vchunikhin commented on code in PR #22967:
URL: https://github.com/apache/beam/pull/22967#discussion_r960608751


##########
learning/tour-of-beam/backend/internal/storage/datastore.go:
##########
@@ -227,5 +227,34 @@ func (d *DatastoreDb) SaveContentTrees(ctx 
context.Context, trees []tob.ContentT
        return nil
 }
 
+// Get learning unit content by unitId
+func (d *DatastoreDb) GetUnitContent(ctx context.Context, sdk tob.Sdk, unitId 
string) (unit *tob.Unit, err error) {
+       var tbNodes []TbLearningNode
+       rootKey := pgNameKey(TbLearningPathKind, sdkToKey(sdk), nil)
+
+       query := datastore.NewQuery(TbLearningNodeKind).
+               Namespace(PgNamespace).
+               Ancestor(rootKey).
+               FilterField("id", "=", unitId)
+
+       _, err = d.Client.GetAll(ctx, query, &tbNodes)
+       if err != nil {
+               return nil, fmt.Errorf("query unit failed: %w", err)
+       }
+
+       switch {
+       case len(tbNodes) == 0:
+               return nil, nil

Review Comment:
   From my perspective, it's not a good approach to return the double nil to 
handle this case later. I recommend you return error here.
   
   As for the next step:
   ```
        if err != nil {
                log.Println("Get unit content error:", err)
                finalizeErrResponse(w, http.StatusInternalServerError, 
INTERNAL_ERROR, "storage error")
                return
        }
        if unit == nil {
                log.Println("Get unit content error:", err)
                finalizeErrResponse(w, http.StatusNotFound, NOT_FOUND, "unit 
not found")
                return
        }
   ```
   Maybe the best way to create custom errors and handle them using switch-case
   
   It's  a not major because it's related to your code style. I'm sharing to 
you my thoughts about that.



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