SYNOPSIS
const bson_t *doc; mongoc_cursor_t * cursor; cursor = mongoc_collection_find (collection, MONGOC_QUERY_NONE, 0, 0, &query, NULL, /* Fields, NULL for all. */ NULL); /* Read Prefs, NULL for default */ while (mongoc_cursor_next (cursor, &doc)) { do_something(doc); }
DESCRIPTION
mongoc_cursor provides access to a MongoDB query cursor. It wraps up the wire protocol negotation required to initiate a query and retreive an unknown number of documents.
Cursors are lazy, meaning that no network traffic occurs until the first mongoc_cursor_next(3).
At that point we can:
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Determine which host we’ve connected to with mongoc_cursor_get_host(3).
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Retreive more records with repeated calls to mongoc_cursor_next(3)
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Test for more records with mongoc_cursor_more(3)
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Clone a query to repeat execution at a later point with mongoc_cursor_clone(3)
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Test for errors with mongoc_cursor_error(3)
THREAD SAFETY
mongoc_cursor is NOT thread-safe and should only be used from one thread at a time.
LIFECYCLE
The bson objects set in mongoc_cursor_next(3) are ephemeral and good until the next call. mongoc_cursor_destroy(3) must be called to clean up, even in the case of exhausted cursors.
EXAMPLE
The following example connects to a single MongoDB instance and performs a simple query against it. The resulting documents are printed as JSON to standard output.
/* gcc example.c -o example $(pkg-config --cflags --libs libmongoc-1.0) */ /* ./example-client [CONNECTION_STRING [COLLECTION_NAME]] */ #include <mongoc.h> #include <stdio.h> #include <stdlib.h> int main (int argc, char *argv[]) { mongoc_client_t *client; mongoc_collection_t *collection; mongoc_cursor_t *cursor; bson_error_t error; const bson_t *doc; const char *uristr = "mongodb://127.0.0.1/"; const char *collection_name = "test"; bson_t query; char *str; mongoc_init (); if (argc > 1) { uristr = argv [1]; } if (argc > 2) { collection_name = argv [2]; } client = mongoc_client_new (uristr); if (!client) { fprintf (stderr, "Failed to parse URI.\n"); return EXIT_FAILURE; } bson_init (&query); #if 0 bson_append_utf8 (&query, "hello", -1, "world", -1); #endif collection = mongoc_client_get_collection (client, "test", collection_name); cursor = mongoc_collection_find (collection, MONGOC_QUERY_NONE, 0, 0, 0, &query, NULL, /* Fields, NULL for all. */ NULL); /* Read Prefs, NULL for default */ while (!mongoc_cursor_error (cursor, &error) && mongoc_cursor_more (cursor)) { if (mongoc_cursor_next (cursor, &doc)) { str = bson_as_json (doc, NULL); fprintf (stdout, "%s\n", str); bson_free (str); } } if (mongoc_cursor_error (cursor, &error)) { fprintf (stderr, "Cursor Failure: %s\n", error.message); return EXIT_FAILURE; } bson_destroy (&query); mongoc_cursor_destroy (cursor); mongoc_collection_destroy (collection); mongoc_client_destroy (client); return EXIT_SUCCESS; }
SEE ALSO
AUTHORS
This page was written by MongoDB Inc.