Am I on the right track with my SQLiteDecimalBuilder and SQLiteDecimal?

[epatey]

I'm in the process of migrating from PlanetScale to Turso which means I'm now all about SQLite. I need to store decimals. Since SQLite doesn't have decimal support, I'm working on writing a custom column type that can be configured with the number of decimal places via a scale parameter. I'll transform by multiplying/dividing by Math.pow(10, scale) when going to/from the driver.

I did a first pass by using customType, but drizzle-zod turns those columns into any's which is a deal breaker for me.

I took inspiration from this documentation page, and came up with the code below. I don't quite get how all of the config and generics piece together, so I'm looking for guidance.

import { AnySQLiteTable, SQLiteColumn, SQLiteColumnBuilder, SQLiteTable } from "drizzle-orm/sqlite-core"

type DecimalBuilderConfig<TName extends string> = {
  name: TName
  dataType: "number"
  columnType: "SQLiteDecimal"
  data: number
  driverParam: undefined
  enumValues: undefined
}

class SQLiteDecimalBuilder<TName extends string, T extends DecimalBuilderConfig<TName>> extends SQLiteColumnBuilder<T> {
  private scale: number

  constructor(name: T["name"], scale: number) {
    super(name, "number", "SQLiteDecimal")
    this.scale = scale
  }

  build<TTableName extends string>(table: AnySQLiteTable<{ name: TTableName }>): SQLiteDecimal<TName, T> {
    return new SQLiteDecimal(table, this.config, this.scale)
  }
}

class SQLiteDecimal<TName extends string, T extends DecimalBuilderConfig<TName>> extends SQLiteColumn {
  private scale: number

  constructor(table: SQLiteTable, config: SQLiteDecimalBuilder<TName, T>["config"], scale: number) {
    super(table, config)
    this.scale = scale
  }

  getSQLType(): string {
    return "INTEGER"
  }

  toDatabase(value: number): number {
    return value * Math.pow(10, this.scale)
  }

  fromDatabase(value: number): number {
    return value / Math.pow(10, this.scale)
  }
}

export const decimal = <TName extends string>(
  name: TName,
  scale: number,
): SQLiteDecimalBuilder<TName, DecimalBuilderConfig<TName>> => new SQLiteDecimalBuilder(name, scale)