Macro join 

macro_rules! join {
    ($db:expr, $key:expr, $($table:ident => $field:ident),* $(,)?) => { ... };
}

Joins Data of different Tables in the Database together

use light_magic::{
    atomic::DataStore,
    join,
    serde::{Deserialize, Serialize},
    table::{PrimaryKey, Table},
};

#[derive(Default, Debug, Serialize, Deserialize)]
struct Database {
   user: Table<User>,
   criminal: Table<Criminal>,
}

impl DataStore for Database {}

#[derive(Default, Debug, Clone, Serialize, Deserialize, PartialEq)]
struct User {
    id: usize,
    name: String,
    kind: String,
}

impl PrimaryKey for User {
    type PrimaryKeyType = usize;

    fn primary_key(&self) -> &Self::PrimaryKeyType {
        &self.id
    }
}

#[derive(Default, Debug, Clone, Serialize, Deserialize)]
struct Criminal {
    user_name: String,
    entry: String,
}

impl PrimaryKey for Criminal {
    type PrimaryKeyType = String;

    fn primary_key(&self) -> &Self::PrimaryKeyType {
        &self.user_name
    }
}

let db = Database::open_in_memory();
// Firstly specify the Database which should be used, then the key,
// and lastly the joined items with the field which will be compared with the key
let joined = join!(db.read(), "Nils", user => name, criminal => user_name);