#belongs_to

🏭 Macro

#[belongs_to($target_type, $field_name)]

Implements a belongs-to relationship between the current entity and the target entity. The $target_type is another entity which this entity belongs to. $field_name is the field on this structure which implements the relationship. This field must be of the same type as the $target_type’s ID.

📝 Macro Example:

This is a short example of how to use the #belongs_to macro. Here we have Post which belongs to Author via the author_id field.

use repox::Entity;

#[derive(Debug, Clone, PartialEq, Entity)]
pub struct Author {
    pub id: u32,
    pub name: String,
}

#[derive(Debug, Clone, PartialEq, Entity)]
#[belongs_to(Author, author_id)] // <- Post belongs to Author via author_id
pub struct Post {
    pub id: u64,
    pub author_id: u32,
    pub data: String,
}

// Quick Demo of the relationship in action:
let alice = Author { id: 1, name: "Alice".to_string() };
let darin = Author { id: 2, name: "Darin".to_string() };
let post = Post { id: 100, author_id: 1, data: "Hello World".to_string() };
assert!(post.belongs_to(&alice));
assert!(!post.belongs_to(&darin));
assert_eq!(post.belongs_to_key::<Author>(), 1);

🔬 Macro Details:

Here is the same example, but, without using the macro and implementing it ourselves. This highlights the fact that this macro is just a convenient way to implement the BelongsToForeignKey trait and if you have a more complex relationship, you can implement it yourself without the macro. There is no magic here 🧙‍♂️!

use repox::Entity;

#[derive(Debug, Clone, PartialEq, Entity)]
pub struct Author {
    pub id: u32,
    pub name: String,
}

#[derive(Debug, Clone, PartialEq, Entity)]
pub struct Post {
    pub id: u64,
    pub author_id: u32,
    pub data: String,
}

impl ::repox::BelongsToForeignKey<Author> for Post {
    fn key(&self) -> <Author as ::repox::Identity>::ID {
        self.author_id
    }
}

// Same Demo of the relationship in action:
let alice = Author { id: 1, name: "Alice".to_string() };
let darin = Author { id: 2, name: "Darin".to_string() };
let post = Post { id: 100, author_id: 1, data: "Hello World".to_string() };
assert!(post.belongs_to(&alice));
assert!(!post.belongs_to(&darin));
assert_eq!(post.belongs_to_key::<Author>(), 1);

Note: Still deriving Entity to avoid extra boilerplate above.