Bevy inventory system

When to use

Load this when stacks move between containers. UI grids stay on bevy-ui-layout. Economy prices stay on bevy-economy-system.

ECS shape

• Components: item id and stack count you define.
• Resources: run-wide tables live in a resource (bevy-data-resources), not an autoload.
• Systems: mutate those components on Update or the fixed timestep. Use .chain() when damage must land before death.
• Messages: one-shot facts (hit, pickup, quest advance) go through bevy-events-messaging. This file does not add a new event type name.

Coming from Godot

Godot idea	Bevy idiom
Stack	Item id plus count on a component or inside a resource inventory.
Container	An entity that owns stacks. No inventory node.
Equip	A marker component. Stat changes go through bevy-rpg-stats.

Scope

• Item, stack, and inventory data are yours to build as components and resources.
• Check the UI docs for drag-drop widget behavior before writing it.

Expert Knowledge Delta

Target: Bevy 0.20+.

Core ECS types: Component, Resource, Query, Commands, Startup, Update, Fixed / FixedMain (bevy::time), .chain(), Plugin, DefaultPlugins, MinimalPlugins. Messages and observers are an ownership slot. See bevy-events-messaging for their APIs. Systems run in parallel unless .chain() orders the ones that conflict.

Who owns state

Piece	Owner	Who may mutate	Schedule
Data on one entity	Component	One system via Query	Update or FixedMain
One value for the whole app	Resource	One system	Startup to insert, then the schedule that reads it
Spawn	Commands	The spawning system	Startup for the initial world; later schedules for runtime spawn
Order that must not race	.chain()	The chained systems only	Same schedule
Plugin boundary	Plugin	build registers systems and resources	Before the app runs

Borrow rule: two systems that both mutably query the same component must be ordered (.chain()) or split so only one writes. Unrelated systems stay parallel. That is the ECS page rule, not a guess at a system-set API.

Decision

If you need	Do this	Do not
Per-entity data	Component + Query	A Godot node script
App-wide config or clock	Resource	Copy the value onto every entity
Stable simulation step	FixedMain and the Fixed clock	Tie simulation to raw frame Update
Startup spawn	Commands in Startup	Spawn from a render system
Cross-system notice that is not shared state	Message or observer slot in bevy-events-messaging	A new event type invented in this file
An API outside the documented set	Check the official docs first	A made-up crate or API

Load references/ecs-ownership.md for the ownership table.

NEVER

• Do not pin /0.20.0/ in docs URLs. WHY: links stay on latest; the 0.20 target is stated once in prose.

• Do not mutably query the same component from two unordered systems. WHY: the schedule runs systems in parallel unless .chain() orders them.

• Do not invent a physics, navigation, networking, or XR crate here. WHY: this skill only names documented Bevy crates and modules.

• No Godot node, resource, or signal types for this mechanic. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No Godot types in Bevy code. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No invented APIs or unnamed third-party crates as the chosen solver. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

Reference

docs.rs links use the unversioned latest permalink. The library pin on bevy-master stays 0.20.0.

Official Documentation

• Migration guides - Unversioned hop index.
• bevy crate - API reference and Cargo feature list.
• Assets - Official asset catalog. No third-party crate was selected.
• Examples - Example tree on the latest branch.
• ECS - Component, systems, Query, Startup, Update, and .chain().
• Plugins - Plugin, DefaultPlugins, MinimalPlugins, and add_plugins.

Related Skills

Prerequisites

• bevy-master - Hub and schedules.
• bevy-ecs-composition - Components and systems.
• bevy-rpg-stats - Equip bonuses.
• bevy-ui-layout - Slot layout.
• bevy-data-resources - Tables and definitions.
• bevy-events-messaging - One-shot facts.

Complements

• bevy-state-machines - Mode flags.
• godot-inventory-system - Equivalent Godot skill.

Downstream / consumers

• None yet.

Master

• bevy-master - Bevy router.