Mongoose – finding subdocuments by criteria

by

You can use $elemMatch as a query-projection operator in the most recent MongoDB versions. From the mongo shell:

db.parents.find(
    {'children.age': {$gte: 18}},
    {children:{$elemMatch:{age: {$gte: 18}}}})

This filters younger children’s documents out of the children array:

{ "_id" : ..., "children" : [ { "name" : "Margaret", "age" : 20 } ] }
{ "_id" : ..., "children" : [ { "name" : "John", "age" : 22 } ] }

As you can see, children are still grouped inside their parent documents. MongoDB queries return documents from collections. You can use the aggregation framework’s $unwind method to split them into separate documents:

> db.parents.aggregate({
    $match: {'children.age': {$gte: 18}}
}, {
    $unwind: '$children'
}, {
    $match: {'children.age': {$gte: 18}}
}, {
    $project: {
        name: '$children.name',
        age:'$children.age'
    }
})
{
    "result" : [
        {
            "_id" : ObjectId("51a7bf04dacca8ba98434eb5"),
            "name" : "Margaret",
            "age" : 20
        },
        {
            "_id" : ObjectId("51a7bf04dacca8ba98434eb6"),
            "name" : "John",
            "age" : 22
        }
    ],
    "ok" : 1
}

I repeat the $match clause for performance: the first time through it eliminates parents with no children at least 18 years old, so the $unwind only considers useful documents. The second $match removes $unwind output that doesn’t match, and the $project hoists children’s info from subdocuments to the top level.

More Related Contents:

  1. Mongoose always returning an empty array NodeJS
  2. $lookup multiple levels without $unwind?
  3. Avoid “current URL string parser is deprecated” warning by setting useNewUrlParser to true
  4. Mongoose, update values in array of objects
  5. In Mongoose, how do I sort by date? (node.js)
  6. mongoError: Topology was destroyed
  7. Setting expiry time for a collection in mongodb using mongoose
  8. MongoDB/Mongoose querying at a specific date?
  9. Making mongoose.js queries run synchronously
  10. How to populate a sub-document in mongoose after creating it?
  11. Mongoose/mongoDB query joins.. but I come from a sql background
  12. mongoose custom validation using 2 fields
  13. (node:3341) DeprecationWarning: Mongoose: mpromise
  14. Mongoose deleting (pull) a document within an array, does not work with ObjectID
  15. How to set limit for array size in Mongoose schema
  16. Mongoose populate nested array
  17. MongooseError – Operation `users.findOne()` buffering timed out after 10000ms
  18. MongoDB – get documents with max attribute per group in a collection
  19. Connecting Heroku App to Atlas MongoDB Cloud service
  20. how to use populate and aggregate in same statement?
  21. Automatically remove referencing objects on deletion in MongoDB
  22. Mongoose nested query on Model by field of its referenced model
  23. How can I generate an ObjectId with mongoose?
  24. Node.js – Mongoose – Check if a collection exists
  25. Mongoose – caused by :: 11000 E11000 duplicate key error index?
  26. nodejs mongodb object id to string
  27. How do I increment a Number value in Mongoose?
  28. How to reference another schema in my Mongoose schema?
  29. Populate a mongoose model with a field that isn’t an id
  30. MongoDB $lookup vs Mongoose populate

Leave a Comment