MongoDb update

To update a document in MongoDB using the C driver, you can follow these steps:

1. Connect to the MongoDB server using the mongoc_client_t object and the mongoc_client_new function.

2. Select the database and collection using the mongoc_client_get_database and mongoc_database_get_collection functions.

3. Create a query document to specify the criteria for the update using the bson_t object and the bson_new function. You can use various operators such as $set, $inc, etc., to modify specific fields.

4. Create an update document using the bson_t object and the bson_new function. This document contains the modifications you want to make to the matching documents.

5. Use the mongoc_collection_update_many or mongoc_collection_update_one function to perform the update operation. Pass in the collection, query document, and update document as arguments.

6. Check the return value of the update function to see if the update was successful.

Here's an example that demonstrates how to update a document in MongoDB using the C driver:

#include <mongoc.h>

int main() {
    mongoc_init();

    // Connect to the MongoDB server
    mongoc_client_t *client = mongoc_client_new("mongodb://localhost:27017");

    // Select the database and collection
    mongoc_database_t *database = mongoc_client_get_database(client, "mydb");
    mongoc_collection_t *collection = mongoc_database_get_collection(database, "mycoll");

    // Create a query document
    bson_t *query = bson_new();
    BSON_APPEND_UTF8(query, "name", "John");

    // Create an update document
    bson_t *update = bson_new();
    BSON_APPEND_UTF8(update, "$set", "age", "30");

    // Perform the update operation
    bson_t reply;
    bool success = mongoc_collection_update_one(collection, query, update, NULL, &reply, NULL);

    if (success) {
        printf("Update successful!\n");
    } else {
        printf("Update failed!\n");
    }

    // Cleanup
    bson_destroy(query);
    bson_destroy(update);
    bson_destroy(&reply);
    mongoc_collection_destroy(collection);
    mongoc_database_destroy(database);
    mongoc_client_destroy(client);
    mongoc_cleanup();

    return 0;
}

This example connects to the MongoDB server, selects the "mydb" database and "mycoll" collection, creates a query document to find documents with the name "John", creates an update document to set the "age" field to 30, and performs the update operation using the mongoc_collection_update_one function. It then checks the return value to determine if the update was successful and cleans up the resources.

Please note that you need to have the MongoDB C driver installed and linked to your project for this code to work.