Rust cannot represent Postgres numeric type as BigDecimal type

June 15, 2023

I am writing simple rust web application using actix-web and sqlx.
I have struct Book with price field which should be mapped to postgres NUMERIC type. First I got error from sqlx that it was expecting bigdecimal type and suggested to enable this feature from cargo configuration, so I did. Then I imported BigDecimal from sqlx types and tried to use this type in my struct.

use sqlx::types::BigDecimal;

But I get this error:

12 |     pub price: BigDecimal,
   |     ^^^ the trait `configuration::_::_serde::Deserialize<'_>` is not implemented for `BigDecimal`

I tried to find solution to this problem, one possible solution was to use bigdecimal crate directly with serde enabled. So I tried to use bigdecimal type instead of sqlx one:

use bigdecimal::BigDecimal;

But now I got different error:

the trait `sqlx::Type<Postgres>` is not implemented for `bigdecimal::BigDecimal`

Here is code I am using:

Book struct:

use chrono::{DateTime, Utc,};
use chrono::serde::ts_seconds;
//use sqlx::types::BigDecimal;
use bigdecimal::BigDecimal;


#[derive(serde::Deserialize)]
pub struct Book {
    pub author: String,
    pub title: String,
    pub pages: i32,
    pub price: BigDecimal,
    #[serde(with = "ts_seconds")]
    pub published_at: DateTime<Utc>
}

function that tries to insert Book data into database:

pub async fn insert_book(data: &Book, pool: &PgPool) -> Result<(), sqlx::Error> {
    sqlx::query!(
        r#"
            INSERT INTO books
            (id, author, title, pages, price, published_at)
            VALUES ($1, $2, $3, $4, $5, $6)
        "#,
        Uuid::new_v4(),
        data.author,
        data.title,
        data.pages,
        data.price,
        data.published_at
    )
        .execute(pool)
        .await
        .map_err(|e| {
            e
        })?;

    Ok(())
}

Simple POST endpoint:

#[post("/book")]
pub async fn add_new_book(data: web::Form<Book>, pool: web::Data<PgPool>) -> impl Responder {
    match insert_book(&data, &pool).await {
        Ok(_) => HttpResponse::Ok(),
        Err(e) => HttpResponse::InternalServerError()
    }
}

Cargo.toml

[dependencies]
secrecy = { version = "0.8", features = ["serde"] }
actix-web = "4.3.1"
serde = { version = "1", features = ["derive"]}
tokio = { version = "1", features = ["macros", "rt-multi-thread"] }
uuid = { version = "1.3.4", features = ["v4"] }
config = "0.11"
chrono = { version = "0.4.26", features = ["serde"] }
bigdecimal = { version = "0.2.0", features = ["serde"] }


[dependencies.sqlx]
version = "0.6.3"
default-features = false
features = [
    "runtime-actix-rustls",
    "macros",
    "postgres",
    "uuid",
    "chrono",
    "migrate",
    "bigdecimal"
]

Not sure how to fix this problem, any help will be appreciated.