# Merge Branch

## API Name

API Name: Branch – Merge

***

## Overview

This API merges the specified branch into the main (default/master) branch of the given project.

MBSE Core uses this API to:

* Merge temporary or synchronization branches
* Consolidate changes into the primary branch
* Finalize branch-based operations

Connector responsibility:

* Merge the branch identified by `branchId` into the main/master branch.
* Ensure the merge operation is scoped to the given `projectId`.
* Handle merge conflicts according to end system capabilities.
* Return appropriate HTTP status codes based on merge outcome.

***

### API URI

```bash
POST: /mbse/api/1.0/branches/{branchId}/merge
    ?projectId={projectId}
```

***

### Path Parameters

| Name     | Mandatory | Type   | Description                                                |
| -------- | --------- | ------ | ---------------------------------------------------------- |
| branchId | True      | String | ID of the branch to be merged into the main/master branch. |

***

### URI Parameters

| Name      | Mandatory | Type   | Description                                   |
| --------- | --------- | ------ | --------------------------------------------- |
| projectId | True      | String | ID of the project in which the branch exists. |

***

### Behavior Rules

1. The merge must occur within the context of the provided `projectId`.
2. The specified branch must be merged into the main/master branch.
3. Connector must:
   * Call the end system’s merge API.
   * Ensure merge consistency.
4. If merge is successful:
   * Return HTTP `204 No Content`.
5. If branch does not exist:
   * Return HTTP `404 Not Found`.
6. If merge conflicts occur and are not auto-resolved:
   * Return HTTP `409 Conflict`.
7. Connector must not silently ignore merge failures.

***

### Response

This API does not return a response body.

#### Successful Merge

HTTP Status: `204 No Content`

***

### Error Handling

| HTTP Status | Description                                   |
| ----------- | --------------------------------------------- |
| 400         | Invalid request parameters.                   |
| 404         | Branch not found in the specified project.    |
| 409         | Merge conflict or merge not allowed.          |
| 500         | Internal server error during merge operation. |

***

### Example Use Case

#### Merge Branch into Main

```bash
POST /mbse/api/1.0/branches/branch_20260214123045/merge?
projectId=123
```

***

### Implementation Guidelines

* Ensure the branch belongs to the specified project before attempting merge.
* Validate that the branch is not already the main/master branch.
* If the end system generates a new revision during merge:
  * Ensure revision history remains consistent.
* If merge conflicts occur:
  * Either auto-resolve (if supported) or return `409 Conflict`.
* Do not return partial success responses.

***

### Design Rationale

This API completes the branch lifecycle by enabling:

* Controlled integration of branch changes
* Revision history consolidation
* Deterministic synchronization workflows

By clearly separating:

* Branch creation
* Branch deletion
* Branch merge

The MBSE layer remains structured, predictable, and integration-safe.


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