Lister

Overview

Lister is any object that knows how to perform an initial list.

Interface:

type Lister interface {
    // List should return a list type object; the Items field will be extracted, and the
    // ResourceVersion field will be used to start the watch in the right place.
    List(options metav1.ListOptions) (runtime.Object, error)
}

Usage

1. Prepare Indexer (dependency). Read indexer for more details.

   indexer := cache.NewIndexer(
       cache.MetaNamespaceKeyFunc,
       cache.Indexers{cache.NamespaceIndex: cache.MetaNamespaceIndexFunc},
   )
   

   Add object to indexer with/without labels (which will be used as selector when listing with Lister below).

   // Add deployment with label
   err := indexer.Add(getDeployment("deployment-with-label", map[string]string{"watch": "true"}))
   if err != nil {
       t.Errorf("indexer.Add failed %v\n", err)
   }
   // Add deployment without label
   err = indexer.Add(getDeployment("deployment-without-label", map[string]string{}))
   if err != nil {
       t.Errorf("indexer.Add failed %v\n", err)
   }
   

2. Create a Lister for a target resource.

   For a built-in resource:

   import (
       appsv1lister "k8s.io/client-go/listers/apps/v1"
   )
   

   deploymentLister := appsv1lister.NewDeploymentLister(indexer)
   

   For a custom resource: Need to generate lister with code-generator

3. List object with selector.

   selector := labels.SelectorFromSet(labels.Set{"watch": "true"})
   ret, _ := deploymentLister.List(selector)
   
   for _, deploy := range ret {
       fmt.Println(deploy.Name)
   }
   

   Objects are got from the indexers.