Multi-column fields

[gammelalf]

Collection of sub-issues working towards support of mutli-column fields

Vision of feature

1. Structs:

/// Common timestamps to track access to a model
#[derive(FieldType)]
pub struct Timestamps {
    pub created: OffsetDateTime,
    pub updated: OffsetDateTime,
    pub read: OffsetDateTime,
    pub deleted: Option<OffsetDateTime>,
}

#[derive(Model)]
pub struct SomeObject {
    ...

    pub timestamps: Timestamps,
}

(Basicly embed all fields into the parent model)

2. Enums:

#[derive(Model)]
pub struct Tag {
    ...

    pub owner: TagOwner,
}

#[derive(FieldType)]
pub enum TagOwner {
    Item(ForeignModel<Item>),
    Location(ForeignModel<Location>),
    Other(MaxStr<255>),
}

(Embed all variants wrapped in Option into the parent model and "enforce" only one to be set)