I am new to rust and diesel orm. I am trying to execute below things on my query:
but I am getting error.
I am using postgres database.
I have added the exact error above the queries in comment.
Here are my code:
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);
}
Am I missing something ?
Can anybody correct me ?
Thanks!
First of all: Your code is missing a crucial information to actual reproduce the problems described there. Without knowing your underlying database schema it's only possible to guess how that looked like. For my answer I will assume the following schema:
table! {
employee(employee_id) {
employee_id -> Integer,
name -> Nullable<Text>,
age -> Nullable<Integer>,
address -> Nullable<Text>,
email -> Nullable<Text>,
dept_id -> Integer,
salary -> Nullable<Numeric>,
created_on -> Nullable<Timestamp>,
created_by -> Nullable<Text>,
modified_on -> Nullable<Timestamp>,
modified_by -> Nullable<Text>,
is_active -> Nullable<Bool>,
}
}
Now as general rule: Diesel uses this definition as source of truth and only supports certain type mappings. If you encounter an compile error that likely means one of the following things are wrong:
To answer your specific error messages:
//----------------------------------------------
//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);
Rustc needs to know the type of total_employees here as get_result returns a generic type and println consumes a generic type on the other hand. Rustc needs to know exactly which type should be used there. Now the diesel documentation is a bit sparse here on what's the correct return type, but the error message in Daniel Porteous indicates that this query returns a BigInt, which is compatible to a i64 as documented here. That means this query would work:
let total_employees: i64 = employee.count().get_result(&connection).expect("Error");
You next three queries fail to compile esentially with the same error message:
//-----------------------------------------------
//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);
Now this error messages indicate that you try to map a field returned by a query to an incompatible type on rust side. In this case mapping a Text field that is not NOT NULL to a String is not supported because how would diesel represent a NULL value in this case. The documentation states that you need to wrap nullable types in a Option on rust side. That means if you change the return type to Option<String> in all cases everything will compile successfully.