0002756: Allow BSH transforms to control if old data is sent to target

symmetric-assemble/src/asciidoc/configuration/transforms/types.ad

@@ -233,7 +233,8 @@ column.  The query can reference source column names by prefixing them with a co
 ===== BeanShell Script Transform
 
 This transformation allows you to provide a http://www.beanshell.org/[BeanShell] script in the transform expression and executes the script
-at the time of transformation.  Some variables are provided to the script: 
+at the time of transformation.  Beanshell transforms can return either a String value or an instance of NewAndOldValue.
+Some variables are provided to the script: 
 
 .Variables
 |===
@@ -248,7 +249,7 @@ at the time of transformation.  Some variables are provided to the script:
 
 |===
 
-.Tranform Expression Example
+.Tranform Expression Example Returning a String
 ====
 ----
 if (currentValue > oldValue) { 
@@ -259,7 +260,16 @@ if (currentValue > oldValue) {
 ----
 ====
 
-
+.Tranform Expression Example Returning a NewAndOldValue object
+====
+----
+if (currentValue != null && currentValue.length() == 0) { 
+	return org.jumpmind.symmetric.io.data.transform.NewAndOldValue(null, oldValue);
+} else { 
+	return currentValue;
+}
+----
+====
 ifndef::pro[]
 [source, SQL]
 ----

symmetric-core/src/main/java/org/jumpmind/symmetric/io/data/transform/BshColumnTransform.java

@@ -48,7 +48,7 @@
 import bsh.Interpreter;
 import bsh.TargetError;
 
-public class BshColumnTransform implements ISingleValueColumnTransform, IBuiltInExtensionPoint {
+public class BshColumnTransform implements ISingleNewAndOldValueColumnTransform, IBuiltInExtensionPoint {
 
     protected final Logger log = LoggerFactory.getLogger(getClass());
 
@@ -79,7 +79,7 @@ public boolean isLoadColumnTransform() {
         return true;
     }
 
-    public String transform(IDatabasePlatform platform,
+    public NewAndOldValue transform(IDatabasePlatform platform,
             DataContext context,
             TransformColumn column, TransformedData data, Map<String, String> sourceValues,
             String newValue, String oldValue) throws IgnoreColumnException, IgnoreRowException {
@@ -143,10 +143,13 @@ public String transform(IDatabasePlatform platform,
                 interpreter.unset(columnName);
             }
 
-            if (result != null) {
-                return result.toString();
+            if (result == null) {
+            	return null;
+            }
+            else if (result instanceof String) {
+            	return new NewAndOldValue((String) result, null);
             } else {
-                return null;
+                return (NewAndOldValue) result;
             }
         } catch (TargetError evalEx) {
             Throwable ex = evalEx.getTarget();