Support comments on columns (generate down to schema.rs)

[SamuelMarks]

I like to use structs to represent things all the way down to CLIs, OpenAPI [utoipa crate], and more.

My current structs are uninformative:

#[derive(Debug, Clone, serde::Serialize, serde::Deserialize, diesel::Queryable, diesel::Selectable, diesel::QueryableByName, PartialEq, diesel::Identifiable)]
#[diesel(table_name=my_model, primary_key(id))]
pub struct MyModel {
    /// Field representing column `id`
    pub id: i32,
}

(as generated via schema.rs with https://github.com/Wulf/dsync )

How should this be supported? - I'm thinking:

CREATE TABLE "my_model" (
    id             VARCHAR(50) PRIMARY KEY    -- user-modifiable id
);

Or maybe:

COMMENT ON COLUMN my_model.id IS 'user-modifiable id';

Or something else? - What do you think?

Happy to contribute a PR. Related: Wulf/dsync#144

[weiznich]

Diesel already reads comment on tables and columns and emits them as doc comments in your schema.rs file. You need to configure diesel-cli to actually emit the doc comments, but otherwise this already works. See this guide for details about the relevant setting.

[hasezoey]

Didnt know this existed, thanks for pointing this out. Maybe consider mentioning that with-docs (both in help and the mentioned guide) also reads and uses sql comments (and also if it is intended to work with sqlite?)
(and maybe also note that such a sql comment will overwrite the comment otherwise created by diesel?)

---

for anyone seeing this in the future, the output context is:

// @generated automatically by Diesel CLI.

diesel::table! {
    /// hello
    franchise (_id) {
        /// testy
        _id -> Integer,
    }
}

from (mariadb) sql:

-- test comment 1
CREATE TABLE franchise (
	-- test comment 2
	_id INTEGER NOT NULL PRIMARY KEY COMMENT "testy"
) comment = "hello";

[weiznich]

Didnt know this existed, thanks for pointing this out. Maybe consider mentioning that with-docs (both in help and the mentioned guide) also reads and uses sql comments

That sounds reasonable. I'm happy to accept a PR for this.

(and also if it is intended to work with sqlite?)

This doesn't work for sqlite as sqlite doesn't support the COMMENT "your comment" syntax, so it's not expected to work there.