Migrating an endpoint that uses a database. #1046
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@samwho is attempting to deploy a commit to the Effect Team on Vercel. A member of the Team first needs to authorize it. |
| ```ts twoslash {2-5} | ||
| import { Effect } from "effect" | ||
| // ---cut--- | ||
| const promise = Effect.promise(async () => "Hello, world!") |
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Might be worth renaming this from promise to something else to avoid a user interpreting the variable as a Promise instead of an Effect.
| NodeRuntime.runMain( | ||
| Layer.launch( | ||
| Layer.provide( | ||
| HttpServer.serve(router), | ||
| NodeHttpServer.layer(() => createServer(app), { port: 3000 }), | ||
| ), | ||
| ), | ||
| ) |
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Since you've already taught folks about .pipe, you could re-write this to make it flow sequentially:
HttpServer.server(router).pipe(
Layer.provide(NodeHttpServer.layer(() => createServer(app), { port: 3000 })),
Layer.launch,
NodeRuntime.runMain
)| $ bun index.ts | ||
| ``` | ||
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| And in other shell we can test the endpoint: |
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| And in other shell we can test the endpoint: | |
| And in another shell we can test the endpoint: |
| const users = Effect.sync(() => { | ||
| return { users: db.prepare("SELECT * FROM users").all() } | ||
| }).pipe( | ||
| (body) => HttpServerResponse.json(body) | ||
| ) | ||
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| const router = HttpRouter.empty.pipe( | ||
| HttpRouter.get("/health", health), | ||
| HttpRouter.get("/users", users), | ||
| ) | ||
| ``` | ||
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| This no longer gives us a type error. We've split our computation into two | ||
| parts: fetching the data with `Effect.sync`, and serializing it with | ||
| `HttpServerResponse.json`. The call to `pipe` takes the result of the first | ||
| Effect and passes it to `HttpServerResponse.json`, flattening any nesting in | ||
| the process. |
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This is not correct - body in this case has the type Effect<{ users: Array<string> }>, which we're now passing to HttpServerResponse.json. Because HttpServerResponse.json takes data of type unknown, you're going to attempt to serialize an Effect instead of the body.
The reason you don't get a type error here is because the input to HttpServerResponse.json is unknown, which will allow any value.
At this point, you may choose to introduce the concept of sequencing Effects.
const users = Effect.sync(() => {
return { users: db.prepare("SELECT * FROM users").all() }
}).pipe(
// Similar to `Effect.map`, `Effect.flatMap` receives the value of the previous effect
// but instead of returning a new _value_, you return a new _Effect_
Effect.flatMap((body) => HttpServerResponse.json(body))
// Or alternatively `Effect.andThen((body) => ...)` if you prefer that naming
)
// `users` is type `Effect<HttpServerResponse, HttpBodyError>`or you can introduce Effect.suspend, which is the same as Effect.sync, except instead of taking a side effect that returns a value, it takes a side effect that returns an Effect:
const users = Effect.suspend(() => {
// Side effect
const body = { users: db.prepare("SELECT * FROM users").all() }
// return an effect
return HttpServerResponse.json(body)
})
// `users` is type `Effect<HttpServerResponse, HttpBodyError>`
Type
Description
Currently still a work in progress.