MongoDB基本的操作及C接口使用-MongoDB C Driver
官网 http://mongoc.org/libmongoc/current/tutorial.html
下载 wget https://github.com/mongodb/mongo-c-driver/releases/download/1.6.3/mongo-c-driver-1.6.3.tar.gz
$ tar xzf mongo-c-driver-1.6.3.tar.gz
$ cd mongo-c-driver-1.6.3
$ ./configure --disable-automatic-init-and-cleanup
Starting MongoDB¶
To run the examples in this tutorial, MongoDB must be installed and running on localhost on the default port, 27017. To check if it is up and running, connect to it with the MongoDB shell.
$ mongo --host localhost --port 27017
MongoDB shell version: 3.0.6
connecting to: localhost:27017/test
>
Making a Connection¶
The C Driver provides a convenient way to access MongoDB -- regardless of cluster configuration -- via a mongoc_client_t. It transparently connects to standalone servers, replica sets and sharded clusters on demand. Once a connection has been made, handles to databases and collections can be obtained via the structs mongoc_database_t and mongoc_collection_t, respectively. MongoDB operations can then be performed through these handles.
At the start of an application, call mongoc_init() before any other libmongoc functions and call mongoc_cleanup() before exiting. When creating handles to clients, databases and servers, call the appropriate destroy functions when finished.
The example below establishes a connection to a standalone server on localhost, registers the client application as "connect-example," and performs a simple command. More information about database operations can be found in the CRUD Operations and Executing Commands sections. Examples of connecting to replica sets and sharded clusters can be found on the Advanced Connections page.
#include
On a UNIX-like system, the code can be compiled and run like so:
$ gcc -o connect connect.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./connect
{ "ok" : 1.000000 }
Alternatively, if pkg-config is not available, paths and libraries can be managed manually.
$ gcc -o connect connect.c -I/usr/local/include -lmongoc-1.0 -lbson-1.0
$ ./connect
{ "ok" : 1.000000 }
For Windows users, the code can be compiled and run with the following commands. (This assumes that the MongoDB C Driver has been installed to C:\mongo-c-driver; change the include directory as needed.)
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 connect.c
C:\> connect
{ "ok" : 1.000000 }
Creating BSON Documents¶
Documents are stored in MongoDB's data format, BSON. The C driver uses libbson to create BSON documents. There are several ways to construct them: appending key-value pairs, using BCON, or parsing JSON.
Appending BSON¶
A BSON document, represented as a bson_t in code, can be constructed one field at a time using libbson's append functions.
For example, to create a document like this:
{
born : ISODate("1906-12-09"),
died : ISODate("1992-01-01"),
name : {
first : "Grace",
last : "Hopper"
},
languages : [ "MATH-MATIC", "FLOW-MATIC", "COBOL" ],
degrees: [ { degree: "BA", school: "Vassar" }, { degree: "PhD", school: "Yale" } ]
}
Use the following code:
#include
See the libbson documentation for all of the types that can be appended to a bson_t.
Using BCON¶
BSON C Object Notation, BCON for short, is an alternative way of constructing BSON documents in a manner closer to the intended format. It has less type-safety than BSON's append functions but results in less code.
#include
Notice that BCON can create arrays, subdocuments and arbitrary fields.
Creating BSON from JSON¶
For single documents, BSON can be created from JSON strings via bson_new_from_json.
#include
To initialize BSON from a sequence of JSON documents, use bson_json_reader_t.
Basic CRUD Operations¶
This section demonstrates the basics of using the C Driver to interact with MongoDB.
Inserting a Document¶
To insert documents into a collection, first obtain a handle to a mongoc_collection_t via a mongoc_client_t. Then, use mongoc_collection_insert() to add BSON documents to the collection. This example inserts into the database "mydb" and collection "mycoll".
When finished, ensure that allocated structures are freed by using their respective destroy functions.
#include
Compile the code and run it:
$ gcc -o insert insert.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./insert
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 insert.c
C:\> insert
To verify that the insert succeeded, connect with the MongoDB shell.
$ mongo
MongoDB shell version: 3.0.6
connecting to: test
> use mydb
switched to db mydb
> db.mycoll.find()
{ "_id" : ObjectId("55ef43766cb5f36a3bae6ee4"), "hello" : "world" }
>
Finding a Document¶
To query a MongoDB collection with the C driver, use the function mongoc_collection_find_with_opts(). This returns a cursor to the matching documents. The following examples iterate through the result cursors and print the matches to stdout as JSON strings.
Use a document as a query specifier; for example,
{ "color" : "red" }
will match any document with a field named "color" with value "red". An empty document {} can be used to match all documents.
This first example uses an empty query specifier to find all documents in the database "mydb" and collection "mycoll".
#include
Compile the code and run it:
$ gcc -o find find.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./find
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find.c
C:\> find
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
To look for a specific document, add a specifier to query. This example adds a call to BSON_APPEND_UTF8() to look for all documents matching {"hello" : "world"}.
#include
$ gcc -o find-specific find-specific.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./find-specific
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find-specific.c
C:\> find-specific
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
Updating a Document¶
This code snippet gives an example of using mongoc_collection_update() to update the fields of a document.
Using the "mydb" database, the following example inserts an example document into the "mycoll" collection. Then, using its _id field, the document is updated with different values and a new field.
#include
Compile the code and run it:
$ gcc -o update update.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./update
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 update.c
C:\> update
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
To verify that the update succeeded, connect with the MongoDB shell.
$ mongo
MongoDB shell version: 3.0.6
connecting to: test
> use mydb
switched to db mydb
> db.mycoll.find({"updated" : true})
{ "_id" : ObjectId("55ef549236fe322f9490e17b"), "updated" : true, "key" : "new_value" }
>
Deleting a Document¶
This example illustrates the use of mongoc_collection_remove() to delete documents.
The following code inserts a sample document into the database "mydb" and collection "mycoll". Then, it deletes all documents matching {"hello" : "world"}.
#include
Compile the code and run it:
$ gcc -o delete delete.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./delete
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 delete.c
C:\> delete
Use the MongoDB shell to prove that the documents have been removed successfully.
$ mongo
MongoDB shell version: 3.0.6
connecting to: test
> use mydb
switched to db mydb
> db.mycoll.count({"hello" : "world"})
0
>
Counting Documents¶
Counting the number of documents in a MongoDB collection is similar to performing a find operation. This example counts the number of documents matching {"hello" : "world"} in the database "mydb" and collection "mycoll".
#include
Compile the code and run it:
$ gcc -o count count.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./count
1
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 count.c
C:\> count
1
Executing Commands¶
The driver provides helper functions for executing MongoDB commands on client, database and collection structures. These functions return cursors; the _simple variants return booleans indicating success or failure.
This example executes the collStats command against the collection "mycoll" in database "mydb".
#include
Compile the code and run it:
$ gcc -o executing executing.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./executing
{ "ns" : "mydb.mycoll", "count" : 1, "size" : 48, "avgObjSize" : 48, "numExtents" : 1, "storageSize" : 8192,
"lastExtentSize" : 8192.000000, "paddingFactor" : 1.000000, "userFlags" : 1, "capped" : false, "nindexes" : 1,
"indexDetails" : { }, "totalIndexSize" : 8176, "indexSizes" : { "_id_" : 8176 }, "ok" : 1.000000 }
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 executing.c
C:\> executing
{ "ns" : "mydb.mycoll", "count" : 1, "size" : 48, "avgObjSize" : 48, "numExtents" : 1, "storageSize" : 8192,
"lastExtentSize" : 8192.000000, "paddingFactor" : 1.000000, "userFlags" : 1, "capped" : false, "nindexes" : 1,
"indexDetails" : { }, "totalIndexSize" : 8176, "indexSizes" : { "_id_" : 8176 }, "ok" : 1.000000 }
Threading¶
The MongoDB C Driver is thread-unaware in the vast majority of its operations. This means it is up to the programmer to guarantee thread-safety.
However, mongoc_client_pool_t is thread-safe and is used to fetch a mongoc_client_t in a thread-safe manner. After retrieving a client from the pool, the client structure should be considered owned by the calling thread. When the thread is finished, the client should be placed back into the pool.
/* gcc example-pool.c -o example-pool $(pkg-config --cflags --libs
* libmongoc-1.0) */
/* ./example-pool [CONNECTION_STRING] */
#include