How to combine, merge, or otherwise edit Companion entries?

[wanglophile]

Can I combine, merge or otherwise edit Companion entries?

For example, given an initial Companion entry of

final ItemsCompanion data = ItemsCompanion(
  foo: 'foo',
  bar: 'bar',
);

How can I add a baz: 'baz'?

Something like:

Future <int> createItemWithBaz(ItemsCompanion entry) {
  // This obviously does not work
  final ItemsCompanion entryWithBaz = ItemsCompanion(
    baz: 'baz',
  ).merge(entry);

  return into(items).insert(entryWithBaz);
}

with the end goal of having a new Companion of

ItemsCompanion(
  foo: 'foo',
  bar: 'bar',
  baz: 'baz',
);

[simolus3]

I didn't try it, but I think this should work:

extension Merge<T> on Insertable<T> {
  Insertable<T> merge(Insertable<T> other) {
    return _MergeInsertable(this, other);
  }
}

final class _MergeInsertable<T> implements Insertable<T> {
  final Insertable<T> _base;
  final Insertable<T> _mergedIn;

  _MergeInsertable(this._base, this._mergedIn);

  @override
  Map<String, Expression<Object>> toColumns(bool nullToAbsent) {
    return {
      ..._base.toColumns(nullToAbsent),
      ..._mergedIn.toColumns(nullToAbsent),
    };
  }
}

I'm not entirely convinced that this should be a part of drift though. We have copyWith, but I don't think merges are used that often.

[wanglophile]

Thank you!

[wanglophile]

Follow-up question: how can I see if if a property exists in a Companion entry?

So in my original example, if data has a baz property in it?

[simolus3]

Follow-up question: how can I see if if a property exists in a Companion entry?

The only way at the moment is to call toColumns(true) and then check whether the map contains the key for the column you're interested in.