java - IllegalArgumentException: An exception occurred while creating a query in EntityManager:

Question

I have a problem with JPA’s persistence.xml This is the warning that I don't have classes and exception when I try select smth

[EL Warning]: metamodel: 2021-01-26 14:52:53.211-- The collection of metamodel types is empty. Model         
classes may not have been found during entity search for Java SE and some Java EE container managed 
persistence units.  Please verify that your entity classes are referenced in persistence.xml using 
either <class> elements or a global <exclude-unlisted-classes>false</exclude-unlisted-classes> 
element

Exception in thread "main" java.lang.IllegalArgumentException: An exception occurred while creating a 
query in EntityManager: 
Exception Description: Problem compiling [select t from Notatka t].

this is my persistence.xml

        <?xml version="1.0" encoding="UTF-8" ?>
    <persistence xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:schemaLocation="http://java.sun.com/xml/ns/persistence 
          http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
                 version="2.0" xmlns="http://java.sun.com/xml/ns/persistence">
      <persistence-unit name="Notatki" transaction-type="RESOURCE_LOCAL">
    
      <class>test.Notatka</class>
        <properties>
          <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
          <property name="javax.persistence.jdbc.url"
                    value="jdbc:mysql://localhost:3306/test" />
          <property name="javax.persistence.jdbc.user" value="root" />
          <property name="javax.persistence.jdbc.password" value="" />
          <!-- EclipseLink should create the database schema automatically -->
          <property name="eclipselink.ddl-generation" value="create-tables" />
          <property name="eclipselink.ddl-generation.output-mode"
                    value="database" />
        </properties>
      </persistence-unit>
    </persistence>

and my main

        public class Main {
        public static void main(String[] args) {
            EntityManagerFactory factory = Persistence.createEntityManagerFactory("Notatki");
            EntityManager em = factory.createEntityManager();
    
    
            Query q = em.createQuery("select t from Notatka t");
            List<Notatka> todoList = q.getResultList();
            for (Notatka todo : todoList)  {
                System.out.println(todo);
            }
            System.out.println("Size: " + todoList.size());
    
         }
        }

I think problem is in this line (but I'm not sure)

EntityManager em = factory.createEntityManager();

question from:https://stackoverflow.com/questions/65902883/illegalargumentexception-an-exception-occurred-while-creating-a-query-in-entity

Answer 1

Probably you forgot to annotate your test.Notatka class with @Entity, therefore EclipseLink does not add it to the metamodel.

Since you don't have any other classes the resulting metamodel is empty, hence the warning.