MongoEngine / MongoEngine/mongoengine
Can't use $ in fields projection on queryset for selecting array entries
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- Dominant language
- Python
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Description
The following pymongo query can't be recreated with the MongoEngine QuerySet.
customers = db.customers.find({ _id: ObjectId('...'), 'tasks.id': 'task_1' }, { 'tasks.$': 1 })
This query tries to find a document in the customers collection with a given id and a task with the id 'task_1' in the tasks array on the customer document. The projection will only return the first task in that array that matches the query { 'id': 'task_1' }. This is useful for when you need a specific item in an array and it would be easier to fetch the document with only the single array item in the tasks array than fetch the customer document and filter the tasks in the code.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
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Research direction
No repository file or test entry point is named. Start by locating MongoEngine QuerySet projection handling and compare it with the shown PyMongo query; done means an equivalent projection can select the first matching array entry and the behavior is covered by tests.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- mongodb, python
- Domain
- database
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100