libmongoc庫和libbson庫的使用

阿新 • • 發佈：2022-12-08

libmongoc庫和libbson庫的使用

學習一項知識，最好的方式是檢視官方說明書。

前言

工作和學習過程中，需要用到資料庫，這裡挑選了MongoDB 非關係型資料庫。使用資料庫，肯定離不開資料庫的 增、刪、改、查。

MongoDB自帶了客戶端程式：mongosh.exe，基本可以滿足使用者所有的操作需要。但是進行程式二次開發，我們還是需要使用 MongoDB Client Library.

本文主要介紹 libmongoc庫 和 libbson庫的常用函式，以及使用過程中的注意事項

一、libmongoc庫和libbson庫的介紹

官網介紹：

A Cross Platform MongoDB Client Library for C

The MongoDB C Driver, also known as “libmongoc”, is a library for using MongoDB from C applications, and for writing MongoDB drivers in higher-level languages.

It depends on libbson to generate and parse BSON documents, the native data format of MongoDB.

MongoDB的資料儲存格式：bson ，那麼就需要libbson庫。

資料庫原始資料：

{"id":1001,"name":"ZhangSan","age":18,"sex":"male","Chinese":93.0,"Math":100.0,"English":80.0}
{"id":1002,"name":"LiSi","age":18,"sex":"male","Chinese":100.0,"Math":60.0,"English":80.0}
{"id":1003,"name":"WangWu","age":19,"sex":"male","Chinese":90.0,"Math":100.0,"English":90.0}
{"id":1004,"name":"ZhaoLiu","age":19,"sex":"male","Chinese":95.0,"Math":70.0,"English":80.0}
{"id":1005,"name":"XiaoLi","age":18,"sex":"female","Chinese":100.0,"Math":100.0,"English":80.0}

二、libmongoc庫的使用

資料庫的CRUD(即create、read、update、delete)操作

2-1 create（增操作）

以json格式傳入，在表中建立一條bson。

實現程式碼

#include <mongoc/mongoc.h>

static int lib_collection_create_document(const char *uri_string, const char *database_name, const char *collection_name, const char *json)
{
	mongoc_client_t *client = NULL;
	mongoc_collection_t *collection = NULL;
	bson_error_t error;
	bson_oid_t oid;
	bson_t *doc = NULL;
	bson_t *json_d = NULL;
	int result = 0;

	/* create mongoc client instace */
	client = mongoc_client_new(uri_string);

	/* create collection instace */
	collection = mongoc_client_get_collection(client, database_name, collection_name);

	/* create bson instace */
	doc = bson_new();

	/* init bson oid.
	*  oid is primary key in collection
	*/
	bson_oid_init(&oid, NULL);

	/* bson oid append bson_t */
	BSON_APPEND_OID(doc, "_id", &oid);

	json_d = bson_new_from_json((unsigned char *)json, -1, &error);
	if (!json_d)
	{
		fprintf(stderr, "%s\n", error.message);
		result = -1;
	}
	bson_concat(doc, json_d);
	bson_destroy(json_d);
	if (!mongoc_collection_insert_one(collection, doc, NULL, NULL, &error))
	{
		fprintf(stderr, "%s\n", error.message);
		result = -2;
	}

	/* free bson_t memory */
	bson_destroy(doc);
	/* free mongoc_collection_t */
	mongoc_collection_destroy(collection);
	/* free mongoc_client_t */
	mongoc_client_destroy(client);
	
	return result;
}

int main(int argc, char *argv[])
{
	mongoc_init();

	const char *uri_string = "mongodb://10.8.198.55:27017";
	const char *database = "event_database";
	const char *collection = "student_coll";

	// add a json to collection
	char json[500] = {"{\"id\":1006,\"name\":\"XiaoHong\",\"age\":24,\"sex\":\"female\",\"Chinese\":74.0,\"Math\":85.0,\"English\":81.0}"};
	if (0 == lib_collection_create_document(uri_string, database, collection, json))
	{
		printf("Create successful : %s\n", json);
	}

	mongoc_cleanup();
	return 0;
}

執行結果：

2-2 read（查操作）

在表中查詢符合條件的document，通過陣列返回

實現程式碼：

#include <mongoc/mongoc.h>

static int lib_collection_read_document(const char *uri_string, const char *database_name, const char *collection_name, const char *json_opts,
	char doc_list_arr[][300], int *num_of_docs)
{
	mongoc_client_t *client = NULL;
	mongoc_collection_t *collection = NULL;
	mongoc_cursor_t *cursor = NULL;
	bson_error_t error;
	const bson_t *doc = NULL;
	bson_t *query = NULL;
	bson_t *json_d = NULL;
	char *str = NULL;
	int result = 0;

	client = mongoc_client_new(uri_string);
	collection = mongoc_client_get_collection(client, database_name, collection_name);

	query = bson_new();
	json_d = bson_new_from_json((unsigned char *)json_opts, -1, &error);
	if (!json_d)
	{
		fprintf(stderr, "%s\n", error.message);
		result = -1;
	}
	bson_concat(query, json_d);
	bson_destroy(json_d);

	cursor = mongoc_collection_find_with_opts(collection, query, NULL, NULL);
	while (mongoc_cursor_next(cursor, &doc))
	{
		//str = bson_as_canonical_extended_json(doc, NULL);
		//str = bson_as_relaxed_extended_json(doc, NULL);
		str = bson_as_json(doc, NULL);
		sprintf(doc_list_arr[*num_of_docs], "%s", str);
		(*num_of_docs)++;
		bson_free(str);
	}

	bson_destroy(query);
	mongoc_cursor_destroy(cursor);
	mongoc_collection_destroy(collection);
	mongoc_client_destroy(client);
	
	return result;
}

int main(int argc, char *argv[])
{
	mongoc_init();

	const char *uri_string = "mongodb://10.8.198.55:27017";
	const char *database = "event_database";
	const char *collection = "student_coll";

	/* read jsons from collection with options */
	char json_opts[300] = {"{\"age\":18,\"sex\":\"male\"}"};
	char doc_list_arr[100][300] = {0};
	int num_of_docs = 0;
	lib_collection_read_document(uri_string, database, collection, json_opts, doc_list_arr, &num_of_docs);
	for (int i = 0; i < num_of_docs; i++)
	{
		printf("%s\n", doc_list_arr[i]);
	}

	mongoc_cleanup();
	return 0;
}

執行結果：

2-3 update（改操作）

在表中查詢指定的json，符合條件的json進行修改
注意：這裡修改值的型別為string

實現程式碼：

#include <mongoc/mongoc.h>
#include <bson/bson.h>

static int lib_collection_update_document(const char *uri_string, const char *database_name, const char *collection_name, const char *json_opts, 
	const char *key, const char *value_string)
{
	mongoc_collection_t *collection = NULL;
	mongoc_client_t *client = NULL;
	bson_error_t error;
	mongoc_cursor_t *cursor = NULL;
	const bson_t *doc = NULL;
	bson_t *update = NULL;
	bson_t *query = NULL;
	int result = 0;

	client = mongoc_client_new(uri_string);
	collection = mongoc_client_get_collection(client, database_name, collection_name);

	update = BCON_NEW("$set",
		"{",
		key,
		BCON_UTF8(value_string),
		"}");
	query = bson_new_from_json((unsigned char *)json_opts, -1, &error);
	if (!query)
	{
		fprintf(stderr, "%s\n", error.message);
		result = -1;
	}
	cursor = mongoc_collection_find_with_opts(collection, query, NULL, NULL);
	while (mongoc_cursor_next(cursor, &doc))
	{
		if (!mongoc_collection_update_one(collection, doc, update, NULL, NULL, &error))
		{
			fprintf(stderr, "%s\n", error.message);
			result = -2;
			break;
		}
	}

	bson_destroy(query);
	bson_destroy(update);
	mongoc_cursor_destroy(cursor);
	mongoc_collection_destroy(collection);
	mongoc_client_destroy(client);

	return result;
}

int main(int argc, char *argv[])
{
	mongoc_init();

	const char *uri_string = "mongodb://10.8.198.55:27017";
	const char *database = "event_database";
	const char *collection = "student_coll";

	/* update documents from collection wiht options */
	char json_opts[300] = { "{\"id\":1006}" };
	const char *key = "name";
	const char *value = "XiaoHe";
	if (0 == lib_collection_update_document(uri_string, database, collection, json_opts, key, value))
	{
		printf("Update successful\n");
	}

	mongoc_cleanup();
	return 0;
}

執行結果：

2-4 delete（刪操作）

在表中查詢指定的json，符合條件的json進行刪除

實現程式碼：

#include <mongoc/mongoc.h>
#include <bson/bson.h>

static int lib_collection_delete_document(const char *uri_string, const char *database_name, const char *collection_name, const char *json_opts)
{
	mongoc_client_t *client = NULL;
	mongoc_collection_t *collection = NULL;
	mongoc_cursor_t *cursor = NULL;
	bson_error_t error;
	const bson_t *doc = NULL;
	bson_t *query = NULL;
	int result = 0;

	client = mongoc_client_new(uri_string);
	collection = mongoc_client_get_collection(client, database_name, collection_name);

	query = bson_new_from_json((unsigned char *)json_opts, -1, &error);
	if (!query)
	{
		fprintf(stderr, "%s\n", error.message);
		result = -1;
	}

	cursor = mongoc_collection_find_with_opts(collection, query, NULL, NULL);
	while (mongoc_cursor_next(cursor, &doc))
	{
		if (!mongoc_collection_delete_one(collection, doc, NULL, NULL, &error))
		{
			fprintf(stderr, "%s\n", error.message);
			result = -2;
		}
	}

	bson_destroy(query);
	mongoc_cursor_destroy(cursor);
	mongoc_collection_destroy(collection);
	mongoc_client_destroy(client);

	return result;
}

int main(int argc, char *argv[])
{
	mongoc_init();

	const char *uri_string = "mongodb://10.8.198.55:27017";
	const char *database = "event_database";
	const char *collection = "student_coll";

	/* delete documents with options in collection */
	char json_opts[300] = { "{\"age\":19}" };
	if (0 == lib_collection_delete_document(uri_string, database, collection, json_opts))
	{
		printf("Delete successful\n");
	}

	mongoc_cleanup();
	return 0;
}

執行結果：

三、libbson庫的使用

將bson格式轉換成json格式（value不帶型別）

函式：char * bson_as_json (const bson_t *bson, size_t *length);

輸出格式：

注意事項：函式返回值（指標）記得使用函式 void bson_free (void *mem) 釋放
將bson格式轉換成json格式（value帶型別）

函式：char * bson_as_canonical_extended_json (const bson_t *bson, size_t *length)

輸出格式：

注意事項：函式返回值（指標）記得使用函式 void bson_free (void *mem) 釋放