Sunday, August 22, 2010

getting started with DataMapper

I've just spent all day trying to get started with DataMapper

I've found a few gotchas:

say i have two model objects with a many to many relationship,
given two instances of those:
t = Thing.create
w = Whatever.create

creating a joining resource:

ThingWhatever.create(:thing => t, :whatever => w)

[t] == w.things #true
[w] == t.whatevers #true

#then create a second join resource from t to a new Whatever

ThingWhatever.create(:thing => t, :whatever => (w2 = Whatever.create))

[w,w2] == t.whatevers #false

I'm new to DataMapper so this was very confusing.

eventaully i discovered I could work around the problem with:

[w,w2] == t.whatevers #true

however, reload is not mentioned in the getting started documentation and it took me hours to figure out why it wasn't working.

It's a bit of a leaky abstraction. you can see the database through the cracks.

posted a ticket

I considered trying ActiveRecord but it smelled even leakier.