#374 - Update ModelDiff and migration generation

src/main/java/com/avaje/ebean/dbmigration/model/ModelDiff.java

@@ -1,10 +1,12 @@
 package com.avaje.ebean.dbmigration.model;
 
 import com.avaje.ebean.dbmigration.migration.AddColumn;
+import com.avaje.ebean.dbmigration.migration.AddHistoryTable;
 import com.avaje.ebean.dbmigration.migration.AlterColumn;
 import com.avaje.ebean.dbmigration.migration.ChangeSet;
 import com.avaje.ebean.dbmigration.migration.ChangeSetType;
 import com.avaje.ebean.dbmigration.migration.DropColumn;
+import com.avaje.ebean.dbmigration.migration.DropHistoryTable;
 import com.avaje.ebean.dbmigration.migration.Migration;
 
 import java.util.ArrayList;
@@ -31,6 +33,11 @@ public class ModelDiff {
    */
   private final List<Object> dropChanges = new ArrayList<Object>();
 
+  /**
+   * List of 'drop' type changes. Expected to be placed into a separate DDL script.
+   */
+  private final List<Object> dropHistoryChanges = new ArrayList<Object>();
+
   /**
    * Construct with a base model.
    */
@@ -45,6 +52,27 @@ public class ModelDiff {
     this.baseModel = new ModelContainer();
   }
 
+  /**
+   * Return the diff as a migration potentially containing
+   * an apply changeSet and a drop changeSet.
+   */
+  public Migration getMigration() {
+
+    Migration migration = new Migration();
+    ChangeSet applyChangeSet = getApplyChangeSet();
+    if (!applyChangeSet.getChangeSetChildren().isEmpty()) {
+      // add a non empty apply changeSet
+      migration.getChangeSet().add(applyChangeSet);
+    }
+
+    ChangeSet dropChangeSet = getDropChangeSet();
+    if (!dropChangeSet.getChangeSetChildren().isEmpty()) {
+      // add a non empty drop changeSet
+      migration.getChangeSet().add(dropChangeSet);
+    }
+    return migration;
+  }
+
   /**
    * Return the list of 'create' changes.
    */
@@ -52,6 +80,16 @@ public class ModelDiff {
     return createChanges;
   }
 
+  /**
+   * Return the list of 'drop' changes.
+   */
+  public List<Object> getDropChanges() {
+    return dropChanges;
+  }
+
+  /**
+   * Return the 'apply' changeSet.
+   */
   public ChangeSet getApplyChangeSet() {
     // put the changes into a ChangeSet
     ChangeSet createChangeSet = new ChangeSet();
@@ -60,6 +98,9 @@ public class ModelDiff {
     return createChangeSet;
   }
 
+  /**
+   * Return the 'drop' changeSet.
+   */
   public ChangeSet getDropChangeSet() {
     // put the changes into a ChangeSet
     ChangeSet createChangeSet = new ChangeSet();
@@ -68,21 +109,6 @@ public class ModelDiff {
     return createChangeSet;
   }
 
-  public Migration getMigration() {
-
-    Migration migration = new Migration();
-    migration.getChangeSet().add(getApplyChangeSet());
-    migration.getChangeSet().add(getDropChangeSet());
-    return migration;
-  }
-
-  /**
-   * Return the list of 'drop' changes.
-   */
-  public List<Object> getDropChanges() {
-    return dropChanges;
-  }
-
   /**
    * Compare to a 'newer' model and collect the differences.
    */
@@ -116,18 +142,41 @@ public class ModelDiff {
   protected void compareTables(MTable currentTable, MTable newTable) {
 
     currentTable.compare(this, newTable);
-
   }
 
+  /**
+   * Add the AlterColumn to the 'apply' changes.
+   */
   public void addAlterColumn(AlterColumn alterColumn) {
     createChanges.add(alterColumn);
   }
 
+  /**
+   * Add the AlterColumn to the 'apply' changes.
+   */
+  public void addAddColumn(AddColumn addColumn) {
+    createChanges.add(addColumn);
+  }
+
+  /**
+   * Add the DropColumn to the 'drop' changes.
+   */
   public void addDropColumn(DropColumn dropColumn) {
     dropChanges.add(dropColumn);
   }
 
-  public void addAddColumn(AddColumn addColumn) {
-    createChanges.add(addColumn);
+  /**
+   * Add the AddHistoryTable to apply changes.
+   */
+  public void addAddHistoryTable(AddHistoryTable addHistoryTable) {
+    createChanges.add(addHistoryTable);
   }
+
+  /**
+   * Add the DropHistoryTable to the 'drop history' changes.
+   */
+  public void addDropHistoryTable(DropHistoryTable dropHistoryTable) {
+    dropHistoryChanges.add(dropHistoryTable);
+  }
+
 }