Derive macros for custom wrapper types

[tyt2y3]

Right now, custom wrapper types kind of work with SeaORM, e.g. 1) https://github.com/SeaQL/sea-orm/blob/master/tests/common/features/event_trigger.rs
2) https://github.com/nitnelave/lldap/pull/382/files#diff-27e26a3b85b610666d7dd0a3fa3e848582ab2d3999f7b1bdfed61052f82af741R96-R168
but require a lot of boilerplate, it'd be nice if we can make a DeriveValueType macro and remove some entropy.

To start, we can only accept struct in the form of struct MyType(pub T). It would be great if we can also accept Vec<T>, where I think Nullable can also be implemented.

And may be a column_type attribute to allow customizing the column type.

[billy1624]

The idea is to provide a derive macro to implement the necessary traits of a custom wrapper type. For simplicity, we only support struct MyType(T) for now.

Without derive macro, the trait implementations look like below.

use sea_orm::entity::prelude::*;

#[derive(Clone, Debug, PartialEq, Eq, DeriveEntityModel)]
#[sea_orm(table_name = "json_vec")]
pub struct Model {
    #[sea_orm(primary_key)]
    pub id: i32,
    pub str_vec: StringVec,
}

#[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
pub enum Relation {}

impl ActiveModelBehavior for ActiveModel {}

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct StringVec(pub Vec<String>);

impl From<StringVec> for Value {
    fn from(source: StringVec) -> Self {
        source.0.into()
    }
}

impl sea_orm::TryGetable for StringVec {
    fn try_get_by<I: sea_orm::ColIdx>(res: &QueryResult, idx: I) -> Result<Self, sea_orm::TryGetError> {
        <Vec<String> as sea_orm::TryGetable>::try_get_by(res, idx).map(|v| StringVec(v))
    }
}

impl sea_query::ValueType for StringVec {
    fn try_from(v: Value) -> Result<Self, sea_query::ValueTypeErr> {
        <Vec<String> as sea_query::ValueType>::try_from(v).map(|v| StringVec(v))
    }

    fn type_name() -> String {
        stringify!(StringVec).to_owned()
    }

    fn array_type() -> sea_orm::sea_query::ArrayType {
        <Vec<String> as sea_orm::sea_query::ValueType>::array_type()
    }

    fn column_type() -> sea_orm::sea_query::ColumnType {
        <Vec<String> as sea_orm::sea_query::ValueType>::column_type()
    }
}

[tyt2y3]

Let me share my imagination:

#[derive(DeriveColumnType)]
#[sea_orm(column_type = "String")]
pub struct UserId(Uuid);

// generates
impl ValueType for UserId {
    ...
    fn array_type() -> sea_orm::sea_query::ArrayType {
        ArrayType::String
    }

    fn column_type() -> sea_orm::sea_query::ColumnType {
        ColumnType::String
    }
}

I think column type is needed, when there are multiple possible SQL types a Rust type can be mapped to.

It should pretty much work like DeriveEntityModel's column_type, e.g. https://github.com/SeaQL/sea-orm/blob/master/sea-orm-codegen/tests/compact/cake_with_float.rs

#[derive(DeriveEntityModel)]
pub struct Model {
    #[sea_orm(primary_key)]
    pub id: i32,
    #[sea_orm(column_type = "Text")]
    pub name: Option<String>,
}