Re: Multiple Fields as Primary Key in MySQL - Django 1.10

Hi, 

from compositekey import db

On my compositekey project the development is stopped on 1.5 django release.
https://github.com/simone/django-compositekey

The Django 1.6 release, with an huge ORM refactoring and a huge testing refactoring, let my work hard to maintains. What I understand after the 1.6 release is that this fe<ture has to be inside the framework, not in an external library.

As I know Michal Petrucha make a good job on GSoc 2011.
However, I don't know when is in planning the composite key feature in the django release.

best

Simone

On Tue, Jan 3, 2017 at 10:49 AM, ramesh <ramesh.melapu@gmail.com> wrote:

Hi,

Below is the model generated for one of the table from the legacy database using "inspectdb"

class Test(models.Model):
    field1 = models.AutoField(db_column='Field1')  # Field name made lowercase.
    field2 = models.ForeignKey('Field2', models.DO_NOTHING, db_column='Field2')  # Field name made lowercase.
    field3 = models.CharField(db_column='Field3', max_length=200)  # Field name made lowercase.
    field4 = models.CharField(db_column='Field4', max_length=300, blank=True, null=True)  # Field name made lowercase.

    class Meta:
        managed = False
        db_table = 'test'
        unique_together = (('field1', 'field2'),)


Table definition in MySQL:
    CREATE TABLE comment (
        Field1                          INT             UNSIGNED    NOT NULL    AUTO_INCREMENT              COMMENT 'Field1',   
        Field2                          INT             UNSIGNED    NOT NULL                                COMMENT 'Field2',
        Field3                          VARCHAR(200)                NOT NULL                                COMMENT 'Field3',
        Field4                          VARCHAR(300)                            DEFAULT NULL                COMMENT 'Field4',
        KEY ( Field2 ),
        FOREIGN KEY (Field2) REFERENCES item (Field2) ON DELETE CASCADE,
        PRIMARY KEY  ( Field1, Field2 )
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Migrations failed with the error,
    "A model can't have more than one AutoField."
AssertionError: A model can't have more than one AutoField.

Tried work around of

from compositekey import db

id = db.MultiFieldPK("field1", "field2")

Now a different error,

    from django.db.models.sql.aggregates import Aggregate
ImportError: No module named aggregates


Another work around of defining a new auto_increment field as primary key but here one of the composite keys (field1) is auto_incremental causing 2 auto_increment fields in a table.

Also this needs MySQL table alter, as this is a legacy database with many tables, this is quite difficult.

Please advise me on work around, correct me if I am missing some thing here in the process.

Thanks in advance.

Ramesh.

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