MongoDB从数组中检索单个值

Question

Assuming that if i have such document

{ "id":"1", "references":["AD1","AD2","AD3"] }

I would like to retrieve single value ("AD1") within the array. is there anyway that i can do that with mongodb query? i have use various way but that it would instead return me the whole array instead of individual single value.

Answer 1

You can do this via $project and $filter :

db.collection.aggregate([
  {
    $project: {
      references: {
        $filter: {
          input: "$references",
          as: "ref",
          cond: { $eq: [ "AD1", "$$ref" ] }
        }
      }
    }
  }
])

You can see it working here

Note however that $filter is available in mongoDB 3.2 version and higher