How to do PATCH properly in strongly typed languages based on Spring - example

Question

According to my knowledge:

• PUT - update object with its whole representation (replace)
• PATCH - update object with given fiel

Answer 1

What I do in some of the applications is create an OptionalInput class which can distinguish whether a value is set or not:

class OptionalInput {

    private boolean _isSet = false

    @Valid
    private T value

    void set(T value) {
        this._isSet = true
        this.value = value
    }

    T get() {
        return this.value
    }

    boolean isSet() {
        return this._isSet
    }
}

Then in your request class:

class PatchUserRequest {

    @OptionalInputLength(max = 100L)
    final OptionalInput name = new OptionalInput<>()

    void setName(String name) {
        this.name.set(name)
    }
}

The properties can be validated by creating a @OptionalInputLength.

Usage is:

void update(@Valid @RequestBody PatchUserRequest request) {
    if (request.name.isSet()) {
        // Do the stuff
    }
}

NOTE: The code is written in groovy but you get the idea. I've used this approach for a few APIs already and it seems to be doing it's job quite well.