they_are_like_tables.md

They Are Like Tables

The internal data structure of Bevy is like a table. One of the power of Bevy is to let us manipulate the table freely.

For example, let's say we have three players in our app. The table looks like this:

Name	HP
Soldier 1	100
Soldier 2	250
Soldier 3	150

Each row in the table is called an entity, and each column is called a component.

A component is basically a struct in Rust that derives the Component macro. In our table, we have two components: Name and HP.

use bevy::ecs::component::Component;

// ...

#[derive(Component)]
struct Name(String);

#[derive(Component)]
struct Hp(u32);

We can use the spawn method of Commands to add an entity to the App. (Commands were introduced in the previous tutorial for Removing Resources.)

use bevy::{
    app::{App, Startup},
    ecs::{component::Component, system::Commands},
};

fn main() {
    App::new().add_systems(Startup, add_players).run();
}

// ...

fn add_players(mut commands: Commands) {
    commands.spawn((Name("Soldier 1".into()), Hp(100)));
    commands.spawn((Name("Soldier 2".into()), Hp(250)));
    commands.spawn((Name("Soldier 3".into()), Hp(150)));
}

We put some specified components in a pair of parentheses and pass the parentheses to the spawn method. Each spawn creates an entity and add it to the App.

➡️ Next: Searching For Entities By Components

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