actix-web/guide/src/qs_14.md

# Database integration

## Diesel

At the moment of 1.0 release Diesel does not support asynchronous operations.
But it possible to use the `actix` synchronous actor system as a db interface api.
Technically sync actors are worker style actors, multiple of them
can be run in parallel and process messages from same queue (sync actors work in mpsc mode).

Let's create a simple db api that can insert a new user row into an SQLite table.
We have to define sync actor and connection that this actor will use. The same approach
can be used for other databases.

```rust,ignore
use actix::prelude::*;

struct DbExecutor(SqliteConnection);

impl Actor for DbExecutor {
    type Context = SyncContext<Self>;
}
```

This is the definition of our actor. Now we need to define the *create user* message and response.

```rust,ignore
struct CreateUser {
    name: String,
}

impl Message for CreateUser {
    type Result = Result<User, Error>;
}
```

We can send a `CreateUser` message to the `DbExecutor` actor, and as a result we get a
`User` model instance. Now we need to define the actual handler implementation for this message.

```rust,ignore
impl Handler<CreateUser> for DbExecutor {
    type Result = Result<User, Error>;

    fn handle(&mut self, msg: CreateUser, _: &mut Self::Context) -> Self::Result
    {
        use self::schema::users::dsl::*;

        // Create insertion model
        let uuid = format!("{}", uuid::Uuid::new_v4());
        let new_user = models::NewUser {
            id: &uuid,
            name: &msg.name,
        };

        // normal diesel operations
        diesel::insert_into(users)
            .values(&new_user)
            .execute(&self.0)
            .expect("Error inserting person");

        let mut items = users
            .filter(id.eq(&uuid))
            .load::<models::User>(&self.0)
            .expect("Error loading person");

        Ok(items.pop().unwrap())
    }
}
```

That's it. Now we can use the *DbExecutor* actor from any http handler or middleware.
All we need is to start *DbExecutor* actors and store the address in a state where http handler
can access it.

```rust,ignore
/// This is state where we will store *DbExecutor* address.
struct State {
    db: Addr<Syn, DbExecutor>,
}

fn main() {
    let sys = actix::System::new("diesel-example");

    // Start 3 parallel db executors
    let addr = SyncArbiter::start(3, || {
        DbExecutor(SqliteConnection::establish("test.db").unwrap())
    });

    // Start http server
    HttpServer::new(move || {
        App::with_state(State{db: addr.clone()})
            .resource("/{name}", |r| r.method(Method::GET).a(index))})
        .bind("127.0.0.1:8080").unwrap()
        .start().unwrap();

    println!("Started http server: 127.0.0.1:8080");
    let _ = sys.run();
}
```

And finally we can use the address in a request handler. We get a message response
asynchronously, so the handler needs to return a future object, also `Route::a()` needs to be
used for async handler registration.


```rust,ignore
/// Async handler
fn index(req: HttpRequest<State>) -> Box<Future<Item=HttpResponse, Error=Error>> {
    let name = &req.match_info()["name"];

    // Send message to `DbExecutor` actor
    req.state().db.send(CreateUser{name: name.to_owned()})
        .from_err()
        .and_then(|res| {
            match res {
                Ok(user) => Ok(HttpResponse::Ok().json(user)),
                Err(_) => Ok(HttpResponse::InternalServerError().into())
            }
        })
        .responder()
}
```

Full example is available in the
[examples directory](https://github.com/actix/actix-web/tree/master/examples/diesel/).

More information on sync actors can be found in the
[actix documentation](https://docs.rs/actix/0.5.0/actix/sync/index.html).