How can I join two collections spring-data-mongodb?

Question

Collection:

Room

{
    "_id" : ObjectId("6461eb7c1cefe2b485d4ca2e"),
    "AgentId" : "5e7a1caaa08a49ff4d029bbd",
    "roomName" : "My Room101",
    "note" : "note abc",
    "roomStatus" : "Empty",
    "roomTypeId" : "6461db161cefe2b485d4ca1e",
    "createdBy" : "Super Administrator",
    "createdAt" : ISODate("2023-05-15T08:00:00.000+0000"),
    "updatedBy" : "Super Administrator",
    "updatedAt" : ISODate("2023-05-15T08:00:00.000+0000"),
    "isDeleted" : false
}

RoomType

  {
    "_id" : ObjectId("6461db161cefe2b485d4ca1e"),
    "roomTypeName" : "VIP 1",
    "note" : "note xyz",
    "createdBy" : "Super Administrator",
    "createdAt" : ISODate("2023-05-15T08:00:00.000+0000"),
    "updatedBy" : "Super Administrator",
    "updatedAt" : ISODate("2023-05-15T08:00:00.000+0000"),
    "isDeleted" : false
}

in SQL:

select * from Room r inner join RoomType rt on r.roomTypeId=rt._id

I want to display query result using Query in Java

Kindly refer to following : https://stackoverflow.com/questions/2350495/how-do-i-perform-the-sql-join-equivalent-in-mongodb?rq=2 — psybrg, May 17 '23 at 05:29

JavaLearner1 · Accepted Answer · 2023-05-17T06:26:51.567

db.Room.aggregate([
 {
 $lookup: {
  from: "RoomType".
  localField: "roomtypeId",
  foreignField: "_id",
  as: "roomType"
 }
 },
{
 $unwind: "$roomType"
 }
])

Aggregate method for aggregation pipeline
Lookup used to join the collection Room and RoomType
LocalField for the room collection
ForeignField for RoomType collection.
$unwind: is optional mainly used to flatten the resulting array

In java,

LookupOperation lookup = LookupOperation.newLookup()
  .from("roomTypes")
  .localField("roomtypeId")
  .foreignField("_id")
  .as("roomType");

Aggregation aggregation = Aggregation.newAggregation(
  Aggregation.match('add condition'), lookup );

mongoTemplate.aggregate(aggregation, "rooms", 
Room.class).getMappedResults();

If in SQL it's like this: select * from Room r inner join RoomType rt on r.roomTypeId=rt._id where rt._id = 'abc123' What is a query in MongoDB? — Pnmtriet, May 25 '23 at 08:44

How can I join two collections spring-data-mongodb?

Collection:

1 Answers1