DOCSP-41980: Cursor guide

snooty.toml

@@ -27,3 +27,4 @@ php-library = "MongoDB PHP Library"
 php-library = "MongoDB PHP Library"
 mdb-server = "MongoDB Server"
 api = "https://www.mongodb.com/docs/php-library/current/reference"
+php-manual = "https://www.php.net/manual/en"

source/includes/read/cursor.php

@@ -0,0 +1,64 @@
+<?php
+require 'vendor/autoload.php';
+
+$uri = getenv('MONGODB_URI') ?: throw new RuntimeException('Set the MONGODB_URI variable to your Atlas URI that connects to the sample dataset');
+$client = new MongoDB\Client($uri);
+
+// start-db-coll
+$collection = $client->sample_restaurants->restaurants;
+// end-db-coll
+
+// Iterates over and prints all documents that have a "name" value of "Dunkin' Donuts"
+// start-cursor-iterate
+$cursor = $collection->find(['name' => 'Dunkin\' Donuts']);
+foreach ($cursor as $doc) {
+    echo json_encode($doc) . PHP_EOL;
+}
+// end-cursor-iterate
+
+// Retrieves and prints the first document stored in the cursor
+// start-cursor-first
+$cursor = $collection->find(['name' => 'Dunkin\' Donuts']);
+echo json_encode($cursor->current());
+// end-cursor-first
+
+// Converts the documents stored in a cursor to an array
+// start-cursor-array
+$cursor = $collection->find(['name' => 'Dunkin\' Donuts']);
+$array_results = $cursor->toArray();
+// end-cursor-array
+
+// Creates a collection with a maximum size and inserts documents representing vegetables
+// start-capped-coll
+$db = $client->db;
+$create_coll = $db->createCollection(
+    'vegetables', 
+    ['capped' => true, 'size' => 1024 * 1024]
+);
+
+$vegetables = [
+    ['name' => 'cauliflower'],
+    ['name' => 'zucchini']
+];
+
+$collection = $db->vegetables;
+$result = $collection->insertMany($vegetables);
+// end-capped-coll
+
+// Iterates over the initial query results and continues iterating until three documents are stored in the cursor
+// by using a tailable cursor
+// start-tailable
+$cursor = $collection->find([], ['cursorType' => MongoDB\Operation\Find::TAILABLE]);
+
+$docs_found = 0;
+while ($docs_found < 3) {
+    foreach ($cursor as $doc) {
+        echo json_encode($doc) . PHP_EOL;
+        $docs_found++;
+    }
+
+    // Sleeps for 100 milliseconds before trying to access more documents
+    usleep(100000);
+}
+// end-tailable
+

source/read.txt

@@ -10,4 +10,5 @@ Read Data from MongoDB
 
    /read/retrieve
    /read/project
+   /read/cursor
 

source/read/cursor.txt

@@ -0,0 +1,179 @@
+.. _php-cursors:
+
+=========================
+Access Data From a Cursor
+=========================
+
+.. contents:: On this page
+   :local:
+   :backlinks: none
+   :depth: 1
+   :class: singlecol
+
+.. facet::
+   :name: genre
+   :values: reference
+
+.. meta::
+   :keywords: read, results, code example
+
+Overview
+--------
+
+In this guide, you can learn how to access data from a **cursor** by using the
+{+php-library+}.
+
+A cursor is a mechanism that returns the results of a read operation in iterable
+batches. Cursors reduce both memory consumption and network bandwidth usage by holding
+only a subset of documents at any given time rather than returning all documents at
+once.
+
+Whenever the {+php-library+} performs a read operation by using the ``MongoDB\Collection::find()``
+method, it returns the matching documents in a ``MongoDB\Driver\Cursor`` instance.
+
+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 access this collection
+from your PHP application, instantiate a ``MongoDB\Client`` that connects to an Atlas cluster
+and assign the following value to your ``collection`` variable:
+
+.. literalinclude:: /includes/read/cursor.php
+   :language: php
+   :dedent:
+   :start-after: start-db-coll
+   :end-before: end-db-coll
+
+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.
+
+.. _php-cursors-iterate:
+
+Access Cursor Contents Iteratively
+----------------------------------
+
+To iterate over the contents of a ``MongoDB\Driver\Cursor`` instance, use a ``foreach`` loop.
+
+The following example uses the ``MongoDB\Collection::find()`` method to retrieve all documents
+in which the ``name`` value is ``'Dunkin' Donuts'``. It then prints each document from the
+cursor returned by the ``find()`` method:
+
+.. io-code-block::
+   :copyable:
+
+   .. input:: /includes/read/cursor.php
+      :start-after: start-cursor-iterate
+      :end-before: end-cursor-iterate
+      :language: php
+      :dedent:
+
+   .. output::
+      :visible: false
+
+      {"_id":{"$oid":"..."},..."name":"Dunkin' Donuts","restaurant_id":"40379573"}
+      {"_id":{"$oid":"..."},..."name":"Dunkin' Donuts","restaurant_id":"40363098"}
+      {"_id":{"$oid":"..."},..."name":"Dunkin' Donuts","restaurant_id":"40395071"}
+      ...
+
+Retrieve Documents Individually
+-------------------------------
+
+To retrieve an individual document from a cursor, call the ``current()`` method on
+a ``MongoDB\Driver\Cursor`` instance. This method returns the document that the cursor
+initially points to. You can continue to advance the cursor by calling the ``next()``
+method, which instructs the cursor to point to the next retrieved document.
+
+The following example finds all documents in a collection that have a ``name`` value
+of ``'Dunkin' Donuts'``. Then, it prints the first retrieved document by calling the
+``current()`` method on a cursor:
+
+.. io-code-block::
+   :copyable:
+
+   .. input:: /includes/read/cursor.php
+      :start-after: start-cursor-first
+      :end-before: end-cursor-first
+      :language: php
+      :dedent:
+
+   .. output::
+
+      {"_id":{"$oid":"..."},..."name":"Dunkin' Donuts","restaurant_id":"40379573"}
+
+Retrieve All Documents
+----------------------
+
+.. warning::
+
+   If the number and size of documents returned by your query exceeds available
+   application memory, your program will crash. If you expect a large result
+   set, :ref:`access your cursor iteratively <php-cursors-iterate>`.
+
+To retrieve all documents from a cursor, convert the cursor into an array as
+shown in the following example:
+
+.. literalinclude:: /includes/read/cursor.php
+   :language: php
+   :dedent:
+   :start-after: start-cursor-array
+   :end-before: end-cursor-array
+
+Tailable Cursors
+----------------
+
+When querying on a :manual:`capped collection </core/capped-collections/>`, you
+can use a **tailable cursor** that remains open after the client exhausts the
+results in a cursor. To create a tailable cursor, set the ``cursorType`` option to
+``MongoDB\Operation\Find::TAILABLE`` in an array. Then, pass the array as an options
+parameter to the ``MongoDB\Collection::find()`` method.
+
+For example, you can create a capped collection called ``vegetables`` that stores
+documents representing vegetables, as shown in the following code:
+
+.. literalinclude:: /includes/read/cursor.php
+    :language: php
+    :dedent:
+    :start-after: start-capped-coll
+    :end-before: end-capped-coll
+
+The following code uses a tailable cursor to retrieve all documents in the ``vegetables``
+collection. After the cursor is exhausted, it remains open until retrieving three documents:
+
+.. io-code-block::
+   :copyable:
+
+   .. input:: /includes/read/cursor.php
+      :start-after: start-tailable
+      :end-before: end-tailable
+      :language: php
+      :dedent:
+
+   .. output::
+      :visible: false
+
+      {"_id":{"$oid":"..."},"name":"cauliflower"}
+      {"_id":{"$oid":"..."},"name":"zucchini"}
+
+If you insert another document into the ``vegetables`` collection, the preceding code prints
+the new document and closes the ``while`` loop.
+
+To learn more about tailable cursors, see the :manual:`Tailable Cursors guide
+</core/tailable-cursors/>` in the {+mdb-server+} manual.
+
+Additional Information
+----------------------
+
+To learn more about read operations, see the :ref:`php-retrieve` guide.
+
+To learn more about cursors, see the following pages in the PHP manual:
+
+- `MongoDB\\Driver\\Cursor <{+php-manual+}/class.mongodb-driver-cursor.php>`__
+- `MongoDB\\Driver\\Cursor::current() <{+php-manual+}/mongodb-driver-cursor.current.php>`__
+- `MongoDB\\Driver\\Cursor::toArray() <{+php-manual+}/mongodb-driver-cursor.toarray.php>`__
+
+API Documentation
+~~~~~~~~~~~~~~~~~
+
+To learn more about the ``find()`` method, see `MongoDB\\Collection::find() 
+<{+api+}/method/MongoDBCollection-find/>`__ in the API documentation.