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<page id="finding-document"
type="topic"
xmlns="http://projectmallard.org/1.0/">
<info>
<link type="guide" xref="tutorial#crud-operations"/>
</info>
<title>Finding a Document</title>
<p>To query a MongoDB collection with the C driver, use the function <code xref="mongoc_collection_find">mongoc_collection_find()</code>. This returns a <link xref="mongoc_cursor_t">cursor</link> to the matching documents. The following examples iterate through the result cursors and print the matches to <code>stdout</code> as JSON strings.</p>
<p>Note that <code>mongoc_collection_find</code> uses a document as a query specifier; for example,</p>
<screen><code mime="x-js">{ "color" : "red" }</code></screen>
<p>will match any document with a field named "color" with value "red". An empty document <code>{}</code> can be used to match all documents.</p>
<p>This first example uses an empty query specifier to find all documents in the database "mydb" and collection "mycoll".</p>
<listing>
<title><file>find.c</file></title>
<synopsis><code mime="text/x-csrc"><![CDATA[#include <bson.h>
#include <mongoc.h>
#include <stdio.h>
int
main (int argc,
char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_cursor_t *cursor;
const bson_t *doc;
bson_t *query;
char *str;
mongoc_init ();
client = mongoc_client_new ("mongodb://localhost:27017/");
collection = mongoc_client_get_collection (client, "mydb", "mycoll");
query = bson_new ();
cursor = mongoc_collection_find (collection, MONGOC_QUERY_NONE, 0, 0, 0, query, NULL, NULL);
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_json (doc, NULL);
printf ("%s\n", str);
bson_free (str);
}
bson_destroy (query);
mongoc_cursor_destroy (cursor);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
]]></code></synopsis>
</listing>
<p>Compile the code and run it: </p>
<screen><output style="prompt">$ gcc -o find find.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./find
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }</output></screen>
<p>On Windows:</p>
<screen><output style="prompt">C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find.c
C:\> find
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }</output></screen>
<p>To look for a specific document, add a specifier to <code>query</code>. This example adds a call to <code>BSON_APPEND_UTF8()</code> to look for all documents matching <code mime="text/x-js">{"hello" : "world"}</code>.</p>
<listing>
<title><file>find-specific.c</file></title>
<synopsis><code mime="text/x-csrc"><![CDATA[#include <bson.h>
#include <mongoc.h>
#include <stdio.h>
int
main (int argc,
char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_cursor_t *cursor;
const bson_t *doc;
bson_t *query;
char *str;
mongoc_init ();
client = mongoc_client_new ("mongodb://localhost:27017/");
collection = mongoc_client_get_collection (client, "mydb", "mycoll");
query = bson_new ();
BSON_APPEND_UTF8 (query, "hello", "world");
cursor = mongoc_collection_find (collection, MONGOC_QUERY_NONE, 0, 0, 0, query, NULL, NULL);
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_json (doc, NULL);
printf ("%s\n", str);
bson_free (str);
}
bson_destroy (query);
mongoc_cursor_destroy (cursor);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
]]></code></synopsis>
</listing>
<screen><output style="prompt">$ gcc -o find-specific find-specific.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./find-specific
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }</output></screen>
<screen><output style="prompt">C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find-specific.c
C:\> find-specific
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }</output></screen>
</page>
|
