SAP OData Service PUT, Patch and Merge

In SAP OData services, PUT, PATCH, and MERGE are HTTP methods used to update resources, but they have different purposes and behaviors:

1. PUT:

   • Purpose: Replaces an existing resource entirely.
   • Behavior: When you send a PUT request, you must provide a complete representation of the resource. The existing resource is entirely overwritten with the data in the PUT request.
   • Use Case: Suitable when you want to completely replace a resource or ensure the resource has specific state with all fields provided.
   • Example: Updating an entire customer record with all fields, including those that might not have changed.

2. PATCH:

   • Purpose: Partially updates an existing resource.
   • Behavior: With a PATCH request, you send only the fields that need to be updated. The server applies the changes to the resource without altering other fields that are not provided in the request.
   • Use Case: Useful for making small changes to a resource without sending the entire resource data. It reduces the amount of data sent over the network.
   • Example: Updating just the email address of a customer without needing to send the entire customer data.

3. MERGE:

   • Purpose: Also partially updates an existing resource, similar to PATCH.
   • Behavior: Like PATCH, the MERGE method updates only the specified fields of a resource. The key difference is more historical and nuanced, depending on the implementation by the server. In the context of SAP OData, MERGE behaves very similarly to PATCH.
   • Use Case: Historically, it was used by some systems to differentiate partial updates. However, in modern implementations, PATCH is more commonly used.
   • Example: Updating only specific attributes of an employee record, such as their job title or department.

Summary

• PUT is for full resource replacement.
• PATCH is for partial updates with a focus on minimal data transfer.
• MERGE is also for partial updates, often similar to PATCH, but is less commonly used in modern practices.

When designing or using SAP OData services, it's essential to understand the intended behavior of these methods to ensure correct data handling and efficient network usage.