UUID usage example

[mann-ed]

I used the diesel_demo app. I added needed dependencies and a uuid column to posts. Just for simplicity i only ran the show_posts.rs. I can't seem to figure out how to use a uuid column. Error i get is

 Running `rustc bin/show_posts.rs --crate-name show_posts --crate-type bin -g --cfg feature=\"diesel_codegen\" --cfg feature=\"diesel\" --cfg feature=\"default\" --cfg feature=\"nightly\" --cfg feature=\"dotenv_macros\" --out-dir /home
/emann/sandbox/rust/diesel_demo/target/debug --emit=dep-info,link -L dependency=/home/emann/sandbox/rust/diesel_demo/target/debug -L dependency=/home/emann/sandbox/rust/diesel_demo/target/debug/deps --extern diesel_codegen=/home/emann/sand
box/rust/diesel_demo/target/debug/deps/libdiesel_codegen-ab384d78b3e11a0e.rlib --extern diesel_codegen=/home/emann/sandbox/rust/diesel_demo/target/debug/deps/libdiesel_codegen-ab384d78b3e11a0e.so --extern dotenv=/home/emann/sandbox/rust/di
esel_demo/target/debug/deps/libdotenv-695bff8444756e3d.rlib --extern uuid=/home/emann/sandbox/rust/diesel_demo/target/debug/deps/libuuid-5b93bff81ff3c817.rlib --extern diesel=/home/emann/sandbox/rust/diesel_demo/target/debug/deps/libdiesel
-314df7bf9433c77b.rlib --extern dotenv_macros=/home/emann/sandbox/rust/diesel_demo/target/debug/deps/libdotenv_macros-b005ef1b47b27d5c.so --extern diesel_demo=/home/emann/sandbox/rust/diesel_demo/target/debug/libdiesel_demo.rlib`
bin/show_posts.rs:15:10: 15:14 error: the trait bound `uuid::Uuid: diesel::types::FromSqlRow<diesel::types::Nullable<diesel::types::Uuid>, _>` is not satisfied [E0277]
bin/show_posts.rs:15         .load::<Post>(&connection)
                              ^~~~
bin/show_posts.rs:15:10: 15:14 help: run `rustc --explain E0277` to see a detailed explanation
bin/show_posts.rs:15:10: 15:14 help: the following implementations were found:
bin/show_posts.rs:15:10: 15:14 help:   <uuid::Uuid as diesel::types::FromSqlRow<diesel::types::Uuid, DB>>
bin/show_posts.rs:15:10: 15:14 note: required because of the requirements on the impl of `diesel::types::FromSqlRow<(diesel::types::Integer, diesel::types::Text, diesel::types::Text, diesel::types::Bool, diesel::types::Nullable<diesel::types::Uuid>), _>` for `(i32, std::string::String, std::string::String, bool, uuid::Uuid)`
bin/show_posts.rs:15:10: 15:14 note: required because of the requirements on the impl of `diesel::Queryable<(diesel::types::Integer, diesel::types::Text, diesel::types::Text, diesel::types::Bool, diesel::types::Nullable<diesel::types::Uuid>), _>` for `diesel_demo::models::Post`
error: aborting due to previous error
error: Could not compile `diesel_demo`.

This is my second day on learning Rust so i don't have a lot of experience. Is this just a newbie error?
models.rs

use uuid::Uuid;

#[derive(Queryable)]
pub struct Post {
    pub id: i32,
    pub title: String,
    pub body: String,
    pub published: bool,
    pub post_id: Uuid,
}

Cargo.toml

[package]
name = "diesel_demo"
version = "0.1.0"
authors = ["Sean Griffin <sean@seantheprogrammer.com>"]
build = "build.rs"

[build-dependencies]
syntex = { version = "0.31.0", optional = true }
diesel_codegen = {git = "https://github.com/diesel-rs/diesel.git" , default-features = false, features = ["nightly", "postgres"] }
dotenv_codegen = { version = "0.8.1",  optional = true }

[dependencies]
diesel = { git = "https://github.com/diesel-rs/diesel.git",  default-features=true, features = ["uuid"] }
diesel_codegen = {git = "https://github.com/diesel-rs/diesel.git" , default-features = false, features = ["nightly", "postgres"] }
dotenv = "0.8.0"
dotenv_macros = { version = "0.8.0", optional = true }
uuid = { version = "^0.2.0" }

[features]
default = ["nightly"]
with-syntex = ["syntex", "diesel_codegen/with-syntex", "dotenv_codegen"]
nightly = ["diesel/unstable", "diesel_codegen/nightly", "dotenv_macros"]

lib.rs

#![cfg_attr(feature = "nightly", feature(custom_derive, custom_attribute, plugin))]
#![cfg_attr(feature = "nightly", plugin(diesel_codegen, dotenv_macros))]

#[macro_use]
extern crate diesel;
extern crate dotenv;
extern crate uuid;

#[cfg(feature = "nightly")]
include!("lib.in.rs");

#[cfg(feature = "with-syntex")]
include!(concat!(env!("OUT_DIR"), "/lib.rs"));

use diesel::prelude::*;
use diesel::pg::PgConnection;
use dotenv::dotenv;
use std::env;

pub fn establish_connection() -> PgConnection {
    dotenv().ok();

    let database_url = env::var("DATABASE_URL")
        .expect("DATABASE_URL must be set");
    PgConnection::establish(&database_url)
        .expect(&format!("Error connecting to {}", database_url))
}

extern crate diesel_demo;
extern crate diesel;

use self::diesel_demo::*;
use self::diesel_demo::models::*;
use self::diesel::prelude::*;

fn main() {
    use diesel_demo::schema::posts::dsl::*;

    let connection = establish_connection();
    let results = posts.filter(published.eq(true))
        .limit(5)
        .load::<Post>(&connection)
        .expect("Error loading posts");

    println!("Displaying {} posts", results.len());
    for post in results {
        println!("{}", post.title);
        println!("----------\n");
        println!("{}", post.body);
    }
}

Sorry if this should not be posted this way. If so i'm sure i will get educated on the correct way.
Thanks

[sgrif]

The problem is that you have a nullable field but you are attempting to load it into a type which does not handle it. Rust does not have a concept of null, so you need to have the type reflect this. You either need to change post_id to have the type Option<Uuid>, or you need to change your schema so that the column is NOT NULL

[Eijebong]

Are you sure you're having the same problem ? Can you paste the error you're seeing too ?

[vityafx]

@Eijebong No, it's okay. I have just realized that the problem is in another table where I had simple

user_id uuid references users(id)

So it was nullable.