#custom_id

🏭 Macro

#[custom_id($id_type, $func_path)]

At the heart of the entity concept is the Identifier trait. Every entity must have an identifier, and the Identifier trait defines what type that is and a method of id(&self) to retrieve it. By default the Entity macro selects a field named id; however, this macro is a convenient shortcut to specify a custom function that can implement the Identifier trait for you. The first argument is the ID type, and the second is a path to a function that takes a reference to the entity and returns the ID.

📝 Macro Example:

In this example, we have a UserRole entity which has a composite key of UserRoleID consisting of user_id and role_id. We use the defined From<&UserRole> implementation to convert a &UserRole into a UserRoleID and specify that as the custom ID function in the macro.

use repox::{Entity, Identity};

#[derive(Debug, Clone, Copy, PartialEq, Eq, Ord, Hash, PartialOrd)]
pub struct UserRoleID {
    pub user_id: u32,
    pub role_id: u32,
}

#[derive(Debug, Clone, PartialEq, Entity)]
#[custom_id(UserRoleID, UserRoleID::from)]
pub struct UserRole {
    pub user_id: u32,
    pub role_id: u32,
    pub created_at: u64,
}

impl From<&UserRole> for UserRoleID {
    fn from(user_role: &UserRole) -> Self {
        Self { user_id: user_role.user_id, role_id: user_role.role_id }
    }
}

// Quick Demo of the custom ID in action:
let user_role = UserRole { user_id: 1, role_id: 2, created_at: 123456789 };
assert_eq!(user_role.id(), UserRoleID { user_id: 1, role_id: 2 });

🔬 Macro Details:

Here is the same example, but, without using the macro and implementing it ourselves.

use repox::{Entity, Identity};

#[derive(Debug, Clone, Copy, PartialEq, Eq, Ord, Hash, PartialOrd)]
pub struct UserRoleID {
    pub user_id: u32,
    pub role_id: u32,
}

#[derive(Debug, Clone, PartialEq, Entity)]
pub struct UserRole {
    pub user_id: u32,
    pub role_id: u32,
    pub created_at: u64,
}

impl From<&UserRole> for UserRoleID {
    fn from(user_role: &UserRole) -> Self {
        Self { user_id: user_role.user_id, role_id: user_role.role_id }
    }
}

// this is what the `custom_id` macro generates for us
impl Identity for UserRole {
    type ID = UserRoleID;
    fn id(&self) -> Self::ID { UserRoleID::from(self) }
}

// Quick Demo of the custom ID in action:
let user_role = UserRole { user_id: 1, role_id: 2, created_at: 123456789 };
assert_eq!(user_role.id(), UserRoleID { user_id: 1, role_id: 2 });