我想使用带有存储库的种子堆栈在数据库上应用 Max() 函数

Question

I am trying to get max value of float column using SeedStack Java code where I am using seedstack Repository. But I am not able understand how to do it. As repository do not max function to be called. it has the only count function. I have applied the filters using Specification. But got stuck with Max function. can anyone help?

I can not share the code due to restrictions.

Answer 1

The repository abstraction allows you to manage aggregate persistence with a collection-like facade but generic methods can only return objects of the type of the aggregate.

When doing data aggregation like in your case, you don't return an aggregate but individual columns and aggregation results. This is not compatible with generic Repository methods and Specification objects.

To achieve what you want, you have to define a custom repository method. Define it in a custom interface:

public interface ProductRepository extends Repository<Product, Long> {
    int getMaximumProductPrice();
}

Then implement it:

public class ProductJpaRepository 
        extends BaseJpaRepository<Product, Long> 
        implements ProductRepository {

    @Override
    public int getMaximumProductPrice() {
        // implement query using getEntityManager()
    }
}

Now you inject your repository with your own interface directly:

public class SomeClass {
    @Inject
    private SomeRepository someRepository;
}

The example above is very simple but note that you can also return more complex values like:

• An array of Object to hold arbitrary values,
• A custom object designed to hold all the returned values,
• A Product or list of Product if you do a join.