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This article explains the operators in MongoDB. What is the purpose of $push and $addToSet operators.

Furthermore, the difference between these two operators is given in the code snippet. This article discusses the following topics.

1. Operators in MongoDB
2. $push in MongoDB
3. $addToSet in MongoDB

Operators in MongoDB

Operators are special symbols or keywords that tell the compiler or interpreter to perform mathematical or logical operations.

Query operators enhance the functionality of MongoDB by allowing developers to create complex queries to interact with data sets that match their applications.

Different types of operators in MongoDB are explained below.

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

The $push operator in MongoDB is used to append the given value to an array. The $push operator is an update operator.

If the specified field does not exist in the document to be updated, the $push operator adds it as a new field with the specified value as its element. If the update field is not an array type, the operation fails.

If the value is an array, the $push operator appends the entire array as a single element when updating. If you want to add each value element individually, use the $push operator with the $each modifier.

grammar:

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

The following database collection will be used in all examples.

Simple collection:

db={
  "student": [
    {
      "_id": 1,
      "sem": 1,
      "subjects": [
        "phys",
        "chem",
        "maths",
        "gkn",
        "stat",
        "astro"
      ],
      "achieve": [
        70,
        87,
        90,
        90,
        65,
        81
      ]
    }
  ]
}

MongoDB $push Operator Example

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

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

Because the condition described in the previous example matches 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

MongoDB $push example using $each modifier

If we want to append many entries or multiple elements (77, 49, 83) to the array completed for the record student with the condition subject being “Mathematics”, we can use the following MongoDB command.

db.student.update( { "subjects" : "maths" },{ $push: { "achieve": {$each : [77,49,83 ]} } });

The $each modifier is used in the example above to append multiple entries 77, 49, 83 to an array completion matching the standard subject "maths".

View the latest updated documentation:

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

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

$addToSet in MongoDB

$addToSetThe operator adds or appends a value to an array only if the value does not already exist in the array. When the value is already in the array, $addToSet returns the same array without changing it.

$addToSetoperator ensures that there are no duplicate entries in the array when updating; however, the order of elements in the display can be modified after the values ​​have been added.

grammar:

db.collection.update( { <field>: <value> }, { $addToSet: { <field>: <addition> } } );

The collection used above:

 { "_id" : 1, "sem" : 1, "achieve" : [  80,  70,  90 ] }

$addToSet Example of appending a value

If we want to append the value 92 to the array, we can use the following MongoDB command.

db.student.update( { "sem": 1}, { $addToSet: { "achieve": 92 } } );

The preceding code appends 92 to the array field completion.

View the latest updated documentation:

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

Output of the command:

{ "_id" : 1, "achieve" : [ 70, 80, 90, 92 ], "sem" : 1 }

$addToSet Example of adding multiple values ​​using the $each modifier

The following MongoDB command can be completed to append the numbers 10 and 11 to the array field.

db.student.update( { "sem": 1}, { $addToSet: { "achieve":{$each:[10,11]}}});

In the above example, the numbers 10 and 11 are appended to the array field implemented using the $each modifier.

View the latest updated documentation:

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

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