=== modified file 'dhis-2/dhis-services/dhis-service-core/src/main/java/org/hisp/dhis/preheat/DefaultPreheatService.java'
--- dhis-2/dhis-services/dhis-service-core/src/main/java/org/hisp/dhis/preheat/DefaultPreheatService.java	2016-01-25 04:56:01 +0000
+++ dhis-2/dhis-services/dhis-service-core/src/main/java/org/hisp/dhis/preheat/DefaultPreheatService.java	2016-01-25 06:22:42 +0000
@@ -60,12 +60,19 @@
     private IdentifiableObjectManager manager;
 
     @Override
+    @SuppressWarnings( "unchecked" )
     public Preheat preheat( PreheatParams params )
     {
         Preheat preheat = new Preheat();
 
         if ( PreheatMode.ALL == params.getPreheatMode() )
         {
+            if ( params.getClasses().isEmpty() )
+            {
+                schemaService.getMetadataSchemas().stream().filter( Schema::isIdentifiableObject )
+                    .forEach( schema -> params.getClasses().add( (Class<? extends IdentifiableObject>) schema.getKlass() ) );
+            }
+
             for ( Class<? extends IdentifiableObject> klass : params.getClasses() )
             {
                 List<? extends IdentifiableObject> objects = manager.getAllNoAcl( klass ); // should we use getAll here? are we allowed to reference unshared objects?
@@ -99,10 +106,7 @@
     {
         if ( PreheatMode.ALL == params.getPreheatMode() )
         {
-            if ( params.getClasses().isEmpty() )
-            {
-                throw new PreheatException( "PreheatMode.ALL, but no classes was provided." );
-            }
+            // nothing to validate for now, if classes is empty it will get all metadata classes
         }
         else if ( PreheatMode.REFERENCE == params.getPreheatMode() )
         {

=== modified file 'dhis-2/dhis-services/dhis-service-core/src/test/java/org/hisp/dhis/preheat/PreheatServiceTest.java'
--- dhis-2/dhis-services/dhis-service-core/src/test/java/org/hisp/dhis/preheat/PreheatServiceTest.java	2016-01-25 04:37:41 +0000
+++ dhis-2/dhis-services/dhis-service-core/src/test/java/org/hisp/dhis/preheat/PreheatServiceTest.java	2016-01-25 06:22:42 +0000
@@ -38,6 +38,7 @@
 import org.hisp.dhis.legend.LegendSet;
 import org.hisp.dhis.option.OptionSet;
 import org.hisp.dhis.user.User;
+import org.junit.Ignore;
 import org.junit.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 
@@ -59,6 +60,7 @@
     @Autowired
     private IdentifiableObjectManager manager;
 
+    @Ignore
     @Test( expected = PreheatException.class )
     public void testValidateAllFail()
     {
@@ -274,6 +276,50 @@
 
     @Test
     @SuppressWarnings( "unchecked" )
+    public void testPreheatAllMetadataUID()
+    {
+        DataElementGroup dataElementGroup = new DataElementGroup( "DataElementGroupA" );
+        dataElementGroup.setAutoFields();
+
+        DataElement de1 = createDataElement( 'A' );
+        DataElement de2 = createDataElement( 'B' );
+        DataElement de3 = createDataElement( 'C' );
+
+        manager.save( de1 );
+        manager.save( de2 );
+        manager.save( de3 );
+
+        User user = createUser( 'A' );
+        manager.save( user );
+
+        dataElementGroup.addDataElement( de1 );
+        dataElementGroup.addDataElement( de2 );
+        dataElementGroup.addDataElement( de3 );
+
+        dataElementGroup.setUser( user );
+        manager.save( dataElementGroup );
+
+        PreheatParams params = new PreheatParams();
+        params.setPreheatMode( PreheatMode.ALL );
+
+        preheatService.validate( params );
+        Preheat preheat = preheatService.preheat( params );
+
+        assertFalse( preheat.isEmpty() );
+        assertFalse( preheat.isEmpty( PreheatIdentifier.UID ) );
+        assertFalse( preheat.isEmpty( PreheatIdentifier.UID, DataElement.class ) );
+        assertFalse( preheat.isEmpty( PreheatIdentifier.UID, DataElementGroup.class ) );
+        assertFalse( preheat.isEmpty( PreheatIdentifier.UID, User.class ) );
+
+        assertTrue( preheat.containsKey( PreheatIdentifier.UID, DataElement.class, de1.getUid() ) );
+        assertTrue( preheat.containsKey( PreheatIdentifier.UID, DataElement.class, de2.getUid() ) );
+        assertTrue( preheat.containsKey( PreheatIdentifier.UID, DataElement.class, de3.getUid() ) );
+        assertTrue( preheat.containsKey( PreheatIdentifier.UID, DataElementGroup.class, dataElementGroup.getUid() ) );
+        assertTrue( preheat.containsKey( PreheatIdentifier.UID, User.class, user.getUid() ) );
+    }
+
+    @Test
+    @SuppressWarnings( "unchecked" )
     public void testPreheatReferenceUID()
     {
         DataElementGroup dataElementGroup = new DataElementGroup( "DataElementGroupA" );