C＃Mongo驱动程序错误：无法从BsonType'Document'反序列化'Int32'

Question

下面的MongoDB查询在Robo3T 1.2上运行良好，并返回正确的“计数”。

db.runCommand( {
aggregate: "User",
pipeline: [
{$unwind: '$UserSubscriptions'},
{$group: {
    _id: '$_id',
    codes: {$addToSet: '$UserSubscriptions.Subscription.Publication'}
}},
{$unwind: '$codes'},
{$group: {
    _id: '$codes',
    count: {$sum: 1}
}}
]
} )

我正在尝试将上述查询转换为C＃MongoDriver查询

 var unwind = new BsonDocument { { "$unwind", "$UserSubscriptions" } };
        var group1 = new BsonDocument
            {
                { "$group",
                    new BsonDocument
                        {
                            { "_id", new BsonDocument
                                         {
                                             {
                                                 "Id","$_id"
                                             }
                                         }
                            },
                            {
                                "codes", new BsonDocument
                                             {
                                                 {
                                                     "$addToSet","$UserSubscriptions.Subscription.Publication.Code"
                                                 }
                                             }
                            }
                        }
              }
            };
        var unwindCode = new BsonDocument { { "$unwind", "$codes" } };
        var group2 = new BsonDocument
            {
                { "$group",
                    new BsonDocument
                        {
                            { "_id", new BsonDocument
                                         {
                                             {
                                                 "Id","$codes"
                                             }
                                         }
                            },
                            {
                                "codes", new BsonDocument
                                             {
                                                 {
                                                     "$sum",1
                                                 }
                                             }
                            }
                        }
              }
            };
        var pipeline = new[] { unwind, group1 , unwindCode , group2 };
    var result = coll.Aggregate<T>(pipeline);

但是出现错误无法从BsonType'Document'反序列化'Int32'。

Id是集合中的主键

public int ID {get;组; }

请告知如何实现此目标。

（Robo 3T 1.2.1）（MongoDB.Driver 2.4.4）

Answer 1

您正试图通过为“ _id”创建BsonDocument将BsonDocument反序列化为“ Int32”。您只需要这样做：

var group1 = new BsonDocument
{
    { 
        "$group", new BsonDocument
        {
            { 
                "_id", "$_id"
            },
            {
                "codes", new BsonDocument
                {
                     {
                        "$addToSet", "$UserSubscriptions.Subscription.Publication.Code"
                     }
                }
            }
        }
    }
};

var group2 = new BsonDocument
{
    { 
        "$group", new BsonDocument
        {
            { 
                "_id", "$codes"
            },
            {
                "count", new BsonDocument
                {
                     {
                        "$sum", 1
                     }
                }
            }
        }
    }
};