MongoCollection::validate
One *VERY* important note, if You do:
$cursor = $collection->find(array(), array('_id' => 0)); // ommit '_id' field in result
then:
var_dump(iterator_to_array($cursor));
will return only *ONE* document, not all!
The MongoCursor class
(No version information available, might only be in SVN)
Introduction
A cursor is used to iterate through the results of a database query. For example, to query the database and see all results, you could do:
<?php
$cursor = $collection->find();
var_dump(iterator_to_array($cursor));
?>
You don't generally create cursors using the MongoCursor constructor, you get a new cursor by calling MongoCollection::find() (as shown above).
Suppose that, in the example above, $collection was a 50GB collection. We certainly wouldn't want to load that into memory all at once, which is what a cursor is for: allowing the client to access the collection in dribs and drabs.
If we have a large result set, we can iterate through it, loading a few megabytes of results into memory at a time. For example, we could do:
<?php
$cursor = $collection->find();
foreach ($cursor as $doc) {
// do something to each document
}
?>
Note that this means that a cursor does not "contain" the database results, it just manages them. Thus, if you print a cursor (with, say, var_dump() or print_r()), you'll just get the cursor object, not your documents. To get the documents themselves, you can use one of the methods shown above.
Cursor Stages
A MongoCursor has two "life stages": pre- and post- query. When a cursor is created, it has not yet contacted the database, so it is in its pre-query state. In this state, the client can further specify what they want the query to do, including adding limits, skips, sorts, and more advanced options.
When the client attempts to get a result (by calling MongoCursor::next(), directly or indirectly), the cursor moves into the post-query stage. At this point, the query has been executed by the database and cannot be modified anymore.
<?php
$cursor = $collection->find()->limit(10);
// database has not yet been queried, so more search options can be added
$cursor = $cursor->sort(array("a" => 1));
var_dump($cursor->getNext());
// now database has been queried and more options cannot be added
// so this will throw an exception:
$cursor->skip(4);
?>
Class synopsis
MongoCursor
implements
Iterator
{
/* Static Fields */
/* Methods */
public MongoCursor::__construct
( Mongo $connection
, string $ns
[, array $query = array()
[, array $fields = array()
]] )
}Static Variables
- slaveOkay
-
If the query should have the "slaveOkay" flag set, which allows reads on the slave (slaves are, by default, just for backup and unreadable). Can be overridden with MongoCursor::slaveOkay().
- timeout
-
Set timeout in milliseconds for all database responses. To wait forever, use -1. Can be overridden with MongoCursor::timeout(). This does not cause the MongoDB server to cancel the operation, it just causes the driver to stop waiting for a response and throw a MongoCursorTimeoutException.
See Also
MongoDB core docs on » cursors.
Table of Contents
- MongoCursor::addOption — Adds a top-level key/value pair to a query
- MongoCursor::batchSize — Sets the number of results returned per result set
- MongoCursor::__construct — Create a new cursor
- MongoCursor::count — Counts the number of results for this query
- MongoCursor::current — Returns the current element
- MongoCursor::dead — Checks if there are documents that have not been sent yet from the database for this cursor
- MongoCursor::doQuery — Execute the query.
- MongoCursor::explain — Return an explanation of the query, often useful for optimization and debugging
- MongoCursor::fields — Sets the fields for a query
- MongoCursor::getNext — Return the next object to which this cursor points, and advance the cursor
- MongoCursor::hasNext — Checks if there are any more elements in this cursor
- MongoCursor::hint — Gives the database a hint about the query
- MongoCursor::immortal — Sets whether this cursor will timeout
- MongoCursor::info — Gets the query, fields, limit, and skip for this cursor
- MongoCursor::key — Returns the current result's _id
- MongoCursor::limit — Limits the number of results returned
- MongoCursor::next — Advances the cursor to the next result
- MongoCursor::partial — If this query should fetch partial results from mongos if a shard is down
- MongoCursor::reset — Clears the cursor
- MongoCursor::rewind — Returns the cursor to the beginning of the result set
- MongoCursor::skip — Skips a number of results
- MongoCursor::slaveOkay — Sets whether this query can be done on a slave
- MongoCursor::snapshot — Use snapshot mode for the query
- MongoCursor::sort — Sorts the results by given fields
- MongoCursor::tailable — Sets whether this cursor will be left open after fetching the last results
- MongoCursor::timeout — Sets a client-side timeout for this query
- MongoCursor::valid — Checks if the cursor is reading a valid result.
add a note
User Contributed Notes
MongoCursor
adrian dot zurek at netmedia dot com dot pl
24-Oct-2011 04:08
Adil Baig @ AiDezigns
07-Sep-2011 07:28
If you want to know whether a cursor returned any results it is faster to use 'hasNext()' than 'count'