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# Copyright 2015 - present MongoDB, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
use strict;
use warnings;
package MongoDB::Op::_Explain;
# Encapsulate code path for explain commands/queries
use version;
our $VERSION = 'v2.2.2';
use Moo;
use MongoDB::Op::_Command;
use Types::Standard qw(
InstanceOf
);
use Tie::IxHash;
use boolean;
use namespace::clean;
has query => (
is => 'ro',
required => 1,
isa => InstanceOf['MongoDB::Op::_Query'],
);
with $_ for qw(
MongoDB::Role::_PrivateConstructor
MongoDB::Role::_CollectionOp
MongoDB::Role::_ReadOp
);
sub execute {
my ( $self, $link, $topology ) = @_;
my $res =
$link->supports_explain_command
? $self->_command_explain( $link, $topology )
: $self->_legacy_explain( $link, $topology );
return $res;
}
sub _command_explain {
my ( $self, $link, $topology ) = @_;
my $cmd = Tie::IxHash->new( @{ $self->query->_as_command } );
# XXX need to standardize error here
if ($self->query->has_hint) {
# cannot use hint on explain, throw error
MongoDB::Error->throw(
message => "cannot use 'hint' with 'explain'",
);
}
my $op = MongoDB::Op::_Command->_new(
db_name => $self->db_name,
query => [
explain => $cmd,
@{ $self->read_concern->as_args( $self->session ) }
],
query_flags => {},
read_preference => $self->read_preference,
bson_codec => $self->bson_codec,
session => $self->session,
monitoring_callback => $self->monitoring_callback,
);
my $res = $op->execute( $link, $topology );
return $res->{output};
}
sub _legacy_explain {
my ( $self, $link, $topology ) = @_;
my $orig_query = $self->query;
my $cloned_opts = { %{ $orig_query->options } };
$cloned_opts->{explain} = 1;
# per David Storch, drivers *must* send a negative limit to instruct
# the query planner analysis module to add a LIMIT stage. For older
# explain implementations, it also ensures a cursor isn't left open.
$cloned_opts->{limit} = ( -1 * abs( $cloned_opts->{limit} ) );
my $new_query = MongoDB::Op::_Query->_new(
%$orig_query,
# override options from original
options => $cloned_opts
);
return $new_query->execute( $link, $topology )->next;
}
1;
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