Invalid deserialization for MySQL's Decimal type

[marcustut]

I'm having a MySQL table as follows:

model expenses {
  id                     Int      @id @default(autoincrement())
  name                   String   @db.VarChar(255)
  amount                 Decimal  @db.Decimal(15, 2)
  date                   DateTime @db.Date
  comment                String?  @db.VarChar(255)
  expenses_categories_id Int?
}

and I'm querying it like this

    let db = prisma::new_client()
        .await
        .expect("failed to connect to database (prisma)");

    let expenses = db.expenses().find_many(vec![]).exec().await.unwrap();
    println!("{:?}", expenses);

however I'm getting an error

    Finished dev [unoptimized + debuginfo] target(s) in 0.68s
     Running `target/debug/marcustutcore`
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Deserialize(InvalidType(Str("7.95"), "f64"))', core/src/main.rs:96:65
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

it seems to me that the deserialization failed for the amount field which in MySQL Type is a decimal and in rust it should be returned as a f64. Somehow string type got mixed in and the deserialization failed.

[marcustut]

Upon further inspection, I found that the data struct in the generated code is

    pub struct Data {
        #[serde(rename = "id")]
        pub id: i32,
        #[serde(rename = "name")]
        pub name: String,
        #[serde(rename = "amount")]
        pub amount: f64,
        #[serde(rename = "date")]
        pub date: chrono::DateTime<chrono::FixedOffset>,
        #[serde(rename = "comment")]
        pub comment: Option<String>,
        #[serde(rename = "incomes_categories_id")]
        pub incomes_categories_id: Option<i32>,
    }

Notice that the amount field is f64. However, to my knowledge the bigdecimal crate internally deserialize into string. Hence, the error Deserialize(InvalidType(Str("7.95"), "f64")), it is because the underlying value is string but serde expects it to be f64.

I manually change the field from pub amount: f64 to pub amount: String, then the error goes away. It's just that the value is returned as a string. However, to solve this I suggest swapping the bigdecimal crate to rust_decimal, this crate allow deserialization to float with the feature flag serde-with-float.

[Brendonovich]

Native types like Decimal aren't properly supported yet, and won't be for a while - see #83. If you can get away with using Float then that should deserialize to f64 correctly, but for now I don't have much good news for you 😅

[cameronbraid]

Is there a way to configure the schema so that a decimal field can be deserialized into a string without having to hand edit the generated code ?

[Brendonovich]

Not right now, sorry