[Fixed]-Django error on migration: "There is no unique constraint matching given keys for referenced table

by

4👍

✅

Codejoy,

When you define a primarykey, it is automatically set as unique.. So, just go by:

class ZoneEntity(models.Model):
    zone_number = models.CharField(max_length=100, primary_key=True)
    ....

class CesiumEntity(models.Model):
    ...
    zone_id = models.ForeignKey('ZoneEntity', null=True, blank=True)
    ...

This will automatically bind the PK of ZoneEntity with zone_id!

If the field you are trying to make the relation IS NOT the primary key, then you can add unique=True and to_field='foo'

 - python manage.py. makemigration
s
Migrations for 'module1':
  0002_auto_20170214_1503.py:
    - Create model CesiumEntity
    - Create model ZoneEntity
    - Add field zone_id to cesiumentity

 - python manage.py migrate
Operations to perform:
  Synchronize unmigrated apps: staticfiles, messages
  Apply all migrations: admin, contenttypes, module1, auth, sessions
Synchronizing apps without migrations:
  Creating tables...
    Running deferred SQL...
  Installing custom SQL...
Running migrations:
  Rendering model states... DONE
  Applying module1.0002_auto_20170214_1503... OK
👤bobleujr

11👍

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

👤Mahmoud Hanora

7👍

This problem appears most times because you copied or created your database from a dump and somewhere the unique constraint on your primary key column(as well as other constraints got lost.

Solution:

Open your DB with pg4admin or any client,    Databases>your_database>schema>public>tables>your_table right-click   
on the table name, 
Choose Properties 
Select columns tabs 
switch primary key on your pk column
save/exit
run migration again
👤Otobong Jerome

1👍

I too had same issue while migrating DB from SQLite to PostgreSQL 14.4, even when referenced Foreign key had primary_key=True set.

Deleting the old migrations, solved my issue.

👤Aashutosh Kumar

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