ondelete('cascade') code example

Example 1: on_delete=models.cascade

on_delete=models.CASCADE will delete anything created by the admin if
the admin user is deleted.

Example 2: on delete of foreign key delete corresponding rows in other table

ALTER TABLE ReferencingTable DROP 
   CONSTRAINT fk__ReferencingTable__MainTable;

ALTER TABLE ReferencingTable ADD 
   CONSTRAINT fk__ReferencingTable__MainTable 
      FOREIGN KEY (pk_col_1)
      REFERENCES MainTable (pk_col_1)
      ON DELETE CASCADE;

Example 3: on delete cascade

CREATE TABLE child_table
(
  column1 datatype [ NULL | NOT NULL ],
  column2 datatype [ NULL | NOT NULL ],
  ...

  CONSTRAINT fk_name
    FOREIGN KEY (child_col1, child_col2, ... child_col_n)
    REFERENCES parent_table (parent_col1, parent_col2, ... parent_col_n)
    ON DELETE CASCADE
    [ ON UPDATE { NO ACTION | CASCADE | SET NULL | SET DEFAULT } ] 
);