Mongo query: find document where each embeded element equals to given value

Question

I have a collection with embedded array of objects. I need a query to select only those documents where each of embedded objects prop equals to some value:

    {
     {
      _id: 1,
      objects: [{prop_1: ..., foo: true}, {prop_1: ..., foo: false}, {prop_1: ...}]
     },
     {
      _id: 2,
      objects: [{prop_1: ..., foo: false}, {prop_1: ..., foo: false}, {prop_1: ...}]
     },
     {
      _id: 3,
      objects: [
         {prop_1: ..., foo: true}, {prop_1: ..., foo: true}, {prop_1: ..., foo: true}
      ]
     }
    }

I need a query to get all the documents where each element of objects has foo === true. If one of objects.foo is not exists or not equals true do not return this document in result. In this case only record with _id : 3 meets this condition.

Answer 1

1. you can use $allElementsTrue directly if checking explicitly true

edit
as pointed out by @aneroid this one's shorter if directly checking true

db.collection.find({ $expr: { $allElementsTrue: "$objects.foo" } })

playground

db.collection.aggregate([
  {
    $match: {
      $expr: {
        $allElementsTrue: {
          $map: {
            input: "$objects",
            in: "$$this.foo"
          }
        }
      }
    }
  }
])

playground

or with a small addition if you want to check other values too

db.collection.aggregate([
  {
    $match: {
      $expr: {
        $allElementsTrue: {
          $map: {
            input: "$objects",
            in: { $eq: [ "$$this.foo", yourValue ] }
          }
        }
      }
    }
  }
])

playground

2. or by comparing the filtered objects array size with the actual object array size

db.collection.aggregate([
  {
    $match: {
      $expr: {
        $eq: [
          {
            $size: "$objects"
          },
          {
            $size: {
              $filter: {
                input: "$objects",
                cond: { $eq: [ "$$this.foo", yourValue ] }
              }
            }
          }
        ]
      }
    }
  }
])

playground

3. or using $reduce by keeping a boolean accumulator and by checking if it finally ends up being true

db.collection.aggregate([
  {
    $match: {
      $expr: {
        $eq: [
          true,
          {
            $reduce: {
              input: "$objects",
              initialValue: true,
              in: { $and: ["$$value", { $eq: ["$$this.foo", yourValue ] }] }
            }
          }
        ]
      }
    }
  }
]);

playground

4. or using $setIsSubset since now the first array (without dupes) is a subset(equal) of the second

db.collection.aggregate([
  {
    $match: {
      $expr: {
        $setIsSubset: [
          { $map: { input: "$objects", in: "$$this.foo" } },
          [ yourValue ]
        ]
      }
    }
  }
])

playground

5. or with a .find by getting the negation of all the docs that do not have foo as yourValue

db.collection.find({
  objects: {
    $not: {
      $elemMatch: { foo: { $ne: yourValue } }
    }
  }
})

playground