Comment by kilburn | Hacker News Reader

Comment by kilburn | Hacker News Reader

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I'm also awed by this!

> Just worried about forcing colleagues having to learn SQL instead of using a fancy wrapper.

My current team is pretty junior, and I don't see any problem with this. Simple SQL queries are really easy to learn, and complex queries are harder to understand with ORMs than in raw SQL.

Moreover, knowing SQL is a useful, marketable skill that will stay relevant for many years to come. If there's some resistance, I can easily convince the team that going this route will benefit them personally.

Back to the README, there are two questions I'd like to see addressed:

1. Whether `Selectable[]` can be used to query for a subset of fields and how.

2. In the `to_jsonb(authors)` example, what would you get back in the `author` field if there were multiple authors with the same `author.id` value? An array of `author.Selectable` objects? This part is awesome but brittle, isn't it?

I would love to see this move forward! I will definitely play with it and consider it for my next project.

I'm also awed by this!

:)

1. Whether `Selectable[]` can be used to query for a subset of fields and how.

Right — this is not (currently) supported. I guess if you had wide tables of large values, this could be an important optimisation, but it hasn't been a need for me as yet.

2. In the `to_jsonb(authors)` example, what would you get back in the `author` field if there were multiple authors with the same `author.id` value? An array of `author.Selectable` objects? This part is awesome but brittle, isn't it?

Multiple authors with the same id isn't going to happen, since id is intended as a primary key, so I'd argue that the example as given isn't brittle. On the other hand, there's a fair question about what happens for many-to-many joins, and since my use case hasn't yet required this I haven't given it much thought.

OK, I gave the one-to-many queries a bit more thought, and the converse join query (getting each author with all their books, rather than all books each with their author) works nicely with a GROUP BY:

    type authorBookSQL = s.authors.SQL | s.books.SQL;
    type authorBookSelectable = s.authors.Selectable & { books: s.books.Selectable };

    const
      query = db.sql<authorBookSQL>`
        SELECT ${"authors"}.*, jsonb_agg(${"books"}.*) AS ${"books"}
        FROM ${"books"} JOIN ${"authors"} 
          ON ${"authors"}.${"id"} = ${"books"}.${"authorId"}
        GROUP BY ${"authors"}.${"id"}`,

      authorBooks: authorBookSelectable[] = await query.run(db.pool);

This exploits the fact that selecting all fields is, logically enough, permitted when grouping by primary key (https://www.postgresql.org/docs/current/sql-select.html#SQL-... and https://dba.stackexchange.com/questions/158015/why-can-i-sel...)

I'll update demo.ts and README shortly.

Right, only querying a few fields seems not to be a builtin feature. Looks like you have to create the partial selectable type yourself and there is no support to typecheck that the correct columns in the select are included.

Your second case, if I recall this correctly (ActiveRecord made my SQL skills fade away), this plain JOIN would just return a row with the same book but a different author. `to_jsonb(authors.*)` is just operating on a single row. But what you want is possible (aggregating rows into a JSON object) by using `jsonb_agg`. Whether the lib supports inferring the correct typings for that is another question though.

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