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MongoDB-v0.999.998.6-TRIAL
River stage two • 48 direct dependents • 56 total dependents
/ MongoDB::Cursor

NAME

MongoDB::Cursor - A lazy cursor for Mongo query results

VERSION

version v0.999.998.6

SYNOPSIS

while (my $object = $cursor->next) {
    ...
}

my @objects = $cursor->all;

USAGE

Multithreading

Cursors are cloned in threads, but not reset. Iterating the same cursor from multiple threads will give unpredictable results. Only iterate from a single thread.

ATTRIBUTES

started_iterating

If this cursor has queried the database yet. Methods modifying the query will complain if they are called after the database is queried.

GLOBAL VARIABLES

slave_okay

$MongoDB::Cursor::slave_okay = 1;

Whether it is okay to run queries on the slave. Defaults to 0.

timeout

Deprecated, use MongoDB::MongoClient::query_timeout instead.

How many milliseconds to wait for a response from the server. Set to 30000 (30 seconds) by default. -1 waits forever (or until TCP times out, which is usually a long time).

This value is overridden by MongoDB::MongoClient::query_timeout and never used.

QUERY MODIFIERS

These methods modify the query to be run. An exception will be thrown if they are called after results are iterated.

immortal

$cursor->immortal(1);

Ordinarily, a cursor "dies" on the database server after a certain length of time (approximately 10 minutes), to prevent inactive cursors from hogging resources. This option sets that a cursor should not die until all of its results have been fetched or it goes out of scope in Perl.

Boolean value, defaults to 0.

immortal is not equivalent to setting a client-side timeout. If you are getting client-side timeouts (e.g., "recv timed out"), set query_timeout on your connection.

# wait forever for a query to return results
$connection->query_timeout(-1);

See "query_timeout" in MongoDB::MongoClient.

Returns this cursor for chaining operations.

fields

$coll->insert({name => "Fred", age => 20});
my $cursor = $coll->find->fields({ name => 1 });
my $obj = $cursor->next;
$obj->{name}; "Fred"
$obj->{age}; # undef

Selects which fields are returned. The default is all fields. When fields are specified, _id is returned by default, but this can be disabled by explicitly setting it to "0". E.g. _id => 0. Argument is either a hash reference, a Tie::IxHash or an array reference of key/value pairs.

See Limit fields to return in the MongoDB documentation for details.

Returns this cursor for chaining operations.

sort

# sort by name, descending
$cursor->sort([name => -1]);

Adds a sort to the query. Argument is either a hash reference or a Tie::IxHash or an array reference of key/value pairs. Because hash references are not ordered, do not use them for more than one key.

Returns this cursor for chaining operations.

limit

$cursor->limit(20);

Sets cursor to return a maximum of N results.

Returns this cursor for chaining operations.

max_time_ms

$cursor->max_time_ms( 500 );

Causes the server to abort the operation if the specified time in milliseconds is exceeded.

Returns this cursor for chaining operations.

tailable

$cursor->tailable(1);

If a cursor should be tailable. Tailable cursors can only be used on capped collections and are similar to the tail -f command: they never die and keep returning new results as more is added to a collection.

They are often used for getting log messages.

Boolean value, defaults to 0.

If you want the tailable cursor to block for a few seconds, use "tailable_await" instead. Note calling this with a false value disables tailing, even if tailable_await was previously called.

Returns this cursor for chaining operations.

tailable_await

$cursor->tailable_await(1);

Sets a cursor to be tailable and block for a few seconds if no data is immediately available.

Boolean value, defaults to 0.

If you want the tailable cursor without blocking, use "tailable" instead. Note calling this with a false value disables tailing, even if tailable was previously called.

skip

$cursor->skip( 50 );

Skips the first N results.

Returns this cursor for chaining operations.

snapshot

$cursor->snapshot;

Uses snapshot mode for the query. Snapshot mode assures no duplicates are returned due an intervening write relocating a document. Note that if an object is inserted, updated or deleted during the query, it may or may not be returned when snapshot mode is enabled. Short query responses (less than 1MB) are always effectively snapshotted. Currently, snapshot mode may not be used with sorting or explicit hints.

Returns this cursor for chaining operations.

hint

$cursor->hint({'x' => 1});
$cursor->hint(['x', 1]);
$cursor->hint('x_1');

Force Mongo to use a specific index for a query.

Returns this cursor for chaining operations.

partial

$cursor->partial(1);

If a shard is down, mongos will return an error when it tries to query that shard. If this is set, mongos will just skip that shard, instead.

Boolean value, defaults to 0.

Returns this cursor for chaining operations.

read_preference

$cursor->read_preference($read_preference_object);
$cursor->read_preference('secondary', [{foo => 'bar'}]);

Sets read preference for the cursor's connection.

If given a single argument that is a MongoDB::ReadPreference object, the read preference is set to that object. Otherwise, it takes positional arguments: the read preference mode and a tag set list, which must be a valid mode and tag set list as described in the MongoDB::ReadPreference documentation.

Returns this cursor for chaining operations.

slave_okay (DEPRECATED)

$cursor->slave_okay(1);

If a query can be done on a slave database server.

Boolean value, defaults to 0.

Returns this cursor for chaining operations.

QUERY INTROSPECTION AND RESET

These methods run introspection methods on the query conditions and modifiers stored within the cursor object.

explain

my $explanation = $cursor->explain;

This will tell you the type of cursor used, the number of records the DB had to examine as part of this query, the number of records returned by the query, and the time in milliseconds the query took to execute.

See also core documentation on explain: http://dochub.mongodb.org/core/explain.

count

my $num = $cursor->count;
my $num = $cursor->skip(20)->count(1);

Returns the number of document this query will return. Optionally takes a boolean parameter, indicating that the cursor's limit and skip fields should be used in calculating the count.

QUERY ITERATION

These methods allow you to iterate over results.

result

my $result = $cursor->result;

This method will return a MongoDB::QueryResult object with the result of the query. The query will be executed on demand.

Iterating with a MongoDB::QueryResult object directly instead of a MongoDB::Cursor will be slightly faster, since the MongoDB::Cursor methods below just internally call the corresponding method on the result object.

has_next

while ($cursor->has_next) {
    ...
}

Checks if there is another result to fetch. Will automatically fetch more data from the server if necessary.

next

while (my $object = $cursor->next) {
    ...
}

Returns the next object in the cursor. Will automatically fetch more data from the server if necessary. Returns undef if no more data is available.

all

my @objects = $cursor->all;

Returns a list of all objects in the result.

reset

Resets the cursor. After being reset, pre-query methods can be called on the cursor (sort, limit, etc.) and subsequent calls to next, has_next, or all will re-query the database.

info

Returns a hash of information about this cursor. This is intended for debugging purposes and users should not rely on the contents of this method for production use. Currently the fields are:

  • cursor_id -- the server-side id for this cursor as. This is an opaque string. A cursor_id of "\0\0\0\0\0\0\0\0" means there are no more results on the server.

  • num -- the number of results received from the server so far

  • at -- the (zero-based) index of the document that will be returned next from "next"

  • flag -- if the database could not find the cursor or another error occurred, flag may contain a hash reference of flags set in the response (depending on the error). See http://www.mongodb.org/display/DOCS/Mongo+Wire+Protocol#MongoWireProtocol-OPREPLY for a full list of flag values.

  • start -- the index of the result that the current batch of results starts at.

If the cursor has not yet executed, only the num field will be returned with a value of 0.

SEE ALSO

Core documentation on cursors: http://dochub.mongodb.org/core/cursors.

AUTHORS

  • David Golden <david@mongodb.com>

  • Mike Friedman <friedo@mongodb.com>

  • Kristina Chodorow <kristina@mongodb.com>

  • Florian Ragwitz <rafl@debian.org>

COPYRIGHT AND LICENSE

This software is Copyright (c) 2015 by MongoDB, Inc..

This is free software, licensed under:

The Apache License, Version 2.0, January 2004