Evgeny Evgeny - 10 months ago 42
Python Question

How to introspect django model fields?

I am trying to obtain class information on a field inside a model, when I only know name of the field and name of the model (both plain strings). How is it possible?

I can load the model dynamically:

from django.db import models
model = models.get_model('myapp','mymodel')

Now I have field - 'myfield' - how can I get the class of that field?

If the field is relational - how to get related field?

Thanks a bunch!


You can use model's _meta attribute to get field object and from field you can get relationship and much more e.g. consider a employee table which has a foreign key to a department table

In [1]: from django.db import models

In [2]: model = models.get_model('timeapp', 'Employee')

In [3]: dep_field = model._meta.get_field_by_name('department')

In [4]: dep_field[0].rel.field_name
Out[4]: 'id'

In [5]: dep_field[0].rel.to
Out[5]: <class 'timesite.timeapp.models.Department'>

from django/db/models/options.py

def get_field_by_name(self, name):
    Returns the (field_object, model, direct, m2m), where field_object is
    the Field instance for the given name, model is the model containing
    this field (None for local fields), direct is True if the field exists
    on this model, and m2m is True for many-to-many relations. When
    'direct' is False, 'field_object' is the corresponding RelatedObject
    for this field (since the field doesn't have an instance associated
    with it).

    Uses a cache internally, so after the first access, this is very fast.