MongoDB – $setOnInsert Operator

MongoDB $setOnInsert Operator is a type of field update operator. The $setOnInsert operator is used in MongoDB update operations with the upsert option. When a new document is inserted, it assigns specified values to the fields in the document. This operator only acts during the insertion of a new document.

This operator can also work with embedded/nested documents. You can use this operator in methods like update(), findAndModify(), etc., according to your requirements.

If the update() or findAndModify() method with upsert: true has found a matching document, then MongoDB will ignore $setOnInsert and apply the $set operator.

Syntax

db.collection.update(
   <query>,
   { $setOnInsert: { <field1>: <value1>, <field1>: <value2>, ... } },
   { upsert: true }
)

MongoDB $setOnInsert Operator Example

In these examples, we will work with:

Database: GeeksforGeeks

Collection: Example

Document: one documents that contain the details of the employees in the form of field-value pairs.

Example 1: Inserting new fields in new documents using $setOnInsert

In this example, we are creating a new document in the Example collection with the help of update() method by setting the value of an upsert field to true and using $setOneInsert operator assign the values to the department and salary fields in the document.

Query:

db.Example.update({name: {first: "Mina", last: "Singh"},
... personalDetails: {age: 24, contactInfo: 345678901}},
... { $setOnInsert: {department: "Development", salary: 45000}},
... {upsert: true}
... )

Output:

Example 2: Inserting new embedded fields in new document using $setOnInsert

In this example, we are creating a new document in the Example collection with the help of update() method by setting the value of an upsert field to true and using $setOneInsert operator assign the values to embedded fields i.e., in the document.

Query:

db.Example.update({"name.first": "Vinod", expreienceYear: 5}, 
                  {$setOnInsert: {"personalDetails.age": 27, 
                                  "personalDetails.contactInfo": 345678901}},
                  {upsert: true})

Output:

Example 3: Effect of $setOnInsert operator on Matched documents

In this example, we are checking if $setOnInsert operator work with matched document or not. This $setOnInsert operator does not work with already present documents.

Query:

db.Example.update({"name.first": "Mina"}, 
                  {$setOnInsert: {"personalDetails.age": 27, 
                                  "personalDetails.contactInfo": 345678001}}, 
                  {upsert: true})

Before:

Output After:

Key Takeaways About $setOnInsert Operator

• The $setOnInsert operator in MongoDB is used to insert specific values during an upsert operation.
• It does not affect existing documents or update operations that do not result in an insert.
• The operator can also be used with embedded/nested documents using dot notation.
• If an update operation finds a matching document, MongoDB will ignore the $setOnInsert operator and apply the $set operator instead.
• The $setOnInsert operator is useful for setting default values or initializing fields only during the insertion of new documents.