CODEWITHSUNDEEP
pythonsqlsqlite
kravitz
kravitz

Reputation: 1063

How to make ON DELETE CASCADE work in sqlite 3.7.4?

I checked the feature list several times, and it seems that cascading should work. When I execute this python script:

#!/usr/bin/env python3
import sqlite3

print(sqlite3.sqlite_version)

con = sqlite3.connect(':memory:')

a = "create table a (id integer primary key, name text)"
con.execute(a)

b = "create table b (id integer primary key, r integer, foreign key(r) references a(id) on delete cascade)"
con.execute(b)
con.commit()

a = "insert into a (name) values (\"abc\")"
con.execute(a)
con.commit()

print(con.execute("select * from a").fetchall())

a = "insert into b (r) values (1)"
con.execute(a)
con.commit()

print(con.execute("select * from b").fetchall())

a = "delete from a where id=1"
con.execute(a)
con.commit()

print(con.execute("select * from b").fetchall())
print(con.execute("select * from a").fetchall())

I get these results:

3.7.4
[(1, 'abc')]
[(1, 1)]
[(1, 1)]
[]

Which proves that cascading didn't happened. What I did wrong or what are the solutions to get same result as cascading?

Upvotes: 8

Views: 6260

Answers (2)

slacy
slacy

Reputation: 11763

There's a better answer by user Thibault J over in this question: Enable integrity checking with sqlite in django which says:

from django.db.backends.signals import connection_created
def activate_foreign_keys(sender, connection, **kwargs):
    """Enable integrity constraint with sqlite."""
    if connection.vendor == 'sqlite':
        cursor = connection.cursor()
        cursor.execute('PRAGMA foreign_keys = ON;')

connection_created.connect(activate_foreign_keys)

Upvotes: 2

Rosh Oxymoron
Rosh Oxymoron

Reputation: 21055

SQLite foreign keys are disabled for compatibility purposes. You need to enable them manually right after each connection to the database.

con.execute("PRAGMA foreign_keys = ON")

Upvotes: 11

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