Ok. Case. I have one duck, which has many ducklings.. Some of these ducklings ceases to exist (dies) or duck gives birth to new ducklings... However.. A duckling is not an empty entity. There are some constraints in the db which we must conform to. So. Whenever a duck dies or new ones gets born, details needs to be provided before we actually want to persist it to the database. So i can't do: @duck = Duck.find(:first) @duck.ducklings << Duck.new ...since i've observed that the new duck is persisted right away. This violates some constraints and i do not want to persist the duck yet. Furthermore. A duck usually gives birth to more than one duckling at a time, so we want to manipulate a lot of ducklings from the same form at the same time. If i remove a duckling, if i add a duckling or if i alter a duckling's information, i first want this to be persisted when i hit update. Now this has caused me some issues... Loading the duck and listing form rows for duck.ducklings gives me text fields with: ducklings[name], ducklings[birth_date].. That is. Form submitted back is translated into a hash with key matching the db id.. However. Now i click add and a new row is created via RJS from a new instance of Duckling... However. Since this is not persisted, i'll now have a row-field with id: ducklings[name]... Hitting update will now cause an application error: Conflicting types for parameter containers. Expected an instance of Array, but found an instance of Hash. This can be caused by passing Array and Hash based paramters qs=value&qs[key]=value. Well. I do understand the error message, however. Expected rails to have some magic in this sense giving me a cleaner view, such that non-keyed entries were treated as new entries thus would yield a save instead of update. Do i really have to distinguish new from existing entries by alternative field names? Aren't there any prettier ways to do this? Haven't been able to find anyone discussing this particular issue.. What is the rails way? :) I'd really like that new and old persisted entries came back in the same params collection in some way.
on 2007-05-22 16:33
on 2007-05-22 17:58
A few thoughts: The first thing is to understand when Rails will automatically persist records. In a 1:n relationship where a Duck has_many Ducklings and a Duckling belongs_to Duck, the foreign key is stored in the Duckling. If you assign a Duckling to Duck it will persist it right away because it assumes you are working on the Duck and their is just a single change to the Duckling that must be saved right away. If you want to make the association without saving, you assign @duckling.duck_id = @duck.id because that appears you are primarily editing the Duckling and will manage your own saving. The first scenario is really just a convience since you would have to individually save all the ducklings anyway, and if you forget, Rails has no efficient way of remember which to save when you do @duck.save. Regarding your second scenario, there is no magic I'm afraid. I could definitely see some improvements being made to support this kind of thing, but ultimately I think you can roll something up that's pretty clean. The first thing is the whole concept of objects[name]&objects[age] is failed even in the absence of a conflicting hash because there's no way to keep the groups coherent. I suppose this could be fixed as long as you can guarantee the presence of every field (been burned by checkboxes in this situation in PHP). But really if you have more than one, you need to index them somehow. So you can stick your own index in there to make it a hash. But you will also need to distinguish the new from the updates. So it should have a different name such as new_ducklings, new_ducklings. Then you can create a new_ducklings=(hash) method on the Duck model that processes these accordingly. However, if you are just adding one at a time using RJS, you can just skip the whole index, and have a plain new_duckling hash of fields. Hopefully that will help a bit. It's definitely not a trivial problem.