"where ANCESTOR IS :1", oya_key

http://googleappengine.blogspot.com/2008/04/posted-by-ken-ashcraft-software.html

• Avoid large entity groups. Any two entities that share a common ancestor belong to the same entity groups. All writes to an entity group are sequential, so large entity groups can bog down popular apps quickly if there are a lot of writes to that group. Instead, use small, localized groups in your design.

#490 のようなbugはあるようだけれども

NewBand = Band(Name="Test", URL="Test", Description="A test description")
NewBand.put()

NewSection = Section(parent=NewBand, Title="News", URL="News", Type="News")
NewSection.put()

子のput ()の際に parent を設定しておけば、ancector is に親キーを指定して、検索する
ことができる。

oya_key = db.GqlQuery("select * from Band")[0].key()
ko = db.GqlQuery("select * from Section where ANCESTOR IS :1", oya_key )

http://groups.google.com/group/google-appengine/browse_thread/thread/ad5175429f2f61f2
App works locally, but fails when uploaded
x = Section.all().ancestor(self).filter("URL = ", SectionURL).get