Simultaneous support for multiple backends?

[vdods]

I'm wondering if anyone's used sqlx in a program that supports multiple DB backends (I'm thinking postgres + sqlite in particular) with as little code repeat as possible? There's a lot (but not 100%) overlap in the SQL for each backend. The usecase is having DB-using code that can run on either a server (postgres) or an edge device (sqlite). I've done this in diesel, and I'd like to gauge how hard it would be to achieve something similar in sqlx. Thanks!

[vdods]

I'm attempting a small proof of concept for this, in which I have

pub enum Pool2 {
    Postgres(sqlx::PgPool),
    Sqlite(sqlx::SqlitePool),
}

And branch on the variant to handle each DB backend:

    match &pool2 {
        Pool2::Postgres(pool) => {
            // This returns `struct Record { value: Option<i64> }` (or i32? not sure)
            let value1 = sqlx::query!("SELECT 1 AS value;").fetch_one(pool).await?;
            println!("value1: {:?}", value1);
            // This returns `Option<i64>` (or i32? not sure)
            let value2 = sqlx::query_scalar!("SELECT 1;").fetch_one(pool).await?;
            println!("value2: {:?}", value2);
        }
        Pool2::Sqlite(pool) => {
            // This returns `struct Record { value: Option<i64> }` (or i32? not sure)
            let value1 = sqlx::query!("SELECT 1 AS value;").fetch_one(pool).await?;
            println!("value1: {:?}", value1);
            // This returns `Option<i64>` (or i32? not sure)
            let value2 = sqlx::query_scalar!("SELECT 1;").fetch_one(pool).await?;
            println!("value2: {:?}", value2);
        }
    }

AnBut sqlx::query! checks that the DB backend is equal to Postgres (based on the value of DATABASE_URL env var). I've played around with offline mode, but from relevant documentation I've been reading, I think it may not be possible to have different DB backends both compiling in the same codebase. At best, one backend could be chosen at a time, since the compile time checks have to use DATABASE_URL or sqlx-data.json, and there's no way (that I see at least) to specify which DB backend any given sqlx query or statement should run against.

Can anyone comment on this? Is there some way around the problem that I'm not seeing?

[vdods]

Ah, I see: #916