# 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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