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我正在尝试过滤掉嵌套数组中的数据。我的数据如下：

{
    "_id" : ObjectId("5836afca6dbd62de8d654h9"),
    "name" : "First Test Event",
    "registered_users" : [ 
        {
            "user_id" : ObjectId("5836e433e17ea92ea7a499a5"),
            "user_name" : "Malavika",            
            "user_state" : "registered"
        }, 
        {
            "user_id" : ObjectId("5836e433e17ea92ea7a455b5"),
            "user_name" : "Piyush",            
            "user_state" : "joined"
        },
        {
            "user_id" : ObjectId("58369783e17e6e63c35f36ac"),
            "user_name" : "Jingi",
            "user_state" : "notified"
        }
    ]
},
{
    "_id" : ObjectId("5836afca6dbd62de8d622b3"),
    "name" : "Test Event",
    "registered_users" : [ 
        {
            "user_id" : ObjectId("5836e433e17ea92ea7a499a5"),
            "user_name" : "Malavika",            
            "user_state" : "registered"
        }, 
        {
            "user_id" : ObjectId("5836e433e17ea92ea7a455b5"),
            "user_name" : "Piyush",            
            "user_state" : "left"
        },
        {
            "user_id" : ObjectId("58369783e17e6e63c35f36ac"),
            "user_name" : "Jingi",
            "user_state" : "notified"
        }
    ]
}

在上面的集合中，我只想在“注册，加入”两种状态下获得第一个事件“第一个测试事件”的“注册用户”。

我的预期结果应该是：

{
    "registered_users" : [ 
        {
            "user_id" : ObjectId("5836e433e17ea92ea7a499a5"),
            "user_name" : "Malavika",
            "user_state" : "registered"
        }, 
        {
            "user_id" : ObjectId("58369783e17e6e63c35f36ac"),
            "user_name" : "Piyush",
            "user_state" : "joined"
        }
    ]
}

所以我准备了如下查询：

db.events.aggregate([   
{$match: {'registered_users.user_state': 'registered', "_id": ObjectId("5836afca6dbd62de8d654h9")}},
   {$project: {
        registered_users: {$filter: {
            input: '$registered_users',
            as: 'register',
            cond: {$eq: ['$$register.user_state', 'registered']}
        }},
        _id: 0,
        name: 0
    }}
])

上述查询的问题不是一个状态“注册”，我需要一个 $in 运算符来处理多个状态“注册”、“加入”、“离开”等......

谁能帮我这个？

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