mirror of
https://github.com/bevyengine/bevy
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71f8b4a92f
# Objective
Currently for entities we serialize only `id`. But this is not very expected behavior. For example, in networking, when the server sends its state, it contains entities and components. On the client, I create new objects and map them (using `EntityMap`) to those received from the server (to know which one matches which). And if `generation` field is missing, this mapping can be broken. Example:
1. Server sends an entity `Entity{ id: 2, generation: 1}` with components.
2. Client puts the received entity in a map and create a new entity that maps to this received entity. The new entity have different `id` and `generation`. Let's call it `Entity{ id: 12, generation: 4}`.
3. Client sends a command for `Entity{ id: 12, generation: 4}`. To do so, it maps local entity to the one from server. But `generation` field is 0 because it was omitted for serialization on the server. So it maps to `Entity{ id: 2, generation: 0}`.
4. Server receives `Entity{ id: 2, generation: 0}` which is invalid.
In my game I worked around it by [writing custom serialization](https://github.com/dollisgame/dollis/blob/master/src/core/network/entity_serde.rs) and using `serde(with = "...")`. But it feels like a bad default to me.
Using `Entity` over a custom `NetworkId` also have the following advantages:
1. Re-use `MapEntities` trait to map `Entity`s in replicated components.
2. Instead of server `Entity <-> NetworkId ` and `Entity <-> NetworkId`, we map entities only on client.
3. No need to handling uniqueness. It's a rare case, but makes things simpler. For example, I don't need to query for a resource to create an unique ID.
Closes #6143.
## Solution
Use default serde impls. If anyone want to avoid wasting memory on `generation`, they can create a new type that holds `u32`. This is what Bevy do for [DynamicEntity](https://docs.rs/bevy/latest/bevy/scene/struct.DynamicEntity.html) to serialize scenes. And I don't see any use case to serialize an entity id expect this one.
---
## Changelog
### Changed
- Entity now serializes / deserializes `generation` field.
## Migration Guide
- Entity now fully serialized. If you want to serialze only `id`, as it was before, you can create a new type that wraps `u32`.
48 lines
1.2 KiB
TOML
48 lines
1.2 KiB
TOML
[package]
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name = "bevy_ecs"
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version = "0.9.0-dev"
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edition = "2021"
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description = "Bevy Engine's entity component system"
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homepage = "https://bevyengine.org"
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repository = "https://github.com/bevyengine/bevy"
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license = "MIT OR Apache-2.0"
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keywords = ["ecs", "game", "bevy"]
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categories = ["game-engines", "data-structures"]
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[features]
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trace = []
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default = ["bevy_reflect"]
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[dependencies]
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bevy_ptr = { path = "../bevy_ptr", version = "0.9.0-dev" }
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bevy_reflect = { path = "../bevy_reflect", version = "0.9.0-dev", optional = true }
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bevy_tasks = { path = "../bevy_tasks", version = "0.9.0-dev" }
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bevy_utils = { path = "../bevy_utils", version = "0.9.0-dev" }
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bevy_ecs_macros = { path = "macros", version = "0.9.0-dev" }
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async-channel = "1.4"
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event-listener = "2.5"
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thread_local = "1.1.4"
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fixedbitset = "0.4"
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fxhash = "0.2"
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downcast-rs = "1.2"
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serde = { version = "1", features = ["derive"] }
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[dev-dependencies]
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rand = "0.8"
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[[example]]
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name = "events"
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path = "examples/events.rs"
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[[example]]
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name = "resources"
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path = "examples/resources.rs"
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[[example]]
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name = "change_detection"
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path = "examples/change_detection.rs"
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[[example]]
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name = "derive_label"
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path = "examples/derive_label.rs"
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