Implemented DatabaseField annotation parameter that allows to specify more java side field than in postgres type

Author: Maciej Rosiek

src/main/java/de/zalando/typemapper/annotations/DatabaseField.java

@@ -35,4 +35,5 @@
 
     Class<? extends ObjectMapper<?>> mapper() default DefaultObjectMapper.class;
 
+    boolean optional() default false;
 }

src/main/java/de/zalando/typemapper/core/DatabaseFieldDescriptor.java

@@ -11,18 +11,21 @@ public class DatabaseFieldDescriptor {
     private int position;
     private Class<? extends ValueTransformer<?, ?>> transformer;
     private Class<? extends ObjectMapper<?>> mapper;
+    private boolean optional;
 
     public DatabaseFieldDescriptor(final DatabaseField databaseField) {
         this.name = databaseField.name();
         this.position = databaseField.position();
         this.transformer = databaseField.transformer();
         this.mapper = databaseField.mapper();
+        this.optional = databaseField.optional();
     }
 
     public DatabaseFieldDescriptor(final Column column) {
         this.name = column.name();
         this.position = -1;
         this.transformer = AnyTransformer.class;
+        this.optional = false;
     }
 
     public String getName() {
@@ -40,4 +43,9 @@ public int getPosition() {
     public Class<? extends ObjectMapper<?>> getMapper() {
         return mapper;
     }
+
+    public boolean isOptional() {
+        return optional;
+    }
+
 }

src/main/java/de/zalando/typemapper/postgres/PgTypeHelper.java

@@ -305,29 +305,33 @@ public int compare(final Field a, final Field b) {
                     DbTypeField dbField = null;
                     if (dbFields != null) {
 
+                        if (resultPositionMap == null) {
+                            resultPositionMap = new TreeMap<Integer, Object>();
+                        }
+
                         // we have type information from database (field positions)
                         final String dbFieldName = Mapping.getDatabaseFieldName(f, databaseFieldDescriptor.getName());
                         dbField = dbFields.get(dbFieldName);
 
                         if (dbField == null) {
-                            throw new IllegalArgumentException("Field " + f.getName() + " (" + dbFieldName
-                                    + ") of class " + clazz.getSimpleName() + " could not be found in database type "
-                                    + typeName);
-                        }
-
-                        if (resultPositionMap == null) {
-                            resultPositionMap = new TreeMap<Integer, Object>();
+                            if (!databaseFieldDescriptor.isOptional()) {
+                                throw new IllegalArgumentException("Field " + f.getName() + " (" + dbFieldName
+                                        + ") of class " + clazz.getSimpleName()
+                                        + " could not be found in database type " + typeName);
+                            }
+                        } else {
+                            resultPositionMap.put(dbField.getPosition(), value);
                         }
-
-                        resultPositionMap.put(dbField.getPosition(), value);
                     }
 
                     if (dbField == null) {
                         if (resultList == null) {
                             resultList = new ArrayList<Object>();
                         }
 
-                        resultList.add(value);
+                        if (!databaseFieldDescriptor.isOptional()) {
+                            resultList.add(value);
+                        }
                     }
                 }
             }