按父实体过滤数据存储结果

Question

This question as already been answered for Python: How to get all records from GAE datastore with particular parent?

How do I do it in Go? I would like to do something like:

t := new(TagRecord)
k, err := datastore.DecodeKey(r.URL.Path[1:])
...
_, err = datastore.NewQuery("TagRecord").
  Filter("Parent =", k). 
  Order("-CreatedAt").
  Limit(1).
  Run(c).Next(t)

...but this fails miserably with the following error:

datastore: query has no more results

When I try filtering by other properties, including those hard coded into the filter and those passed through the URL, the query runs properly and populates t with the proper properties. With what humiliating simplicity can my problem be fixed?

Answer 1

What's tripping you up here is that querying by parent does not use Filter(). Instead, you use an ancestor constraint:

q := datastore.NewQuery("TagRecord").
    Ancestor(k).
    Order("-CreatedAt").
    Limit(1)

// etc...