Helm lookup always empty - kubernetes

Question

While deploying a Kubernetes application, I want to check if a resource is already present. If so it shall not be rendered. To archive this behaviour the lookup function of helm is used. As it seems is always empty while deploying (no dry-run). Any ideas what I am doing wrong?
---
{{- if not (lookup "v1" "ServiceAccount" "my-namespace" "my-sa") }}
apiVersion: v1
kind: ServiceAccount
metadata:
name: {{ .Chart.Name }}-{{ .Values.environment }}
namespace: {{ .Values.namespace }}
labels:
app: {{ $.Chart.Name }}
environment: {{ .Values.environment }}
annotations:
"helm.sh/resource-policy": keep
iam.gke.io/gcp-service-account: "{{ .Chart.Name }}-{{ .Values.environment }}#{{ .Values.gcpProjectId }}.iam.gserviceaccount.com"
{{- end }}
running the corresponding kubectl command return the expected service account
kubectl get ServiceAccount my-sa -n my-namespace lists the expected service account
helm version: 3.5.4

Answer 1

i think you cannot use this if-statement to validate what you want.
the lookup function returns a list of objects that were found by your lookup. so, if you want to validate that there are no serviceaccounts with the properties you specified, you should check if the returned list is empty.
test something like
---
{{ if eq (len (lookup "v1" "ServiceAccount" "my-namespace" "my-sa")) 0 }}
apiVersion: v1
kind: ServiceAccount
metadata:
name: {{ .Chart.Name }}-{{ .Values.environment }}
namespace: {{ .Values.namespace }}
labels:
app: {{ $.Chart.Name }}
environment: {{ .Values.environment }}
annotations:
"helm.sh/resource-policy": keep
iam.gke.io/gcp-service-account: "{{ .Chart.Name }}-{{ .Values.environment }}#{{ .Values.gcpProjectId }}.iam.gserviceaccount.com"
{{- end }}
see: https://helm.sh/docs/chart_template_guide/functions_and_pipelines/#using-the-lookup-function