Support alias for enum values

[biruburu]

I have found these related issues/pull requests

There is an issue about supporting alias on columns for joined tables, but that appears to be unrelated to the present feature request.

Description

I am transitioning with a large legacy postgresql schema from typescript to rust/sqlx. In the schema, I have a dataset(id, "dataType") table, where dataType is a TEXT column with entries DataType.Unknown and DataType.Image, which I'm mapping to an enum like so:

#[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize, sqlx::Type)]
#[sqlx(type_name = "\"DataType\"")]
pub enum DataType {
    #[sqlx(rename = "DataType.Unknown")]
    Unknown = 0,
    #[sqlx(rename = "DataType.Image")]
    Image = 1,
}

let result = sqlx::query!(r#"SELECT id, "dataType: DataType" FROM dataset LIMIT 10;"#).execute(db).await;

While this approach appears to be working fine in most cases, some legacy developer at some point added unexpected None entries to the column, which causes a runtime error in the query: invalid value \"None\" for enum DataType.

Prefered solution

While I could add a new DataType::None to the enum, I would like to avoid that because it is against the defined spec. Instead, I would love to add an alias so that either DataType.Unknown | None decode to the same DataType::Unknown value.

In serde, I can do that with:

pub enum DataType {
    #[serde(rename = "DataType.Unknown", alias = "None")]
    Unknown,
    ...
}

However, alias is not currently available in sqlx.

• Is that something that could be added to cover such legacy use-cases in the future?
• Is there any available workaround to decode both values to DataType::Unknown? Upd: I can manually implement the Decode/Encode/TypeInfo traits, which worked at the cost of significant amount of boilerplate.

Is this a breaking change? Why or why not?

Probably not.