describe a database schema in rust

To describe a database schema in Rust, you can use the diesel crate which is a popular ORM (Object-Relational Mapping) framework in the Rust ecosystem.

You first need to define a simple Rust structure to model your database table. Here is an example schema for a table called users with columns id (integer), name (text), and age (integer):

main.rs
use diesel::sql_types::*;

#[derive(Queryable)]
struct User {
    id: i32,
    name: String,
    age: i32,
}
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The #[derive(Queryable)] attribute tells diesel to generate SQL statements for fetching records from the database based on the fields of the struct.

To define a migration that creates the users table and its columns, you can use the following code:

main.rs
use diesel::prelude::*;

embed_migrations!("migrations");

fn main() {
    let connection = establish_connection();
    embedded_migrations::run(&connection).unwrap();
}

fn establish_connection() -> SqliteConnection {
    SqliteConnection::establish("database.db").unwrap()
}

#[migration]
struct CreateUsersTable;

impl Migration for CreateUsersTable {
    fn up(&self, conn: &SqliteConnection) -> diesel::migration::Result<()> {
        conn.execute(
            "CREATE TABLE users (
                id INTEGER PRIMARY KEY,
                name TEXT NOT NULL,
                age INTEGER NOT NULL
            )",
        )?;
        Ok(())
    }

    fn down(&self, conn: &SqliteConnection) -> diesel::migration::Result<()> {
        conn.execute("DROP TABLE users")?;
        Ok(())
    }
}
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This defines a struct CreateUsersTable that implements diesel::migration::Migration trait. The up method creates the table and the down method reverses the migration.

To apply the migrations, you can call embedded_migrations::run function which reads the migration scripts from the migrations folder and applies them to the database.

main.rs
    embedded_migrations::run(&connection).unwrap();
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Once the table is created, you can use diesel's query builder to perform CRUD operations on the database.

For more information on diesel and its usage in Rust, you can refer to the official documentation at https://diesel.rs/.