> Can you make a concrete example? It will help us improve.
The oft-cited ListProperty is a great example. Because GAE/BigTable
doesn't provide substr support, we have a couple options for a search
facility. One is to take a string, say "foobar" and tokenize it into
parts.
['fo','oo','ba','ar','foo','bar','foob','obar','fooba','oobar','foobar']
Using ListProperty, this would be a single write. Our BigTable model
looks as such:
id name tokens
1 foobar ['fo','oo','ob','ba','ar','foo','bar',...]
And a search query:
# Get all entities where numbers contains a 6.
results = db.GqlQuery("SELECT * FROM MyModel WHERE tokens = 'foo'")
GQL natively returns all entities contain an element in a list.
http://code.google.com/appengine/docs/python/datastore/entitiesandmodels.html#Lists
Conversely, using the oft cited IS_IN_DB pattern for web2py, we would
have 12 rows inserted, one for each token with a column of comma
delimited foreign key ids to each full-string entity matching the
token and a bunch of code to manage the integrity across tokens/
entities instead of what is relevant in this case: tokens *per*
entity. Duplication of a token is irrelevant.
So in this scenario, which is key for the project I'm working on with
a friend, a single SELECT using GAE's API would produce the results
needed versus a series of queries to a) SELECT the token in a tokens
table, then iterate over the elements execute SELECTs on each to get
the representation.
While the ListProperty may be unique to GAE/BigTable, omitting it
removes the ability to harness GAE's power. It is also representative
of the difference between data store paradigms, I think.
Hope this helps.
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