Array operators ($all $elemMatch $size)

Array operators query the contents and size of array fields.

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Array operators ($all $elemMatch $size)

Syntax

javascript

{ array_field: { $all: [value1, value2] } }
{ array_field: { $elemMatch: { key: value } } }
{ array_field: { $size: n } }

Array operators ($all $elemMatch $size)

Matching a value in an array field works with plain equality. $all requires several values to be present, $size matches an exact length and $elemMatch requires one element to satisfy several conditions at once.

Without $elemMatch, conditions may be satisfied by different elements.

Note: Use $elemMatch when multiple conditions must hold for the same array element.

Example: Array operators ($all $elemMatch $size)

bash

test> db.posts.insertMany([
...   { _id: 1, tags: ["js", "node", "db"], scores: [{ who: "a", v: 5 }, { who: "b", v: 9 }] },
...   { _id: 2, tags: ["js"], scores: [{ who: "a", v: 9 }, { who: "b", v: 1 }] }
... ])
{ acknowledged: true, insertedIds: { '0': 1, '1': 2 } }
test> db.posts.find({ tags: "node" }, { _id: 1 })
[ { _id: 1 } ]
test> db.posts.find({ tags: { $all: ["js", "db"] } }, { _id: 1 })
[ { _id: 1 } ]
test> db.posts.find({ tags: { $size: 1 } }, { _id: 1 })
[ { _id: 2 } ]
test> db.posts.find({ scores: { $elemMatch: { who: "b", v: { $gt: 5 } } } }, { _id: 1 })
[ { _id: 1 } ]

⚠️ Run this in your own terminal or Node.js environment.

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Array operators ($all $elemMatch $size)

Array operators ($all $elemMatch $size)

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