Finding right yq command

Question

I have a yaml file that looks like

apiVersion: v1
kind: ConfigMap
metadata:
  name: myName
  namespace: default
data:
  values.yaml: |
    people:
    - namespace: "fred"
      identities:
      - name: "one"
      - name: "two"
    - namespace: "bob"
      identities:
      - name: "one"

Now i want to add a third identity to Fred (name: "three"), how do I do this with the yq command

apiVersion: v1
kind: ConfigMap
metadata:
  name: myName
  namespace: default
data:
  values.yaml: |
    people:
    - namespace: "fred"
      identities:
      - name: "one"
      - name: "two"
      - name: "three"
    - namespace: "bob"
      identities:
      - name: "one"

Answer 1

Traverse to .data."values.yaml", and update |= it, by interpreting the YAML string using fromyaml, then finding those .people[] that match the given criteria using select, adding += the new item {"name": "three"} to their array, and encoding all of it again using toyaml:

yq '.data."values.yaml" |= (
  fromyaml
  | (.people[] | select(.namespace == "fred")).identities += {"name": "three"}
  | toyaml
)'

apiVersion: v1
kind: ConfigMap
metadata:
  name: myName
  namespace: default
data:
  values.yaml: |
    people:
      - namespace: "fred"
        identities:
          - name: "one"
          - name: "two"
          - name: three
      - namespace: "bob"
        identities:
          - name: "one"

Tested with mikefarah/yq v4.35.1