PostgreSQL driver

A database connection is necessary for today's enterprise development. WasmEdge provides a PostgreSQL driver for Rust developers, enabling developers to build database applications in Rust and then running in WasmEdge.

note

Before we start, you need to have Rust and WasmEdge installed. Make sure that you read the special notes on networking apps especially if you are compiling Rust programs on a Mac.

Run the example

The wasmedge-db-example/postgres is a PostgreSQL connector example written in Rust.

git clone https://github.com/WasmEdge/wasmedge-db-examples
cd wasmedge-db-examples/postgres

# Compile the rust code into WASM
RUSTFLAGS="--cfg wasmedge --cfg tokio_unstable" cargo build --target wasm32-wasi --release

# Execute SQL statements against a PostgreSQL database at postgres://user:passwd@localhost/testdb
wasmedge --env "DATABASE_URL=postgres://user:passwd@localhost/testdb" target/wasm32-wasi/release/crud.wasm

Configuration

In order to compile the tokio-postgres and tokio crates, we will need to apply patches to add WasmEdge-specific socket APIs to those crates in Cargo.toml.

[patch.crates-io]
tokio = { git = "https://github.com/second-state/wasi_tokio.git", branch = "v1.36.x" }
socket2 = { git = "https://github.com/second-state/socket2.git", branch = "v0.5.x" }
tokio-postgres = { git = "https://github.com/second-state/rust-postgres.git" }

[dependencies]
tokio-postgres = "0.7"
tokio = { version = "1", features = [
    "io-util",
    "fs",
    "net",
    "time",
    "rt",
    "macros",
] }

Code explanation

We first use a Rust struct to represent the database table.

#[derive(Debug)]
struct Order {
    order_id: i32,
    production_id: i32,
    quantity: i32,
    amount: f32,
    shipping: f32,
    tax: f32,
    shipping_address: String,
}

impl Order {
    fn new(
        order_id: i32,
        production_id: i32,
        quantity: i32,
        amount: f32,
        shipping: f32,
        tax: f32,
        shipping_address: String,
    ) -> Self {
        Self {
            order_id,
            production_id,
            quantity,
            amount,
            shipping,
            tax,
            shipping_address,
        }
    }
}

Then, you can use the tokio-postgres API to access the database through its connection URL. The code below shows how to perform basic CRUD operations using SQL commands.

#[tokio::main(flavor = "current_thread")]
async fn main() -> Result<(), Error> {
    // Connect to the database.
    let (client, connection) = tokio_postgres::connect(&*get_url(), NoTls).await?;

    // The connection object performs the actual communication with the database,
    // so spawn it off to run on its own.
    tokio::spawn(async move {
        if let Err(e) = connection.await {
            eprintln!("connection error: {}", e);
        }
    });

    client.execute("CREATE TABLE IF NOT EXISTS orders (order_id INT, production_id INT, quantity INT, amount REAL, shipping REAL, tax REAL, shipping_address VARCHAR(256));", &[]).await?;

    let orders = vec![
        Order::new(1, 12, 2, 56.0, 15.0, 2.0, String::from("Mataderos 2312")),
        Order::new(2, 15, 3, 256.0, 30.0, 16.0, String::from("1234 NW Bobcat")),
        Order::new(3, 11, 5, 536.0, 50.0, 24.0, String::from("20 Havelock")),
        Order::new(4, 8, 8, 126.0, 20.0, 12.0, String::from("224 Pandan Loop")),
        Order::new(5, 24, 1, 46.0, 10.0, 2.0, String::from("No.10 Jalan Besar")),
    ];

    for order in orders.iter() {
        client.execute(
            "INSERT INTO orders (order_id, production_id, quantity, amount, shipping, tax, shipping_address) VALUES ($1, $2, $3, $4, $5, $6, $7)",
            &[&order.order_id, &order.production_id, &order.quantity, &order.amount, &order.shipping, &order.tax, &order.shipping_address]
        ).await?;
    }

    let rows = client.query("SELECT * FROM orders;", &[]).await?;
    for row in rows.iter() {
        let order_id : i32 = row.get(0);
        println!("order_id {}", order_id);

        let production_id : i32 = row.get(1);
        println!("production_id {}", production_id);

        let quantity : i32 = row.get(2);
        println!("quantity {}", quantity);

        let amount : f32 = row.get(3);
        println!("amount {}", amount);

        let shipping : f32 = row.get(4);
        println!("shipping {}", shipping);

        let tax : f32 = row.get(5);
        println!("tax {}", tax);

        let shipping_address : &str = row.get(6);
        println!("shipping_address {}", shipping_address);
    }

    client.execute("DELETE FROM orders;", &[]).await?;

    Ok(())
}