MongoDB::Cursor(3) User Contributed Perl Documentation MongoDB::Cursor(3)NAMEMongoDB::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(3)
