SAP CAP: PATCH call for OData.Draft.enabled Entity returns 404

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06-10-2024

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Solving the 404 Error in PATCH Requests for SAP CAP OData Draft-Enabled Entities

Problem: When making a PATCH request to update a draft-enabled entity in SAP CAP using the OData protocol, you might encounter a 404 Not Found error. This issue can be frustrating, especially when you're sure the entity exists and the data you're trying to update is valid.

Simplified Explanation: Imagine you have a draft-enabled entity, like a "Product" entity, where you can create and edit drafts before publishing them. When you try to update a draft using a PATCH request, the system might not find the draft, leading to a 404 error.

Scenario and Code Example:

Let's consider a simple scenario with a "Product" entity that's draft-enabled:

// Product.cds
using cds.ql.cds;

entity Product {
  key ID : Integer;
  Name : String;
  Description : String;
  Price : Decimal;
}

@cds.odata.draft.enabled
service Products {
  entity Product as projection;
}

Now, imagine you're trying to update a draft of a product with ID 123 using the following PATCH request:

PATCH /Products(123)/Draft
Content-Type: application/json
{
  "Name": "Updated Product Name"
}

This request might result in a 404 error, even though the product with ID 123 exists.

Analysis and Explanation:

The 404 error in this case often arises from a misunderstanding of how draft-enabled entities work in SAP CAP.

• Draft Management: When an entity is draft-enabled, the system automatically creates two versions of the entity:
  • Active version: Represents the published version of the entity, visible to all users.
  • Draft version: Represents a temporary, editable copy of the entity, only accessible to the user creating or editing the draft.
• Accessing Drafts: You need to explicitly use the /Draft suffix in your OData request path to target the draft version of the entity. However, the PATCH method in SAP CAP might not always handle this correctly.

Resolution:

To fix the 404 error and successfully update your draft, you can use the following methods:

1. Use the PUT Method: Instead of PATCH, use the PUT method to completely replace the draft data. This approach guarantees that the entire draft entity is updated.

   PUT /Products(123)/Draft
   Content-Type: application/json
   {
     "Name": "Updated Product Name",
     "Description": "Updated Product Description",
     // Include all other properties you want to update
   }
   

2. Use the @cds.odata.draft.enabled Decorator: Ensure that your entity is correctly marked with the @cds.odata.draft.enabled decorator in your CDS model. This is crucial for enabling draft functionality and ensures that the system handles draft operations correctly.

3. Use the @cds.odata.draft.* Annotations: Explore the various annotations related to drafts provided by SAP CAP. These annotations can provide more control over draft behavior and might help resolve specific issues.

Additional Tips:

• Test your OData service: Use tools like Postman or curl to send requests and validate your implementation.
• Review the SAP CAP documentation: The official documentation provides detailed information about draft-enabled entities, annotations, and best practices for working with drafts.
• Use debugging tools: Utilize the developer tools provided by your IDE or browser to inspect network requests, response codes, and logs for valuable insights into the problem.

Conclusion:

Understanding the nuances of draft-enabled entities in SAP CAP is crucial for building robust and predictable OData applications. By using the correct HTTP methods and annotations, you can avoid the 404 error and seamlessly update your drafts. Remember to test your code thoroughly and refer to the SAP CAP documentation for comprehensive guidance.

References:

• SAP CAP Documentation
• OData Draft Management