Execute a database command that reads on this server

# MongoDB\Driver\Server::executeReadCommand

(mongodb >=1.4.0)

MongoDB\Driver\Server::executeReadCommand — Execute a database command that reads on this server

### Description

final public MongoDB\Driver\Server::executeReadCommand(string `$db`, MongoDB\Driver\Command `$command`, ?array `$options` = `null`): MongoDB\Driver\Cursor

Executes the command on this server, irrespective of the `"readPreference"` option.

This method will apply logic that is specific to commands that read (e.g. » distinct). Default values for the `"readPreference"` and `"readConcern"` options will be inferred from an active transaction (indicated by the `"session"` option), followed by the connection URI.

> Note: The `"readPreference"` option does not control the server to which the driver issues the operation; it will always be executed on this server object. Instead, it may be used when issuing the operation to a secondary (from a replica set connection, not standalone) or mongos node to ensure that the driver sets the wire protocol accordingly or adds the read preference to the operation, respectively.

### Parameters

`db` (string)

  The name of the database on which to execute the command.

`command` (MongoDB\Driver\Command)

  The command to execute.

`options`

  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.

  Warning

  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().

### Return Values

Returns MongoDB\Driver\Cursor on success.

### Errors/Exceptions

- Throws MongoDB\Driver\Exception\InvalidArgumentException if the `"session"` option is used with an associated transaction in combination with a `"readConcern"` or `"writeConcern"` option.
- Throws MongoDB\Driver\Exception\InvalidArgumentException on argument parsing errors.
- Throws MongoDB\Driver\Exception\ConnectionException if connection to the server fails (for reasons other than authentication).
- Throws MongoDB\Driver\Exception\AuthenticationException if authentication is needed and fails.
- Throws MongoDB\Driver\Exception\RuntimeException on other errors (e.g. invalid command).

### See Also

- MongoDB\Driver\Command
- MongoDB\Driver\Cursor
- MongoDB\Driver\Server::executeCommand() - Execute a database command on this server
- MongoDB\Driver\Server::executeReadWriteCommand() - Execute a database command that reads and writes on this server
- MongoDB\Driver\Server::executeWriteCommand() - Execute a database command that writes on this server
- MongoDB\Driver\Manager::executeReadCommand() - Execute a database command that reads

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