title: Unable to build Hibernate SessionFactory; nested exception
body: <p>In my <em>Spring Boot</em> application, I have two models. Actually trying to implement <code>ManyToMany</code> relationship.</p>
  
  <p>A:</p>
  
  <pre><code>@Entity
  public class A {
      @Id
      @GeneratedValue(strategy = GenerationType.AUTO)
      private Long id;
      private Set&lt;B&gt; b=new HashSet&lt;&gt;();
      public A() {
  
      }
  }
  </code></pre>
  
  <p>B:</p>
  
  <pre><code>@Entity
  public class B {
      @Id
      @GeneratedValue(strategy = GenerationType.AUTO)
      private Long id;
      private Set&lt;A&gt; a=new HashSet&lt;&gt;();
      public B() {
  
      }
  
  }
  </code></pre>
  
  <p>When I try to compile this this gives me error, saying :
  <em>Invocation of init method failed; nested exception is javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory; nested exception is org.hibernate.MappingException: Could not determine type for: java.util.Set, at table: a, for columns: [org.hibernate.mapping.Column(b)]</em></p>
  
  <p>Full log : <a href="https://pastebin.com/0EDxnyNa" rel="nofollow noreferrer">here</a></p>