I have this structure in my DB.

[
  {
    _id: ObjectId("6386ef039775398be3620c76"),
    firstName: 'A',
    lastName: 'BA',
    age: 34,
    history: [
      { disease: 'fever', cured: true },
      { disease: 'malaria', cured: false }
    ]
  },
  {
    _id: ObjectId("6386ef239775398be3620c77"),
    firstName: 'AA',
    lastName: 'BA',
    age: 24,
    history: [
      { disease: 'cold', cured: true },
      { disease: 'thyroid', cured: false }
    ]
  }
]

What i'm tying to achieve is a query which will get me data like this:

Query

 db.collection.find({$filter:{history:{$elemMatch:{cured:false}}}

Expected Result:

[
  {
    _id: ObjectId("6386ef039775398be3620c76"),
    firstName: 'A',
    lastName: 'BA',
    age: 34,
    history: [
      { disease: 'malaria', cured: false }
    ]
  },
  {
    _id: ObjectId("6386ef239775398be3620c77"),
    firstName: 'AA',
    lastName: 'BA',
    age: 24,
    history: [
      { disease: 'thyroid', cured: false }
    ]
  }
]

What i have tried is

1.

db.collection.find({$filter:{history:{$elemMatch:{cured:false}}}

db.collection.aggregate([{$project:{history:{$filter:{input:"$history",as:"items",cond:{cured:false}}}}}])

db.collection.find({history:{$elemMatch:{cured:true}}},{'history.cured':1})

But none of these queries are giving desired result, Doubts/ Questions

1. Is it possible to get expected result straight from a query?
2. Where my queries went wrong?
3. What material should i go through to cover more advance concepts related to this query?

Any help would be much appreciated. My apologies if this question is too basic.

CodePudding user response：

One option is to merge your query attempts to:

1. Get all documents that have an item with cured: false
2. $filter history array to include only such items

db.collection.aggregate([
  {$match: {
      history: {$elemMatch: {cured: false}}
  }},
  {$set: {
      history: {
        $filter: {
          input: "$history",
          cond: {$eq: ["$$this.cured", false]}
        }
      }
  }}
])

See how it works on the playground example