How to make a static Database Connection

Read first: Documentation on Connection Pool

Everytime we access the database, we need to establish a connection, or as we call it, a "Connection Pool" beforehand. The most trivial way is to create the connection everytime we need to access it:

#![allow(unused)]
fn main() {
// Establish connection
let db = Database::connect(url).await?;

/* Some operations on db */

// Close connection
db.close().await?;
}

This connection is, however, only locally accessible, and each establishment of connection is very costly. To solve it, one would like to create a static connection that only has to be established once. Doing so requires the lazy_static and any runtime crate. Here are 2 of them.

tokio

#![allow(unused)]
fn main() {
lazy_static::lazy_static! {
    static ref DB: DatabaseConnection = {
        tokio::runtime::Runtime::new().unwrap().block_on(async {
            // You have to define `url` yourself!
            Database::connect(url).await.unwrap()
        })
    };
}
}

async-std

#![allow(unused)]
fn main() {
lazy_static::lazy_static! {
    static ref DB: DatabaseConnection = {
        async_std::task::block_on(async {
            // You have to define `url` yourself!
            Database::connect(url).await.unwrap()
        })
    };
}
}

Now any scopes inside of the same module can access the DB static variable and use it as a connection to the database without establishing connection everytime. For example

#![allow(unused)]
fn main() {
fn a_function() -> Result<(), !> {
    DB.do_something().await?;
}
}

For DB to be visible from other modules, simply add pub in front of static ref DB:....

SeaORM Cookbook

How to make a static Database Connection