to the programmer so I really have to get my hands dirty and use isinstance() on the foreign-key column?
In simpler words, a foreign key is a set of attributes that references a candidate key. For example, a table called TEAM may have an attribute, MEMBER_NAME, which is a foreign key referencing a candidate key, PERSON_NAME, in the PERSON table.
A foreign key is a column or a set of columns in a table whose values correspond to the values of the primary key in another table. In order to add a row with a given foreign key value, there must exist a row in the related table with the same primary key value.
Note that foreign keys are not mandatory, and a table may have no foreign keys. Conversely, every column in a table may have a foreign key constraint.
What is ForeignKey in Django? ForeignKey is a Field (which represents a column in a database table), and it's used to create many-to-one relationships within tables. It's a standard practice in relational databases to connect data using ForeignKeys.
You can use get_field_by_name on the models _meta object:
from django.db.models import ForeignKey
def get_fk_model(model, fieldname):
"""Returns None if not foreignkey, otherswise the relevant model"""
field_object, model, direct, m2m = model._meta.get_field_by_name(fieldname)
if not m2m and direct and isinstance(field_object, ForeignKey):
return field_object.rel.to
return None
Assuming you had a model class MyModel you would use this thus:
fk_model = get_fk_model(MyModel, 'fieldname')
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