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Diesel vs SQLx in Raw and ORM Modes

Published at

1/12/2025

Diesel vs SQLx in Raw and ORM Modes

Rust developers often face a choice between Diesel and SQLx for database interactions. Diesel is a full-featured ORM (Object-Relational Mapper), while SQLx is a compile-time checked, async-friendly query library. Here's a quick comparison of their performance and usage in raw and ORM modes.

Performance Comparison

Mode	Diesel	SQLx
Pure ORM Mode	Slightly faster due to optimizations.	Slower compared to Diesel in ORM-like use.
Query Builder	~50% slower than SQLx in raw queries.	Faster, especially for raw SQL execution.

Code Examples

Diesel in ORM Mode

Using Diesel's schema and ORM for managing database queries.

use diesel::prelude::*;
use diesel::pg::PgConnection;
use crate::schema::users;

#[derive(Queryable, Insertable)]
#[table_name = "users"]
struct User {
    id: i32,
    name: String,
}

fn fetch_users(conn: &PgConnection) -> Vec<User> {
    use crate::schema::users::dsl::*;
    users.load::<User>(conn).expect("Error loading users")
}

Diesel in Raw Query Mode

Bypassing Diesel's query builder for raw SQL queries.

use diesel::sql_query;
use diesel::pg::PgConnection;
use diesel::RunQueryDsl;

fn fetch_users_raw(conn: &PgConnection) {
    let query = "SELECT id, name FROM users;";
    let results = sql_query(query).load::<(i32, String)>(conn).expect("Query failed");
    println!("{:?}", results);
}

SQLx in Raw Mode

Direct SQL execution using SQLx's async API.

use sqlx::{PgPool, Row};

async fn fetch_users(pool: &PgPool) {
    let rows = sqlx::query("SELECT id, name FROM users;")
        .fetch_all(pool)
        .await
        .expect("Query failed");

    for row in rows {
        let id: i32 = row.get("id");
        let name: String = row.get("name");
        println!("{} - {}", id, name);
    }
}

SQLx in ORM-Like Mode

Using SQLx structs to map query results.

use sqlx::FromRow;

#[derive(FromRow)]
struct User {
    id: i32,
    name: String,
}

async fn fetch_users(pool: &PgPool) {
    let users: Vec<User> = sqlx::query_as!(User, "SELECT id, name FROM users;")
        .fetch_all(pool)
        .await
        .expect("Query failed");
    println!("{:?}", users);
}

Key Takeaways

Diesel excels in ORM mode for its type safety and compile-time guarantees but slows down with its query builder.
SQLx is faster for raw queries and supports async natively, making it ideal for modern web applications.

For a high-performance, async-friendly environment, SQLx in raw mode is a solid choice. However, if compile-time safety and ease of schema management matter more, Diesel ORM is unbeatable.

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