CODEWITHSUNDEEP
mongodbcollectionsdifference
MAYA
MAYA

Reputation: 1335

difference between collections in mongodb 3.2

Thank you in advance for your help I have two collections and I want to find the difference between a set of values of a specific field I tried $match but it doesn't work

Example

Collection A :

/*1/
{
    { "Origin" : "xx",
     "Destination" : "yy",
     "Duration" : 180}
/*2/

.....

}

Collection B

/*1/
{
    { "Origin" : "xz",
     "Destination" : "yy",
     "Duration" : 20,
      "Departure time ": 21:00,
       "Arrival time " : 21:20}
/*2/
....
}

I want to get the common origin and destination between the two collections. Expected output:

    /*1/
    {
        { "Origin" : "xx",
         "Destination" : "yy",
         }
    /*2/

    .....

}

I tried this but it doesn't work : 

db.A.aggregate([ 
{ $lookup: 
{ from: "B", localField: "origin", localField : "destination", foreignField: "origin", foreignField : "destination", as: "flight_docs" } } ])

Upvotes: 0

Views: 292

Answers (1)

Onosa
Onosa

Reputation: 1273

There a couple of issues with your aggregation. First of all, case-sensitivity matters. Second, you should not have two localFields and two foreignFields. The second field overwrites the first one. I would expect your query to look like this:

db.stack.aggregate(
  [{
    $lookup: {
      "from": "B",
      "localField": "Destination",
      "foreignField": "Destination",
      "as": "flight_docs"
    }
  }]
);

Which would give a result like this (The local document with all the foreign documents found by matching the Destination field):

{ 
    "_id" : ObjectId("571546c7b9c99e9977f7d372"), 
    "Origin" : "xx", 
    "Destination" : "yy", 
    "Duration" : NumberInt(180), 
    "flight_docs" : [
        {
            "_id" : ObjectId("5715470eb9c99e9977f7d376"), 
            "Origin" : "xz", 
            "Destination" : "yy", 
            "Duration" : NumberInt(20)
        }
    ]
}

Upvotes: 1

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