Retrieve Distinct Field Values
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Overview
In this guide, you can learn how to use the Ruby driver to retrieve the distinct values of a specified field across a collection.
Within a collection, documents might contain different values for a
single field. For example, one document in a restaurants collection has a
borough value of 'Manhattan', and another has a borough value of
'Queens'. You can use the Ruby driver to retrieve all the unique values
that a field contains across multiple documents in a collection.
Sample Data
The examples in this guide use the restaurants collection in the sample_restaurants
database from the Atlas sample datasets. To access this collection
from your Ruby application, create a Mongo::Client object that connects to
an Atlas cluster and assign the following values to your database and collection
variables:
database = client.use('sample_restaurants') collection = database[:restaurants]
To learn how to create a free MongoDB Atlas cluster and load the sample datasets, see the Get Started with Atlas guide.
Retrieve Distinct Values
To retrieve the distinct values for a specified field, call the distinct
method and pass in the name of the field you want to find distinct values for.
Retrieve Values Across a Collection
The following example retrieves the distinct values of the borough field in
the restaurants collection:
results = collection.distinct('borough') results.each do |value| puts value end
Bronx Brooklyn Manhattan Missing Queens Staten Island
The operation returns an array 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.
The following example retrieves the distinct values of the borough field for
all documents that have a cuisine field value of 'Italian':
results = collection.distinct('borough', { cuisine: 'Italian' }) results.each do |value| puts value end
Bronx Brooklyn Manhattan Queens Staten Island
Modify Distinct Behavior
You can modify the behavior of the distinct method by passing a
Hash object that specifies option values. The following table describes the
options you can set to customize the operation:
Option | Description |
|---|---|
| The collation to use for the operation. Type: Hash |
| The maximum amount of time in milliseconds that the operation can run. Type: Integer |
| The read preference to use for the operation. To learn more, see
Read Preference in the MongoDB Server manual. Type: Hash |
| The session to use for the operation. Type: Session |
The following example retrieves the distinct values of the name field for
all documents that have a borough field value of 'Bronx' and a
cuisine field value of 'Pizza'. It also sets the read option,
which instructs the operation to use a primary_preferred
read preference:
filter = { borough: 'Bronx', cuisine: 'Pizza' } options = { read: { mode: :primary_preferred } } results = collection.distinct('name', filter, options) results.each do |value| puts value end
$1.25 Pizza 18 East Gunhill Pizza 2 Bros Aenos Pizza Alitalia Pizza Restaurant Amici Pizza And Pasta Angie'S Cafe Pizza Anthony & Joe'S Pizza Anthony'S Pizza Antivari Pizza Arturo'S Pizza Bartow Pizza ...
API Documentation
To learn more about the distinct method, see the
API documentation.