通过ID获取实体

Question

I am using gorilla mux for my routes and I pass an id.

Using that Id how can I get a entity from datastore.

param := mux.Vars(r)
c := appengine.NewContext(r)
item := []Item{}
pr, err := datastore.NewQuery("Item").Filter("ID = ", param["id"]).GetAll(c, &item)

And here I'm stuck, I tried using filter but it doesn't work.

What do I have to do next?

Answer 1

You don't say if you are using integer or string ids for entities. I'll assume integer because it requires a little more code. First, create a key:

 n, err := strconv.ParseInt(param["id"], 10, 64)
 if err != nil {
    // handle error
 }
 key := datastore.NewKey(c, "Item", "", n, nil)

Now that you have key, you can fetch the entity:

 var item Item
 if err := datastore.Get(c, key, &item); err != nil {
     // handle error
 }

It's more efficient to get the entity than to query for the entity. If you do want to query by id, then see key filters in the App Engine docs.