Retrieve Distinct Values

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Overview

Sample Data
Distinct
Modify Behavior
Additional Information
API Documentation

Overview

In this guide, you can learn how to retrieve distinct values for a specified field across a single collection.

Sample Data

The example in this guide uses the following Course struct as a model for documents in the courses collection:

type Course struct {
	Title      string
	Department string
	Enrollment int32
}

To run the example, load the sample data into the db.courses collection with the following snippet:

coll := client.Database("db").Collection("courses")
docs := []interface{}{
	Course{Title: "World Fiction", Department: "English", Enrollment: 35},
	Course{Title: "Abstract Algebra", Department: "Mathematics", Enrollment: 60},
	Course{Title: "Modern Poetry", Department: "English", Enrollment: 12},
	Course{Title: "Plate Tectonics", Department: "Geology", Enrollment: 30},
}
result, err := coll.InsertMany(context.TODO(), docs)

Tip

Nonexistent Databases and Collections

If the necessary database and collection don't exist when you perform a write operation, the server implicitly creates them.

Each document contains a description of a university course that includes the course title, department, and enrollment. These items correspond to the title, department, and enrollment fields in each document.

Distinct

To retrieve distinct values for a specified field across a single collection, pass the following parameters to the Distinct() method:

The field name for which you want to retrieve the distinct values
A non-nil query filter specifying which documents to match

Tip

If you specify an empty query filter, the Distinct() method searches for distinct values across all documents in a collection.

Modify Behavior

You can modify the behavior of the Distinct() method by passing in a DistinctOptions. If you don't specify a DistinctOptions, the driver uses the default values for each option.

The DistinctOptions type allows you to configure options with the following methods:

Method	Description
`SetCollation()`	The type of language collation to use when sorting results. Default: `nil`
`SetComment()`	Sets a comment to attach to the distinct operation. Default: `nil`

Example

The following example matches documents with an enrollment field value less than 50 and prints the distinct values of the department field by using the Distinct() method:

filter := bson.D{{"enrollment", bson.D{{"$lt", 50}}}}
var arr []string
err = coll.Distinct(context.TODO(), "department", filter).Decode(&arr)
if err != nil {
	panic(err)
}
fmt.Printf("%s\n", arr)

[English Geology]

Additional Information

For a runnable example that retrieves distinct values, see Retrieve Distinct Values of a Field.

To learn about constructing a query filter, see Specify a Query.

API Documentation

To learn more about any of the methods or types discussed in this guide, see the following API Documentation:

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