try 在Mongo DB中使用此$LOOKUP查询.
db.request_user.aggregate( [
{
$lookup:
{
from: 'request',
let: {req_id: "$requestId",curr_user:"$user"},
pipeline: [
{ $match:
{ $expr:
{ $and:
[
{$eq: [ "$requestId","$$req_id"]}
{$eq: [ "$currentUser","$$curr_user"]}
]
}
}
},
],
as: "result"
}
}
] )
我收到以下错误:
{
"message" : "arguments to $lookup must be strings, let: { req_id: '$requestId' } is type object",
"ok" : 0,
"code" : 4570,
"codeName" : "Location4570"
}
找到一些来源,说let与MongoDB 3~版本不兼容.我使用的是3.4版.如果这是真的..能不能请一些人推荐一种替代方案.