Document that Insertable isn't derived for borrowed structs if the struct uses serialize_as

[inklesspen]

diesel/diesel_derives/src/insertable.rs

Line 117 in b5e4324

generate_borrowed_insert = false; // as soon as we hit one field with #[diesel(serialize_as)] there is no point in generating the impl of Insertable for borrowed structs

This was tripping me up today because the guides and API docs were all saying using &mystruct should work, but the compiler said nuh-uh.

[weiznich]

We are happy to accept a PR for this.

For future issues you open: Please always use the issue template. It's mandatory.

[inklesspen]

Ah; I'd opened the issue from the line of code, and Github didn't present me with a choice of template when doing that… Sorry.

[inklesspen]

Anyway I suppose I could send a PR to document the fact of this. But I do not understand why it is done like this. So I think it would be better for someone who knows such things to write the PR.

[weiznich]

But I do not understand why it is done like this.

The underlying problem there is that #[serialize_as] calls .into() internally which consumes the value. Therefore it requires to take ownership of that value, which in turn is not possible to do if the value is behind a shared reference.