I'm setting up my db model using datamapper and dm-contraints. I have two models which have a many to many relationship but when I try to destroy one, the only message I get is false.
Is it possible to get datamapper to give me more feedback one which relationship is exactly causing the problem?
With datamapper 1.2.1:
def why_you_no_destroy? model
preventing = []
model.send(:relationships).each do |relationship|
next unless relationship.respond_to?(:enforce_destroy_constraint)
preventing << relationship.name unless relationship.enforce_destroy_constraint(model)
end
preventing
end
Unfortunately DM doesn't provide a way to report why destroy failed.
Most of time the destroy failed because of its associations. DM have a mechanism to avoid orphan records.
To avoid this kind of destroy failed, you can Use dm-constraints(https://github.com/datamapper/dm-constraints ) to set up true database level foreign key references, which default to protect, but can be set to cascade deletes instead.
class List
has n, :todos, :constraint => :destroy (or :destroy!)
end
Sadly, Currently dm-constraints only supports PostgreSQL and MySQL.
For other database, you can check all the associations manually and delete them first, then delete the model。
You can get information on DataMapper errors from
model.destroy
if model
model.errors.each do |error|
p error
end
end
Sometimes that doesn't tell you anything though, in which case you can put your code inside of a begin/rescue block e.g.
begin
model.destroy
rescue Exception => exc
p exc
end
