StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
primarykey
Id
4348077
data
AcceptedAnswerId
0
AnswerCount
0
ClosedDate
CommentCount
1
CommunityOwnedDate
CreationDate
2010-12-03T17:17:48.210
FavoriteCount
0
LastActivityDate
2010-12-03T17:17:48.210
LastEditDate
LastEditorUserId
0
OwnerUserId
280474
ParentId
4347671
PostTypeId
2
Score
2
ViewCount
0
LastEditorDisplayName
text
Body
<a href="http://code.google.com/appengine/docs/python/datastore/typesandpropertyclasses.html#ReferenceProperty" rel="nofollow">ReferenceProperties</a> add <a href="http://code.google.com/appengine/docs/python/datastore/queryclass.html" rel="nofollow">query-objects</a> as attributes to the referenced class. So look carefully at your mappings: <pre><code>class BookAuthor(db.Model): # This adds a query-object as an attribute named 'books' to Book entities. book = db.ReferenceProperty(Book, required=True, collection_name='books') # This adds a query-object as an attribute named 'authors' to Author entities. author = db.ReferenceProperty(Author, required=True, collection_name='authors') </code></pre> In your code: <pre><code>b = Book(title="My Book") a = Author(name="Author of My Book") </code></pre> So, <code>b</code> would have a <code>books</code> attribute, not <code>authors</code>. And, <code>a</code> would have a <code>authors</code> attribute, not <code>books</code>. If you change the collection names, your code should run. <pre><code>class BookAuthor(db.Model): # This adds a query-object as an attribute named 'authors' to Book entities. book = db.ReferenceProperty(Book, required=True, collection_name='authors') # This adds a query-object as an attribute named 'books' to Author entities. author = db.ReferenceProperty(Author, required=True, collection_name='books') </code></pre> Also, if <code>BookAuthor</code> does not have additional properties, make sure you look at the list-of-keys method outlined in the article you referenced.
Tags
Title
singulars
PostAcceptedAnswerId
1. This table or related slice is empty.
PostParentId
1. POMany-to-many relationship modeling in google app engine
 singulars
 PostTypePostTypeId
 PTQuestion
PostTypePostTypeId
1. PTAnswer
UserLastEditorUserId
1. This table or related slice is empty.
UserOwnerUserId
1. USRobert Kluin
plurals
PostLinksPostIdRelatedPostId
1. This table or related slice is empty.
PostLinksRelatedPostIdPostId
1. This table or related slice is empty.
PostsAcceptedAnswerId
1. This table or related slice is empty.
PostsParentIdCreationDate
1. This table or related slice is empty.
VotesPostIdCreationDate
1. VO
 singulars
 PostPostId
 PO
 UserUserId
 This table or related slice is empty.
 VoteTypeVoteTypeId
 VTUpMod
2. VO
 singulars
 PostPostId
 PO
 UserUserId
 This table or related slice is empty.
 VoteTypeVoteTypeId
 VTUpMod
CommentsPostId
1. COexcellent! Thank you very much.
 singulars
 PostPostId
 PO
 UserUserId
 USmarco

Querying!

Guidance

A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.