gh-108364: In sqlite3, disable foreign keys before dumping SQL schema

[erlend-aasland]

• Issue: Align sqlite3.Connection.iterdump with the .dump() command of the SQLite shell #108364

[erlend-aasland]

I'm not sure who in the core team to call upon for a review of this. @felixxm, are you up for a review? 😃

[CorvinM]

This is consistent with the sqlite CLI .dump but seems to contradict the documentation here (section 2). Perhaps we should query foreign_keys for future proofing?

Excerpt from section 2:
Foreign key constraints are disabled by default (for backwards compatibility), so must be enabled separately for each database connection. (Note, however, that future releases of SQLite might change so that foreign key constraints enabled by default. Careful developers will not make any assumptions about whether or not foreign keys are enabled by default but will instead enable or disable them as necessary.)

[felixxm]

I don't think we can make assumptions about a connection on which the dump will be imported. We can check if there is any foreign key violation on the source database before adding this, e.g.

violations = cursor.execute("PRAGMA foreign_key_check").fetchall()
if len(violations) > 0:
    yield('PRAGMA foreign_keys=OFF;')

[felixxm]

@erlend-aasland Do you need help with this patch?

[erlend-aasland]

@felixxm: I currently have very little bandwidth for CPython development. Feel free to take this over, if you want.

[felixxm]

Updated in #113957.