Generate Active Model from Two Models' Differences

[SamuNatsu]

Motivation

The model is serialized then edited by an external editor, which would deserialize back to a new model after editing.

Do a full update is ok, while find the diffs between old and new model for on-demand updating is more clever.

Proposed Solutions

Provide a new method for derive macros like fn create_diff_active_model(old_model: &Model) -> ActiveModel is enough.

Additional Information

[mansiverma897993]

@SamuNatsu can you assign this issue to me ?? or I can directly raise PR ?

[SamuNatsu]

@SamuNatsu can you assign this issue to me ?? or I can directly raise PR ?

I'm not the maintainer of the project, so assigning the issue to you is technically impossible :(

Raise PR with a reference #3067 is enough

[Expurple]

I just encountered a case where this would be useful at my job! This is a great idea.

Until it's implemented by a SeaORM derive macro, I suggest using "Destructure as a Reminder" idiom to make sure to cover all fields in your manual implementation. Mine looks like this:

fn merge_models_and_mark_changes(old: foo::Model, new: foo::Model) -> foo::ActiveModel {
  let mut result = old.into_active_model();
  // Intentionally unpack so that we get warnings for unused fields
  // and a compiler error here when a new fields is added.
  let foo::ActiveModel { bar, baz } = &mut result;
  bar.set_ne(new.bar);
  baz.set_ne(new.baz);
  result
}

Also note that a reference (old_model: &Model) in your proposed signature is a tradeoff. It requires you to clone out the value when it's Unchanged. Which is actually more work when you no longer need the old model and are fine with consuming it.