Theo's Typesafe Cult•12mo ago

Tagged Union in a Relational Database

really specific question, how does one represent a tagged union in a relational database? take the following typescript type as an example:

type TaggedUnionTable = {
    id: string;
} & (
    | {
            type: 'tag_a';
            specific_info_to_tag_a: object;
      }
    | {
            type: 'tag_b';
            specific_info_to_tag_b: object;
      }
);

type TaggedUnionTable = {
    id: string;
} & (
    | {
            type: 'tag_a';
            specific_info_to_tag_a: object;
      }
    | {
            type: 'tag_b';
            specific_info_to_tag_b: object;
      }
);

I implemented it in postgresql using jsonb type, but there has to be a better option. (answer with sql pls)

3 Replies

🟠 CHANCE•12mo ago

Following — I too ended up going the json route and am still convinced there has to be a better way

Keef•12mo ago

I generally just use jsonb and when i decode I handle the type narrowing. Serde has some nice handling around it in rust but in typescript I just do the usual if tag .... This looks like a good read as well: https://www.parsonsmatt.org/2019/03/19/sum_types_in_sql.html

Sum Types In SQL

Algebraic datatypes are a powerful feature of functional programming languages.By combining the expressive power of “and” and “or,” we can solve all kinds of...

Keef•12mo ago

https://news.ycombinator.com/item?id=34838213 Also useful

enugu

Any idea of how to implement tagged unions in Postgres. For example, Tree a = Leaf a | Branch (Tree a, Tree a)This is one data type feature which would be great to have. I know you can create separate tables for each option in the type and use an id, but is a direct type implementation possible?Dont need polymorphism(say a = String). Even a non ...

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Tagged Union in a Relational Database