Django script for changing the settings of field with foreign key. Foreign key changes in several steps: 1) Retrieve foreign keys from database; 2) Delete foreign keys; 3) Change fields; 4) Add foreign keys.

change_field_with_foreign_key.py

from django.db import connection
from pprint import pprint, pformat

# Database name
referenced_table_schema = connection.settings_dict['NAME']
# Table being referenced by foreign keys of another tables
referenced_table_name = "lang"
# Field being referenced by another tables
referenced_column_name = "id_lang"


with connection.cursor() as cursor:
    # 1. Get tables and fields, whose FK reference field referenced_column_name of the table referenced_table_name
    cursor.execute(
        """
        SELECT
             TABLE_NAME
            ,COLUMN_NAME
            ,CONSTRAINT_NAME
            ,REFERENCED_TABLE_NAME
            ,REFERENCED_COLUMN_NAME
        FROM
            INFORMATION_SCHEMA.KEY_COLUMN_USAGE
        WHERE
            REFERENCED_TABLE_SCHEMA = %s AND
            REFERENCED_TABLE_NAME = %s AND
            REFERENCED_COLUMN_NAME = %s
        """, [referenced_table_schema, referenced_table_name, referenced_column_name])
    columns = [col[0] for col in cursor.description]
    result = [dict(zip(columns, row)) for row in cursor.fetchall()]
    for foreignkey in result:
        # 2. Remove FK of the tables, which reference the field referenced_column_name of table referenced_table_name
        cursor.execute(
            """
            ALTER TABLE {db}.{table} DROP FOREIGN KEY {fk}
            """.format(db=referenced_table_schema, table=foreignkey['TABLE_NAME'], fk=foreignkey['CONSTRAINT_NAME'])
        )
        # 3. Once the FK is removed the function of field changing is available
        cursor.execute(
            """
            ALTER TABLE {db}.{table} CHANGE {column} {column} INT(11) NOT NULL;
            """.format(db=referenced_table_schema, table=foreignkey['TABLE_NAME'], column=foreignkey['COLUMN_NAME'])
        )
    # 4. Change field, that foreign keys are referenced
    cursor.execute(
        """
        ALTER TABLE {db}.{table} CHANGE {column} {column} INT(11) NOT NULL AUTO_INCREMENT;
        """.format(db=referenced_table_schema, table=referenced_table_name, column=referenced_column_name)
    )
    # 5. Create FK for tables
    for foreignkey in result:
        cursor.execute(
            """
            ALTER TABLE {db}.{table} ADD FOREIGN KEY ({column})
            REFERENCES {referenced_table}({referenced_column}) ON DELETE CASCADE ON UPDATE CASCADE;
            """.format(
                db=referenced_table_schema,
                table=foreignkey['TABLE_NAME'],
                column=foreignkey['COLUMN_NAME'],
                referenced_table=referenced_table_name,
                referenced_column=referenced_column_name
            )
        )

print('finish')