> For the complete documentation index, see [llms.txt](https://sniveler-code.gitbook.io/dots/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://sniveler-code.gitbook.io/dots/project-ai-behavior-architect/section-6/using-entity-command-buffers-structural-changes.md).

# 🏗 Using Entity Command Buffers (Structural Changes)

In DOTS, you cannot add components, remove components, or destroy entities on the main thread while jobs are iterating over chunks. You must use an `EntityCommandBuffer` (ECB).

To use an ECB in your custom action, declare a struct field with the `[BtCommandBuffer]` attribute and specify which `System Group` should execute the buffer (usually `EndSimulationEntityCommandBufferSystem`).

```csharp
using SnivelerCode.AiBehavior.Runtime.Attributes;
using SnivelerCode.AiBehavior.Runtime.Components;
using Unity.Entities;

namespace MyGame.AI
{
    [BtCustom("Combat/Destroy Self")]
    public partial struct DestroySelfAction
    {
        // 1. Declare the ECB Parallel Writer
        [BtCommandBuffer(typeof(EndSimulationEntityCommandBufferSystem))]
        public EntityCommandBuffer.ParallelWriter CommandBuffer;

        private NodeStatus Process([BtEntityIndex] int queryIndex, in Entity selfEntity)
        {
            // 3. Queue the destruction safely
            CommandBuffer.DestroyEntity(queryIndex, selfEntity);
            
            return NodeStatus.Success;
        }
    }
}
```

> ⚠️ **Critical ECB Rule:** Always use a deterministic sort key  `[BtEntityIndex]` as the first argument in CommandBuffer methods when writing multithreaded DOTS code


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://sniveler-code.gitbook.io/dots/project-ai-behavior-architect/section-6/using-entity-command-buffers-structural-changes.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.