Can not use .eq(Decimal_field + xxx)

[kakalos12]

Hi,
Really love diesel, but I got some trouble with the diesel Decimal. Please help.

Setup

Versions

• Rust: latest
• Diesel: 2.1.4
• **Database: mysql **
• **Operating System : Macos **

Feature Flags

• diesel: numeric, mysql

Problem Description

use std::borrow::Cow;

use bigdecimal::BigDecimal;
use diesel::prelude::*;
diesel::table! {
    customer_wallets (id) {
        id -> Unsigned<Integer>,
        #[max_length = 36]
        customer_uuid -> Char,
        balance -> Decimal,
        credits -> Decimal,
    }
}

#[derive(Queryable, Selectable)]
#[diesel(table_name = customer_wallets)]
#[diesel(check_for_backend(diesel::mysql::Mysql))]
pub struct CustomerWallet<'a> {
    pub id: u32,
    pub customer_uuid: Cow<'a, str>,
    pub balance: BigDecimal,
    pub credits: BigDecimal,
}
fn main() {
    let a = BigDecimal::from_u32(3).unwrap();
    diesel::update(customer_wallets::table)
        .set(customer_wallets::balance.eq(customer_wallets::balance + a));
    println!("Hello, world!");
}

What are you trying to accomplish?

What is the expected output?

What is the actual output?

Are you seeing any additional errors?

   Compiling app v0.1.0 (/Users/dongnguyen/Projects/learning/app)
error[E0369]: cannot add `BigDecimal` to `columns::balance`
  --> src/main.rs:27:69
   |
27 |         .set(customer_wallets::balance.eq(customer_wallets::balance + a));
   |                                           ------------------------- ^ - BigDecimal
   |                                           |
   |                                           columns::balance
   |
note: an implementation of `std::ops::Add<BigDecimal>` might be missing for `columns::balance`
  --> src/main.rs:10:9
   |
10 |         balance -> Decimal,
   |         ^^^^^^^ must implement `std::ops::Add<BigDecimal>`
note: the trait `std::ops::Add` must be implemented
  --> /Users/dongnguyen/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/ops/arith.rs:76:1
   |
76 | pub trait Add<Rhs = Self> {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0369`.
error: could not compile `app` (bin "app" test) due to 1 previous error

Steps to reproduce

Checklist

• I have already looked over the issue tracker and the discussion forum for similar possible closed issues.

• This issue can be reproduced on Rust's stable channel. (Your issue will be
  closed if this is not the case)
• This issue can be reproduced without requiring a third party crate

[weiznich]

Thanks for opening this bug report.

Seems like it's just missing the BigDecimal type in this list of allowed types:

diesel/diesel_derives/src/table.rs

Line 577 in 12429cb

const NUMERIC_TYPES: &[&str] = &[

Mind submitting a PR that adds it there + adds a test somewhere in diesel_test

[kakalos12]

ok @weiznich , Let me try it.

[kakalos12]

Hi @weiznich , Sorry, I'm new to rust, Can you guide me how to setup the working env for the diesel. When I clone the repository to my local machine and try to run cargo t, it has some errors

error[E0432]: unresolved import `diesel`
  --> diesel/src/expression/functions/date_and_time.rs:30:1
   |
30 | / define_sql_function! {
31 | |     /// Represents the SQL `DATE` function. The argument should be a Timestamp
32 | |     /// expression, and the return value will be an expression of type Date.
33 | |     ///
...  |
50 | |     fn date(expr: Timestamp) -> Date;
51 | | }
   | |_^ could not find `sqlite` in the crate root
   |
   = note: this error originates in the macro `define_sql_function` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0432]: unresolved import `diesel`
  --> diesel/src/sql_types/mod.rs:40:48
   |
40 | #[derive(Debug, Clone, Copy, Default, QueryId, SqlType)]
   |                                                ^^^^^^^ could not find `pg` in the crate root
   |
   = note: this error originates in the derive macro `SqlType` (in Nightly builds, run with -Z macro-backtrace for more info)

Thanks so much.

[weiznich]

It depends a bit on where exactly you've called cargo test, but in general you always need to set some feature flags to enable one or the other backend. The contribution documentation has some more details and there is the bin/test script which executes most of the tests in the repo.

For the diesel crate itself you usually want something like DATABASE_URL=… cargo test --features "{backend_to_test} extras" where {backend_to_test} is one of postgres, mysql or sqlite.