Querying in Google Cloud Datastore

So far, we have only been putting and getting single objects into and out of Google Cloud Datastore. When we display a list of answers to a question, we want to load all of these answers in a single operation, which we can do with datastore.Query.

The querying interface is a fluent API, where each method returns the same object or a modified object, allowing you to chain calls together. You can use it to build up a query consisting of ordering, limits, ancestors, filters, and so on. We will use it to write a function that will load all the answers for a given question, showing the most popular (those with a higher Score value) first.

Add the following function to answers.go:

func GetAnswers(ctx context.Context, questionKey *datastore.Key)  
([]*Answer, error) { 
  var answers []*Answer 
  answerKeys, err := datastore.NewQuery("Answer"). 
    Ancestor(questionKey). 
    Order("-Score"). 
    Order("-CTime"). 
    GetAll(ctx, &answers) 
  for i, answer ...