array-operators.md

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Array query operators

Array query operators allow you to search for specific elements within an array field in a document.

Operator	Description
$all	Selects an array that contains all elements from a given query.
$elemMatch	Matches a document that contains an array field with at least one element that matches all the specified query criteria
$size	Matches an array with a specified number of elements

For the examples in this section, insert the following documents into the team collection:

db.team.insertMany([
  {
    id: 1,
    name: 'Jack Smith',
    position: 'Manager',
    skills: ['leadership', 'communication', 'project management'],
    contact: {
      email: 'john@example.com',
      phone: '123-456-7890'
    },
    active: true
  },
  {
    id: 2,
    name: 'Jane Mark',
    position: 'Software Developer',
    skills: ['Java', 'Python', 'C++'],
    contact: {
      email: 'jane@example.com',
      phone: '123-456-7891'
    },
    active: false
  },
  {
    id: 3,
    name: 'Bob Johnson',
    position: 'Graphic Designer',
    skills: ['Adobe Photoshop', 'Illustrator', 'InDesign'],
    contact: {
      email: 'bob@example.com',
      phone: '123-456-7892'
    },
    active: true
  },
  {
    id: 4,
    name: 'Alice Williams',
    position: 'Marketing Coordinator',
    skills: ['communication', 'content creation', 'event planning'],
    contact: {
      email: 'alice@example.com',
      phone: '123-456-7893'
    },
    active: true
  }
])

$all

Syntax: { <field>: { $all: [ <element1>, <element2>, ... <elementN> ] } }

Use the $all operator when you want to select documents that contain every single element in a specified array.

:::note When using an $all operator, the order of the elements and array size does not matter, as long as the array contains all the elements in the query. :::

Example: Find all documents in the team collection where the skills field contains both communication and content creation as elements using the following query operation:

db.team.find({
  skills: {
    $all: ['communication', 'content creation']
  }
})

The output:

[
  {
    _id: ObjectId("63a5bb4acf72d6203bb45bb5"),
    id: 4,
    name: 'Alice Williams',
    position: 'Marketing Coordinator',
    skills: ['communication', 'content creation', 'event planning'],
    contact: { email: 'alice@example.com', phone: '123-456-7893' },
    active: true
  }
]

$elemMatch

Syntax: { <field>: { $elemMatch: { <condition1>, <condition2>, ... <conditionN>} } }

To select documents in a specified array field where one or more elements match all listed query conditions, use the $elemMatch operator.

Example: Find documents in the team collection where the skills field is an array that contains the element "Java", and array does not contain the element communication. Use the following query operation:

db.team.find({
  skills: {
    $elemMatch: {
      $eq: 'Java',
      $nin: ['communication']
    }
  }
})

The output:

[
  {
    _id: ObjectId("63aa247e69c82de72bd40b93"),
    id: 2,
    name: 'Jane Mark',
    position: 'Software Developer',
    skills: ['Java', 'Python', 'C++'],
    contact: { email: 'jane@example.com', phone: '123-456-7891' },
    active: false
  }
]

$size

Syntax: { <field>: { $size: <number-of-elements> } }

The $size operator is ideal for selecting array fields containing a specified number of elements.

Example: Select the documents in the team collection where the skills array contains only three elements.

db.team.find({
  skills: {
    $size: 3
  }
})

The output:

[
  {
    _id: ObjectId("63aa247e69c82de72bd40b92"),
    id: 1,
    name: 'Jack Smith',
    position: 'Manager',
    skills: ['leadership', 'communication', 'project management'],
    contact: { email: 'john@example.com', phone: '123-456-7890' },
    active: true
  },
  {
    _id: ObjectId("63aa247e69c82de72bd40b93"),
    id: 2,
    name: 'Jane Mark',
    position: 'Software Developer',
    skills: ['Java', 'Python', 'C++'],
    contact: { email: 'jane@example.com', phone: '123-456-7891' },
    active: false
  },
  {
    _id: ObjectId("63aa247e69c82de72bd40b94"),
    id: 3,
    name: 'Bob Johnson',
    position: 'Graphic Designer',
    skills: ['Adobe Photoshop', 'Illustrator', 'InDesign'],
    contact: { email: 'bob@example.com', phone: '123-456-7892' },
    active: true
  },
  {
    _id: ObjectId("63aa247e69c82de72bd40b95"),
    id: 4,
    name: 'Alice Williams',
    position: 'Marketing Coordinator',
    skills: ['communication', 'content creation', 'event planning'],
    contact: { email: 'alice@example.com', phone: '123-456-7893' },
    active: true
  }
]