How to filter by calculated field using Querydsl Predicate (BooleanExpression) with Spring Data?

Question

There're two numeric columns in database like actual and plan.

I can add third column like difference and write WHERE part of query filtering by this column.

But instead having additional column in database, I want to calculate it in Predicate.

Something like (qProduct.actualPrice - qProduct.planPrice).gt(20L)

Entity:

public class Product {
    private String type;
    private Long actualPrice;
    private Long planPrice;
}

Predicate:

QProduct qProduct = QProduct.product;
BooleanExpression predicate = qProduct.type.eq("pizza")
            .and((qProduct.actualPrice - qProduct.planPrice).gt(20L));

Page<Product> productPage = productRepository.findAll(predicate, pageable);

Thx

Answer 1

You can use the subtract method of NumberExpression class

QProduct qProduct = QProduct.product;
BooleanExpression predicate = qProduct.type.eq("pizza")
          .and((qProduct.actualPrice.subtract(qProduct.planPrice)).gt(20L));

Page<Product> productPage = productRepository.findAll(predicate, pageable);