我正在学习 Rust,我正在尝试使用 Diesel 从数据库中加载关联。我定义了以下模型:
#[derive(Identifiable, Queryable, PartialEq, Debug)]
#[table_name = "contacts"]
pub struct Contact {
pub id: i32,
pub firstname: String,
pub lastname: String,
}
#[derive(Identifiable, Queryable, Associations, PartialEq, Debug)]
#[belongs_to(Contact)]
#[table_name = "emails"]
pub struct Email {
pub id: i32,
pub contact_id: i32,
pub label: String,
pub email: String,
}
现在我正在尝试使用以下代码获取所有联系人及其相关电子邮件:
let result = match contacts::table
.inner_join(emails::table)
.load::<models::Contact, Vec<models::Email>>(&self.conn)
{
Ok(rows) => rows,
Err(_) => return Err(io::Error::new(io::ErrorKind::Other, "Database error")),
};
但这不起作用。我错过了什么?该错误与不满足的特征界限有关。
完整的错误信息:
error[E0107]: wrong number of type arguments: expected 1, found 2
--> src/db.rs:44:38
|
44 | .load::<models::Contact, Vec<models::Email>>(&self.conn) {
| ^^^^^^^^^^^^^^^^^^ unexpected type argument
error[E0277]: the trait bound `(i32, std::string::String, std::string::String): diesel::Queryable<((diesel::sql_types::Integer, diesel::sql_types::Text, diesel::sql_types::Text), (diesel::sql_types::Integer, diesel::sql_types::Nullable<diesel::sql_types::Integer>, diesel::sql_types::Text, diesel::sql_types::Text)), _>` is not satisfied
--> src/db.rs:44:14
|
44 | .load::<models::Contact, Vec<models::Email>>(&self.conn) {
| ^^^^ the trait `diesel::Queryable<((diesel::sql_types::Integer, diesel::sql_types::Text, diesel::sql_types::Text), (diesel::sql_types::Integer, diesel::sql_types::Nullable<diesel::sql_types::Integer>, diesel::sql_types::Text, diesel::sql_types::Text)), _>` is not implemented for `(i32, std::string::String, std::string::String)`
|
= help: the following implementations were found:
<(A, B, C) as diesel::Queryable<(SA, SB, SC), __DB>>
<(A, B, C) as diesel::Queryable<diesel::sql_types::Record<(SA, SB, SC)>, diesel::pg::Pg>>
= note: required because of the requirements on the impl of `diesel::Queryable<((diesel::sql_types::Integer, diesel::sql_types::Text, diesel::sql_types::Text), (diesel::sql_types::Integer, diesel::sql_types::Nullable<diesel::sql_types::Integer>, diesel::sql_types::Text, diesel::sql_types::Text)), _>` for `models::Contact`
= note: required because of the requirements on the impl of `diesel::query_dsl::LoadQuery<_, models::Contact>` for `diesel::query_builder::SelectStatement<diesel::query_source::joins::JoinOn<diesel::query_source::joins::Join<schema::contacts::table, schema::emails::table, diesel::query_source::joins::Inner>, diesel::expression::operators::Eq<diesel::expression::nullable::Nullable<schema::emails::columns::contact_id>, diesel::expression::nullable::Nullable<schema::contacts::columns::id>>>>`