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MongoDB::Cursor(3pm) User Contributed Perl Documentation MongoDB::Cursor(3pm)
NAME
MongoDB::Cursor - A lazy cursor for Mongo query results
VERSION
version v2.2.2
SYNOPSIS
while (my $object = $cursor->next) {
...
}
my @objects = $cursor->all;
USAGE
Multithreading
NOTE: Per threads documentation, use of Perl threads is discouraged by the maintainers of
Perl and the MongoDB Perl driver does not test or provide support for use with threads.
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
A boolean indicating if this cursor has queried the database yet. Methods modifying the
query will complain if they are called after the database is queried.
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 indicates 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.
Note: "immortal" only affects the server-side timeout. If you are getting client-side
timeouts you will need to change your client configuration. See "max_time_ms" in
MongoDB::MongoClient and "socket_timeout_ms" 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 must be either a hash reference or a Tie::IxHash object.
See Limit fields to return <http://docs.mongodb.org/manual/tutorial/project-fields-from-
query-results/> 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_await_time_ms
$cursor->max_await_time_ms( 500 );
The maximum amount of time in milliseconds for the server to wait on new documents to
satisfy a tailable cursor query. This only applies to a cursor of type 'tailble_await'.
This is ignored if the cursor is not a 'tailable_await' cursor or the server version is
less than version 3.2.
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.
hint
Hint the query to use a specific index by name:
$cursor->hint("index_name");
Hint the query to use index based on individual keys and direction:
$cursor->hint([field_1 => 1, field_2 => -1, field_3 => 1]);
Use of a hash reference should be avoided except for single key indexes.
The hint must be a string or ordered document.
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.
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>.
QUERY ITERATION
These methods allow you to iterate over results.
result
my $result = $cursor->result;
This method will execute the query and return a MongoDB::QueryResult object with the
results.
The "has_next", "next", and "all" methods call "result" internally, which executes the
query "on demand".
Iterating with a MongoDB::QueryResult object directly instead of a MongoDB::Cursor will be
slightly faster, since the MongoDB::Cursor methods below just internally call the
corresponding method on the result object.
has_next
while ($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.
batch
while (my @batch = $cursor->batch) {
...
}
Returns the next batch of data from the cursor. Will automatically fetch more data from
the server if necessary. Returns an empty list 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 result, 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:
o "cursor_id" -- the server-side id for this cursor. See below for details.
o "num" -- the number of results received from the server so far
o "at" -- the (zero-based) index of the document that will be returned next from "next"
o "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.
o "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.
The "cursor_id" could appear in one of three forms:
o MongoDB::CursorID object (a blessed reference to an 8-byte string)
o A perl scalar (an integer)
o A Math::BigInt object (64 bit integer on 32-bit perl)
When the "cursor_id" is zero, there are no more results to fetch.
SEE ALSO
Core documentation on cursors: <http://dochub.mongodb.org/core/cursors>.
AUTHORS
o David Golden <david AT mongodb.com>
o Rassi <rassi AT mongodb.com>
o Mike Friedman <friedo AT friedo.com>
o Kristina Chodorow <k.chodorow AT gmail.com>
o Florian Ragwitz <rafl AT debian.org>
COPYRIGHT AND LICENSE
This software is Copyright (c) 2020 by MongoDB, Inc.
This is free software, licensed under:
The Apache License, Version 2.0, January 2004
perl v5.30.3 2020-08-15 MongoDB::Cursor(3pm)
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On Apache
Under GNU General Public License
2024-12-12 19:38 @18.188.218.103 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)