Partial update in resolver

[KrifaYounes]

it's possible to do partial update in the resolver ?
i have a input to update with only field specified by user like this blog
thanks
https://medium.com/workflowgen/graphql-mutations-partial-updates-implementation-bff586bda989

[oliemansm]

I read the article, but this feature relies on the Javascript feature that a variable can be undefined or null. Java doesn't have an equivalent of undefined. That would mean that null values would be automatically passed in for parameters that aren't provided in the mutation. How would you know when you would actually have to set them to null and when would you have to ignore them and leave the value as is? Long story short: partial updates are not supported.

[KrifaYounes]

@oliemansm it's possible
show my code :
https://github.com/KrifaYounes/spring-boot-graphql/blob/master/src/main/java/com/example/demo/graphql/mutation/AuthorMutationResolver.java

[lilianchiassai]

I am late to the party but it is possible to implement an Undefined class, inspired from Optional to deal with this use case (code improved from @KrifaYounes idea):

public final class Undefined<T> {

  private static Undefined<?> UNDEFINED = new Undefined();
  private boolean defined;
  private T value;

  private Undefined() {
    this.defined = false;
    this.value = null;
  }

  public static <T> Undefined<T> getInstance() {
    @SuppressWarnings("unchecked")
    Undefined<T> t = (Undefined<T>) UNDEFINED;
    return t;
  }

  public Undefined(T value) {
    this.defined = true;
    this.value = value;
  }

  public boolean isDefined() {
    return defined;
  }

  public T getValue() {
    return value;
  }
}

The schema:

input BookInput {
  title: String
}

The input:

public class BookInput {
  Undefined<String> title = Undefined.getInstance();

  public Undefined<String> getTitle() {
    return this.title;
  } 
  public void setTitle(String title) {
    this.title=new Undefined(title);
  }
}

In the resolver use:

if(input.getTitle().isDefined()) {
  book.setTitle(input.getTitle().getValue();
}

This approach removes the needs to perform several contains operations and to have the literal key hard-coded.
I also use this with spring validation: I can annotate the undefined input field with a custom annotation that can use the undefined state to perform the validation.

[DirkLachowski]

@AllirionX
Shouldn't the resolver part be:

if(input.getTitle().isDefined()) {
  book.setTitle(input.getTitle().getValue();
}

[lilianchiassai]

Indeed it should be! I updated the code snippet.

[kliakos]

I am late to the party but it is possible to implement an Undefined class, inspired from Optional to deal with this use case

Why not use Optional<T> directly? Null field value to indicate the undefined and Option.empty() to indicate the explicit null. (as suggested here)