Todo on MongoDB

Package: examples/todo_mongo. The todo CRUD API from todo_sqlite, backed by MongoDB through the same ORM models and handlers — without foreign keys, because joins are a capability error.

Run

export MONGODB_URL='mongodb://127.0.0.1:57017/siderite?directConnection=true'
MONGODB_DATABASE=todos ADDR=127.0.0.1:18080 cargo run -p todo_mongo
curl -XPOST localhost:18080/todos -H 'content-type: application/json' -d '{"title":"try mongo"}'
curl 'localhost:18080/todos?done=false&limit=10&offset=0'
curl localhost:18080/todos/stats

Start MongoDB from the root docker-compose.yml (single-node replica set). cargo test -p todo_mongo uses MONGODB_URL and a throw-away database per test; without the variable the tests print a notice and pass.

What works

Single-collection CRUD, filter / exclude, ordering, limit / offset, count, save (update by key). The id column is stored as _id; when it is omitted the backend generates increasing i64 keys from siderite_counters.

What the backend rejects

The MongoDB backend rejects, before any I/O, with a capability error (HTTP 501): joins (select_related, foreign-key traversal), subqueries (in_subquery, exists), set operations (union, …), window functions, row locking, DISTINCT ON, and array aggregates. Consequently there is no ForeignKey between models here, and no many-to-many (its queries use subqueries).

Other differences:

• No SQL migrations: collections appear on first write. Unique constraints exist only for _id unless created with MongoBackend::create_unique_index.
• Transactions need a replica set and are flat (no savepoints), so nested Db::transaction and bulk_create on a transactional handle are rejected.
• Timestamps have millisecond precision.

See also

• Backends
• Backend matrix
• Todo on SQLite