(mongodb >=1.4.0)
MongoDB\Driver\Manager::executeReadCommand — Execute a database command that reads
$db, MongoDB\Driver\Command $command, array $options = array()): MongoDB\Driver\Cursor
   Selects a server according to the "readPreference" option
   and executes the command on that server. By default, the read preference from
   the MongoDB Connection
   URI will be used.
  
   This method will apply logic that is specific to commands that read (e.g.
   » count)
   and take the MongoDB server version into account. The
   "readConcern" option will default to the corresponding
   value from the MongoDB
   Connection URI.
  
db (string)The name of the database on which to execute the command.
command (MongoDB\Driver\Command)The command to execute.
options
| Option | Type | Description | 
|---|---|---|
| readConcern | MongoDB\Driver\ReadConcern | A read concern to apply to the operation. This option is available in MongoDB 3.2+ and will result in an exception at execution time if specified for an older server version. | 
| readPreference | MongoDB\Driver\ReadPreference | A read preference to use for selecting a server for the operation. | 
| session | MongoDB\Driver\Session | A session to associate with the operation. | 
       If you are using a "session" which has a transaction
       in progress, you cannot specify a "readConcern" or
       "writeConcern" option. This will result in an
       MongoDB\Driver\Exception\InvalidArgumentException
       being thrown. Instead, you should set these two options when you create
       the transaction with
       MongoDB\Driver\Session::startTransaction().
      
Returns MongoDB\Driver\Cursor on success.
"session" option is used with an associated transaction in combination with a "readConcern" or "writeConcern" option.