The trait diesel::Expression is not implemented for diesel_ltree::Ltree about diesel_ltree HOT 4 CLOSED

A potential workaround is to tell Diesel not to generate missing SQL type definitions and then manually specify them yourself. For my MWE the [print_schema] section of diesel.toml will become

[print_schema]
file = "src/schema.rs"
generate_missing_sql_type_definitions = false
import_types = ["diesel::sql_types::*", "diesel_ltree::sql_types::Ltree"]

And then the schema generated by diesel will work fine.

Edit: If you need the functionality provided by Diesel automatically generating missing types, an alternative is to use the patch file functionality described in the Diesel CLI docs. Using the patch file, I can target specific lines in schema.rs to replace the auto-generated ltree type with the one provided by this library.

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Can you let me know how I can reproduce this same compile error locally? What do your project's Cargo.toml and Cargo.lock look like? (or at least all the lines related to Diesel/diesel_ltree.) What line of which file is actually shown there?

I've spent half an hour trying to reproduce what I thought the problem would be, given what you've described, but no luck. Let me know!

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I ran into this problem, given the lack of MWE I think I can help out by contributing one. The problem here seems to be with how diesel_ltree interacts with the code generated by Diesel. In my MWE, this table

CREATE TABLE foo (
  id SERIAL PRIMARY KEY,
  tree_path LTREE NOT NULL
);

Ends up creating the following schema.rs:

// @generated automatically by Diesel CLI.

pub mod sql_types {
    #[derive(diesel::sql_types::SqlType)]
    #[diesel(postgres_type(name = "ltree"))]
    pub struct Ltree;
}

diesel::table! {
    use diesel::sql_types::*;
    use super::sql_types::Ltree;

    foo (id) {
        id -> Int4,
        tree_path -> Ltree,
    }
}

And in its current state, if you attempt to do anything with the foo table (select, insert etc) you will end up with the errors reported by the poster. If you replace use super::sql_types::Ltree; with diesel_ltree::sql_types::Ltree;, all of the traits implemented by diesel_ltree are picked up and everything works fine.

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Oof, I see. It looks like this is the best we can do with print_schema, so I'd say import_types + patch_file is indeed the path forward for such uses.

In #25 I'm updating the built-in tests to use this instead of issuing table! manually.

@TheConner — thank you so much for putting that example together! I appreciate it a heap. ❤️

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