技術メモ: Many-to-many JOIN

2008年6月14日土曜日

Many-to-many JOIN

Many-to-many JOIN のサンプル、Intersection Table にあたるものに Reference Property だけの db.Model を作成することで対応。
back-references を使っているので注意。
def books() 　などは必須ではないと思う。（当初、かえってこれで混乱してしまった）

Google App Engine: [A Better] Many-to-many JOIN
http://blog.arbingersys.com/2008/04/google-app-engine-better-many-to-many.html

ER-Modeling with Google App Engine (updated)
http://daily.profeth.de/search/label/entity%20relationship%20model

Google App Engine　入門6 検索件数
http://webdba.blogspot.com/2008/04/google-app-engine6.html

SQL and GQL　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　TOP

is null	from google.appengine.ext import db r = db.GqlQuery ("SELECT * FROM model WHERE property=:1",None) # None is the python Null. / see
count(*)	r.count()
like	r = db.GqlQuery("SELECT * FROM model WHERE property >= :1 and property < :2 ", search_key, urllib.unquote(search_key).decode("utf8") + u"\uFFFD" )
update	see
!=	!= # see
date	yymm = '2008-05-10 22:22:22' # see ydate = datetime.datetime.strptime(yymm, '%Y-%m-%d %H:%M:%S')
日付検索	from datetime import * import datetime d1 = datetime.datetime.strptime('2008-06-01', '%Y-%m-%d') d2 = d1 + timedelta(days=10) r = db.GqlQuery("select * from model where date >=:1 and date <:2 ",d1,d2) 　for rr in r: print datetime.datetime.strftime(rr,'%Y-%m-%d %H:%M:%S') Dates and Times
	datastore viewer http://localhost:8080/_ah/admin/datastore?kind=StockSum&order=-nikkei_max&order_type=float&num=100&start=0
reference	see (back-references), Many-to-many Join
key, key_name ,id	Key names and IDs cannot be used like property values × select * from Greeting where key = "xxxx" × select * from Greeting where id = xxx ○ r = Greeting.get(db.Key.from_path('Greeting', id)) # or key_name ○ r = db.get("agpoZWxsb3dvcmxkcgsLEgRCbG9nGNQBDA") key = r.key() id = r.key().id()