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This article will cover the various ways to add to an array in MongoDB.

Adding to an array in MongoDB

Use the $push operator to add values ​​to an array

The $push operator is one of the various array update operators provided by MongoDB and is used to update the contents of an array field in a document. The $push operator can add a specific value to an array.

The $push operator adds an item to the end of an array. This operation fails if the field specified by the $push operator is not an array.

grammar:

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

In this case, you can use arrays, embedded/nested documents, or dot notation to specify the fields. Depending on your needs, you can use this operator in conjunction with methods like update(), findAndModify(), etc.

If the provided field is not present in the document, the $push operator will add the array field with the value as its element.

If the value of the $push operator is an array, the entire array will be added as a single element. Alternatively, if you wish to add each value component independently, you can use the $each modifier with the $push operator.

Consider the following example to help you better understand the previous 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 professional_skills array contains technical skills, communication skills, etc., which is what we store here.

We transform the new technical expertise of employees into technical skills by integrating their experience as objects. Run the above line of code in a MongoShell that 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 values ​​to an array

When adding a value to an array, the $addToSet operator checks if the value already exists in the array; otherwise, it does nothing. This operator does not add duplicates to the array, nor does it affect duplicates that already exist.

In this case, the order of the values ​​does not matter.

grammar:

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

In this case, you can use arrays, embedded/nested documents, or dot notation to specify the fields. Depending on your needs, you can use this operator in conjunction with methods like update(), findAndModify(), etc.

Fields other than arrays cannot be used with this operator. If the requested field does not exist, the $addToSet operator generates an array field in the document containing the value or item.

Consider the following example to help you better understand the previous 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 professional_skills array contains technical skills, communication skills, etc., which is what we store here.

We transform the new technical expertise of employees into technical skills by integrating their experience as an object. The main difference between them is that $addToSet will add the element if it does not exist, while $push will append the new element to an array or list.

Run the above code in a MongoShell that 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}
            ]
        },
    ]
}