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This post will show you how to add elements to an array in MongoDB using various techniques. Pushing or appending elements to an array is very convenient for quickly appending lists by adding or moving objects in an existing MongoDB document.

This course teaches how to use push operations with negative and positive integers. Negative integers provide additional push possibilities for putting data into an array.

Prerequisites:

1. MongoDB must be installed and configured correctly to add elements to an array in MongoDB.
2. Gain a basic understanding of the functionality of arrays.

Let’s first take a look at the table of contents of this article.

1. Operators in MongoDB
2. $push operator in MongoDB
3. Pushing elements to an array
4. Push an element to the beginning of an array
5. Push elements to the end of the array

Operators in MongoDB

Operators are special symbols or keywords that tell the compiler or interpreter how to perform mathematical or logical operations. Query operators extend the functionality of MongoDB by allowing developers to write complex queries to interact with data sets relevant to their applications.

Following are the various operators in MongoDB.

1. Query and Projection Operators - Query operators help discover data in the database, while projection operators change the way the data is displayed.
2. Update Operators − Update operators allow you to change or add data to your database.
3. Aggregation Pipeline Stages - Available aggregation stages for the aggregation pipeline.
4. Aggregation Pipeline Operators − Aggregation pipeline operations have a set of operators that can be used to define and operate on documents in pipeline stages.
5. Query Modifiers – Query modifiers determine how the query will be executed.

$push operator in MongoDB

In MongoDB, the $push operator is used to append values ​​to an array. The $push operator is an update operator.

If the provided field is not in the document being changed, the $push operator creates it as a new field with the specified value as its element. If the update field is not an array type, the operation fails.

When updating, if the value is an array, the $push operator appends the entire array as a single element. Use the $push operator with the $each modifier to add each value element individually.

grammar:

db.collection.update( <query>,{ $push: { <field>: <value> } })

MongoDB $push operator example:

If you want to append 95 to the completed array field when the conditional subject is maths, we can use the following MongoDB command.

db.student.update( { "subjects" : "maths" },{ $push: { "achieve": 95 } });

Because the conditions described in the previous example match this action, the value 95 is appended to the completed array.

View the latest updated documentation:

db.student.find().pretty();

The output of the query given above can be seen in this screenshot.

MongoDB $push example when field is not an array:

If you want to add 2 to the sem column which is not an array type field, we can use the following MongoDB command.

db.student.update( { "subjects" : "maths" },{ $push: { "sem": 2 } });

Because the sem field in the above example is not an array type, the operation will fail and produce the following result.

Cannot apply $push/$push All modifier to non-array

Pushing elements to an array in MongoDB

This section describes how to use the $push operator, such as an update operation, to add elements to an array.

First, create a sample dataset containing fruits as shown below.

use fruitdb
switched to db fruitdb
db.fruit.insert({
      "_id": "100",
      "fruitArray": ['mango', 'banana', 'orange']
   });
WriteResult({ "nInserted" : 1 })

Now verify the insertion process using the following command.

db.fruit.find({_id: "100"});

The results should resemble the following.

Now let's add another fruit to the fruitArray. In this example, execute the following command to add a pineapple.

db.fruit.update(
      { "_id": "100" },
      {
          $push: {
              fruitArray: "pineapple"
          }
      }
  );

The results should resemble the following.

WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

Execute the following command to verify that the pineapple has been successfully added as an element to the fruitArray.

db.fruit.find({_id: "100"}).pretty();

The output should look like this.

The result shows that the $push operator inserted the word pineapple at the end of fruitArray.

Pushing an element to the beginning of an array in MongoDB

The previous section described how to append new elements to the beginning of an array. This section will demonstrate how to insert the element grapes at the beginning of an array.

The following commands are used to do this.

db.fruit.update(
      { "_id": "100" },
      {
          $push: {
              fruitArray: {
                  $each: ['grapes'],
                  $position: 0
              }
          }
      }
  );

Then, the following command can confirm whether the update process was successful.

db.fruit.find({_id: "100"}).pretty();

The output should be similar to the following.

The operator $position was used in the previous operation. As the name suggests, this command places an element in a user-defined array.

Also, remember that positive integers used for $position values ​​are pushed in from the left, or beginning, of the array.

Pushing elements to the end of an array in MongoDB

The previous section demonstrated how to insert an element at the beginning of an array using a positive integer as the value of the $position operator. This section teaches you how to push items using a negative integer as the value, as shown here.

db. fruit.update(
      { "_id": "100" },
      {
          $push: {
              fruitArray: {
              $each: ['apple'],
              $position: -1
          }
      }
  });

The output should be similar to the following.

Using -1 as the value, apple is placed at the second-to-last position in the list of elements, with the last element at position 0.

Pushing multiple elements in MongoDB

This section describes how to insert, or push, multiple elements into an array.

First, in the fruit document, add another array.

db. fruit.insert({
      "_id": "101",
      "fruitArray": ["strawberry","guava","lemon"]
  });

A new document should be generated containing the following information.

Now, add a large number of elements to the new document using the following command.

db.fruit.update(
      { "_id": "101" },
      {
          $push: {
              fruitArray: {
                  $each: ['pear', 'cherry', 'lime'],
                  $position: -2
              }
          }
      }
  );

Since the items ['pear', 'cherry', and 'lime']are pushed in the code above, the array can be considered as one element. This pushes or moves pear to the specified position -2, followed by cherry and lime.

It should be noted that the elements will be added to the array in the order given.

This article introduces you to various ways to add elements to an array in MongoDB. First, the lesson demonstrates how to use the $push operator to add elements to an array, such as an update operation.

It then demonstrates how to generate a sample data set, insert elements into an array, and finally test the insertion process. The article also discusses how to push elements at the beginning, middle, and end of an array and how to push multiple elements.

Remember that negative integers as values ​​push elements to the end of the array, while positive integers push elements in from the left or beginning of the array.