Debugging GQL Queries

Question

I have been trying to run this query:

my_post = db.GqlQuery("SELECT * FROM Post where __key__ = KEY('Post', 1)")
self.render("showpost.html", my_post = my_post)

and my template showpost.html looks like this:

<div class="post">
  <h3 class="post-subject">{{ my_post.subject }}</h3>
  <div class="post-content">{{ my_post.content }}</div>
</div

Instead of getting the details of the Post of id=1 I'm getting a blank page. Although there exists a post with id=1 i'm not sure how to confirm if the GQLquery is actually returning something. Is there a way to check? On trying the following:

my_post = db.GqlQuery("SELECT * FROM Post where subject = 'hello_world')
self.render("showpost.html", my_post = my_post)

I get the same issue (blank page), even though there is post who's subject is hello_world

Thanks a lot

mechanical_meat · Accepted Answer · 2012-05-03T15:35:55.437

GqlQuery is a class.
Your code has created an instance of the GqlQuery class.
To return something from the datastore you need to use either of the following instance methods:

.fetch() # requires number of entities as first argument
.get()

Example:

my_query = db.GqlQuery("SELECT * FROM Post WHERE subject = :subject", 
                       subject="hello_world")
my_post = my_query.get() # the magic happens here
self.render("showpost.html", my_post = my_post)

score 2 · Answer 2 · answered May 03 '12 at 17:17

Bernie is right in that you need to use .fetch or .get to actually retrieve results from the GqlQuery that you created, but for the first version, where you have a key or an id, you don't want to create a query at all. Rather, use the methods that are provided for using them directly.

If you have an id, use:

my_post = Post.get_by_id(id)

this will be much faster than using a query object.

If you have an entire key, use:

my_post = Post.get(key)

That is the fastest and most efficient way to get an entity out of the database.

Debugging GQL Queries

2 Answers2