USING PUSH & PULL OPERATORS IN MONGODB

The $push and $pull operators are a part of array operators designed to modify arrays in MongoDB

documents. In this tutorial, I’ll show you how the push and pull operators work and how to use them

with additional modifiers and conditions.

(This article is part of our MongoDB Guide. Use the right-hand menu to navigate.)

What are push and pull operators?

Push and Pull are the two operations used to add and remove elements from arrays in MongoDB

documents. Pushing and pulling elements are done using the MongoDB $push and $pull operators,

respectively:

Let’s look at each in more detail, including how they work and how you can use them.

How MongoDB $push operator works

You can see the $push operator takes two arguments:

The array field

The value to be appended to the specified array field

If the array field is not present in the document, the $push operator will create a new array field.

However, if the specified field is not an array, MongoDB will return an error.

$push operator modifiers

The functionality of the $push operator can be further extended using the following modifiers.

$each. The $each modifier is used to append multiple values to an array. If the $each operator

$position. The $push operator appends a new item to the end of an array by default. Use the

$position modifier if you want to explicitly specify the location where the item should be

appended.

The $push operation is carried out in the following order, regardless of the order in which the

modifiers are defined:

Update the array to add elements in the specified positions.1.

Sort the array if $sort modifier is specified.2.

Slice the array if $slice modifier is specified.3.

Store the array.4.

Next, we will look at how we can use MongoDB $push operations to manipulate documents. I’ll

db.vehicledetails.find().pretty()

Result:

Append a single value to an array

Let us see how we can append a single value to an array when an array field is present, and it's not

present. In all examples, the "_id" field is used to indicate which document the array should be

added.

Example: No Array Field

A new array field will be created with the field name specified in the $push operator.

db.vehicledetails.update({"_id": ObjectId("5fbc52f05f9a62418038240d")},

{$push: {"vehicle_colours": "red"}})

If we try to use the $push operator for a non-array field, it will result in an error. The following code

returns an error as we are trying to append a value to the non-array field “make”.

db.vehicledetails.update({"_id": ObjectId("5fbc52f05f9a62418038240d")},

{$push: {"make": "green"}})

Result:

Append Multiple Values to an Array

You can append multiple values to an array with or without $each modifier.

Example: Multiple Values without $each modifier

If the $each modifier is not present, MongoDB will append all the values as a single value to the

specified array field.

When a $push operation is defined with the $each modifier, each element in the $push operation

will be added to the array as individual items.

db.vehicledetails.update({"_id": ObjectId("5fbc52f55f9a62418038240e")},

{$push: {"vehicle_colours": { $each :}}})

Result:

Here, “vehicle_colours” has three elements after $push operation.

Using the $sort and $slice Modifiers

In this section, we will demonstrate how to use the $sort and $slice modifiers using the following

document in the “vehicledetails” collection.

Let us add the color "silver" to the "vehicle_colours" array field and sort the contents alphabetically

sorting alphabetically and using the $slice modifier to limit the array to 5 elements.

db.vehicledetails.update({"_id": ObjectId("5fbc52fb5f9a62418038240f")},

{$push: {"vehicle_colours": { $each :, $sort: 1, $slice: 5}}})

Result:

Using the $position Modifier

The $position modifier is used to specify the location in the array where the new item should be

added. This will override the default behavior of appending the items to the end of the array.

In the following example, we will add the color "white" to the beginning of the array field

"vehicle_colours". In the "$position" modifier, zero (0) is used to indicate the first position (index 0) of

the array.

the specified $pull operator condition will be applied to each array element as if each array element

were a document in a collection.

When the specified value to be removed is an array, the $pull operator only removes the elements

in the array that matches the exact value specified, including the order in which the elements are

defined. If the specified value to remove is a document, the $pull operator will remove elements

that match the fields and values specified. In this instance order of fields is discarded.

Now I’ll walk you through a few examples of the $pull operator. Jump to the ones you need:

Remove a single item from an array

Remove all items that equal a specific value

Remove items that match a specified $pull