MongoDB using C


This document is an introduction to the usage of the MongoDB database from a C program.

First, install MongoDB – see this blog for how to install and here we will work on MSYS software.

What is MSYS software?


MSYS is a collection of GNU utilities such as bash, make, gawk and grep to allow the building of applications and programs which depend on traditionally UNIX tools to be present.

A common misunderstanding is MSYS is "UNIX on Windows", MSYS by itself does not contain a compiler or a C library, therefore does not give the ability to magically port UNIX programs over to Windows nor does it provide any UNIX specific functionality like case-sensitive filenames.

Why are We using this?

An example would be building a library that uses the build system. Users will typically run "./configure" then "make" to build it. The configure shell script requires a shell script interpreter which is not present on Windows systems, but provided by MSYS.

To establish a connection in Mongodb by C and C++, you will get the source code of the driver for it, which will have to be implemented according to your platform.


How to install MSYS Software and MongoDB C Driver

Download MSYS after Download Install It.
open command prompt you can now move to c:\msys64 there type mingw64 to start the environment 

type pacman -Syu
exit the window

again open and type pacman -Syu (this will take a lot of time please wait)

install all module one by one:-
--pacman --noconfirm -S mingw-w64-x86_64-gcc mingw-w64-x86_64-cmake

--pacman --noconfirm -S mingw-w64-x86_64-extra-cmake-modules make tar

--pacman --noconfirm -S mingw64/mingw-w64-x86_64-cyrus-sasl

--curl -LO https://github.com/mongodb/mongo-c-driver/releases/download/1.16.2/mongo-c-driver-1.16.2.tar.gz

--tar xzf mongo-c-driver-1.16.2.tar.gz

--cd mongo-c-driver-1.16.2

--mkdir cmake-build

--cd cmake-build

--CC=/mingw64/bin/gcc.exe /mingw64/bin/cmake -G "MSYS Makefiles" -DCMAKE_INSTALL_PREFIX="C:/mongo-c-driver" -DCMAKE_C_FLAGS="-D__USE_MINGW_ANSI_STDIO=1" ..

--make install

Now check-in mongo-c-driver you will find  "bin" this contains dll file which is window specific according to your system platform "include", "lib" and "share" folder in parallel

Initialization

Initialize the MongoDB C Driver by calling mongoc_init() exactly once at the beginning of your program. It is responsible for initializing global state such as process counters, SSL, and threading primitives.


mongo_init();


Connection

let create a connection to the database and access or create a collection


mongoc_client_t *client;
mongoc_collection_t *collection;

client=mongoc_client_new("mongodb://localhost:27017");
collection=mongoc_client_get_collection(client,"tmdb","students");


Here we establish a connection to MongoDB server and we assign a database and collection reference to "collection" variable. if there exists a database/collection then it return existing reference if not exist then it will create a new database/collection and return to the variable

 Creating Document

The MongoDB database stores data in BSON format. BSON is a binary object format that is JSON-like in terms of the data which can be stored (some extensions exist, for example, a Date datatype). So we create a document here a document is a struct and store all data in it


bson_t *doc;

doc=bson_new();
BSON_APPEND_UTF8(doc,"rollNumber","101");
BSON_APPEND_UTF8(doc,"firstName","Prakash");
BSON_APPEND_UTF8(doc,"lastName","Pandey");


Insert

We insert a document "doc" to a collection using  mongoc_collection_insert_one()


bson_error_t error;

mongoc_collection_insert_one(collection,doc,NULL,NULL,&error)

As mongoc_collection_insert_one() required 5 parameter 

Collection: as mongo_Collection_t reference to a database/collection 

Document: as A bson_t new created document need to insert, 

Opts: may be NULL or a BSON document with additional command.

Reply: it is Optional. An uninitialized bson_t populated with the insert result, or NULL. 

Error: An optional location for a bson_error_t or NULL


Releasing Memory

Dynamic memory allocation in C/C++ refers to performing memory allocation manually by the programmer. So we need to free all memory allocated


bson_destroy(doc);
mongoc_collection_destroy(collection);
mongoc_client_destroy(client);
mongoc_cleanup(); 

Call mongo_cleanup() exactly once at the end of your program to release all memory and other resources allocated by the driver. You must not call any other MongoDB C Driver functions after mongoc_cleanup.

Let grab all in one call eg1.c 


eg1.c

#include<mongoc.h>
#include<stdio.h>
int main()
{
mongoc_client_t *client;
mongoc_collection_t *collection;
bson_error_t error;
bson_t *doc;
mongoc_init();
client=mongoc_client_new("mongodb://localhost:27017");
collection=mongoc_client_get_collection(client,"tmdb","students");

doc=bson_new();
BSON_APPEND_UTF8(doc,"rollNumber","101");
BSON_APPEND_UTF8(doc,"firstName","Prakash");
BSON_APPEND_UTF8(doc,"lastName","Pandey");
if(!mongoc_collection_insert_one(collection,doc,NULL,NULL,&error))
{
printf("%s\n",error.message);
}
bson_destroy(doc);
mongoc_collection_destroy(collection);
mongoc_client_destroy(client);
mongoc_cleanup(); 
printf("DONE");
return 0;
}

compile :-
gcc eg1.c -o eg1.out -I /mongo-c-driver/include/libmongoc-1.0/ -I /mongo-c-driver/include/libbson-1.0/ -L . libmongoc-1.0.dll.a libbson-1.0.dll.a

execute:- ./eg1.out


This end of insertion document in collection/database similarly you can do update, delete and find a document in database/collection;

Update


eg2.c

#include<mongoc.h>
#include<stdio.h>
int main()
{
mongoc_client_t *client;
mongoc_collection_t *collection;
bson_error_t error;
bson_t *doc;
bson_t *quary;
mongoc_init();
client=mongoc_client_new("mongodb://localhost:27017");
collection=mongoc_client_get_collection(client,"tmdb","student");
quary=bson_new();
BSON_APPEND_UTF8(quary,"rollNumber","101");
doc=bson_new();
BSON_APPEND_UTF8(doc,"firstName","Ram");
BSON_APPEND_UTF8(doc,"lastName","Pandey");
if(!mongoc_collection_update(collection,MONGOC_UPDATE_NONE,quary,doc,NULL,&error))
{
printf("%s\n",error.message);
}
else
{
printf("updated\n");
}
bson_destroy(quary);
bson_destroy(doc);
mongoc_collection_destroy(collection);
mongoc_client_destroy(client);
mongoc_cleanup(); 
printf("DONE");
return 0;
}

compile :-
gcc eg2.c -o eg2.out -I /mongo-c-driver/include/libmongoc-1.0/ -I /mongo-c-driver/include/libbson-1.0/ -L . libmongoc-1.0.dll.a libbson-1.0.dll.a

execute:- ./eg2.out

Delete


eg3.c

#include<mongoc.h>
#include<stdio.h>
int main()
{
mongoc_client_t *client;
mongoc_collection_t *collection;
bson_error_t error;
bson_t *quary;
mongoc_init();
client=mongoc_client_new("mongodb://localhost:27017");
collection=mongoc_client_get_collection(client,"tmdb","students");
quary=bson_new();
BSON_APPEND_UTF8(quary,"rollNumber","101");
if(!mongoc_collection_remove(collection,MONGOC_REMOVE_NONE,quary,NULL,&error))
{
printf("%s\n",error.message);
}
else
{
printf("removed\n");
}
bson_destroy(quary);
mongoc_collection_destroy(collection);
mongoc_client_destroy(client);
mongoc_cleanup(); 
printf("DONE");
return 0;
}

compile :-
gcc eg3.c -o eg3.out -I /mongo-c-driver/include/libmongoc-1.0/ -I /mongo-c-driver/include/libbson-1.0/ -L . libmongoc-1.0.dll.a libbson-1.0.dll.a

execute:- ./eg3.out

Find a document in a collection


eg4.c

#include<mongoc.h>
#include<stdio.h>
int main()
{
mongoc_client_t *client;
mongoc_collection_t *collection;
bson_error_t error;
mongoc_cursor_t *cursor;
const bson_t *document;
const bson_t query=BSON_INITIALIZER;
char *str;

mongoc_init();
client=mongoc_client_new("mongodb://localhost:27017");
collection=mongoc_client_get_collection(client,"tmdb","student");

cursor = mongoc_collection_find_with_opts (collection,&query, NULL, NULL);
while (mongoc_cursor_next (cursor, &document)) 
{
str = bson_as_json (document, NULL);
printf ("%s\n", str);
bson_free (str);
}
if(mongoc_cursor_error(cursor,&error))
{
printf("problem%s",error.message);
}
mongoc_cursor_destroy (cursor);
mongoc_collection_destroy(collection);
mongoc_client_destroy(client);
mongoc_cleanup(); 
printf("DONE");
return 0;
}

compile :-
gcc eg4.c -o eg4.out -I /mongo-c-driver/include/libmongoc-1.0/ -I /mongo-c-driver/include/libbson-1.0/ -L . libmongoc-1.0.dll.a libbson-1.0.dll.a

execute:- ./eg4.out

Hope you find it helpful and feel free to add a comment and I’ll make sure to improve my self.

Thank You

Prakash Pandey


I am a hardworking final year student, specialized in computer science engineering. I want to help others, so that they do not have to face the difficulties I have faced. Here are some of my blogs, you can suggest me if there is something wrong with it and what topic to write in future, you can give me suggestions, I will help you.

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