CriteriaBuilder在JPA - where子句

Question

是新来的JPA。使用where子句构建select查询。我需要从表联系人中选择与String名称的值相等的所有ContactName。

使用下面的代码来创建数据库表：

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; 

以下是我的实体类;

 @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; 
    } 

以下是我的ContactServlet类代码，我试图编写我的CriteriaBuilder代码。

  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(); 

.....

不知道我要去哪里错了？

以下是错误在执行我的项目： java.lang.IllegalArgumentException异常：无法在org.hibernate.jpa.criteria.path.Abs​​tractPathImpl.unknownAttribute解析属性[用户名]针对路径（AbstractPathImpl.java:117）在org.hibernate.jpa.criteria.path.Abs​​tractPathImpl.locateAttribute（AbstractPathImpl.java:214）在org.hibernate.jpa.criteria.path.Abs​​tractPathImpl.get（AbstractPathImpl.java:185）在com.ContactServlet.doPost（ContactServlet .java：110）at javax.servlet.http.HttpServlet.service（HttpServlet.java:644）at javax.servlet.http.HttpServlet.service（HttpServlet.java:725）at org.apache.catalina.core.ApplicationFilterChain。 internalDoFilter（ApplicationFilterChain.java:291）在org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:206）在org.apache.tomcat.websocket.server.WsFilter.doFilter（W在org.apache.catalina上的org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:206）处的org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:239）上的sFilter.java:52） .core.StandardWrapperValve.invoke（StandardWrapperValve.java:219）at org.apache.catalina.core.StandardContextValve.invoke（StandardContextValve.java:106）at org.apache.catalina.authenticator.AuthenticatorBase.invoke（AuthenticatorBase.java:505 ）在org.apache.catalina.core.StandardHostValve.invoke（StandardHostValve.java:142）org.apache.catalina.valves.ErrorReportValve.invoke（ErrorReportValve.java:79）at org.apache.catalina.valves.AbstractAccessLogValve。在org.apache的org.apache.catalina.connector.CoyoteAdapter.service（CoyoteAdapter.java:534）处调用（AbstractAccessLogValve.java:610）org.apache.catalina.core.StandardEngineValve.invoke（StandardEngineValve.java:88） .coyote.http11.AbstractHttp11Processor.process（AbstractHttp11Processor.java:1081）at org.apache .coyote.AbstractProtocol $ AbstractConnectionHandler.process（AbstractProtocol.java:658）at org.apache.coyote.http11.Http11NioProtocol $ Http11ConnectionHandler.process（Http11NioProtocol.java:222）at 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（ThreadPoolExecutor.java:1142）在java.util.concurrent.ThreadPoolExecutor $ Worker.run（ThreadPoolExecutor.java:617）at org.apache.tomcat.util.threads.TaskThread $ WrappingRunnable.run（TaskThread.java:61）at java.lang.Thread.run（ Thread.java:745）

Answer 1

尝试：

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

UserName属性的小写字母的u。