How to Add Element to Array in MongoDB

This article will look at many methods to add to an array in MongoDB.

Add to Array in MongoDB

Use the $push Operator to Add Value to an Array

The $push operator is one of the various array update operators MongoDB offers to update the contents of array fields in documents. The $push operator can add a specific value to an array.

The $push operator adds items to the end of the array. This action will fail if the field specified by the $push operator is not an array.

Syntax:

{
    $push: {
        <field1>: <value1>,
        <field2>: <value2>,
        ...
    }
}

In this case, the field can be specified using arrays, embedded/nested documents, or dot notation. Depending on your needs, you can combine this operator with methods like update(), findAndModify(), etc.

The $push operator will add the array field with the value as its elements if the provided field is not already in the document.

The entire array will be added as a single element if the value of the $push operator is an array. Additionally, you may use the $each modifier and the $push operator if you wish to add each value component independently.

Consider the following example to help you better understand the prior idea.

db.employees.update(
    {name: "John Doe"},
    {$push: {'professional_skills.$.technical': { skill: "C++", exp: '1' }}}
)

In the above example, we are changing the user "John Doe" in the employees collection. The array of professional_skills contains the technical skills, communication skills, etc. is what we are storing in this place.

We are pushing an employee’s new technical expertise into technical skill by integrating their experience as an object. Run the above line of code in MongoShell, which is compatible with MongoDB.

Output:

{
  "_id" : ObjectId("54f612b6029b47919a90cesd"),
  "email" : "johndoe@exampledomain.com",
  "name" : "John Doe",
  "country" : "USA",
  professional_skills: [
        {
            technical:[
                { skill:'javascript', exp: 4},
                { skill:'c', exp: 3}
            ]
        },
    ]
}

Use the $addToSet Operator to Add Value to an Array

When adding a value to an array, the $addToSet operator checks to see if the value already exists in the array; otherwise, it does nothing. This operator does not add duplicate items to the array and does not affect duplicate items already there.

The values’ order is irrelevant in this situation.

Syntax:

{
    $addToSet: {
        <field1>: <value1>,
        <field2>: <value2>,
        ...
    }
}

In this case, the field can be specified using arrays, embedded/nested documents, or dot notation. Depending on your needs, you can combine this operator with methods like update(), findAndModify(), etc.

Fields other than arrays cannot be used with this operator. The $addToSet operator generates an array field in the document with values or items if the requested field does not exist.

Consider the following example to help you better understand the prior idea.

db.employees.update(
   {name: "John Doe"},
   {$addToSet: {'professional_skills.$.technical': { skill: "C++", exp: '1' }}}
)

In the above example, we are changing the user "John Doe" in the employees collection. The array of professional_skills contains the technical skills, communication skills, etc. is what we are storing in this place.

We are pushing an employee’s new technical expertise into technical skill by integrating their experience as an object. The primary difference between them is that $addToSet will add the element if it does not already exist, whereas $push will append the new element to the array or list.

Run the above line of code in MongoShell, which is compatible with MongoDB.

Output:

{
  "_id" : ObjectId("54f612b6029b47919a90cesd"),
  "email" : "johndoe@exampledomain.com",
  "name" : "John Doe",
  "country" : "USA",
  professional_skills: [
        {
            technical:[
                { skill:'javascript', exp: 4},
                { skill:'c', exp: 3}
            ]
        },
    ]
}