Test that shows a issue of morphia with an inheritance stucture of @Embedded objects.

MorphiaEmbeddedInheritanceTest.java

import static org.junit.Assert.assertEquals;

import org.junit.Before;
import org.junit.Test;

import com.google.code.morphia.Morphia;
import com.google.code.morphia.annotations.Converters;
import com.google.code.morphia.annotations.Embedded;
import com.google.code.morphia.annotations.Entity;
import com.google.code.morphia.annotations.Id;
import com.google.code.morphia.converters.SimpleValueConverter;
import com.google.code.morphia.converters.TypeConverter;
import com.google.code.morphia.mapping.MappedField;
import com.google.code.morphia.mapping.MappingException;
import com.mongodb.BasicDBObjectBuilder;
import com.mongodb.DBCollection;
import com.mongodb.DBObject;
import com.mongodb.DefaultDBDecoder;
import com.mongodb.DefaultDBEncoder;

/**
 * This test shows an issue with an <code>@Embedded</code> class A inheriting from an
 * <code>@Embedded</code> class B that both have a Converter assigned (A has AConverter,
 * B has BConverter).
 * <p>
 * When an object (here MyEntity) has a property/field of type A and is deserialized,
 * the deserialization fails with a
 * "com.google.code.morphia.mapping.MappingException: No usable constructor for A".
 * </p>
 */
public class MorphiaEmbeddedInheritanceTest {

   @Entity(noClassnameStored = true)
   static class MyEntity {

      @Id
      private Long id;
      @Embedded
      private A a;

      public MyEntity() {
      }

      public MyEntity(final Long id, final A a) {
         this.id = id;
         this.a = a;
      }

      @Override
      public int hashCode() {
         final int prime = 31;
         int result = 1;
         result = prime * result + ((id == null) ? 0 : id.hashCode());
         result = prime * result + ((a == null) ? 0 : a.hashCode());
         return result;
      }

      @Override
      public boolean equals(final Object obj) {
         if (this == obj) {
            return true;
         }
         if (obj == null) {
            return false;
         }
         if (getClass() != obj.getClass()) {
            return false;
         }
         final MyEntity other = (MyEntity) obj;
         if (id == null) {
            if (other.id != null) {
               return false;
            }
         } else if (!id.equals(other.id)) {
            return false;
         }
         if (a == null) {
            if (other.a != null) {
               return false;
            }
         } else if (!a.equals(other.a)) {
            return false;
         }
         return true;
      }

   }

   @Converters(B.BConverter.class)
   @Embedded
   static class B {

      static class BConverter extends TypeConverter implements SimpleValueConverter {

         public BConverter() {
            this(B.class);
         }

         public BConverter(final Class<? extends B> clazz) {
            super(clazz);
         }

         @SuppressWarnings({ "rawtypes" })
         @Override
         public B decode(final Class targetClass, final Object fromDBObject, final MappedField optionalExtraInfo)
               throws MappingException {
            if (fromDBObject == null) {
               return null;
            }
            final Long source = (Long) fromDBObject;
            return create(source);
         }

         protected B create(final Long source) {
            return new B(source);
         }

         @Override
         public Long encode(final Object value, final MappedField optionalExtraInfo) {
            if (value == null) {
               return null;
            }
            final B source = (B) value;
            return source.value;
         }

      }

      private final long value;

      public B(final long value) {
         super();
         this.value = value;
      }

      @Override
      public int hashCode() {
         final int prime = 31;
         int result = 1;
         result = prime * result + (int) (value ^ (value >>> 32));
         return result;
      }

      @Override
      public boolean equals(final Object obj) {
         if (this == obj) {
            return true;
         }
         if (obj == null) {
            return false;
         }
         if (getClass() != obj.getClass()) {
            return false;
         }
         final B other = (B) obj;
         if (value != other.value) {
            return false;
         }
         return true;
      }

    @Override
    public String toString() {
        return getClass().getSimpleName() + " [value=" + value + "]";
    }
    
   }

   @Converters(A.AConverter.class)
   @Embedded
   static class A extends B {

      static final class AConverter extends B.BConverter {

         public AConverter() {
            super(A.class);
         }

         @Override
         protected A create(final Long source) {
            return new A(source);
         }

      }

      public A(final long value) {
         super(value);
      }
   }

   private Morphia morphia;

   @Before
   public void setup() {
      morphia = new Morphia();
      morphia.map(MyEntity.class);
      morphia.map(B.class);
      morphia.map(A.class);
   }

   /**
    * This test is green when {@link MyEntity#a} is annotated with <code>@Property</code>,
    * as in this case the field is not serialized at all. However, the bson encoder would
    * fail to encode the object of type A (as shown by {@link #testFullBSONSerialization()}).
    */
   @Test
   public void testDBObjectSerialization() {
      final MyEntity entity = new MyEntity(1l, new A(2));
      final DBObject dbObject = morphia.toDBObject(entity);
      assertEquals(BasicDBObjectBuilder.start("_id", 1l).add("a", 2l).get(), dbObject);
      // fails with a
      // com.google.code.morphia.mapping.MappingException: No usable constructor
      // for InheritanceTest$A
      final MyEntity actual = morphia.fromDBObject(MyEntity.class, dbObject);
      assertEquals(entity, actual);
   }

   /**
    * This test shows the full serialization, including bson encoding/decoding.
    */
   @Test
   public void testFullBSONSerialization() {
      final MyEntity entity = new MyEntity(1l, new A(2));
      final DBObject dbObject = morphia.toDBObject(entity);

      final byte[] data = new DefaultDBEncoder().encode(dbObject);

      final DBObject decoded = new DefaultDBDecoder().decode(data, (DBCollection)null);
      // fails with a
      // com.google.code.morphia.mapping.MappingException: No usable constructor
      // for InheritanceTest$A
      final MyEntity actual = morphia.fromDBObject(MyEntity.class, decoded);
      assertEquals(entity, actual);
   }

}