Question

我需要使用PyMongo驱动程序通过无序的不同字段对（sender和recipient）对特定集合中的记录进行分组。例如，对（sender_field_value，recipient_field_value）和（recipient_field_value，sender_field_value）被认为是相等的。

我的汇总管道

groups = base.flow.records.aggregate([
    {'$match': {'$or': [
                {'sender': _id},
                {'recipient': _id}
            ]
        }
    },
    {'$group': {
            '_id': {
                'sender': '$sender',
                'recipient': '$recipient',
            }, 
            'data_id': {
                '$max': '$_id'
            }
        }
    },            
    {'$limit': 20}
])

应用于数据

{ "_id" : ObjectId("533950ca9c3b6222569520c2"), "recipient" : ObjectId("533950ca9c3b6222569520c1"), "sender" : ObjectId("533950ca9c3b6222569520c0") }
{ "_id" : ObjectId("533950ca9c3b6222569520c4"), "recipient" : ObjectId("533950ca9c3b6222569520c0"), "sender" : ObjectId("533950ca9c3b6222569520c1") }

产生以下

{'ok': 1.0,
 'result': [
    {'_id': {'recipient': ObjectId('533950ca9c3b6222569520c0'), 'sender': ObjectId('533950ca9c3b6222569520c1')},
     'data_id': ObjectId('533950ca9c3b6222569520c4')},
    {'_id': {'recipient': ObjectId('533950ca9c3b6222569520c1'), 'sender': ObjectId('533950ca9c3b6222569520c0')},
     'data_id': ObjectId('533950ca9c3b6222569520c2')}
  ]
}

但所需的结果只是

{'ok': 1.0,
 'result': [
    {'_id': {'recipient': ObjectId('533950ca9c3b6222569520c0'), 'sender': ObjectId('533950ca9c3b6222569520c1')},
     'data_id': ObjectId('533950ca9c3b6222569520c4')}
  ]
}

什么是合适的管道？

Answer 1

实现独特配对分组的技巧是将$ group _id传递给同一个＆＃39;无论哪种情况。我会使用正常的比较来做到这一点（你可以提出一些更适合你的情况的东西 - 如果你的发件人和收件人不能直接比较我的解决方案不起作用）：

{$project : {
    "_id" : 1,
    "groupId" : {"$cond" : [{"$gt" : ['$sender', '$recipient']}, {big : "$sender", small : "$recipient"}, {big : "$recipient", small : "$sender"}]}
}},
{$group: {
    '_id': "$groupId",
    'data_id': {
        '$max': '$_id'
    }
}}

完整的聚合管道如下所示：

{$match : {
    '$or': [{'sender': userId},{'recipient': userId}]
}},
{$project : {
    "_id" : 1,
    "groupId" : {"$cond" : [{"$gt" : ['$sender', '$recipient']}, {big : "$sender", small : "$recipient"}, {big : "$recipient", small : "$sender"}]}
}},
{$group: {
    '_id': "$groupId",
    'data_id': {
        '$max': '$_id'
    }
}},
{$limit: 20}

MongoDB聚合 - 按不同对进行分组

1 个答案: