table of contents
COMMON_TASKS(3) | Library Functions Manual | COMMON_TASKS(3) |
NAME¶
Common_Tasks - None Drivers for some other languages provide helper functions to perform certain common tasks. In the C Driver we must explicitly build commands to send to the server.This snippet contains example code for the explain , copydb and cloneCollection commands.
SETUP¶
First we'll write some code to insert sample data:/* Don't try to compile this file on it's own. It's meant to be #included by example code */ /* Insert some sample data */ bool insert_data (mongoc_collection_t* collection) { mongoc_bulk_operation_t *bulk; enum N { ndocs = 4 }; bson_t* docs[ndocs]; bson_error_t error; int i = 0; bool ret; bulk = mongoc_collection_create_bulk_operation (collection, true, NULL); docs[0] = BCON_NEW ("x", BCON_DOUBLE (1.0), "tags", "[", "dog", "cat", "]"); docs[1] = BCON_NEW ("x", BCON_DOUBLE (2.0), "tags", "[", "cat", "]"); docs[2] = BCON_NEW ("x", BCON_DOUBLE (2.0), "tags", "[", "mouse", "cat", "dog", "]"); docs[3] = BCON_NEW ("x", BCON_DOUBLE (3.0), "tags", "[", "]"); for (i = 0; i < ndocs; i++) { mongoc_bulk_operation_insert (bulk, docs[i]); bson_destroy (docs[i]); docs[i] = NULL; } ret = mongoc_bulk_operation_execute (bulk, NULL, &error); if (!ret) { fprintf (stderr, "Error inserting data: %s\n", error.message); } mongoc_bulk_operation_destroy (bulk); return ret; } /* A helper which we'll use a lot later on */ void print_res (const bson_t* reply) { BSON_ASSERT (reply); char *str = bson_as_json (reply, NULL); printf ("%s\n", str); bson_free (str); }
EXPLAIN COMMAND¶
This is how to use the explain command in MongoDB 3.2+:bool explain (mongoc_collection_t* collection) { bson_t* command; bson_t reply; bson_error_t error; bool res; command = BCON_NEW ("explain", "{", "find", BCON_UTF8 (COLLECTION_NAME), "filter", "{", "x", BCON_INT32 (1), "}", "}"); res = mongoc_collection_command_simple (collection, command, NULL, &reply, &error); if (!res) { fprintf (stderr, "Error with explain: %s\n", error.message); goto cleanup; } /* Do something with the reply */ print_res (&reply); cleanup: bson_destroy(&reply); bson_destroy (command); return res; }
COPYDB COMMAND¶
This example requires two instances of mongo to be running.Here's how to use the copydb command to copy a database from another instance of MongoDB:
bool copydb (mongoc_client_t* client, const char* other_host_and_port) { mongoc_database_t* admindb; bson_t* command; bson_t reply; bson_error_t error; bool res; BSON_ASSERT (other_host_and_port); /* Must do this from the admin db */ admindb = mongoc_client_get_database (client, "admin"); command = BCON_NEW ("copydb", BCON_INT32 (1), "fromdb", BCON_UTF8 ("test"), "todb", BCON_UTF8 ("test2"), /* If you want from a different host */ "fromhost", BCON_UTF8 (other_host_and_port)); res = mongoc_database_command_simple (admindb, command, NULL, &reply, &error); if (!res) { fprintf (stderr, "Error with copydb: %s\n", error.message); goto cleanup; } /* Do something with the reply */ print_res (&reply); cleanup: bson_destroy(&reply); bson_destroy (command); mongoc_database_destroy (admindb); return res; }
CLONECOLLECTION COMMAND¶
This example requires two instances of mongo to be running.Here's an example of the cloneCollection command to clone a collection from another instance of MongoDB:
bool clone_collection (mongoc_database_t* database, const char* other_host_and_port) { bson_t* command; bson_t reply; bson_error_t error; bool res; BSON_ASSERT (other_host_and_port); command = BCON_NEW ("cloneCollection", BCON_UTF8 ("test.remoteThings"), "from", BCON_UTF8 (other_host_and_port), "query", "{", "x", BCON_INT32 (1), "}"); res = mongoc_database_command_simple (database, command, NULL, &reply, &error); if (!res) { fprintf (stderr, "Error with clone: %s\n", error.message); goto cleanup; } /* Do something with the reply */ print_res (&reply); cleanup: bson_destroy (&reply); bson_destroy (command); return res; }
RUNNING¶
/* * Copyright 2016 MongoDB, Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE‐2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #include <mongoc.h> #include <stdio.h> const char* COLLECTION_NAME = "things"; #include "../doc‐common‐insert.c" #include "explain.c" #include "copydb.c" #include "clone‐collection.c" int main (int argc, char *argv[]) { mongoc_database_t *database = NULL; mongoc_client_t *client = NULL; mongoc_collection_t *collection = NULL; char *host_and_port; int res = 0; char* other_host_and_port = NULL; if (argc < 2 || argc > 3) { fprintf (stderr, "usage: %s MONGOD‐1‐CONNECTION‐STRING " "[MONGOD‐2‐HOST‐NAME:MONGOD‐2‐PORT]\n", argv[0]); fprintf (stderr, "MONGOD‐1‐CONNECTION‐STRING can be " "of the following forms:\n"); fprintf (stderr, "localhost\t\t\t\tlocal machine\n"); fprintf (stderr, "localhost:27018\t\t\t\tlocal machine on port 27018\n"); fprintf (stderr, "mongodb://user:pass@localhost:27017\t" "local machine on port 27017, and authenticate with username " "user and password pass\n"); return 1; } mongoc_init (); if (strncmp (argv[1], "mongodb://", 10) == 0) { host_and_port = bson_strdup (argv [1]); } else { host_and_port = bson_strdup_printf ("mongodb://%s", argv[1]); } other_host_and_port = argc > 2 ? argv[2] : NULL; client = mongoc_client_new (host_and_port); if (!client) { fprintf(stderr, "Invalid hostname or port: %s\n", host_and_port); res = 2; goto cleanup; } mongoc_client_set_error_api (client, 2); database = mongoc_client_get_database (client, "test"); collection = mongoc_database_get_collection (database, COLLECTION_NAME); printf ("Inserting data\n"); if (!insert_data (collection)) { res = 3; goto cleanup; } printf ("explain\n"); if (!explain (collection)) { res = 4; goto cleanup; } if (other_host_and_port) { printf ("copydb\n"); if (!copydb (client, other_host_and_port)) { res = 5; goto cleanup; } printf ("clone collection\n"); if (!clone_collection (database, other_host_and_port)) { res = 6; goto cleanup; } } cleanup: if (collection) { mongoc_collection_destroy (collection); } if (database) { mongoc_database_destroy (database); } if (client) { mongoc_client_destroy (client); } bson_free (host_and_port); mongoc_cleanup (); return res; }
First launch two separate instances of mongod (must be done from separate shells):
$ mongod
$ mkdir /tmp/db2 $ mongod --dbpath /tmp/db2 --port 27018 # second instance
Now compile and run the example program:
$ cd examples/common_operations/ $ gcc -Wall -o example common-operations.c $(pkg-config --cflags --libs libmongoc-1.0) $ ./example localhost:27017 localhost:27018
Inserting data explain { "executionStats" : { "allPlansExecution" : [], "executionStages" : { "advanced" : 19, "direction" : "forward" , "docsExamined" : 76, "executionTimeMillisEstimate" : 0, "filter" : { "x" : { "$eq" : 1 } }, "invalidates" : 0, "isEOF" : 1, "nReturned" : 19, "needTime" : 58, "needYield" : 0, "restoreState" : 0, "saveState" : 0, "stage" : "COLLSCAN" , "works" : 78 }, "executionSuccess" : true, "executionTimeMillis" : 0, "nReturned" : 19, "totalDocsExamined" : 76, "totalKeysExamined" : 0 }, "ok" : 1, "queryPlanner" : { "indexFilterSet" : false, "namespace" : "test.things", "parsedQuery" : { "x" : { "$eq" : 1 } }, "plannerVersion" : 1, "rejectedPlans" : [], "winningPlan" : { "direction" : "forward" , "filter" : { "x" : { "$eq" : 1 } }, "stage" : "COLLSCAN" } }, "serverInfo" : { "gitVersion" : "05552b562c7a0b3143a729aaa0838e558dc49b25" , "host" : "MacBook‐Pro‐57.local", "port" : 27017, "version" : "3.2.6" } } copydb { "ok" : 1 } clone collection { "ok" : 1 }
COLOPHON¶
This page is part of MongoDB C Driver. Please report any bugs at https://jira.mongodb.org/browse/CDRIVER.2016‐10‐12 | MongoDB C Driver |