Why doesn't Iden impl From<String>, but it does From<&str>? #2621

tgrushka · 2025-06-09T23:14:11Z

tgrushka
Jun 9, 2025

Say I'm generating my enums from a file:

let values: Vec<String> = vec!["one".into(), "two".into(), "three".into()];

manager
    .create_type(
        TypeCreateStatement::new()
            .as_enum("my_enum")
            .values(values)
            .to_owned(),
    )
    .await?;

error[E0277]: the trait bound `std::string::String: sea_orm_migration::prelude::IntoIden` is not satisfied
   --> migration/src/m20250608_230255_create_my_enum.rs:69:22
    |
69  |                     .values(values)
    |                      ^^^^^^ the trait `sea_orm_migration::prelude::Iden` is not implemented for `std::string::String`
    |
    = help: the trait `sea_orm_migration::prelude::Iden` is implemented for `&str`
    = note: required for `std::string::String` to implement `sea_orm_migration::prelude::IntoIden`
note: required by a bound in `sea_orm_migration::prelude::extension::postgres::TypeCreateStatement::values`
   --> /Users/tom/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/sea-query-0.32.6/src/extension/postgres/types.rs:207:12
    |
205 |     pub fn values<T, I>(&mut self, values: I) -> &mut Self
    |            ------ required by a bound in this associated function
206 |     where
207 |         T: IntoIden,
    |            ^^^^^^^^ required by this bound in `TypeCreateStatement::values`

Why the heck not?

However, this EDIT: DOES NOT WORK (I had to dig for it, which should not have been necessary, and now after I cleared another error, rust-analyzer finally showed me this won't work either):

let values: Vec<String> = vec!["one".into(), "two".into(), "three".into()];

// Source: https://users.rust-lang.org/t/vec-string-to-str/12619
let values: Vec<&str> = values.iter().map(|x| &**x).collect();

manager
    .create_type(
        TypeCreateStatement::new()
            .as_enum("my_enum")
            .values(values)
            .to_owned(),
    )
    .await?;

NOPE!!!

values does not live long enough
borrowed value does not live long

So how about this monstrosity?

struct IdString(String);

impl Iden for IdString {
    fn unquoted(&self, s: &mut dyn std::fmt::Write) {
        write!(s, "{}", self.0).unwrap();
    }
}

impl From<String> for IdString {
    fn from(value: String) -> Self {
        IdString(value)
    }
}

Then convert every value in the Vec to an IdString. Seems ridiculous, but unfortunately, quite necessary today.

Since impl From<&str> for Iden exists, why not impl From<String> for Iden, since Iden basically is a string?

Expurple · 2025-06-12T18:36:25Z

Expurple
Jun 12, 2025
Maintainer

I'm in full agreement with you! Unfortunately, not implementing for String is the intentional position of the maintainer. See SeaQL/sea-query#882.

Instead of implementing your own IdString, for now you can use Alias. It's the same hack, but "official" (lol)

By the way, it's possible that in the upcoming major release we'll get rid of trait Iden altogether and instead user types will need to implement something similar to Into<Cow<'static, str>>. You can contribute to the discussions, if you're interested in this area:

0 replies

Expurple · 2025-07-25T06:34:37Z

Expurple
Jul 25, 2025
Maintainer

impl IntoIden for String was merged recently: SeaQL/sea-query#909

It will be released in SeaQuery 1.0 (SeaORM 2.0) 🎉

0 replies

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Why doesn't Iden impl From<String>, but it does From<&str>? #2621

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tgrushka Jun 9, 2025

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