django error on migration: "There is no unique constraint matching given keys for referenced table

Question

So I have seen that a lot of these kinds of questions have popped up (few answered) and none in a Django aspect that I saw. I am confused why I am getting the error, I am guessing i am missing something on my field decorator or what not in my model definition. Here are the two models... (one abbreviated). I thought I did everything right with unique and primary key set to true in the one table that the foreign key gives reference to but upon migrate I get this error:

django.db.utils.ProgrammingError: there is no unique constraint matching given keys for referenced table "swsite_zoneentity"

Edit up dated the code ...

class ZoneEntity(models.Model):
    zone_number = models.CharField(max_length=100, primary_key=True)
    mpoly = models.PolygonField() #this should grow and shrink for the most representative one...
    objects = models.GeoManager() 
    created_at=models.DateField(auto_now_add=True)
    updated_at=models.DateField(auto_now=True)

class CesiumEntity(models.Model):
    be_number = models.CharField(max_length=100) #the number assigned to a foot print to distinguish
    #zone_id = models.CharField(max_length=100, null=True, blank=True)
    zone_id = models.ForeignKey('ZoneEntity', null=True, blank=True)

Answer 1

To solve this, needed to add the unique constraint on the postgres table id myself.

psql <your-database-name>
ALTER TABLE swsite_zoneentity ADD CONSTRAINT zone_unique_id UNIQUE(id);

Like this answer