视点！libmongoc库和libbson库的使用

2022-12-08 16:24:03 来源：博客园

libmongoc库和libbson库的使用

学习一项知识，最好的方式是查看官方说明书。

前言

工作和学习过程中，需要用到数据库，这里挑选了MongoDB 非关系型数据库。使用数据库，肯定离不开数据库的 增、删、改、查。

MongoDB自带了客户端程序：mongosh.exe，基本可以满足用户所有的操作需要。但是进行程序二次开发，我们还是需要使用 MongoDB Client Library.

(资料图片仅供参考)

本文主要介绍 libmongoc库和 libbson库的常用函数，以及使用过程中的注意事项

一、libmongoc库和libbson库的介绍

官网介绍：

A Cross Platform MongoDB Client Library for CThe 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的数据存储格式：bson，那么就需要libbson库。

数据库原始数据：

{"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库的使用

数据库的CRUD(即create、read、update、delete)操作

2-1 create（增操作）

以json格式传入，在表中创建一条bson。

实现代码

#include 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 collectionchar 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;}

运行结果：

2-2 read（查操作）

在表中查找符合条件的document，通过数组返回

实现代码：

#include 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;}

运行结果：

2-3 update（改操作）

在表中查找指定的json，符合条件的json进行修改注意：这里修改值的类型为string

实现代码：

#include #include 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;}

运行结果：

2-4 delete（删操作）

在表中查找指定的json，符合条件的json进行删除

实现代码：

#include #include 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;}

运行结果：

三、libbson库的使用

将bson格式转换成json格式（value不带类型）
函数：char * bson_as_json (const bson_t *bson, size_t *length);
输出格式：
注意事项：函数返回值（指针）记得使用函数 void bson_free (void *mem)释放
将bson格式转换成json格式（value带类型）
函数：char * bson_as_canonical_extended_json (const bson_t *bson, size_t *length)
输出格式：
注意事项：函数返回值（指针）记得使用函数 void bson_free (void *mem)释放

关键词：注意事项输出格式原始数据