如何在JOIN中使用JPA Criteria API [英] How to use JPA Criteria API in JOIN

问题描述

• 我有五个表:公司，产品/服务，地址，国家和地区 城市.
• 一个公司可以有n个产品的类别，1个地址和1个国家 地址实体内还有1个城市.
• 用户选择了英格兰-利兹".
• 我现在知道，我必须从db所在城市选择所有公司 是利兹，并用这些公司的产品填充产品/服务列表 产品或服务.之后，该用户可以选择例如牙医 从第三个列表开始.
• 此后，我认识了Enlgand-Leeds-牙医，我必须填充 最后一张有补遗的清单(利兹的牙医)

• I have five tables: Company, Product/Service, Address, Country and City.
• A Company can have n products with category, 1 address with 1 country and 1 city inside the address entity.
• A user has chosen "England - Leeds".
• I know now that I have to select every companies from db where city is Leeds and populate product/service-list with those companies' products or services. After that user can select for instance dentist from the third list.
• After that I know Enlgand - Leeds - Dentist and I have to populate the last list with compenies (dentists in Leeds)

public class Company implements java.io.Serializable {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Short companyId;
@OneToOne(cascade=CascadeType.PERSIST)
private Address address;
private String companyName;
@OneToMany(fetch = FetchType.LAZY, mappedBy = "company",cascade=CascadeType.PERSIST)
private Set<Product> products = new HashSet<Product>(0);

---

public class Product implements java.io.Serializable {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "productId", unique = true, nullable = false)
private Integer productId;
private Short branchId;
private String productName;
private String sku;
private String category; ------> I am using this field in company search (dentists, garages etc.)

我如何仅查询那些产品具有类别牙医的公司?

How can I query only those companies which have products with category dentist?

CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();

CriteriaQuery<Company> criteria = criteriaBuilder.createQuery( Company.class );
Root<Company> companyRoot = criteria.from( Company.class );
//criteria.select(companyRoot);

TypedQuery<Company> q = em.createQuery(criteria);
List<Company> results = q.getResultList();

现在我有了每家公司，我如何只选择类别正确的公司?我想我需要JOIN，但是我不知道如何使用它.

Now I've got every company, how can I select only the companies with the correct category? I think I will need JOIN but how I don't know how to use it.

推荐答案

使用join()，

criteriaBuilder.equal(companyRoot.join("products").get("category"), "dentist")

看， http://en.wikibooks.org/wiki/Java_Persistence/Querying#Joining.2C_querying_on_a_OneToMany_relationship

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