| Subject: | Order of columns in hint() not preserved, name of index invalid |
Trying to use a hint:
$connection->collection()->find()->hint({ index_column_1 => 1,
index_column_2 => 1, index_column_3 => 1 })
Results in a query:
{ query : {}, $hint : { index_column_2 : 1, index_column_3 : 1,
index_column_1 : 1 } }
which results in "query error: bad hint" in the case of an index created
like this:
db.collection.ensureIndex({ index_column_1 : 1, index_column_2 : 1,
index_column_3 : 1 }).
It turns out that despite the hint() function in the mongo shell
accepting a "hash", mongodb does care about the order in which the
columns are specified.
So db.collection.find().hint({ a : 1, b : 1 }) is not the same as
db.collection.find().hint({ b : 1, a : 1 }) (the latter causing a query
error: bad hint).
By supporting this behavior, the perl driver should keep the order of
the columns specified within the hint. This might not be possible with
perl, as the order of the keys in a hash is "random". Maybe an array,
instead of a hash, would be preferable (eg. find()->hint([
index_column_1, index_column_2, index_column_3 ]) ).
Also, specifying the name of the index
("index_column_1_1_index_column_2_1_index_column_3_1") instead of a hash
gives the same "bad hint" error. Specifying the name of the index in the
hint works in the mongo shell, though.
Also, the documentation is a bit ambiguous, as under the "hint" chapter
in the MongoDB::Cursor page says "Force Mongo to use a specific index
for a query." and the example code says "my $cursor =
$coll->query->hint({'x' => 1});", not specifying what 'x' can be:
columns from an index or the name of the index? (both are accepted ways
of forcing an index by the mongodb).
Error reproduced on mongodb versions 2.0.2 and 2.0.4.
Perl version: 5.12.4.
Linux distro: 3.1.0-gentoo.