title: GreenDAO support multiple relations between tables
body: <p>I've been trying to create a DB model using GreenDAO. the problem started when I tried to create more than one relationship between a different tables.</p>
  
  <p>basically, I have a <code>Message</code> table, a <code>Conversation</code> table and a <code>User</code> table.</p>
  
  <p>the User has a list of messages, and the message has a parent conversation.</p>
  
  <p>I tried writing this code for creating the DB:</p>
  
  <pre><code>    private static void addUser(Schema schema) {
              user = schema.addEntity("User");
              userId = user.addIdProperty().getProperty();
              user.addStringProperty("facebookId").unique().index();
  
              user.addStringProperty("firstName");
              user.addStringProperty("lastName");
              user.addStringProperty("fullName");
              user.addStringProperty("photoUrl");
      }
  
      private static void addMessage(Schema schema) {
              message = schema.addEntity("Message");
              messageId = message.addIdProperty().getProperty();
              message.addStringProperty("messageId").primaryKey();
  
              message.addDateProperty("date");
              message.addStringProperty("content");
              message.addStringProperty("typeString");
      }
  
      private static void addConversation(Schema schema) {
            conversation = schema.addEntity("Conversation");
            conversation.addIdProperty();
  
            conversation.addStringProperty("conversationId");
            // REST OF THE CODE
      }
  
      private static void fakeRelationship(Schema schema) {
              Property author = message.addLongProperty("author").getProperty();
              Property parent = message.addLongProperty("parent").getProperty();
  
              message.addToOne(user, author);
              message.addToOne(conversation, parent);
  
              user.addToMany(message, author);
              conversation.addToMany(message, parent);
      }
  </code></pre>
  
  <p>after running this code, I got this error: </p>
  
  <pre><code>Exception in thread "main" java.lang.RuntimeException: Currently only single FK columns are supported: ToOne 'parent' from Message to Conversation
  at de.greenrobot.daogenerator.ToOne.init3ndPass(ToOne.java:91)
  at de.greenrobot.daogenerator.Entity.init3rdPassRelations(Entity.java:557)
  at de.greenrobot.daogenerator.Entity.init3ndPass(Entity.java:550)
  at de.greenrobot.daogenerator.Schema.init3ndPass(Schema.java:185)
  at de.greenrobot.daogenerator.DaoGenerator.generateAll(DaoGenerator.java:94)
  at de.greenrobot.daogenerator.DaoGenerator.generateAll(DaoGenerator.java:79)
  at com.glidetalk.dao.generator.GlideDaoGenerator.main(GlideDaoGenerator.java:27)
  </code></pre>
  
  <p>does this actually meen that I can't create more than one relation for each table in my DB?!</p>
  
  <p>do I have to write everything manually?</p>