Question

Well, I’ve finally decided that I’m not crazy. So, that leaves DataMapper.

Here’s what I’m doing. I have a model Msrun which has 1 Metric.

tmp = Msrun.first_or_create # I'll skip the boring details
tmp.metric = Metric.first_or_create( {msrun_id: tmp.id}, {metric_input_file: @metricsfile} )
p tmp.metric # => #<Metric @metric_input_file=nil @msrun_id=1>
tmp.metric.metric_input_file = @metricsfile
p tmp.metric # => #<Metric @metric_input_file=#<Pathname:/home/ryanmt/Dropbox/coding/rails/metrics_site/spec/tfiles/single_metric.txt> @msrun_id=1>

So, why doesn’t this work? I’m reading http://datamapper.org/docs/create_and_destroy and doing what it shows working. This has been terribly arduous. Thanks for any help.

Update:
I still can’t figure out what is going on, but to prove I’m not insane…

puts Metric.all # => []
tmp.metric = Metric.first_or_create( {msrun_id: tmp.id}, {metric_input_file: @metricsfile} )
puts Metric.all # => [] #??????????????
tmp.metric.metric_input_file = @metricsfile
p tmp.metric # => #<Metric @metric_input_file=#<Pathname:/home/ryanmt/Dropbox/coding/rails/metrics_site/spec/tfiles/single_metric.txt> @msrun_id=1>
tmp.metric.save
puts Metric.all # => [#<Metric @metric_input_file=#<Pathname:/home/ryanmt/Dropbox/coding/rails/metrics_site/spec/tfiles/single_metric.txt> @msrun_id=1>]

So, not only is first_or_create not delivering on the behavior I expect by reading the source

def first_or_create(conditions = {}, attributes = {})
  first(conditions) || create(conditions.merge(attributes))
end

but it is also not even creating.

Answer 1

I’m probably missing something here (more of those boring details might help) but if the metric exists, it’s metric_input_file shouldn’t be updated, i.e., it’s only set when new. If you’re after updating then you can do

.first_or_create(msrun_id: tmp.id).update(metric_input_file: @metricsfile)

Or if not hitting the database twice is relevant, then

m = Metric.first_or_new(msrun_id: tmp.id)
[set..save..assign]

But if it’s not being set on new models, I don’t see what would cause that from the code posted so far, more..?

[UPDATED]

Based on your new code, I’d say this is “a classic case” of a false DM save. I usually add the following line to an initialization section, e.g., application.rb in Rails.

DataMapper::Model.raise_on_save_failure = true

Unfortunately, the exception raised never tells you why (there’s a special place in hell for that choice, right next to people who talk in theaters.) But it’s typically one of:

• a slightly incorrect association definition
• a has/belongs_to that isn’t “required: false” and isn’t set
• putting the wrong datatype into a field, e.g., a string into a decimal
• a validation failing

If you want to post your model definitions, the problem may be spottable there.