I recently needed to take Django field lookup/query strings and find out what model field they were referencing. For example, imagine we have the following models:
class Business(models.Model): name = models.CharField(max_length=255) business_type = models.IntegerField(choices=zip(range(5), range(5)), default=1) class Department(models.Model): name = models.CharField(max_length=255) business = models.ForeignKey(Business) class Staff(models.Model): first_name = models.CharField(max_length=255) last_name = models.CharField(max_length=255) department = models.ForeignKey(Department)
I needed a function that would take a string like
department__business__business_type and return
field (I needed to access the
choices attribute of fields).
Here's a short function which will do that sort of lookup:
def find_field(cls, lookup): """Take a root class and a field lookup string and return the model field if it exists or raise a django.db.models.fields.FieldDoesNotExist if the field is not found.""" lookups = list(reversed(lookup.split("__"))) field = None while lookups: f = lookups.pop() # will raise FieldDoesNotExist exception if not found field = cls._meta.get_field(f) try: cls = field.rel.to except AttributeError: if lookups: # not all lookup fields were used # must be an incorrect lookup raise django.db.models.fields.FieldDoesNotExist(lookup) return field # use like: >> find_field(Staff, "department__business__business_type") <django.db.models.fields.IntegerField: business_type> >> >> find_field(Staff, "department__business") <django.db.models.fields.related.ForeignKey: business> >> >> find_field(Staff, "department__foo") FieldDoesNotExist: Department has no field named 'foo' >>