JPA-WHERE子句中的CriteriaBuilder

Question

我是JPA的新手。使用where子句构建select查询。我需要从表Contacts中选择所有等于字符串名称值的ContactName。

CREATE TABLE Contacts (
ContactId BIGINT UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT,
ContactName VARCHAR(100) NOT NULL,
ContactEmailID VARCHAR(100) NOT NULL,
 UserName VARCHAR(100) NOT NULL,
 INDEX Contact_Names (ContactName)
 ) ENGINE = InnoDB;

     @Entity

   private String UserName; 

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "ContactId")
     public long getContactId() {
        return ContactId;
    }

    public void setContactId(long contactId) {
        ContactId = contactId;
    }


    @Basic
    @Column(name = "UserName")
    public String getUserName() {
    return UserName;
    }

    public void setUserName(String UserName) {
    this.UserName = UserName;
    }

         EntityManager manager = null;
         EntityTransaction transaction = null;
         try{

        manager = this.factory.createEntityManager();
        transaction = manager.getTransaction();
        transaction.begin();

      CriteriaBuilder cb = manager.getCriteriaBuilder();
       CriteriaQuery<Contact> q1 = cb.createQuery(Contact.class);
       Root<Contact> postRoot = q1.from(Contact.class);

       q1.select(postRoot).where(cb.equal(postRoot.get("UserName"), name));
       TypedQuery<Contact> qry = manager.createQuery(q1);

       List<Contact> result = qry.getResultList();
        for (Contact contactInstance : result)  
        {

         DBContactName = contactInstance.getContactName().trim();
         DBContactEmail = contactInstance.getContactEmailID().trim();

以下是执行我的项目时出现的错误：java.lang.IllegalArgumentException：无法根据在org.hibernate.jpa.criteria.path.abstractPathimpl.unknownatAttribute(abstractPathimpl.java:117)在org.hibernate.jpa.criteria.path.abstractPathimpl.locateAttribute(abstractPathimpl.java:214)在com.contactServlet.doPost（pservlet.service(httpservlet.java:725)在org.apache.catalina.core.applicationFilterChain.InternaldoFilter（applicationFilterChain.java:291)在org.apache.catalina.core.applicationFilterChain.doFilter（applicationFilterChain.java:206)在org.apache.catalina.core.applicationFilterChain.java:206)在org.apache.tomcat.websocket.server.wsfilter.doFilter（IonFilterChain.doFilter(ApplicationFilterChain.java:206)在org.apache.catalina.core.standardWrapperValve.invoke(StandardWrapperValve.java:219)在org.apache.catalina.core.standardContextValve.invoke(StandardContextValve.invoke(StandardContextValve.java:106)在在org.apache.catalina.valves.AbstractAccessLogValve.Invoke(AbstractAccessLogValve.java:610)在org.apache.catalina.core.standardEnginEvalve.Invoke(StandardEnginEvalve.java:88)在org.apache.catalina.connector.coyoteAdapter.Service(CoyoteAdapter.java:534)在$HTTP11ConnectionHandler.process(http11nioProtocol.java:222)在org.apache.tomcat.util.net.nioEndpoint$socketprocessor.dorun(NioEndpoint.java:1566)在org.apache.tomcat.util.net.nioEndpoint$socketprocessor.run(NioEndpoint.java:1523)在java.util.concurrent.threadpoolexecutor.runworker(taskthread.java:61)位于java.lang.thread.run(thread.java:745)

Answer 1

尝试：

q1.select(postRoot).where(cb.equal(postRoot.get("userName"), name));

UserName属性的u以小写形式表示。