# mongoc_collection_read_command_with_opts()

## Synopsis

    bool
    mongoc_collection_read_command_with_opts (mongoc_collection_t *collection,
                                              const bson_t *command,
                                              const mongoc_read_prefs_t *read_prefs,
                                              const bson_t *opts,
                                              bson_t *reply,
                                              bson_error_t *error);

Execute a command on the server, applying logic that is specific to commands that read, and taking the MongoDB server version into account. To send a raw command to the server without any of this logic, use mongoc_collection_command_simple().

Use this function for commands that read such as “count” or “distinct”.

Read preferences, read concern, and collation can be overridden by various sources. In a transaction, read concern and write concern are prohibited in `opts` and the read preference must be primary or NULL. The highest-priority sources for these options are listed first in the following table. No write concern is applied.

Read Preferences | Read Concern | Collation
--- | --- | ---
`read_prefs` | `opts` | `opts`
Transaction | Transaction |
`collection` |  |

See the example for transactions and for the “distinct” command with opts.

`reply` is always initialized, and must be freed with `bson_destroy()`.

This function is considered a retryable read operation. Upon a transient error (a network error, errors due to replica set failover, etc.) the operation is safely retried once. If `retryreads` is false in the URI (see mongoc_uri_t) the retry behavior does not apply.

Retry logic occurs regardless of the underlying command. Retrying `mapReduce` has the potential for degraded performance. Retrying a `getMore` command has the potential to miss results. For those commands, use generic command helpers (like mongoc_collection_command_with_opts()) instead.

## Parameters

- `collection`: A mongoc_collection_t.

- `command`: A `bson_t` containing the command specification.

- `read_prefs`: An optional mongoc_read_prefs_t.

- `opts`: A `bson_t` containing additional options.

- `reply`: A location for the resulting document.

- `error`: An optional location for a bson_error_t or `NULL`.

`opts` may be NULL or a BSON document with additional command options:

- `readConcern`: Construct a mongoc_read_concern_t and use mongoc_read_concern_append() to add the read concern to `opts`. See the example code for mongoc_client_read_command_with_opts(). Read concern requires MongoDB 3.2 or later, otherwise an error is returned.

- `sessionId`: First, construct a mongoc_client_session_t with mongoc_client_start_session(). You can begin a transaction with mongoc_client_session_start_transaction(), optionally with a mongoc_transaction_opt_t that overrides the options inherited from `collection`, and use mongoc_client_session_append() to add the session to `opts`. See the example code for mongoc_client_session_t.

- `collation`: Configure textual comparisons. See Setting Collation Order, and the MongoDB Manual entry on Collation. Collation requires MongoDB 3.2 or later, otherwise an error is returned.

- `serverId`: To target a specific server, include an int32 “serverId” field. Obtain the id by calling mongoc_client_select_server(), then mongoc_server_description_id() on its return value.

Consult the MongoDB Manual entry on Database Commands for each command’s arguments.

## Errors

Errors are propagated via the `error` parameter.

## Returns

Returns `true` if successful. Returns `false` and sets `error` if there are invalid arguments or a server or network error.

## Example

See the example code for mongoc_client_read_command_with_opts().