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Limit the Number of Returned Results

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  • Overview
  • Limit
  • Multiple Options
  • Aggregation
  • Additional Information

Overview

In this guide, you can learn how to limit the number of documents returned from a read operation.

Sample Data

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

type Course struct {
	Title      string
	Enrollment int32
}

To run the examples in this guide, load the sample data into the db.courses collection with the following snippet:

coll := client.Database("db").Collection("courses")
docs := []interface{}{
	Course{Title: "Romantic Era Music", Enrollment: 15},
	Course{Title: "Concepts in Topology", Enrollment: 35},
	Course{Title: "Ancient Greece", Enrollment: 100},
	Course{Title: "Physiology I", Enrollment: 60},
}
result, err := coll.InsertMany(context.TODO(), docs)

Tip

Non-existent 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 and maximum enrollment, corresponding to the title and enrollment fields in each document.

Limit

To limit the number of documents returned from a query, pass the number of documents you want returned to the SetLimit() method of the read operation's options.

The following read operations take an options object as a parameter:

  • Find()

  • CountDocuments()

  • gridfs.Bucket.Find()

If the limit is 0 or exceeds the number of matched documents, the method returns all the documents. If the limit is a negative number, the method uses the absolute value of the negative number as the limit and closes the cursor after retrieving documents.

Example

The following example shows how to return two documents that have an enrollment field value greater than 20:

filter := bson.D{{"enrollment", bson.D{{"$gt", 20}}}}
opts := options.Find().SetLimit(2)
cursor, err := coll.Find(context.TODO(), filter, opts)
var results []Course
if err = cursor.All(context.TODO(), &results); err != nil {
    panic(err)
}
for _, result := range results {
    res, _ := json.Marshal(result)
    fmt.Println(string(res))
}

Multiple Options

The driver performs the limit behavior last regardless of the order in which you set any other options.

Example

The following example performs a Find() operation with the following behavior:

  • Sorts the results in descending order on the enrollment field

  • Skips the first document

  • Returns the first two of the remaining documents

filter := bson.D{}
opts := options.Find().SetSort(bson.D{{"enrollment", -1}}).SetLimit(2).SetSkip(1)
cursor, err := coll.Find(context.TODO(), filter, opts)
var results []Course
if err = cursor.All(context.TODO(), &results); err != nil {
    panic(err)
}
for _, result := range results {
    res, _ := json.Marshal(result)
    fmt.Println(string(res))
}

Tip

Using any of the following option configurations also produces the same result:

opts := options.Find().SetSort(bson.D{{"enrollment", -1}}).SetSkip(1).SetLimit(2)
opts := options.Find().SetLimit(2).SetSort(bson.D{{"enrollment", -1}}).SetSkip(1)
opts := options.Find().SetLimit(2).SetSkip(1).SetSort(bson.D{{"enrollment", -1}})
opts := options.Find().SetSkip(1).SetSort(bson.D{{"enrollment", -1}}).SetLimit(2)
opts := options.Find().SetSkip(1).SetLimit(2).SetSort(bson.D{{"enrollment", -1}})

Aggregation

You can also include the $limit stage to specify a limit in an aggregation pipeline.

Example

The following example shows how to return three documents:

limitStage := bson.D{{"$limit", 3}}
cursor, err := coll.Aggregate(context.TODO(), mongo.Pipeline{limitStage})
if err != nil {
    panic(err)
}
var results []Course
if err = cursor.All(context.TODO(), &results); err != nil {
    panic(err)
}
for _, result := range results {
    res, _ := json.Marshal(result)
    fmt.Println(string(res))
}

Additional Information

To learn more about the operations mentioned, see the following guides:

API Documentation

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

←  Skip Returned ResultsSpecify Which Fields to Return →

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