如何使用PathBuilder在Spring JPA + Query DSL中创建求和函数

import com.querydsl.core.types.Expression;
import com.querydsl.core.types.dsl.Expressions;
import com.querydsl.core.types.dsl.NumberExpression;
import com.querydsl.jpa.impl.JPAQueryFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.jpa.repository.support.QuerydslRepositorySupport;
import org.springframework.stereotype.Repository;

import javax.persistence.EntityManager;

@Repository
public class MyEntityRepositoryImpl extends QuerydslRepositorySupport implements MyEntityRepositoryCustom {

    private final JPAQueryFactory queryFactory;

    @Autowired
    public MyEntityRepositoryImpl(EntityManager entityManager) {
        super(MyEntity.class);
        this.queryFactory = new JPAQueryFactory(entityManager);
    }

    @Override
    public Long sumOfValue() {
        QMyEntity myEntity = QMyEntity.myEntity;
        NumberExpression<Long> sumExpression = Expressions.numberPath(Long.class, myEntity.value.getMetadata());
        Expression<Long> sum = queryFactory
                .select(sumExpression.sum())
                .from(myEntity)
                .fetchOne();
        return sum != null ? sum : 0L;
    }
}