Concat in MongoDB Aggregate | An Introduction

The Concat operator in MongoDB’s aggregate framework is used to concatenate multiple strings or expressions into a single string. Bobcares, as a part of our Server Management Service offers solutions to every query that comes our way.

CONCAT operator in MongoDB’s aggregate framework

Using the $concat operator, we can combine many strings or expressions into a single string in MongoDB’s aggregation framework. It enables us to create new concatenated strings within an aggregation pipeline by combining field values, constant strings, or the output of other expressions.

The Syntax is as follows:

CONCAT operator in MongoDB’s aggregate framework: Different Scenarios

1. Concatenating Field Values: This will join the values of field1 and field2 into a single string.

{ $concat: [ "$field1", "$field2" ] }

2. Concatenating Field Values with Constant Strings: This will combine the values of field1, the constant ” is “, and the value of field2.

{ $concat: [ "$field1", " is ", "$field2" ] }

3. Using Expressions: Here, the $toString operator converts field2 to a string before concatenating it with field1 and the constant string.

{ $concat: [ "$field1", " is ", { $toString: "$field2" } ] }

4. Concatenating Multiple Fields: This will join the values of field1, field2, and field3 into a single string.

{ $concat: [ "$field1", "$field2", "$field3" ] }

Depending on the particular use case, we can use the $concat operator at any level of the aggregate pipeline, such as in the $project, $addFields, or $group stages.

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Conclusion

The article explains the Concat in MongoDB aggregate framework, along with the syntax of the operator to use in different cases.