issue_comments: 655652679
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| html_url | issue_url | id | node_id | user | created_at | updated_at | author_association | body | reactions | issue | performed_via_github_app |
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| https://github.com/simonw/sqlite-utils/issues/121#issuecomment-655652679 | https://api.github.com/repos/simonw/sqlite-utils/issues/121 | 655652679 | MDEyOklzc3VlQ29tbWVudDY1NTY1MjY3OQ== | 79913 | 2020-07-08T17:24:46Z | 2020-07-08T17:24:46Z | CONTRIBUTOR | Better transaction handling would be really great. Some of my thoughts on implementing better transaction discipline are in https://github.com/simonw/sqlite-utils/pull/118#issuecomment-655239728. My preferences: - Each CLI command should operate in a single transaction so that either the whole thing succeeds or the whole thing is rolled back. This avoids partially completed operations when an error occurs part way through processing. Partially completed operations are typically much harder to recovery from gracefully and may cause inconsistent data states. - The Python API should be transaction-agnostic and rely on the caller to coordinate transactions. Only the caller knows how individual insert, create, update, etc operations/methods should be bundled conceptually into transactions. When the caller is the CLI, for example, that bundling would be at the CLI command-level. Other callers might want to break up operations into multiple transactions. Transactions are usually most useful when controlled at the application-level (like logging configuration) instead of the library level. The library needs to provide an API that's conducive to transaction use, though. - The Python API should provide a context manager to provide consistent transactions handling with more useful defaults than Python's `sqlite3` module. The latter issues implicit `BEGIN` statements by default for most DML (`INSERT`, `UPDATE`, `DELETE`, … but not `SELECT`, I believe), but **not** DDL (`CREATE TABLE`, `DROP TABLE`, `CREATE VIEW`, …). Notably, the `sqlite3` module doesn't issue the implicit `BEGIN` until the first DML statement. It _does not_ issue it when entering the `with conn` block, like other DBAPI2-compatible modules do. The `with conn` block for `sqlite3` only arranges to commit or rollback an existing transaction when exiting. Including DDL and `SELECT`s in transactions is important for operation consistency, though. There are several existing bugs.python.org tickets about this and future changes are in the works, but sqlite-utils can provide its own API sooner. sqlite-utils's `Database` class could itself be a context manager (built on the `sqlite3` connection context manager) which additionally issues an explicit `BEGIN` when entering. This would then let Python API callers do something like: ```python db = sqlite_utils.Database(path) with db: # ← BEGIN issued here by Database.__enter__ db.insert(…) db.create_view(…) # ← COMMIT/ROLLBACK issue here by sqlite3.connection.__exit__ ``` | {"total_count": 1, "+1": 1, "-1": 0, "laugh": 0, "hooray": 0, "confused": 0, "heart": 0, "rocket": 0, "eyes": 0} | 652961907 |