Spring Data JPA How to use Predicate in Specifiaction - spring

Question

I would like to create Specification to dynamic search.
In database I have fields like radius, width and height - depends on type of shape.
I want to add request paramter like for example areaTo - which will be returing shapes with area smaller or equal to paramter.
I was thinking about adding some Predicate but I can not find any example how to do it.
What I mean, I would like to add something like that:
public static Specification<ShapeEntity> areaTo(double areaTo) {
return (root, query, criteriaBuilder) -> {
double area;
switch (root.get("type").toString()) {
case "CIRCLE":
area = Math.pow(Double.parseDouble(root.get("radius").toString()), 2) * Math.PI;
break;
case "RECTANGLE":
area = Double.parseDouble(root.get("width").toString()) * Double.parseDouble(root.get("height").toString());
break;
case "SQUARE":
area = Math.pow(Double.parseDouble(root.get("width").toString()), 2);
break;
default:
throw new IllegalArgumentException();
}
return criteriaBuilder.lessThanOrEqualTo(????, areaTo);
};
}

Answer 1

I found a solution that somewhat answers your question, what you need to create here is an Expression.
you could try to modify this code to suit what you need:
private Specification<Shape> areaTo(double areaTo, String type) {
return (root, query, criteriaBuilder) -> {
Expression<Double> area;
switch (type) {
case "CIRCLE":
Expression<Double> radius = root.get("radius");
Expression<Double> power = criteriaBuilder.prod(radius, radius);
area = criteriaBuilder.prod(power, Math.PI);
break;
case "RECTANGLE":
Expression<Double> width = root.get("width");
Expression<Double> height = root.get("height");
area = criteriaBuilder.prod(width, height);
break;
case "SQUARE":
Expression<Double> width_s = root.get("width");
area = criteriaBuilder.prod(width_s, width_s);
break;
default:
throw new IllegalArgumentException();
}
return criteriaBuilder.lessThanOrEqualTo(area, areaTo);
};
}
your switch (root.get("type").toString()) won't work in the switch statement because there is no value return here, they creating a query. In this situation, you could create a Predicate for each type of shape and then add them to criteriaBuilder with operator or
for further information about my solution you should take a look at this link