Added code to check that objects have @Column annotations

If a class to be encoded has no @Column annotations the CodecGen
should throw an Exception, as a class with no @Column annotations
cannot be correctly represented on protobuf. I added a check to
scanFields to check for this, and throw an appropriate exception.

Change-Id: Ib6962d1b2e05e5b494ca0cee2091caa1f5daa731

1 files changed, 4 insertions, 0 deletions

diff --git a/src/main/java/com/google/gwtorm/protobuf/CodecGen.java b/src/main/java/com/google/gwtorm/protobuf/CodecGen.java
index 5a5342b..2aaf841 100644
--- a/src/main/java/com/google/gwtorm/protobuf/CodecGen.java
+++ b/src/main/java/com/google/gwtorm/protobuf/CodecGen.java
@@ -121,6 +121,10 @@ class CodecGen<T> implements Opcodes {
       }
       in = in.getSuperclass();
     }
+    if (col.isEmpty()) {
+      throw new OrmException(
+          "Cannot create new encoder, no @Column fields found");
+    }
     return sort(col);
   }