# mongoc_collection_update_one()

## Synopsis

    bool
    mongoc_collection_update_one (mongoc_collection_t *collection,
                                  const bson_t *selector,
                                  const bson_t *update,
                                  const bson_t *opts,
                                  bson_t *reply,
                                  bson_error_t *error);

## Parameters

- `collection`: A mongoc_collection_t.

- `selector`: A `bson_t` containing the query to match the document for updating.

- `update`: A `bson_t` containing the update to perform. If updating with a pipeline, a `bson_t` array.

- `reply`: Optional. An uninitialized `bson_t` populated with the update result, or `NULL`.

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

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

- `writeConcern`: Construct a mongoc_write_concern_t and use mongoc_write_concern_append() to add the write concern to `opts`. See the example code for mongoc_client_write_command_with_opts().

- `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.

- `validate`: Construct a bitwise-or of all desired `bson_validate_flags_t`. Set to `false` to skip client-side validation of the provided BSON documents.

- `comment`: A `bson_value_t` specifying the comment to attach to this command. The comment will appear in log messages, profiler output, and currentOp output. Requires MongoDB 4.4 or later.

- `bypassDocumentValidation`: Set to `true` to skip server-side schema validation of the provided BSON documents.

- `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.

- `hint`: A document or string that specifies the index to use to support the query predicate.

- `upsert`: When true, creates a new document if no document matches the query.

- `let`: A BSON document consisting of any number of parameter names, each followed by definitions of constants in the MQL Aggregate Expression language.

- `arrayFilters`: An array of filters specifying to which array elements an update should apply.

## Description

This function updates at most one document in `collection` that matches `selector`.

To update multiple documents see mongoc_collection_update_many().

If you pass a non-NULL `reply`, it is filled out with fields `matchedCount`, `modifiedCount`, and optionally `upsertedId` if applicable. If there is a server error then `reply` contains either a “writeErrors” array with one subdocument or a “writeConcernErrors” array. The reply must be freed with `bson_destroy()`.

## 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.

A write concern timeout or write concern error is considered a failure.

## Example

example-update.c

    #include "mongoc/mongoc.h"

    int
    main (void)
    {
       bson_t *to_insert = BCON_NEW ("_id", BCON_INT32 (1));
       bson_t *selector = BCON_NEW ("_id", "{", "$gt", BCON_INT32 (0), "}");
       bson_t *update = BCON_NEW ("$set", "{", "x", BCON_INT32 (1), "}");
       const bson_t *next_doc;
       char *to_str;
       bson_error_t error = {0};
       mongoc_cursor_t *cursor;
       mongoc_client_t *client;
       mongoc_collection_t *coll;
       const char *uri_string = "mongodb://localhost:27017/?appname=example-update";
       mongoc_uri_t *uri = mongoc_uri_new_with_error (uri_string, &error);

       if (!uri) {
          fprintf (stderr,
                   "failed to parse URI: %s\n"
                   "error message:       %s\n",
                   uri_string,
                   error.message);
          return EXIT_FAILURE;
       }

       client = mongoc_client_new_from_uri (uri);
       if (!client) {
          return EXIT_FAILURE;
       }

       coll = mongoc_client_get_collection (client, "db", "example_coll");

       mongoc_client_set_error_api (client, 2);
       /* insert a document */
       if (!mongoc_collection_insert_one (coll, to_insert, NULL, NULL, &error)) {
          fprintf (stderr, "insert failed: %s\n", error.message);
          return EXIT_FAILURE;
       }

       if (!mongoc_collection_update_one (
              coll, selector, update, NULL, NULL, &error)) {
          fprintf (stderr, "update failed: %s\n", error.message);
          return EXIT_FAILURE;
       }

       to_str = bson_as_relaxed_extended_json (to_insert, NULL);
       printf ("inserted: %s\n", to_str);
       bson_free (to_str);

       cursor = mongoc_collection_find_with_opts (coll, selector, NULL, NULL);
       BSON_ASSERT (mongoc_cursor_next (cursor, &next_doc));
       printf ("after update, collection has the following document:\n");

       to_str = bson_as_relaxed_extended_json (next_doc, NULL);
       printf ("%s\n", to_str);
       bson_free (to_str);

       BSON_ASSERT (mongoc_collection_drop (coll, NULL));

       bson_destroy (to_insert);
       bson_destroy (update);
       bson_destroy (selector);
       mongoc_collection_destroy (coll);
       mongoc_uri_destroy (uri);
       mongoc_client_destroy (client);

       return EXIT_SUCCESS;
    }

See also

MongoDB update command documentation for more information on the update options.
mongoc_collection_update_many()
mongoc_collection_replace_one()