CriteriaBuilder in JPA - where clause

Question

Am new to JPA. Building the select query with the where clause. I need to select from table Contacts all ContactName's that equals the value of the String name.

Used the code below to create DB table:

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;

Following is my Entity class;

     @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;
    }

Following is my ContactServlet class code where i am trying to write my CriteriaBuilder code.

         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();

.....

Don't know where am i going wrong??

Following is the error while executing my project: java.lang.IllegalArgumentException: Unable to resolve attribute [UserName] against path at org.hibernate.jpa.criteria.path.AbstractPathImpl.unknownAttribute(AbstractPathImpl.java:117) at org.hibernate.jpa.criteria.path.AbstractPathImpl.locateAttribute(AbstractPathImpl.java:214) at org.hibernate.jpa.criteria.path.AbstractPathImpl.get(AbstractPathImpl.java:185) at 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) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.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) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:534) at org.apache.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$SocketProcessor.doRun(NioEndpoint.java:1566) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1523) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at 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

Try with:

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

The u of UserName attribute in lower case.