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我正在尝试使用 Diesel 的推理功能来处理包含可为空的时间戳列的 SQLite 表。此GitHub 项目的旧版本中提供了完整示例。

该books表定义如下：

create table books (
    id integer not null primary key,
    title varchar null,
    save_date timestamp null 
)

我正在尝试使用以下结构查询它：

pub mod domain {
    use chrono::naive;

    #[derive(Queryable)]
    pub struct Book {
        id : i32,
        title : Option<String>,
        save_date : Option<naive::NaiveDateTime>, 
    }
}

但是，当我尝试实际执行查询时，如下所示：

fn main() {
    use self::schema::books::dsl::*;
    let database_url = env::var("DATABASE_URL").unwrap();
    let conn = sqlite::SqliteConnection::establish(&database_url).unwrap();
    let res = books.load::<domain::Book>(&conn);
}

我收到以下错误消息：

error[E0277]: the trait bound `std::option::Option<chrono::NaiveDateTime>: diesel::types::FromSqlRow<diesel::types::Nullable<diesel::types::Timestamp>, _>` is not satisfied
  --> src/main.rs:32:21
   |
32 |     let res = books.load::<domain::Book>(&conn);
   |                     ^^^^ the trait `diesel::types::FromSqlRow<diesel::types::Nullable<diesel::types::Timestamp>, _>` is not implemented for `std::option::Option<chrono::NaiveDateTime>`
   |
   = help: the following implementations were found:
             <std::option::Option<chrono::naive::date::NaiveDate> as diesel::types::FromSqlRow<diesel::types::Nullable<diesel::types::Date>, DB>>
             <std::option::Option<chrono::naive::time::NaiveTime> as diesel::types::FromSqlRow<diesel::types::Nullable<diesel::types::Time>, DB>>
             <std::option::Option<chrono::naive::datetime::NaiveDateTime> as diesel::types::FromSqlRow<diesel::types::Nullable<diesel::types::Timestamp>, DB>>
             <std::option::Option<bool> as diesel::types::FromSqlRow<diesel::types::Nullable<diesel::types::Bool>, DB>>
           and 26 others
   = note: required because of the requirements on the impl of `diesel::types::FromSqlRow<(diesel::types::Integer, diesel::types::Nullable<diesel::types::Text>, diesel::types::Nullable<diesel::types::Timestamp>), _>` for `(i32, std::option::Option<std::string::String>, std::option::Option<chrono::NaiveDateTime>)`
   = note: required because of the requirements on the impl of `diesel::Queryable<(diesel::types::Integer, diesel::types::Nullable<diesel::types::Text>, diesel::types::Nullable<diesel::types::Timestamp>), _>` for `domain::Book`

我不明白为什么没有执行 forchrono::naive::datetime::NaiveDateTime 以及我应该做些什么来实现它。

我正在使用稳定的工具链，目前是 1.18.0，这些是我的依赖项：

[dependencies]
chrono = "0.4.0"
diesel = { version = "0.13.0", features = [ "chrono", "sqlite" ] }
diesel_codegen = { version = "0.13.0", features = [ "sqlite" ] }
dotenv = "0.9.0"
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