我可以通过ObjCMongoDB库使用Mongo Aggregation Framework吗？(Can I use the Mongo Aggregation Framework via the O

我可以通过ObjCMongoDB库使用Mongo Aggregation Framework吗？(Can I use the Mongo Aggregation Framework via the ObjCMongoDB library?)

我使用ObjCMongoDB库来支持一个简单的iPad应用程序。 我理解基本的CRUD操作以及使用-[MongoConnection runCommandWithDictionary:onDatabaseName:error:]来执行数据库命令，例如findAndModify 。

关于聚合框架或一般只是聚合，看起来我可以通过以下方式执行简单的数据库命令，如count ：

NSDictionary *commandDict = @{@"count": @"myCollection"}: [myMongoConnection runCommandWithDictionary:commandDict onDatabaseName:@"myDB" error:&err];

是否可以像这里的例子那样执行更复杂的命令/查询？ 我尝试了以下无济于事。

NSDictionary *commandDict = @{@"aggregate":@"myCollection", @"query": @{@"group":@"myDocType"}};

如果这是一个不知情的问题，我仍然在学习Obj-C和MongoDB。

I am using the ObjCMongoDB library to back a simple iPad application. I understand the basic CRUD operations as well as use of -[MongoConnection runCommandWithDictionary:onDatabaseName:error:] to execute database commands such as findAndModify.

With respect to the Aggregation Framework or just aggregation in general, it looks like I can execute simple database commands like count in the following manner:

NSDictionary *commandDict = @{@"count": @"myCollection"}: [myMongoConnection runCommandWithDictionary:commandDict onDatabaseName:@"myDB" error:&err];

Is it possible to execute more complex commands/queries like the examples here? I tried the following to no avail.

NSDictionary *commandDict = @{@"aggregate":@"myCollection", @"query": @{@"group":@"myDocType"}};

Am still learning both Obj-C as well as MongoDB so apologies if this is an uninformed question.

最满意答案

您的aggregate命令的语法似乎不正确。

从聚合的文档中查看此示例：

db.runCommand( { aggregate : "article", pipeline : [ { $project : { author : 1, tags : 1, } }, { $unwind : "$tags" }, { $group : { _id : "$tags", authors : { $addToSet : "$author" } } } ] } );

如果从命令行运行Mongo shell，则可以在Objective-C中编写命令之前直接测试命令。

Your syntax for the aggregate command appears to be incorrect.

See this example from the docs for aggregate:

db.runCommand( { aggregate : "article", pipeline : [ { $project : { author : 1, tags : 1, } }, { $unwind : "$tags" }, { $group : { _id : "$tags", authors : { $addToSet : "$author" } } } ] } );

If you run the Mongo shell from the command line, you can test your command directly right there, before writing it in Objective-C.