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bevy_scene: Serialize entities to map (#6416)
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# Objective

Entities are unique, however, this is not reflected in the scene format. Currently, entities are stored in a list where a user could inadvertently create a duplicate of the same entity. 

## Solution

Switch from the list representation to a map representation for entities.

---

## Changelog

* The `entities` field in the scene format is now a map of entity ID to entity data

## Migration Guide

The scene format now stores its collection of entities in a map rather than a list:

```rust
// OLD
(
  entities: [
    (
      entity: 12,
      components: {
        "bevy_transform::components::transform::Transform": (
          translation: (
            x: 0.0,
            y: 0.0,
            z: 0.0
          ),
          rotation: (0.0, 0.0, 0.0, 1.0),
          scale: (
            x: 1.0,
            y: 1.0,
            z: 1.0
          ),
        ),
      },
    ),
  ],
)

// NEW
(
  entities: {
    12: (
      components: {
        "bevy_transform::components::transform::Transform": (
          translation: (
            x: 0.0,
            y: 0.0,
            z: 0.0
          ),
          rotation: (0.0, 0.0, 0.0, 1.0),
          scale: (
            x: 1.0,
            y: 1.0,
            z: 1.0
          ),
        ),
      },
    ),
  },
)
```
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@MrGVSV
MrGVSV committed Oct 31, 2022
1 parent 8cdd977 commit bb968f4
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Showing 2 changed files with 44 additions and 58 deletions.
10 changes: 4 additions & 6 deletions assets/scenes/load_scene_example.scn.ron
View file
Original file line number Diff line number Diff line change
@@ -1,7 +1,6 @@
(
entities: [
(
entity: 0,
entities: {
0: (
components: {
"bevy_transform::components::transform::Transform": (
translation: (
Expand All @@ -25,14 +24,13 @@
),
},
),
(
entity: 1,
1: (
components: {
"scene::ComponentA": (
x: 3.0,
y: 4.0,
),
},
),
]
}
)
92 changes: 40 additions & 52 deletions crates/bevy_scene/src/serde.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ use bevy_utils::HashSet;
use serde::ser::SerializeMap;
use serde::{
de::{DeserializeSeed, Error, MapAccess, SeqAccess, Visitor},
ser::{SerializeSeq, SerializeStruct},
ser::SerializeStruct,
Deserialize, Deserializer, Serialize, Serializer,
};
use std::fmt::Formatter;
Expand All @@ -15,7 +15,6 @@ pub const SCENE_STRUCT: &str = "Scene";
pub const SCENE_ENTITIES: &str = "entities";

pub const ENTITY_STRUCT: &str = "Entity";
pub const ENTITY_FIELD_ENTITY: &str = "entity";
pub const ENTITY_FIELD_COMPONENTS: &str = "components";

pub struct SceneSerializer<'a> {
Expand Down Expand Up @@ -56,12 +55,15 @@ impl<'a> Serialize for EntitiesSerializer<'a> {
where
S: Serializer,
{
let mut state = serializer.serialize_seq(Some(self.entities.len()))?;
let mut state = serializer.serialize_map(Some(self.entities.len()))?;
for entity in self.entities {
state.serialize_element(&EntitySerializer {
entity,
registry: self.registry,
})?;
state.serialize_entry(
&entity.entity,
&EntitySerializer {
entity,
registry: self.registry,
},
)?;
}
state.end()
}
Expand All @@ -77,8 +79,7 @@ impl<'a> Serialize for EntitySerializer<'a> {
where
S: serde::Serializer,
{
let mut state = serializer.serialize_struct(ENTITY_STRUCT, 2)?;
state.serialize_field(ENTITY_FIELD_ENTITY, &self.entity.entity)?;
let mut state = serializer.serialize_struct(ENTITY_STRUCT, 1)?;
state.serialize_field(
ENTITY_FIELD_COMPONENTS,
&ComponentsSerializer {
Expand Down Expand Up @@ -120,7 +121,6 @@ enum SceneField {
#[derive(Deserialize)]
#[serde(field_identifier, rename_all = "lowercase")]
enum EntityField {
Entity,
Components,
}

Expand Down Expand Up @@ -167,7 +167,7 @@ impl<'a, 'de> Visitor<'de> for SceneVisitor<'a> {
if entities.is_some() {
return Err(Error::duplicate_field(SCENE_ENTITIES));
}
entities = Some(map.next_value_seed(SceneEntitySeqDeserializer {
entities = Some(map.next_value_seed(SceneEntitiesDeserializer {
type_registry: self.type_registry,
})?);
}
Expand All @@ -184,7 +184,7 @@ impl<'a, 'de> Visitor<'de> for SceneVisitor<'a> {
A: SeqAccess<'de>,
{
let entities = seq
.next_element_seed(SceneEntitySeqDeserializer {
.next_element_seed(SceneEntitiesDeserializer {
type_registry: self.type_registry,
})?
.ok_or_else(|| Error::missing_field(SCENE_ENTITIES))?;
Expand All @@ -193,42 +193,44 @@ impl<'a, 'de> Visitor<'de> for SceneVisitor<'a> {
}
}

pub struct SceneEntitySeqDeserializer<'a> {
pub struct SceneEntitiesDeserializer<'a> {
pub type_registry: &'a TypeRegistry,
}

impl<'a, 'de> DeserializeSeed<'de> for SceneEntitySeqDeserializer<'a> {
impl<'a, 'de> DeserializeSeed<'de> for SceneEntitiesDeserializer<'a> {
type Value = Vec<DynamicEntity>;

fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
where
D: Deserializer<'de>,
{
deserializer.deserialize_seq(SceneEntitySeqVisitor {
deserializer.deserialize_map(SceneEntitiesVisitor {
type_registry: self.type_registry,
})
}
}

struct SceneEntitySeqVisitor<'a> {
struct SceneEntitiesVisitor<'a> {
pub type_registry: &'a TypeRegistry,
}

impl<'a, 'de> Visitor<'de> for SceneEntitySeqVisitor<'a> {
impl<'a, 'de> Visitor<'de> for SceneEntitiesVisitor<'a> {
type Value = Vec<DynamicEntity>;

fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
formatter.write_str("list of entities")
formatter.write_str("map of entities")
}

fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
where
A: SeqAccess<'de>,
A: MapAccess<'de>,
{
let mut entities = Vec::new();
while let Some(entity) = seq.next_element_seed(SceneEntityDeserializer {
type_registry: self.type_registry,
})? {
while let Some(id) = map.next_key::<u32>()? {
let entity = map.next_value_seed(SceneEntityDeserializer {
id,
type_registry: self.type_registry,
})?;
entities.push(entity);
}

Expand All @@ -237,6 +239,7 @@ impl<'a, 'de> Visitor<'de> for SceneEntitySeqVisitor<'a> {
}

pub struct SceneEntityDeserializer<'a> {
pub id: u32,
pub type_registry: &'a TypeRegistry,
}

Expand All @@ -249,15 +252,17 @@ impl<'a, 'de> DeserializeSeed<'de> for SceneEntityDeserializer<'a> {
{
deserializer.deserialize_struct(
ENTITY_STRUCT,
&[ENTITY_FIELD_ENTITY, ENTITY_FIELD_COMPONENTS],
&[ENTITY_FIELD_COMPONENTS],
SceneEntityVisitor {
id: self.id,
registry: self.type_registry,
},
)
}
}

struct SceneEntityVisitor<'a> {
pub id: u32,
pub registry: &'a TypeRegistry,
}

Expand All @@ -272,16 +277,9 @@ impl<'a, 'de> Visitor<'de> for SceneEntityVisitor<'a> {
where
A: MapAccess<'de>,
{
let mut id = None;
let mut components = None;
while let Some(key) = map.next_key()? {
match key {
EntityField::Entity => {
if id.is_some() {
return Err(Error::duplicate_field(ENTITY_FIELD_ENTITY));
}
id = Some(map.next_value::<u32>()?);
}
EntityField::Components => {
if components.is_some() {
return Err(Error::duplicate_field(ENTITY_FIELD_COMPONENTS));
Expand All @@ -294,15 +292,11 @@ impl<'a, 'de> Visitor<'de> for SceneEntityVisitor<'a> {
}
}

let entity = id
.as_ref()
.ok_or_else(|| Error::missing_field(ENTITY_FIELD_ENTITY))?;

let components = components
.take()
.ok_or_else(|| Error::missing_field(ENTITY_FIELD_COMPONENTS))?;
Ok(DynamicEntity {
entity: *entity,
entity: self.id,
components,
})
}
Expand Down Expand Up @@ -420,29 +414,26 @@ mod tests {
let scene = builder.build();

let expected = r#"(
entities: [
(
entity: 0,
entities: {
0: (
components: {
"bevy_scene::serde::tests::Foo": (123),
},
),
(
entity: 1,
1: (
components: {
"bevy_scene::serde::tests::Foo": (123),
"bevy_scene::serde::tests::Bar": (345),
},
),
(
entity: 2,
2: (
components: {
"bevy_scene::serde::tests::Foo": (123),
"bevy_scene::serde::tests::Bar": (345),
"bevy_scene::serde::tests::Baz": (789),
},
),
],
},
)"#;
let output = scene
.serialize_ron(&world.resource::<AppTypeRegistry>().0)
Expand All @@ -455,29 +446,26 @@ mod tests {
let world = create_world();

let input = r#"(
entities: [
(
entity: 0,
entities: {
0: (
components: {
"bevy_scene::serde::tests::Foo": (123),
},
),
(
entity: 1,
1: (
components: {
"bevy_scene::serde::tests::Foo": (123),
"bevy_scene::serde::tests::Bar": (345),
},
),
(
entity: 2,
2: (
components: {
"bevy_scene::serde::tests::Foo": (123),
"bevy_scene::serde::tests::Bar": (345),
"bevy_scene::serde::tests::Baz": (789),
},
),
],
},
)"#;
let mut deserializer = ron::de::Deserializer::from_str(input).unwrap();
let scene_deserializer = SceneDeserializer {
Expand Down

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