MongoDB - Query an Array

In this MongoDB tutorial we will learn to query arrays.

Login to your MongoDB server and insert the following documents.

For this tutorial I will insert the following documents in the posts collection.

> db.posts.insertMany([
  {
    "title": "This is my first post!",
    "tags": ["awesome", "post", "blog"]
  },
  {
    "title": "Dinner time :)",
    "tags": ["food", "dinner", "fun"]
  },
  {
    "title": "Birthday Treat",
    "tags": ["fun", "food", "birthday", "treat", "party"]
  }
]);

Match exact array

In the following example we are going to fetch documents having exactly 3 elements in the array and values are awesome, post and blog in that order.

> db.posts.find({
  "tags": ["awesome", "post", "blog"]
}).pretty();


{
  "_id" : ObjectId("5d1b43d9085e37060f4c36b5"),
  "title" : "This is my first post!",
  "tags" : [
    "awesome",
    "post",
    "blog"
  ]
}

Note! If we change the positions of the array elements in the above query then we will not get the same result.

Query an array for an element

In the following example we are going to fetch all the documents having an array field tags that contains food as one of the element in the array.

> db.posts.find({ "tags": "food" }).pretty();


{
  "_id" : ObjectId("5d1b43d9085e37060f4c36b6"),
  "title" : "Dinner time :)",
  "tags" : [
    "food",
    "dinner",
    "fun"
  ]
}
{
  "_id" : ObjectId("5d1b43d9085e37060f4c36b7"),
  "title" : "Birthday Treat",
  "tags" : [
    "fun",
    "food",
    "birthday",
    "treat",
    "party"
  ]
}

Query an array for some elements

In the following example we are going to fetch all the documents having an array field tags with some or all of the values from a list of values food, dinner and fun in any order.

Any document having "food", "fun" or "dinner" in any order in the tags array is fetched.

> db.posts.find({
  tags: { $in: ["food", "fun", "dinner"] }
}).pretty();



{
  "_id" : ObjectId("5d1b43d9085e37060f4c36b6"),
  "title" : "Dinner time :)",
  "tags" : [
    "food",
    "dinner",
    "fun"
  ]
}
{
  "_id" : ObjectId("5d1b43d9085e37060f4c36b7"),
  "title" : "Birthday Treat",
  "tags" : [
    "fun",
    "food",
    "birthday",
    "treat",
    "party"
  ]
}

Query an array for given elements not in any order

In the following example we are going to fetch all documents that has an array field tags having all of the values from a list of values food, dinner and fun in any order.

> db.posts.find({
  tags: { $all: ["food", "fun", "dinner"] }
}).pretty();



{
	"_id" : ObjectId("5d1b43d9085e37060f4c36b6"),
	"title" : "Dinner time :)",
	"tags" : [
		"food",
		"dinner",
		"fun"
	]
}

Query by array length

In the following example we are going to fetch all the documents having an array field tags with 3 elements.

> db.posts.find({
  "tags": { $size: 3 }
}).pretty();


{
  "_id" : ObjectId("5d1b43d9085e37060f4c36b5"),
  "title" : "This is my first post!",
  "tags" : [
    "awesome",
    "post",
    "blog"
  ]
}
{
  "_id" : ObjectId("5d1b43d9085e37060f4c36b6"),
  "title" : "Dinner time :)",
  "tags" : [
    "food",
    "dinner",
    "fun"
  ]
}