ModelForm model=class not honoring reference fields with secondary database

[furbeenator@…]

When using a separate database for objects used as an instance in a ModelForm, reference fields are not searching the secondary database. For example, a secondary database (not default) is created, and set up in settings.py as database 'my_employee'. Two tables are created. One for employees, and one for departments they work in.

The tables contain these rows:

employee
username | department_id
'mark' | 1

department
department_id | name
1 | 'Dept1'
2 | 'Dept2'

The models are as follows:

class Department(models.Model):
    name = models.CharField(max_length=32)
    def __unicode__(self):
        return self.name

class Employee(models.Model):
    username = models.CharField(max_length=32)
    department = models.ForeignKey(Department)
    def __unicode__(self):
        return self.username + ": <dept: " + self.department.name + ">"

class EmployeeForm(ModelForm):
    class Meta:
        model = Employee

In a view:

emp = Employee.objects.using('my_employee').get(id=1)

print emp
'mark <dept: Dept1>'

frm = EmployeeForm(instance=emp)

print frm

This generates a DatabaseError Exception, relation 'department' does not exist. It exists in the secondary database, but not in the default database.

If I create a department table in the default database, the Employee object still gets retrieved, including the id for the Department, but the department details are retrieved from the default database instead of the secondary. As follows:

In default database:

department
department_id | name
1 | 'DefaultDBDept1'
2 | 'DefaultDBDept2'

No employee table exists in default database. The view below:

emp = Employee.objects.using('my_employee').get(id=1)

print emp
'mark <dept: Dept1>'

frm = EmployeeForm(instance=emp)

print frm

This generates a form as normal, but the Department details from the default database are included instead of details from the secondary database. So, two select options are created with the labels 'DefaultDBDept1' and 'DefaultDBDept2' and the selected one is correctly 'DefaultDBDept1.' If I update the secondary table so that employee 'mark' has department_id 2, the selected option is 'DefaultDBDept2.' If I remove the default department table, the DatabaseError exception, relation 'department' does not exist, returns.

[Karen Tracey]

Fixed formatting. PLEASE use WikiFormatting and preview before posting.

[Karen Tracey]

Near as I can tell you are trying to have ForeignKeys that cross database boundaries. This is not supported by Django's multiple database support, see: ​https://docs.djangoproject.com/en/1.3/topics/db/multi-db/#cross-database-relations

[anonymous]

This does not span multiple databases. The employee and department tables are both in the secondary database. I can print the employee's department just fine, it is when I use it as an instance to a ModelForm that the references do not work. It is forcefully looking in the default database for the department, even though the employee object looks to the secondary database correctly.

[Karen Tracey]

Why have you forked this discussion off to django-users as well, and then re-opened this here? Please see my response there. You don't seem to have done anything to tell Django to look in the secondary DB for this 2nd model, therefore the default is where it is looking for it. I think you need to code database routing to do what you are looking for, automatic routing so far as I know does not propagate database stickiness in the way you are looking for.

[anonymous]

Thank you for your help, Karen. The issue is that everything is honored up to the point that I use the employee as an instance to a ModelForm. This works fine and the employee's department name is printed:

employee = Employee.objects.using('my_employee').get(id=1)
print employee.department.name

As soon as I assign a ModelForm:

frm = EmployeeForm(instance=employee)
print frm

The DatabaseError Exception is raised. What I was explaining in the original post was that if I have a table in the default database that has the name department, it works to attach the employee from 'my_employee' to the corresponding department from default. Perhaps I added TOO much detail in the original description. I have been trying to nail down exactly what the behavior is.