Retrieve Distinct Values
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: "Earth Science", 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 you want distinct values for
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 |
SetMaxTime() | The maximum amount of time that the query can run on the server. 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 using the Distinct()
method:
results, err := coll.Distinct(context.TODO(), "department", bson.D{{"enrollment", bson.D{{"$lt", 50}}}}) if err != nil { panic(err) } for _, result := range results { fmt.Println(result) }
Additional Information
For a runnable example of retrieving 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: