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DOCSP-39721: Distinct (#73)
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‎source/includes/read-ops/distinct.java

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import com.mongodb.ConnectionString;
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import com.mongodb.MongoClientSettings;
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import com.mongodb.client.model.Filters;
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import com.mongodb.reactivestreams.client.*;
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import org.bson.Document;
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import org.bson.conversions.Bson;
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import reactor.core.publisher.Flux;
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public class Distinct {
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public static void main(String[] args) {
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String uri = "<connection string URI>";
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MongoClientSettings settings = MongoClientSettings.builder()
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.applyConnectionString(new ConnectionString(uri))
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.build();
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try (MongoClient mongoClient = MongoClients.create(settings))
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{
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MongoDatabase database = mongoClient.getDatabase("sample_restaurants");
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MongoCollection<Document> collection = database.getCollection("restaurants");
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// start-distinct
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DistinctPublisher<String> distinctPublisher = collection
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.distinct("borough", String.class);
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Flux.from(distinctPublisher)
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.doOnNext(System.out::println)
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.blockLast();
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// end-distinct
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// start-distinct-query
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Bson filter = Filters.eq("cuisine", "Italian");
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DistinctPublisher<String> distinctPublisher = collection
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.distinct("borough", String.class)
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.filter(filter);
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Flux.from(distinctPublisher)
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.doOnNext(System.out::println)
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.blockLast();
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// end-distinct-query
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// start-distinct-comment
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Bson filter = Filters.and(
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Filters.eq("borough", "Bronx"),
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Filters.eq("cuisine", "Pizza")
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);
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DistinctPublisher<String> distinctPublisher = collection
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.distinct("name", String.class)
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.filter(filter)
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.comment("Bronx pizza restaurants");
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Flux.from(distinctPublisher)
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.doOnNext(System.out::println)
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.blockLast();
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// end-distinct-comment
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}
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}
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}

‎source/read-data-from-mongo.txt

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/read/specify-fields-return
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/read/specify-documents-to-return
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/read/count-documents
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/read/distinct
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/read/read-preference
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/read/text-search
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/read/geo
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:language: java
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:copyable:
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To learn more about the ``distinct()`` method, see :manual:`distinct()
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<reference/method/db.collection.distinct/>` in the {+mdb-server+} manual.
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To learn more about the ``distinct()`` method, see the :ref:`<java-rs-distinct>` guide.
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Monitor Data Changes
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--------------------

‎source/read/distinct.txt

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.. _java-rs-distinct:
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==============================
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Retrieve Distinct Field Values
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==============================
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.. contents:: On this page
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:local:
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:backlinks: none
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:depth: 2
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:class: singlecol
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.. facet::
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:name: genre
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:values: reference
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.. meta::
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:keywords: read, unique, code example
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Overview
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--------
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Within a collection, different documents might contain different values for a single field.
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For example, one document in the ``restaurant`` collection has a ``borough`` value of ``"Manhattan"``, and
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another has a ``borough`` value of ``"Queens"``. With the {+driver-short+}, you can
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retrieve all the distinct values that a field contains across multiple documents
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in a collection.
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Sample Data
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~~~~~~~~~~~
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The examples in this guide use the ``sample_restaurants.restaurants`` collection
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from the :atlas:`Atlas sample datasets </sample-data>`. To learn how to create a
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free MongoDB Atlas cluster and load the sample datasets, see
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:ref:`<java-rs-getting-started>`.
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.. include:: includes/reactor-note.rst
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``distinct()`` Method
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---------------------
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To retrieve the distinct values for a specified field, call the ``distinct()``
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method and pass in the name of the field you want to find distinct values for.
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Retrieve Distinct Values Across a Collection
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The following example retrieves the distinct values of the ``borough`` field in
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the ``restaurants`` collection:
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.. io-code-block::
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.. input:: /includes/read-ops/distinct.java
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:start-after: start-distinct
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:end-before: end-distinct
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:language: java
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:dedent:
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.. output::
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Bronx
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Brooklyn
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Manhattan
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Missing
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Queens
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Staten Island
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The results show every distinct value that appears in the ``borough`` field
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across all documents in the collection. Although several documents have the same
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value in the ``borough`` field, each value appears in the results only once.
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Retrieve Distinct Values Across Specified Documents
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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You can provide a **query filter** to the ``distinct()`` method to find the distinct
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field values across a subset of documents in a collection. A query filter is an expression that specifies search
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criteria used to match documents in an operation. For more information about
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creating a query filter, see :ref:`java-rs-specify-query`.
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The following example retrieves the distinct values of the ``borough`` field for
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all documents that have a ``cuisine`` field value of ``"Italian"``:
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.. io-code-block::
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.. input:: /includes/read-ops/distinct.java
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:start-after: start-distinct-query
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:end-before: end-distinct-query
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:language: java
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:dedent:
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.. output::
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Bronx
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Brooklyn
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Manhattan
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Queens
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Staten Island
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Modify Distinct Behavior
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~~~~~~~~~~~~~~~~~~~~~~~~
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The ``distinct()`` method can be modified by chaining methods to the ``distinct()`` method
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call. If you don't specify any options, the driver does not customize the operation.
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The following table describes some methods you can use to customize the
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``distinct()`` operation:
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.. list-table::
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:widths: 30 70
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:header-rows: 1
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* - Method
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- Description
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* - ``batchSize()``
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- | Sets the number of documents to return per batch.
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* - ``collation()``
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- | Specifies the kind of language collation to use when sorting
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results. For more information, see :manual:`Collation </reference/collation/#std-label-collation>`
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in the {+mdb-server+} manual.
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* - ``comment()``
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- | Specifies a comment to attach to the operation.
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* - ``filter()``
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- | Sets the query filter to apply to the query.
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* - ``maxTime()``
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- | Sets the maximum amount of time to allow the operation to run, in milliseconds.
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For a complete list of methods you can use to modify the ``distinct()`` method, see
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the `DistinctPublisher <{+api+}/mongodb-driver-reactivestreams/com/mongodb/reactivestreams/client/DistinctPublisher.html>`__ API documentation.
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The following example retrieves the distinct values of the ``name`` field for
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all documents that have a ``borough`` field value of ``"Bronx"`` and a
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``cuisine`` field value of ``"Pizza"``. It also uses
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the ``comment`` option to add a comment to the operation.
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.. io-code-block::
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.. input:: /includes/read-ops/distinct.java
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:start-after: start-distinct-comment
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:end-before: end-distinct-comment
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:language: java
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:dedent:
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.. output::
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$1.25 Pizza
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18 East Gunhill Pizza
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2 Bros
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Aenos Pizza
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Alitalia Pizza Restaurant
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...
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Additional Information
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----------------------
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To learn more about the distinct command, see the :manual:`Distinct guide
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</reference/command/distinct/>` in the MongoDB Server Manual.
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API Documentation
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~~~~~~~~~~~~~~~~~
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To learn more about any of the methods or types discussed in this
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guide, see the following API documentation:
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- `distinct() <{+api+}/mongodb-driver-reactivestreams/com/mongodb/reactivestreams/client/MongoCollection.html#distinct(java.lang.String,java.lang.Class)>`__
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- `DistinctPublisher <{+api+}/mongodb-driver-reactivestreams/com/mongodb/reactivestreams/client/DistinctPublisher.html>`__

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