Php/docs/class.mongocursor

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(PECL mongo >=0.9.0)

简介

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:

Example #1 MongoCursor basic usage

<?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:

'Example #2 Iterating over MongoCursor'

<?php$cursor = $collection->find();foreach ($cursor as $doc) {    // do something to each document}?>

This will go through each document in the collection, loading and garbage collecting documents as needed. 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.

'Example #3 Adding options to MongoCursor'

<?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);?>

类摘要


MongoCursor implements MongoCursorInterface , Iterator {

/* Static Fields */

static bool $slaveOkay = false

static int $timeout = 30000

/* 方法 */

public addOption ( string $key , mixed $value ) : MongoCursor

public awaitData ([ bool $wait = true ] ) : MongoCursor

public batchSize ( int $batchSize ) : MongoCursor

public __construct ( MongoClient $connection , string $ns [, array $query = array() [, array $fields = array() ]] )

public count ([ bool $foundOnly = false ] ) : int

public current ( ) : array

public dead ( ) : bool

protected doQuery ( ) : void

public explain ( ) : array

public fields ( array $f ) : MongoCursor

public getNext ( ) : array

public getReadPreference ( ) : array

public hasNext ( ) : bool

public hint ( mixed $index ) : MongoCursor

public immortal ([ bool $liveForever = true ] ) : MongoCursor

public info ( ) : array

public key ( ) : string|int

public limit ( int $num ) : MongoCursor

public maxTimeMS ( int $ms ) : MongoCursor

public next ( ) : array

public partial ([ bool $okay = true ] ) : MongoCursor

public reset ( ) : void

public rewind ( ) : void

public setFlag ( int $flag [, bool $set = true ] ) : MongoCursor

public setReadPreference ( string $read_preference [, array $tags ] ) : MongoCursor

public skip ( int $num ) : MongoCursor

public slaveOkay ([ bool $okay = true ] ) : MongoCursor

public snapshot ( ) : MongoCursor

public sort ( array $fields ) : MongoCursor

public tailable ([ bool $tail = true ] ) : MongoCursor

public timeout ( int $ms ) : MongoCursor

public valid ( ) : bool

}

Static Variables

slaveOkay

If the query should have the "slaveOkay" flag set, which allows reads on the secondary (secondaries are, by default, just for backup and not queried). Can be overridden with MongoCursor::slaveOkay().

This functionality is deprecated. Please use 读取首选项 instead.

timeout

Set timeout in milliseconds for all database responses. Use -1 to wait forever. Can be overridden with MongoCursor::timeout(). This does not cause the MongoDB server to cancel the operation; it only instructs the driver to stop waiting for a response and throw a MongoCursorTimeoutException after a set time.


参见

MongoDB core docs on » cursors.


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