HQL或SQL查询以从许多相关实体获取数据

Question

I am using spring with hibernate to store data in MySql database. I am trying to retrieve rows based on filters requested by the user. I have the following tables/entities : Product and Gemstone

Relations:

• Product many2many Gemstone

I am trying to write a query to get products that have Gemstone A and Gemstone B and Gemstone C.. and so on.

Use Case:

If user is asking for a product with gemstones 51 and 46. Query should only return product id 4.

Query:

filterGemstones() method return the gemstone user wants to filter products to. Using the below query I get zero records but if I remove HAVING Count(DISTINCT p.product_id) = 2 I get product id 4, 5

• HQL :

   createQuery("select p.productId from Product p JOIN p.gemstones g where g in :gemstones group by p having count (distinct p) =" + filterGemstones().size() ).setParameter("gemstones",filterGemstones()); 

• SQL generate by hibernate :

   SELECT p.product_id FROM product p INNER JOIN gemstone_product gp ON p.product_id = gp.product_id INNER JOIN gemstone g ON gp.gemstone_id = g.gemstone_id WHERE g.gemstone_id IN ( 51, 46 ) GROUP BY p.product_id HAVING Count(DISTINCT p.product_id) = 2 

Product class:

 @Entity @Table(name = "product") public class Product { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "product_id") private long productId; @ManyToMany() @JoinTable( name = "gemstone_product", joinColumns = {@JoinColumn(name = "product_id")}, inverseJoinColumns = {@JoinColumn(name = "gemstone_id")} ) private Set<Gemstone> gemstones = new HashSet<>(0); // setters and getters } 

Gemstone class:

 @Entity @Table(name = "gemstone") public class Gemstone { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) @Column(name = "gemstone_id") private long gemstoneId; @ManyToMany(fetch = FetchType.LAZY) @JoinTable( name = "gemstone_product", joinColumns = {@JoinColumn(name = "gemstone_id")}, inverseJoinColumns = {@JoinColumn(name = "product_id")} ) private Set<Product> products = new HashSet<>(0); // setters and getters } 

Answer 1

Actually the SQL query that we need here is pretty simple:

SELECT t1.product_id 
FROM gemstone_product AS t1 
WHERE (t1.gemstone_id IN ?1 )  # (51, 46)
GROUP BY  t1.product_id  
HAVING (COUNT(t1.gemstone_id) = ?2) # 2 - # of items

It's a bit frustrating that it's not easy to create it with JPA, but it can be done with FluentJPA (produces the query above):

public List<Integer> getProductsContainingAllStones(List<Long> gemstoneIds) {
    int count = gemstoneIds.size();

    FluentQuery query = FluentJPA.SQL((Gemstone gemstone,
                                       JoinTable<Gemstone, Product> gemstoneProduct) -> {

        discardSQL(gemstoneProduct.joinBy(gemstone.getProducts()));

        long productId = gemstoneProduct.getInverseJoined().getProductId();
        long gemstoneId = gemstoneProduct.getJoined().getGemstoneId();

        SELECT(productId);
        FROM(gemstoneProduct);
        WHERE(gemstoneIds.contains(gemstoneId));
        GROUP(BY(productId));
        HAVING(COUNT(gemstoneId) == count);
    });
    return query.createQuery(em).getResultList();
}

More details on how it works can be found here .