GQL + Join Table Query Replacement for Google App Engine Datastore

Given the following Many to Many Relationship designed in Google App Engine Datastore:

User

PK: UserID

Name

Company

PK: CompanyID

Name

CompanyReview

CK CompanyID

CK UserID ReviewContent

For optimization query, what's the best way to query this relationship tables for showing the selected company's review by users.

Currently, I'm doing the following:

results = CompanyReview.all().filter('owned_by = ', company).filter('written开发者_如何学JAVA_by = ', user).fetch(10)

where I'm able to retrieve the data of CompanyReview table. However, in this case, I would need to check against the UserID from this CompanyReview table against the User table in order to obtain the name of the users who have commented for the selected company.

Is there a better solution to grab the user name as well, all in one statement in this case or at least better optimized solution? Performance is emphasized.

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It dependes on which side of the relationship will have more values. As described is this article of Google App Engine docs, you can model many-to-many relationships by using a list of keys in one side of the relationship. "This means you should place the list on side of the relationship which you expect to have fewer values".

If both sides of the relationship will have many values, then you will really need the CompanyReview model. But pay attention to what the article says:

However, you need to be very careful because traversing the connections of a collection will require more calls to the datastore. Use this kind of many-to-many relationship only when you really need to, and do so with care to the performance of your application.

This is because it uses RefereceProperty in the relationship model:

class ContactCompany(db.Model):
    contact = db.ReferenceProperty(Contact,
                                   required=True,
                                   collection_name='companies')
    company = db.ReferenceProperty(Company,
                                   required=True,
                                   collection_name='contacts')
    title = db.StringProperty()

So if in Contact entities we try to access the companies, it will make a new query. And if in ContactCompany entities we try to get attributes of contact as in contact_company.contact.name, a query for that single contact will be made also. Read the ReferencyProperty docs for more info.

Extra: Since you are performance-savvy, I recommend using a decorator for memcaching function returns and using this excellent layered storage library for Google App Engine.