the trait `diesel::Expression` is not implemented for `bigdecimal::BigDecimal`

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广开言路 2021-01-12 15:22

I am trying to create a struct that I can use in diesel for insertion. Specifically I am making the struct Insertable. On compile I get this error.

I have a struct

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半阙折子戏 (楼主)

2021-01-12 15:50

Diesel uses Cargo features to opt-in to enhanced functionality.

I haven't found a clear documentation page for these, but they are listed in its Cargo.toml:

[features]
default = ["with-deprecated", "32-column-tables"]
extras = ["chrono", "serde_json", "uuid", "deprecated-time", "network-address", "numeric", "r2d2"]
unstable = ["diesel_derives/nightly"]
large-tables = ["32-column-tables"]
huge-tables = ["64-column-tables"]
x32-column-tables = ["32-column-tables"]
32-column-tables = []
x64-column-tables = ["64-column-tables"]
64-column-tables = ["32-column-tables"]
x128-column-tables = ["128-column-tables"]
128-column-tables = ["64-column-tables"]
postgres = ["pq-sys", "bitflags", "diesel_derives/postgres"]
sqlite = ["libsqlite3-sys", "diesel_derives/sqlite"]
mysql = ["mysqlclient-sys", "url", "diesel_derives/mysql"]
with-deprecated = []
deprecated-time = ["time"]
network-address = ["ipnetwork", "libc"]
numeric = ["num-bigint", "bigdecimal", "num-traits", "num-integer"]

You need to enable the numeric feature and ensure you use a version of bigdecimal that is compatible with Diesel:

[dependencies]
diesel = { version = "1.4.2", features = ["numeric"] }
bigdecimal = "0.0.14"

And the code compiles:

#[macro_use]
extern crate diesel;

use crate::schema::threads;
use bigdecimal::BigDecimal;

mod schema {
    table! {
        threads (id) {
            id -> Int4,
            bounty -> Numeric,
        }
    }
}

#[derive(Debug, Insertable)]
#[table_name = "threads"]
pub struct InsertableThread {
    pub bounty: BigDecimal,
}