issues: 1199158210
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| id | node_id | number | title | user | state | locked | assignee | milestone | comments | created_at | updated_at | closed_at | author_association | pull_request | body | repo | type | active_lock_reason | performed_via_github_app | reactions | draft | state_reason |
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| 1199158210 | I_kwDOCGYnMM5HebPC | 423 | .extract() doesn't set foreign key when extracted columns contain NULL value | 37447552 | closed | 0 | 1 | 2022-04-10T20:05:30Z | 2022-08-27T14:45:04Z | 2022-08-27T14:45:04Z | NONE | I've run into an issue with `extract` and I don't believe this is the intended behaviour. I'm working with a database with music listening information. Currently it has one large table `listens` that contains all information. I'm trying to normalize the database by extracting relevant columns to separate tables (`artists`, `tracks`, `albums`). Not every track has an album. A simplified demonstration with just `track_title` and `album_title` columns: ```ipython In [1]: import sqlite_utils In [2]: db = sqlite_utils.Database(memory=True) In [3]: db["listens"].insert_all([ ...: {"id": 1, "track_title": "foo", "album_title": "bar"}, ...: {"id": 2, "track_title": "baz", "album_title": None} ...: ], pk="id") Out[3]: <Table listens (id, track_title, album_title)> ``` The track in the first row has an album, the second track doesn't. Now I extract album information into a separate column: ```ipython In [4]: db["listens"].extract(columns=["album_title"], table="albums", fk_column="album_id") Out[4]: <Table listens (id, track_title, album_id)> In [5]: list(db["albums"].rows) Out[5]: [{'id': 1, 'album_title': 'bar'}, {'id': 2, 'album_title': None}] In [6]: list(db["listens"].rows) Out[6]: [{'id': 1, 'track_title': 'foo', 'album_id': 1}, {'id': 2, 'track_title': 'baz', 'album_id': None}] ``` This behaves as expected -- the `album` table contains entries for both the existing album and the NULL album. The `listens` table has a foreign key only for the first row (since the album in the second row was empty). Now I want to extract the track information as well. Album information belongs to the track so I want to extract both columns to a new table. ```ipython In [7]: db["listens"].extract(columns=["track_title", "album_id"], table="tracks", fk_column="track_id") Out[7]: <Table listens (id, track_id)> In [8]: list(db["tracks"].rows) Out[8]: [{'id': 1, 'track_title': 'foo', 'album_id': 1}, {'id': 2, 'track_title': 'baz', 'album_id': None}] In [9]: list(db["listens"].rows) Out[9]: [{'id': 1, 'track_id': 1}, {'id': 2, 'track_id': None}] ``` Extracting to the `tracks` table worked fine (both tracks are present with correct columns). However, the `listens` table only has a foreign key to the newly created tracks for the first row, the foreign key in the second row is NULL. Changing the order of extracts doesn't help. I poked around in the source a bit and I believe [this line](https://github.com/simonw/sqlite-utils/blob/433813612ff9b4b501739fd7543bef0040dd51fe/sqlite_utils/db.py#L1737) (essentially comparing `NULL = NULL`) is the problem, but I don't know enough about SQL to create a reliable fix myself. | 140912432 | issue | {"url": "https://api.github.com/repos/simonw/sqlite-utils/issues/423/reactions", "total_count": 0, "+1": 0, "-1": 0, "laugh": 0, "hooray": 0, "confused": 0, "heart": 0, "rocket": 0, "eyes": 0} | completed |