DOCSP-41135: Specify Fields

source/includes/read/project.kt

@@ -0,0 +1,68 @@
+package org.example
+import com.mongodb.ConnectionString
+import com.mongodb.MongoClientSettings
+import com.mongodb.client.model.Filters.eq
+import com.mongodb.client.model.Projections
+import com.mongodb.kotlin.client.MongoClient
+import org.bson.codecs.pojo.annotations.BsonId
+import org.bson.types.ObjectId
+
+// start-data-class
+data class Restaurant(
+    @BsonId
+    val id: ObjectId? = null,
+    val name: String,
+    val borough: String,
+    val cuisine: String
+)
+// end-data-class
+
+fun main() {
+    val uri = "<connection string URI>"
+
+    val settings = MongoClientSettings.builder()
+        .applyConnectionString(ConnectionString(uri))
+        .retryWrites(true)
+        .build()
+
+    val mongoClient = MongoClient.create(settings)
+    val database = mongoClient.getDatabase("sample_restaurants")
+    val collection = database.getCollection<Restaurant>("restaurants")
+
+    // start-project
+    val projection = Projections.fields(
+        Projections.include(
+            Restaurant::name.name,
+            Restaurant::cuisine.name,
+            Restaurant::borough.name
+        )
+    )
+
+    val results = collection
+        .find(eq(Restaurant::name.name, "Emerald Pub"))
+        .projection(projection)
+
+    results.forEach { result ->
+        println(result)
+    }
+    // end-project
+
+    // start-project-exclude
+    val projection = Projections.fields(
+        Projections.excludeId(),
+        Projections.include(
+            Restaurant::name.name,
+            Restaurant::cuisine.name,
+            Restaurant::borough.name
+        )
+    )
+
+    val results = collection
+        .find(eq(Restaurant::name.name, "Emerald Pub"))
+        .projection(projection)
+
+    results.forEach { result ->
+        println(result)
+    }
+    // end-project-exclude
+}

source/read.txt

@@ -23,6 +23,7 @@ Read Data from MongoDB
    :maxdepth: 1
 
    /read/count
+   /read/project
 
 Overview
 --------

source/read/project.txt

@@ -0,0 +1,127 @@
+.. _kotlin-sync-project:
+
+========================
+Specify Fields To Return
+========================
+
+.. contents:: On this page
+   :local:
+   :backlinks: none
+   :depth: 2
+   :class: singlecol
+
+.. facet::
+   :name: genre
+   :values: reference
+
+.. meta::
+   :keywords: read, filter, project, select
+
+Overview
+--------
+
+In this guide, you can learn how to specify which fields to return from a read
+operation by using a **projection**. A projection is a document that specifies
+which fields MongoDB returns from a query.
+
+Sample Data
+~~~~~~~~~~~
+
+The examples in this guide use the ``restaurants`` collection in the ``sample_restaurants``
+database from the :atlas:`Atlas sample datasets </sample-data>`. To learn how to create a
+free MongoDB Atlas cluster and load the sample datasets, see the
+:atlas:`Get Started with Atlas </getting-started>` guide.
+
+The documents in this collection are modeled by the following {+language+} data class:
+
+.. literalinclude:: /includes/read/project.kt
+   :start-after: start-data-class
+   :end-before: end-data-class
+   :language: kotlin
+   :copyable:
+
+Projection Types
+----------------
+
+You can use a projection to specify which fields to include in a return
+document, or to specify which fields to exclude.
+
+When specifying certain fields to include in a projection, all other fields are implicitly
+excluded (except the ``_id`` field, which is included by default). You cannot combine
+inclusion and exclusion statements in a single projection, unless you are excluding the
+``_id`` field.
+
+To remove the ``_id`` field from the returned document, you must
+:ref:`explicitly exclude it <kotlin-sync-project-exclude-id>`.
+
+Specify Fields to Include
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Use the following syntax to specify the fields to include in the result:
+
+.. code-block:: kotlin
+
+   val projection = Projection.fields(
+       Projections.include(<fieldName1>, <fieldName2>, ...)
+   )
+
+The following example uses the ``find()`` method to find all restaurants with
+the ``name`` field value of ``"Emerald Pub"``. It then uses a projection to
+return only the ``name``, ``cuisine``, and ``borough`` fields of the returned
+documents.
+
+.. io-code-block::
+   :copyable: true
+
+   .. input:: /includes/read/project.kt
+      :start-after: start-project
+      :end-before: end-project
+      :language: kotlin
+      :dedent:
+
+   .. output::
+      :visible: false
+
+      Restaurant(id=5eb3d668b31de5d588f429e2, name=Emerald Pub, borough=Manhattan, cuisine=American)
+      Restaurant(id=5eb3d668b31de5d588f432dd, name=Emerald Pub, borough=Queens, cuisine=American)
+
+.. _kotlin-sync-project-exclude-id:
+
+Exclude the ``_id`` Field
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When specifying fields to include, you can also exclude the ``_id`` field from
+the returned document.
+
+The following example runs the same query as the preceding example, but
+excludes the ``_id`` field from the projection:
+
+.. io-code-block::
+   :copyable: true
+
+   .. input:: /includes/read/project.kt
+      :start-after: start-project-exclude
+      :end-before: end-project-exclude
+      :language: kotlin
+      :dedent:
+
+   .. output::
+      :visible: false
+
+      Restaurant(id=null, name=Emerald Pub, borough=Manhattan, cuisine=American)
+      Restaurant(id=null, name=Emerald Pub, borough=Queens, cuisine=American)
+
+Additional Information
+----------------------
+
+To learn more about projections, see the :manual:`Project Fields guide
+</tutorial/project-fields-from-query-results/>` in the MongoDB Server Manual.
+
+API Documentation
+~~~~~~~~~~~~~~~~~
+
+To learn more about any of the methods or types discussed in this
+guide, see the following API Documentation:
+
+- `find() <{+api+}/mongodb-driver-kotlin-sync/com.mongodb.kotlin.client/-mongo-collection/find.html>`__
+- `projection() <{+api+}/mongodb-driver-kotlin-sync/com.mongodb.kotlin.client/-find-iterable/projection.html>`__