I feel like there is an easier way to do this, like :unique
=> :key_uniqueness_is_based_on but this seems like it would solve your
problem. You basically don't want a MessageDigest to be created if one
with the same code exists for a specific data_file_id
class DataFile
include DataMapper::Resource
property :id, Serial
property :contents, Text
has n, :message_digests
end
class MessageDigest
include DataMapper::Resource
property :code, Enum[:md5, :sha1, :crc32], :key => true
property :value, String, :required => true, :length => 255
belongs_to :data_file
before :create, :check_unique_code
protected
def check_unique_code
MessageDigest.first(:code => code, :data_file_id => data_file_id)
end
end
On Feb 16, 1:33 pm, franco <flazzar...@gmail.com> wrote:
> I want a DataFile to have at most one MessageDigest of a certain code.
> I've tried a bunch of combinations of :key and :unique_key etc but i
> cant seem to get it right.
>
> if i were to do this in a SQL DDL i'd make data_file_id and code a
> composite key. how can i make it work in datamapper?
>
> example models:
>
> class DataFile
> include DataMapper::Resource
> property :id, Serial, :key => true
> property :contents, Text
> has 0..n, :message_digests
> end
>
> class MessageDigest
> include DataMapper::Resource
> property :code, Enum[:md5, :sha1, :crc32]
> property :value, String, :required => true, :length => 255
> belongs_to :data_file
> end
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