Searching for elements in array and return matching elements in mongodb

Question

I have the following document

db.c.save({a:[{u:3},{u:6},{u:123}]});

I want to fetch matching elements from the array. So I use the following q

Answer 1

Unfortunately, the $ positional operator only returns the first match so you can't use it to do what you are trying to do.

However, you can use either aggregation or map-reduce. The following code does what you want using the aggregation framework :

db.c.aggregate([
  { $unwind : "$a"},
  { $match  : { "a.u" : {$in :[3,123]} } },
  { $group  : {_id : "$_id",a : { $push : "$a" } } }
])