Agent Skills: Dojo Model Generation

Dojo Model Generation

Create Dojo models that define your game's state using Entity Component System (ECS) patterns.

When to Use This Skill

• "Add a Position model"
• "Create a Player entity with health and level"
• "Generate an Inventory model"
• "Define a model for [game concept]"

What This Skill Does

Generates Cairo model structs with:

• #[dojo::model] attribute
• Required trait derivations (Drop, Serde)
• Key field configuration (#[key])
• Field types appropriate to your data

Quick Start

Interactive mode:

"Add a model for player positions"

I'll ask about:

• Model name
• Key fields (what makes it unique)
• Data fields and their types

Direct mode:

"Create a Position model with player as key and x, y coordinates"

Essential Imports for Models

In your model file (e.g., models.cairo):

use starknet::ContractAddress;

// For nested structs that aren't models
use dojo::meta::Introspect;

In systems that use models:

// Import your models
use my_project::models::{Player, Position, Inventory};

// Import Dojo storage traits
use dojo::model::{ModelStorage, ModelValueStorage};

Reading/Writing models in a system:

// Get world storage
let mut world = self.world_default();

// Read - provide all #[key] values
let player: Player = world.read_model(player_address);

// Write - model must contain all keys and data
world.write_model(@player);

Model Structure

Models are Cairo structs annotated with #[dojo::model]. They act as a key-value store where #[key] fields define the lookup key.

#[derive(Drop, Serde)]
#[dojo::model]
struct Moves {
    #[key]
    player: ContractAddress,
    remaining: u8,
}

Required traits:

• Drop - Cairo ownership system
• Serde - Serialization for on-chain storage

Optional traits:

• Copy - Add when you need to copy values (for primitive types)

Model Patterns

Player-Owned Model

Models keyed by player address:

#[derive(Drop, Serde)]
#[dojo::model]
struct Position {
    #[key]
    player: ContractAddress,
    vec: Vec2,
}

#[derive(Drop, Copy, Serde, Introspect)]
struct Vec2 {
    x: u32,
    y: u32,
}

Custom nested structs must derive Introspect for Dojo to understand their structure.

Composite Keys

Multiple keys for relationships (all keys must be provided when reading):

#[derive(Copy, Drop, Serde)]
#[dojo::model]
struct GameResource {
    #[key]
    player: ContractAddress,
    #[key]
    location: ContractAddress,
    balance: u8,
}

Read with tuple of all keys:

let resource: GameResource = world.read_model((player, location));

Global Singleton

Constant key for global settings:

const RESPAWN_DELAY: u128 = 9999999999999;

#[derive(Copy, Drop, Serde)]
#[dojo::model]
struct GameSetting {
    #[key]
    setting_id: u128,
    setting_value: felt252,
}

// Usage
world.write_model(@GameSetting {
    setting_id: RESPAWN_DELAY,
    setting_value: (10 * 60).into()
});

ECS Composition

Small, focused models that can be combined on entities:

#[derive(Copy, Drop, Serde)]
#[dojo::model]
struct Position {
    #[key]
    id: u32,
    x: u32,
    y: u32,
}

#[derive(Copy, Drop, Serde)]
#[dojo::model]
struct Health {
    #[key]
    id: u32,
    health: u8,
}

// Human has Position + Health + Potions
// Orc has Position + Health (no Potions)

Key Rules

1. At least one key required - Every model needs a #[key] field
2. Keys must come first - All key fields before data fields
3. Keys are not stored - Used only for indexing/lookup
4. All keys required for read - Composite keys must all be provided

Model API

Get the world storage in your system:

use dojo::model::{ModelStorage, ModelValueStorage};

let mut world = self.world(@"my_namespace");

Write a Model

world.write_model(@Position { player, vec: Vec2 { x: 0, y: 0 } });

Read a Model

let position: Position = world.read_model(player);

Read with Composite Key

let resource: GameResource = world.read_model((player, location));

Generate Unique ID

let entity_id = world.uuid();
world.write_model(@Health { id: entity_id, health: 100 });

Field Types

• u8, u16, u32, u64, u128, u256 - Unsigned integers
• felt252 - Field elements
• bool - Booleans
• ContractAddress - Starknet addresses
• Custom structs - Must derive Introspect
• Custom enums - Must derive Introspect

Next Steps

After creating models:

1. Use dojo-system skill to create systems that use your models
2. Use dojo-test skill to test model read/write operations
3. Use dojo-config skill to configure permissions

Related Skills

• dojo-system: Create systems that use these models
• dojo-test: Test your models
• dojo-init: Initialize project first
• dojo-review: Review model design