dojo-model

# 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`):**

```cairo
use starknet::ContractAddress;

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

**In systems that use models:**

```cairo
// 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:**

```cairo
// 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.

```cairo
#[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:

```cairo
#[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):

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

Read with tuple of all keys:

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

### Global Singleton

Constant key for global settings:

```cairo
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:

```cairo
#[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:

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

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

### Write a Model

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

### Read a Model

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

### Read with Composite Key

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

### Generate Unique ID

```cairo
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