使用选定字段和 mongodb 中的 where 子句连接两个表

Question

我有两个合集如下：-

table1

{"_id" : ObjectId("5b9a.."), "item_id" :"1.1", "m_date" : "20130401","ref_id":"12R","sub_item_id":"1.1.1"}
{"_id" : ObjectId("5c37.."), "item_id" :"1.1", "m_date" :  "20140401","ref_id":"12R","sub_item_id":"1.1.2"}
{"_id" : ObjectId("123cb.."), "item_id" :"1.2", "m_date" : "20140401","ref_id":"12R","sub_item_id":"1.1.3"}

table2

{"_id" : ObjectId("7cb3.."), "item_id" :"1.1", "m_date" : "20130401","ref_id":"12R","sub_item_id":"1.1.1"}
{"_id" : ObjectId("8f34.."), "item_id" :"1.1", "m_date" : "20140401","ref_id":"13R","sub_item_id":"1.1.2"}
{"_id" : ObjectId("5ec8b.."), "item_id" :"1.2", "m_date" : "20150401","ref_id":"14R","sub_item_id":"1.1.3"}

我想显示来自 table1 :item_id, m_date, sub_item_id 和 table2 : ref_id 的字段，其中 item_id:1。1 这必须在两个表中。所以预期的结果应该显示这个：-

{"item_id" :"1.1", "m_date" : "20130401","sub_item_id":"1.1.1","ref_id":"12R"}
{"item_id" :"1.1", "m_date" : "20140401","sub_item_id":"1.1.2","ref_id":"13R"}

我尝试使用 $lookup 编写以下查询，但发现 0 个 Doc

db.table1.aggregate([

{$project:{
    item_id:1,
     m_date: 1, 
     sub_item_id : 1,
    ref_id :1
}},
{
    $lookup: {
        from: 'table2',
        localField: 'item_id',
        foreignField: 'item_id',
        as: 'table2_values'
     },
 },
{$unwind:'$table2_values'},

{ $group: { 
    _id: {ref_id: "$table2_values.ref_id", m_date:  "$m_date"
    ,sub_item_id:'$sub_item_id' },

}},    
{$project:{_id:0,m_date:'$_id.m_date',ref_id:'$_id.ref_id'
,sub_item_id:'$_id.sub_item_id',item_id:1}},
{
 $match: {"table2_values.item_id": "1.1"}
 }

])

请帮助我获得上述预期结果

Answer 1

您可以尝试使用 mongodb 3.6

进行以下聚合

db.table1.aggregate([
  { "$match": { "item_id": "1.1" }},
  { "$lookup": {
    "from": "table2",
    "let": { "item_id": "$item_id", "m_date": "$m_date" },
    "pipeline": [
      { "$match": {
        "$expr": { "$eq": ["$$item_id", "$item_id" ] },
        "$expr": { "$eq": ["$$m_date", "$m_date"] }
      }}
    ],
    "as": "table2_values"
  }},
  { "$addFields": { "ref_id": { "$arrayElemAt": ["$table2_values.ref_id", 0] }}},
  { "$project": { "_id": 0, "item_id": 1, "ref_id": 1 }}
])

使用选定字段和 mongodb 中的 where 子句连接两个表

Join two tables with selected fields and where clause in mongodb

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