Join two collectios and update in MongoDB

Question

Is there any equivalent to below MYSQL query in MongoDB?

update table_name1 as a
join table_name2 as b
on a.uniqueid=b.uniqueid
set a.column1=b.column1,a.column2=b.column2 ;

lookup might be a possible solution but don't know how to use it for updating.

Answer 1

You can do something like this,

db.table1.find({}).forEach(function (t1) { // foreach on table one
    var t2 = db.table2.findOne({ uniqueid: t1.uniqueid}, 
             { column1: 1,column2:1 }); // finding unique id of table1 with table2
    if (t2 != null) { // checking if not null
        t1.column1 = t2.column1; // assigning tabl2's value to table1
        db.table1.save(t1); // save it
    }
});

Please remove my comments