Querying an interface is similar to inserting and deleting, with the findOne() and find() methods used to retrieve the first result or all results of a query:

$document = $collection->findOne( array("isbn" => "101") );
$cursor = $collection->find( array( "name" => new MongoDBBSONRegex("mongo", "i") ) );

In the second example, we are using a regular expression to search for a key name with the value mongo (case-insensitive).

Embedded documents can be queried using the . notation, as with the other languages that we examined earlier in this chapter:

$cursor = $collection->find( array('meta.price' => 50) );

We do this to query for an embedded document price inside the meta key field.

Similarly to Ruby and Python, in PHP we can query using comparison operators, like this:

$cursor = $collection->find( array( 'price' => array('$gte'=> 60) ) );

A complete list of comparison operators supported in the PHP driver is available at the end of this chapter.

Querying with multiple key-value pairs is an implicit AND, whereas queries using $or, $in, $nin, or AND ($and) combined with $or can be achieved with nested queries:

$cursor = $collection->find( array( '$or' => array(
                                            array("price" => array( '$gte' => 60)),
                                            array("price" => array( '$lte' => 20))
                                   )));

This finds documents that have price>=60 OR price<=20.