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<h1 id="many-to-many-relationships"><a class="header" href="#many-to-many-relationships">Many-to-many relationships</a></h1>
<p>Ergol also supports many-to-many relationships. In order to do so, you need to
use the <code>#[many_to_many]</code> attribute:</p>
<pre><pre class="playground"><code class="language-rust edition2018"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span><span class="boring">extern crate ergol;
</span>use ergol::prelude::*;
#[ergol]
pub struct User {
#[id] pub id: i32,
#[unique] pub username: String,
pub password: String,
pub age: i32,
}
#[ergol]
pub struct Project {
#[id] pub id: i32,
pub name: String,
#[many_to_many(visible_projects)] pub authorized_users: User,
}
<span class="boring">}</span></code></pre></pre>
<p>The same way, you will have plenty of functions that you will be able to use to
manage your objects:</p>
<pre><pre class="playground"><code class="language-rust edition2018"><span class="boring">extern crate tokio;
</span><span class="boring">extern crate ergol;
</span><span class="boring">use ergol::prelude::*;
</span><span class="boring">#[ergol]
</span><span class="boring">pub struct User {
</span><span class="boring"> #[id] pub id: i32,
</span><span class="boring"> #[unique] pub username: String,
</span><span class="boring"> pub password: String,
</span><span class="boring"> pub age: i32,
</span><span class="boring">}
</span><span class="boring">#[ergol]
</span><span class="boring">pub struct Project {
</span><span class="boring"> #[id] pub id: i32,
</span><span class="boring"> pub name: String,
</span><span class="boring"> #[many_to_many(visible_projects)] pub authorized_users: User,
</span><span class="boring">}
</span><span class="boring">#[tokio::main]
</span><span class="boring">async fn main() -> Result<(), ergol::tokio_postgres::Error> {
</span><span class="boring"> let (db, connection) = ergol::connect(
</span><span class="boring"> "host=localhost user=ergol password=ergol dbname=ergol",
</span><span class="boring"> ergol::tokio_postgres::NoTls,
</span><span class="boring"> )
</span><span class="boring"> .await?;
</span><span class="boring"> tokio::spawn(async move {
</span><span class="boring"> if let Err(e) = connection.await {
</span><span class="boring"> eprintln!("connection error: {}", e);
</span><span class="boring"> }
</span><span class="boring"> });
</span><span class="boring">Project::drop_table().execute(&db).await.ok();
</span><span class="boring">User::drop_table().execute(&db).await.ok();
</span><span class="boring">User::create_table().execute(&db).await?;
</span><span class="boring">Project::create_table().execute(&db).await?;
</span><span class="boring">User::create("thomas", "pa$$w0rd", 28).save(&db).await?;
</span><span class="boring">User::create("nicolas", "pa$$w0rd", 28).save(&db).await?;
</span>// Find some users in the database
let thomas = User::get_by_username("thomas", &db).await?.unwrap();
let nicolas = User::get_by_username("nicolas", &db).await?.unwrap();
// Create a project
let first_project = Project::create("My first project").save(&db).await?;
// Thomas can access this project
first_project.add_authorized_user(&thomas, &db).await?;
// The other way round
nicolas.add_visible_project(&first_project, &db).await?;
// The second project can only be used by thomas
let second_project = Project::create("My second project").save(&db).await?;
thomas.add_visible_project(&second_project, &db).await?;
// The third project can only be used by nicolas.
let third_project = Project::create("My third project").save(&db).await?;
third_project.add_authorized_user(&nicolas, &db).await?;
// You can easily retrieve all projects available for a certain user
let projects: Vec<Project> = thomas.visible_projects(&db).await?;
// And you can easily retrieve all users that have access to a certain project
let users: Vec<User> = first_project.authorized_users(&db).await?;
// You can easily remove a user from a project
let _: bool = first_project.remove_authorized_user(&thomas, &db).await?;
// Or vice-versa
let _: bool = nicolas.remove_visible_project(&first_project, &db).await?;
// The remove functions return true if they successfully removed something.
<span class="boring">Ok(())
</span><span class="boring">}</span></code></pre></pre>
<h3 id="extra-information-in-a-many-to-many-relationship"><a class="header" href="#extra-information-in-a-many-to-many-relationship">Extra information in a many-to-many relationship</a></h3>
<p>It is possible to insert some extra information in a many to many relationship. The following
exemple gives roles for the users for projects.</p>
<pre><pre class="playground"><code class="language-rust edition2018"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span><span class="boring">extern crate ergol;
</span>use ergol::prelude::*;
#[ergol]
pub struct User {
#[id] pub id: i32,
#[unique] pub username: String,
pub password: String,
pub age: i32,
}
#[derive(PgEnum, Debug)]
pub enum Role {
Admin,
Write,
Read,
}
#[ergol]
pub struct Project {
#[id] pub id: i32,
pub name: String,
#[many_to_many(projects, Role)] pub users: User,
}
<span class="boring">}</span></code></pre></pre>
<p>With these structures, the signature of generated methods change to take a role as argument,
and to return tuples of (User, Role) or (Project, Role).</p>
<pre><pre class="playground"><code class="language-rust edition2018"><span class="boring">extern crate tokio;
</span><span class="boring">extern crate ergol;
</span><span class="boring">use ergol::prelude::*;
</span><span class="boring">#[ergol]
</span><span class="boring">pub struct User {
</span><span class="boring"> #[id] pub id: i32,
</span><span class="boring"> #[unique] pub username: String,
</span><span class="boring"> pub password: String,
</span><span class="boring"> pub age: i32,
</span><span class="boring">}
</span><span class="boring">#[derive(PgEnum, Debug)]
</span><span class="boring">pub enum Role {
</span><span class="boring"> Admin,
</span><span class="boring"> Write,
</span><span class="boring"> Read,
</span><span class="boring">}
</span><span class="boring">#[ergol]
</span><span class="boring">pub struct Project {
</span><span class="boring"> #[id] pub id: i32,
</span><span class="boring"> pub name: String,
</span><span class="boring"> #[many_to_many(projects, Role)] pub users: User,
</span><span class="boring">}
</span><span class="boring">#[tokio::main]
</span><span class="boring">async fn main() -> Result<(), ergol::tokio_postgres::Error> {
</span><span class="boring"> let (db, connection) = ergol::connect(
</span><span class="boring"> "host=localhost user=ergol password=ergol dbname=ergol2",
</span><span class="boring"> ergol::tokio_postgres::NoTls,
</span><span class="boring"> )
</span><span class="boring"> .await?;
</span><span class="boring"> tokio::spawn(async move {
</span><span class="boring"> if let Err(e) = connection.await {
</span><span class="boring"> eprintln!("connection error: {}", e);
</span><span class="boring"> }
</span><span class="boring"> });
</span><span class="boring">Project::drop_table().execute(&db).await.ok();
</span><span class="boring">User::drop_table().execute(&db).await.ok();
</span><span class="boring">Role::drop_type().execute(&db).await.ok();
</span><span class="boring">Role::create_type().execute(&db).await?;
</span><span class="boring">User::create_table().execute(&db).await?;
</span><span class="boring">Project::create_table().execute(&db).await?;
</span><span class="boring">User::create("thomas", "pa$$w0rd", 28).save(&db).await?;
</span><span class="boring">User::create("nicolas", "pa$$w0rd", 28).save(&db).await?;
</span>let thomas = User::get_by_username("thomas", &db).await?.unwrap();
let nicolas = User::get_by_username("nicolas", &db).await?.unwrap();
let project = Project::create("My first project").save(&db).await?;
project.add_user(&thomas, Role::Admin, &db).await?;
nicolas.add_project(&project, Role::Read, &db).await?;
for (user, role) in project.users(&db).await? {
println!("{} has {:?} rights on project {:?}", user.username, role, project.name);
}
let project = Project::create("My second project").save(&db).await?;
project.add_user(&thomas, Role::Admin, &db).await?;
let project = Project::create("My third project").save(&db).await?;
project.add_user(&nicolas, Role::Admin, &db).await?;
project.add_user(&thomas, Role::Read, &db).await?;
for (project, role) in thomas.projects(&db).await? {
println!("{} has {:?} rights on project {:?}", thomas.username, role, project.name);
}
<span class="boring">Ok(())
</span><span class="boring">}</span></code></pre></pre>
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