在为Diesel结构实现get和delete特性时，溢出评估需求`_:std::marker::Size`

Question

我正在尝试制作一些方便的方法，这样我就可以在Banana的实例上调用banana.get(&conn, &pk)或banana.delete(&conn)，但我无法获得正确的特征边界，并且似乎一直得到递归错误：

货物.toml

[package]
name = "m"
version = "0.1.0"
edition = "2018"
[dependencies]
diesel = { version = "1.4.5", features = ["postgres"] }

src/lib.rs

use diesel::PgConnection;
use diesel::{
associations::{HasTable, Identifiable},
delete,
query_dsl::QueryDsl,
result::QueryResult,
};
pub trait DbModel: HasTable + Identifiable + QueryDsl {
fn get(
conn: &PgConnection,
pk: &<Self as Identifiable>::Id,
) -> QueryResult<Self> {
Self::table().find(pk).first(conn)
}
fn delete(&self, conn: &PgConnection) -> QueryResult<usize> {
delete(self).execute(conn)
}
}

生成错误：

error[E0275]: overflow evaluating the requirement `_: std::marker::Sized`
--> src/lib.rs:14:23
|
14 |         Self::table().find(pk).first(conn)
|                       ^^^^
|
= help: consider adding a `#![recursion_limit="256"]` attribute to your crate (`m`)
= note: required because of the requirements on the impl of `diesel::query_dsl::filter_dsl::FilterDsl<_>` for `<<Self as diesel::associations::HasTable>::Table as diesel::query_builder::AsQuery>::Query`

get被注释掉时delete的错误：

error[E0275]: overflow evaluating the requirement `_: std::marker::Sized`
--> src/lib.rs:18:9
|
18  |         delete(self).execute(conn)
|         ^^^^^^
| 
::: /home/danj/.cargo/registry/src/github.com-1ecc6299db9ec823/diesel-1.4.5/src/query_builder/functions.rs:135:18
|
135 | pub fn delete<T: IntoUpdateTarget>(source: T) -> DeleteStatement<T::Table, T::WhereClause> {
|                  ---------------- required by this bound in `diesel::query_builder::functions::delete`
|
= help: consider adding a `#![recursion_limit="256"]` attribute to your crate (`m`)
= note: required because of the requirements on the impl of `diesel::query_dsl::filter_dsl::FilterDsl<_>` for `<<Self as diesel::associations::HasTable>::Table as diesel::query_builder::AsQuery>::Query`
= note: required because of the requirements on the impl of `diesel::query_builder::update_statement::target::IntoUpdateTarget` for `&Self`

使用cargo 1.46.0-nightly (c26576f9a 2020-06-23)编译

Answer 1

当我尝试使用枚举时，就发生了这种情况。

我在枚举代码中使用了这样的东西：

#[derive(
Debug, Clone, Serialize, Deserialize, GraphQLEnum, DbEnum
)]
#[ExistingTypePath = "crate::models::schema::sql_types::UnitStatus"]
pub enum UnitStatus {
NotStarted,
InProgress,
Completed,
}

用CCD_ 7板条箱导出CCD_。我的问题是，我使用AsExpression和DbEnum，所以它无法解决(我认为(使用哪个

删除AsExpression并仅将DbEnum与ExistingTypePath一起使用就解决了这个问题。