ObjMongoDB list of all collections in a db

Question

Using ObjcMongodb framework- How to find all the collections in a db similar to show collections (shell command)

Answer 1

You can invoke arbitrary database commands using these methods on MongoConnection:

- (NSDictionary *) runCommandWithName:(NSString *) commandName
                       onDatabaseName:(NSString *) databaseName
                                error:(NSError * __autoreleasing *) error;
- (NSDictionary *) runCommandWithDictionary:(NSDictionary *) dictionary
                             onDatabaseName:(NSString *) databaseName
                                      error:(NSError * __autoreleasing *) error;

See this answer for an example.

Answer 2

To list all collections in a database, query the system.namespaces collection.

The system.namespaces collection includes both collection names and indexes so you need to filter the results to ignore any system collections (eg: system.indexes) as well as those containing $ (indexes/special collections).

Example code:

NSError *error = nil;
MongoConnection *dbConn = [MongoConnection connectionForServer:@"127.0.0.1" error:&error];

// For database "mydb", look in "system.namespaces" collection
MongoDBCollection *collection = [dbConn collectionWithName:@"mydb.system.namespaces"];

NSArray *results = [collection findAllWithError:&error];
for (BSONDocument *result in results) {
    NSDictionary *systemNamespace = [BSONDecoder decodeDictionaryWithDocument:result];
    NSString *collName = [systemNamespace objectForKey:@"name"];

    // Namespaces to ignore: mydb.system.* (system) and those containing $ (indexes/special)
    if (
        ([collName rangeOfString:@".system."].location == NSNotFound) &&
        ([collName rangeOfString:@"$"].location == NSNotFound)) {
        NSLog(@"Found collection: %@", collName);
    } else {
        // NSLog(@"Ignoring: %@", collName);
    }
}