effect-ontology: Skill for Claude Code

SQL & Databases

When to use

• You are integrating a SQL client (Drizzle, Kysely, Prisma, mysql2/pg) with Effect
• You want typed errors, retries, transactions, and observability

Provide DB config via Layer

import { Config, Effect, Layer } from "effect"

class DbConfig extends Effect.Service<DbConfig>()("DbConfig", {
  sync: () => ({
    url: process.env.DATABASE_URL ?? ""
  })
}){}

// Provide once at app boundary
export const DbConfigLive = DbConfig.Default

Wrap a client in a Service (typed errors)

import { Effect } from "effect"

class DatabaseError extends Data.TaggedError("DatabaseError")<{ cause: unknown }>{}

export class Database extends Effect.Service<Database>()("Database", {
  effect: Effect.gen(function* () {
    // drizzle() / new PrismaClient() / kysely instance
    const client = makeDbClient() // your factory (validated url)
    return {
      // use-pattern ensures client is passed from a single place
      use: <A>(cb: (c: typeof client) => Promise<A>) =>
        Effect.tryPromise({ try: () => cb(client), catch: (cause) => new DatabaseError({ cause }) })
    }
  })
}){}

Real-world snippet: Drizzle wrapper with use(cb)

// Pattern adapted from Cap
export class Database extends Effect.Service<Database>()("Database", {
  effect: Effect.gen(function* () {
    return {
      use: <T>(cb: (_: DbClient) => Promise<T>) =>
        Effect.tryPromise({ try: () => cb(db()), catch: (cause) => new DatabaseError({ cause }) })
    }
  })
}){}

Transactions with retry-on-deadlock

// Generic transactional helper with selective retry
const isDeadlock = (e: unknown) => typeof e === "object" && e !== null && (e as any).code === "1213" // MySQL

export const transactional = <A>(eff: Effect.Effect<A, DatabaseError, Database>) =>
  Effect.gen(function* () {
    const db = yield* Database
    return yield* Effect.tryPromise({
      try: () => db.use((c) => c.transaction(async (tx) => await Effect.runPromise(eff))),
      catch: (cause) => new DatabaseError({ cause })
    })
  }).pipe(
    Effect.retry({ schedule: Schedule.exponential("100 millis"), times: 3, while: isDeadlock })
  )