MongoDB::Cursor(3pm) User Contributed Perl Documentation MongoDB::Cursor(3pm)
NAME
MongoDB::Cursor - A cursor/iterator for Mongo query results
SYNOPSIS
while (my $object = $cursor->next) {
...
}
my @objects = $cursor->all;
Multithreading
Cloning instances of this class is disabled in Perl 5.8.7+, so forked threads will have to create their own database queries.
SEE ALSO
Core documentation on cursors: <http://dochub.mongodb.org/core/cursors>.
STATIC ATTRIBUTES
slave_okay
$MongoDB::Cursor::slave_okay = 1;
Whether it is okay to run queries on the slave. Defaults to 0.
timeout
Deprecated, use MongoDB::Connection::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::Connection::query_timeout" and never used.
ATTRIBUTES
started_iterating
If this cursor has queried the database yet. Methods mofifying the query will complain if they are called after the database is queried.
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::Connection.
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.
partial
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.
slave_okay
$cursor->slave_okay(1);
If a query can be done on a slave database server.
Boolean value, defaults to 0.
METHODS
fields (\%f)
$coll->insert({name => "Fred", age => 20});
my $cursor = $coll->query->fields({ name => 1 });
my $obj = $cursor->next;
$obj->{name}; "Fred"
$obj->{age}; # undef
Selects which fields are returned. The default is all fields. _id is always returned.
sort ($order)
# sort by name, descending
my $sort = {"name" => -1};
$cursor = $coll->query->sort($sort);
Adds a sort to the query. Argument is either a hash reference or a Tie::IxHash. Returns this cursor for chaining operations.
limit ($num)
$per_page = 20;
$cursor = $coll->query->limit($per_page);
Returns a maximum of N results. Returns this cursor for chaining operations.
skip ($num)
$page_num = 7;
$per_page = 100;
$cursor = $coll->query->limit($per_page)->skip($page_num * $per_page);
Skips the first N results. Returns this cursor for chaining operations.
See also core documentation on limit: <http://dochub.mongodb.org/core/limit>.
snapshot
my $cursor = $coll->query->snapshot;
Uses snapshot mode for the query. Snapshot mode assures no duplicates are returned, or objects missed, which were present at both the
start and end of the query's execution (if an object is new during the query, or deleted during the query, it may or may not be returned,
even with snapshot mode). Note that short query responses (less than 1MB) are always effectively snapshotted. Currently, snapshot mode
may not be used with sorting or explicit hints.
hint
my $cursor = $coll->query->hint({'x' => 1});
Force Mongo to use a specific index for a query.
explain
my $explanation = $cursor->explain;
This will tell you the type of cursor used, the number of records the DB had to examine as part of this query, the number of records
returned by the query, and the time in milliseconds the query took to execute. Requires boolean package.
"explain" resets the cursor, so calling "next" or "has_next" after an explain will requery the database.
See also core documentation on explain: <http://dochub.mongodb.org/core/explain>.
count($all?)
my $num = $cursor->count;
my $num = $cursor->skip(20)->count(1);
Returns the number of document this query will return. Optionally takes a boolean parameter, indicating that the cursor's limit and skip
fields should be used in calculating the count.
reset
Resets the cursor. After being reset, pre-query methods can be called on the cursor (sort, limit, etc.) and subsequent calls to next,
has_next, or all will re-query the database.
has_next
while ($cursor->has_next) {
...
}
Checks if there is another result to fetch.
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.
info
Returns a hash of information about this cursor. Currently the fields are:
"cursor_id"
The server-side id for this cursor. A "cursor_id" of 0 means that there are no more batches to be fetched.
"num"
The number of results returned so far.
"at"
The index of the result the cursor is currently at.
"flag"
If the database could not find the cursor or another error occurred, "flag" may be set (depending on the error). See
http://www.mongodb.org/display/DOCS/Mongo+Wire+Protocol#MongoWireProtocol-OPREPLY
<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.
all
my @objects = $cursor->all;
Returns a list of all objects in the result.
AUTHOR
Kristina Chodorow <kristina@mongodb.org>
perl v5.14.2 2011-09-07 MongoDB::Cursor(3pm)