Retrieve Distinct Field Values

Sample Data

The examples in this guide use the restaurants collection in the sample_restaurants database from the Atlas sample datasets. To learn how to create a free MongoDB Atlas cluster and load the sample datasets, see the MongoDB Get Started guide.

You can access the documents in the restaurants collection as instances of the Document type or a custom data type. To specify which data type represents the collection's data, replace the <T> type parameter with one of the following values:

• <Document>: Represents collection documents as BSON documents

• <Restaurant>: Represents collection documents as instances of the Restaurant struct, defined in the code examples

Retrieve Values Across a Collection

The following example retrieves the distinct values of the borough field in the restaurants collection.

Select the Asynchronous or Synchronous tab to see the corresponding code for each runtime:

let boroughs = my_coll.distinct("borough", None).await?;
println!("List of field values for 'borough':");
for b in boroughs {
    println!("{:?}", b);
}

List of field values for 'borough':
String("Bronx")
String("Brooklyn")
String("Manhattan")
String("Missing")
String("Queens")
String("Staten Island")

let boroughs = my_coll.distinct("borough", None).run()?;
println!("List of field values for 'borough':");
for b in boroughs {
    println!("{:?}", b);
}

List of field values for 'borough':
String("Bronx")
String("Brooklyn")
String("Manhattan")
String("Missing")
String("Queens")
String("Staten Island")

The operation returns a vector that stores each distinct borough field value. Although several documents have the same value in the borough field, each value appears in the results only once.

Retrieve Values Across Specified Documents

You can provide a query filter to the distinct() method to find the distinct field values across a subset of documents in a collection. A query filter is an expression that specifies search criteria used to match documents in an operation. For example, you can use the distinct() method to find distinct field values from only a subset of matched documents.

The following example retrieves the distinct values of the borough field for all documents that have a cuisine field value of "Turkish".

Select the Asynchronous or Synchronous tab to see the corresponding code for each runtime:

let filter = doc! { "cuisine": "Turkish" };
let boroughs = my_coll.distinct("borough", filter).await?;
println!("List of field values for 'borough':");
for b in boroughs {
    println!("{:?}", b);
}

List of field values for 'borough':
String("Brooklyn")
String("Manhattan")
String("Queens")
String("Staten Island")

let filter = doc! { "cuisine": "Turkish" };
let boroughs = my_coll.distinct("borough", filter).run()?;
println!("List of field values for 'borough':");
for b in boroughs {
    println!("{:?}", b);
}

List of field values for 'borough':
String("Brooklyn")
String("Manhattan")
String("Queens")
String("Staten Island")

Modify Distinct Behavior

You can modify the behavior of the distinct() method by chaining one or more option methods to your count_documents() call before the await or run() method call. The following table describes options you can set to customize the distinct operation: