PATCH
Correctly Implementing PATCH with @Validation
PATCH operations are deceptively tricky.
For one, it is not possible to correctly implement PATCH handling passed null values using default deserialization with common web application frameworks. The JSON from both examples below will result in the foo field of a deserialized Pojo being null - It is not possible using this default serialization to detect whether a request intends to set foo to null.
{ "data" : { "foo" : null } }
{ "data" : { "bar" : 123 } }
Additionally, all of the state required for a validation may not be present in the request. It is therefore necessary to merge existing persisted state and request state to accurately perform some validations. The code for detecting and merging this state increases in complexity as more fields are needed for a validation.
Up! is designed to handle PATCH operations and address these problems.
Create and Update operations use custom deserialization to parse request documents with available parser library objects directly (such as, but not necessarily Jackson). This custom deserialization captures the paths requested, so that “foo” can be correctly updated as null in the above example.
Additionally, when using @Validation, persisted state will automatically be merged to request state for validations. For example, below if “foo” is passed in the request, “bar” and “baz” from persisted state will be populated to fooBar so that the validateFooAndBar can apply validation of the 3 fields correctly.
@Validation(path = {"foo", "bar", "baz"})
public void validateFooAndBar(Errors errors, ResourcePath path, FooBar fooBar)