我是新手，对于rust和diesel orm都不太熟悉。我正在尝试在我的查询中执行以下操作：
- 计数
- 选择
- 排序
- 限制
但是我遇到了错误。
我正在使用postgres数据库。
我已经在查询上注释了确切的错误。
这是我的代码：
schema.rs
table! {
employee (employee_id) {
employee_id -> Int4,
name -> Nullable<Text>,
age -> Nullable<Int4>,
address -> Nullable<Text>,
email -> Nullable<Text>,
dept_id -> Int4,
salary -> Nullable<Numeric>,
created_on -> Nullable<Timestamp>,
created_by -> Nullable<Text>,
modified_on -> Nullable<Timestamp>,
modified_by -> Nullable<Text>,
is_active -> Nullable<Bool>,
}
}
models.rs
#![allow(unused)]
#![allow(clippy::all)]
use super::schema::employee;
use bigdecimal::BigDecimal;
use chrono::NaiveDateTime;
#[derive(Queryable, Debug, Identifiable)]
#[table_name = "employee"]
#[primary_key(employee_id)]
pub struct Employee {
pub employee_id: i32,
pub name: Option<String>,
pub age: Option<i32>,
pub address: Option<String>,
pub email: Option<String>,
pub dept_id: i32,
pub salary: Option<BigDecimal>,
pub created_on: Option<NaiveDateTime>,
pub created_by: Option<String>,
pub modified_on: Option<NaiveDateTime>,
pub modified_by: Option<String>,
pub is_active: Option<bool>,
}
cargo.toml
[dependencies]
diesel = { version = "1.4.5", features = ["postgres","chrono","numeric"] }
dotenv = "0.15.0"
chrono = { version = "0.4.19" , features = ["serde"] }
bigdecimal = { version = "0.1.0" }
main.rs
#[macro_use]
extern crate diesel;
extern crate bigdecimal;
extern crate chrono;
extern crate dotenv;
use crate::models::Employee;
use crate::models::Players;
use crate::schema::employee::dsl::*;
use diesel::{pg::PgConnection, prelude::*};
use dotenv::dotenv;
use std::env;
mod models;
mod schema;
fn main() {
dotenv().ok();
let data_url: String = env::var("DATABASE_URL").expect("DATABASE_URL must be set");
let connection: PgConnection =
PgConnection::establish(&data_url).expect(&format!("Error connect to {}", data_url));
//get all employees name
//This is working fine
let _employee: Vec<Employee> = employee
.load::<Employee>(&connection)
.expect("Error loading department");
for emp in _employee {
println!("{}", emp.name.unwrap_or_default());
}
//----------------------------------------------
//get employees count
/*
Error: error[E0282]: type annotations needed
^^^^^^^^^^^^^^^ consider giving `total_employees` a type
*/
let total_employees = employee.count().get_result(&connection).expect("Error");
println!("{}", total_employees);
//-----------------------------------------------
//get all names
/*
Error: error[E0277]: the trait bound `*const str: FromSql<diesel::sql_types::Nullable<diesel::sql_types::Text>, _>` is not satisfied
^^^^ the trait `FromSql<diesel::sql_types::Nullable<diesel::sql_types::Text>, _>` is not implemented for `*const str`
*/
let all_names = employee.select(name).load::<String>(&connection)?;
println!("{}", all_names);
//----------------------------------------------
//order name
/*
Error: error[E0277]: the trait bound `*const str: FromSql<diesel::sql_types::Nullable<diesel::sql_types::Text>, _>` is not satisfied
^^^^ the trait `FromSql<diesel::sql_types::Nullable<diesel::sql_types::Text>, _>` is not implemented for `*const str`
*/
let ordered_names = employee
.select(name)
.order(name.desc())
.load::<String>(&connection)?;
println!("{}", ordered_names);
//------------------------------------------------
/*
Error: error[E0277]: the trait bound `*const str: FromSql<diesel::sql_types::Nullable<diesel::sql_types::Text>, _>` is not satisfied
^^^^ the trait `FromSql<diesel::sql_types::Nullable<diesel::sql_types::Text>, _>` is not implemented for `*const str`
*/
let limited = employee
.select(name)
.order(employee_id)
.limit(1)
.load::<String>(&connection)?;
println!("{}", limited);
}
我有什么遗漏吗？
有人能纠正我吗？
谢谢！
.load上设置了它们，因此只需将.load :: <String>（&connection）？更改为.load :: <Option<String>>（&connection）？。 - weiznich