標準API加入：java.lang.IllegalArgumentException異常：無法解析屬性

Question

我試圖讓通過JPA標準API一個簡單的連接操作，但我得到一個錯誤：

java.lang.IllegalArgumentException: Unable to resolve attribute [Companies] against path at org.hibernate.ejb.criteria.path.AbstractPathImpl.unknownAttribute(AbstractPathImpl.java:120) at org.hibernate.ejb.criteria.path.AbstractPathImpl.locateAttribute(AbstractPathImpl.java:229) at org.hibernate.ejb.criteria.path.AbstractFromImpl.join(AbstractFromImpl.java:411) at com.maven_test.models.jpa.dao.ServicesDAO.findAllWithCompaniesByCriteria(ServicesDAO.java:106) at com.maven_test.models.jpa.ServicesFindByIdByCriteria.test2(ServicesFindByIdByCriteria.java:44) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.junit.runner.JUnitCore.run(JUnitCore.java:137) at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:74) at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:211) at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:67) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)

方法看起來像：

public List findAllWithCompaniesByCriteria() { 

    EntityManager em = EMgrUtil.createEntityManager(); 

    CriteriaBuilder builder = em.getCriteriaBuilder(); 
    CriteriaQuery<Object[]> query = builder.createQuery(Object[].class); 

    Metamodel m = em.getMetamodel(); 

    EntityType<Services> Services_ = m.entity(Services.class); 
    EntityType<Companies> Companies_ = m.entity(Companies.class); 

    /*Root<Services> services = query.from(Services.class); 
    Join<Services, Companies> companies = query.join(Companies_);*/ 

    Root<Services> s = query.from(Services.class); 
    Join<Services, Companies> c = s.join("Companies", JoinType.INNER); 
    query.multiselect(s.get("avatar"), c.get("name")); 

    List<Object[]> list = em.createQuery(query).getResultList(); 

    return list; 

} 

我們必須加入的表的名稱是「zaks_companies」，兩種情況的錯誤都是一樣的。

@Entity 
@Table(name = "zaks_services") 
public class Services { 

@Id 
@GeneratedValue(strategy=GenerationType.IDENTITY) 
@Column(name = "id") 
private Integer id; 

@Column(name = "title", nullable = false) 
@Size(min = 0, max = 255) 
private String title; 

//@Column(name = "descr", length = 65535, columnDefinition = "Text") 
//@Column(name = "descr", length = 4294967295, columnDefinition = "Longtext") 
@Column(name = "descr", nullable = false, length = 16777215, columnDefinition = "Mediumtext") 
private String descr; 

@Column(name = "avatar", nullable = false) 
private String avatar; 

@Column(name = "date_add", nullable = false, insertable = false, updatable = false, columnDefinition = "Datetime DEFAULT CURRENT_TIMESTAMP") 
@Temporal(TemporalType.TIMESTAMP) 
private Date date_add; 

@OneToOne 
@JoinColumn(name = "company_id") 
private Companies companies; 

...getters/setters 
...default constructor 

和公司模型：

@Entity 
@Table(name = "zaks_companies") 
public class Companies { 

@Id 
@GeneratedValue(strategy = GenerationType.IDENTITY) 
@Column(name = "id") 
private Integer id; 

@OneToOne(mappedBy = "companies") 
private Services services; 

@Column(name = "name", nullable = false) 
@Size(min = 0, max = 255) 
private String name; 

...getters/setters 
...default constructor 

我的一個手冊在這裏：https://www.youtube.com/watch?v=J-f4jvljpgQ在16:50

Answer 1

這是因爲持久化屬性的名稱是區分大小寫。在持久化屬性的這種情況下，名稱爲companies：

private Companies companies; 

但查詢嘗試使用Companies：

Join<Services, Companies> c = s.join("Companies", JoinType.INNER);