Predicate alternative in Kotlin

Question

I try to create lambda in Kotlin. I has following Java interface:

public interface Specification<T> extends Serializable { @Nullable Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder builder); }

And in Java I can return new Specification from method like:

private Specification<Product> nameLike(String name){ return new Specification<Product>() { @Override public Predicate toPredicate(Root<Product> root, CriteriaQuery<?> query, CriteriaBuilder criteriaBuilder) { return criteriaBuilder.like(root.get(Product_.NAME), "%"+name+"%"); } }; }

And with Java 8 I can cut it to labda like:

private Specification<Product> nameLike(String name) { return (root, query, criteriaBuilder) -> criteriaBuilder.like(root.get(Product_.NAME), "%"+name+"%"); }

How to do it in Kotlin with lamba? I already tried many options, but they do not compile. help please.

Update: Last option in Kotlin:

class ProductSpecification { fun nameLike(name: String): (Root<Product>, CriteriaQuery<Product>, CriteriaBuilder) -> Predicate = { root, query, builder -> builder.like(root.get("name"), "%$name%") } }

It compiles, but when I pass it in function with argument Specification, I have error None of the following functions can be called with the arguments supplied.. Code example of invoking:

repository.findAll(ProductSpecification().nameLike("fff"))

Plus you can use Java's multiple lambda arguments as well as in kotlin — Ananiya J. Kesto
– Ananiya J. Kesto, Commented May 31, 2021 at 13:39

Stanislau Listratsenka · Accepted Answer · 2021-05-31 13:58:49Z

I found solution! When I started to implement roughly option like of the second code example in my question, IDE suggests to do like:

fun nameLike(name: String) = Specification { root: Root<Product>, query: CriteriaQuery<*>, builder: CriteriaBuilder -> builder.like(root.get("name"), "%$name%") }

That's fine for me

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