Using Circe optics to modify all fields of an object, or all items of an array

Question

I am trying to modify a nested JSON structure using Circe's optics. However, all the examples are only modifying a single field within the object with the known name.

What I need to do:

Assuming foo key of my object contains an array of objects, increment the counter key in each of those.
Assuming bar key of my object contains an object, increment the counter key in values mapped to each key in that object.
Keep all the other values in the object intact.

Example:

{
  "foo": [
    {
      "counter": 1
    },
    {
      "counter": 2
    }
  ],
  "bar": {
    "three": {
      "counter": 3
    },
    "four": {
      "counter": 4
    }
  }
}

should become

{
  "foo": [
    {
      "counter": 2
    },
    {
      "counter": 3
    }
  ],
  "bar": {
    "three": {
      "counter": 4
    },
    "four": {
      "counter": 5
    }
  }
}

The behavior when the types of the object and its members are not what I expect is not important.

I expect something like this:

val incrementCounterArray: Json => Json =
    root.foo.eachArrayItem.counter.modify(_ + 1)
val incrementCounterObject: Json => Json =
    root.bar.eachObjectValue.counter.modify(_ + 1)

but I don't see any definitions for what would be eachArrayItem or eachObjectValue in the tutorial.

score 2 · Accepted Answer · answered Jun 24 '19 at 04:59

The correct syntax is

val incrementCounterArray: Json => Json =
  root.foo.each.counter.int.modify(_ + 1)

val incrementCounterObject: Json => Json =
  root.bar.each.counter.int.modify(_ + 1)

Have a look at the example in the official circe-optics documentation for more details:

Using Circe optics to modify all fields of an object, or all items of an array

1 Answers1