DB migration initial

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

@@ -0,0 +1,98 @@
+package com.avaje.ebean.dbmigration.model;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Used to prepare a diff in terms of changes required to migrate from
+ * the base model to the newer model.
+ */
+public class ModelDiff {
+
+  /**
+   * The base model to which we compare the newer model.
+   */
+  protected final ModelContainer baseModel;
+
+  /**
+   * List of 'create' type changes.
+   */
+  protected final List<Object> createChanges = new ArrayList<Object>();
+
+  /**
+   * List of 'drop' type changes. Potential for putting into a separate changeSet.
+   */
+  protected final List<Object> dropChanges = new ArrayList<Object>();
+
+  /**
+   * Construct with a base model.
+   */
+  public ModelDiff(ModelContainer baseModel) {
+    this.baseModel = baseModel;
+  }
+
+  /**
+   * Construct with a base model.
+   */
+  public ModelDiff() {
+    this.baseModel = new ModelContainer();
+  }
+
+  /**
+   * Return the list of 'create' changes.
+   */
+  public List<Object> getCreateChanges() {
+    return createChanges;
+  }
+
+  /**
+   * Return the list of 'drop' changes.
+   */
+  public List<Object> getDropChanges() {
+    return dropChanges;
+  }
+
+  /**
+   * Compare to a 'newer' model and collect the differences.
+   */
+  public void compareTo(ModelContainer newModel) {
+
+    for (MTable newTable : newModel.getTables().values()) {
+
+      MTable currentTable = baseModel.getTable(newTable.getName());
+      if (currentTable == null) {
+        addNewTable(newTable);
+      } else {
+        compareTables(currentTable, newTable);
+      }
+    }
+
+    //TODO: other parts of the model? views, indexes etc
+
+  }
+
+  /**
+   * Add CreateTable to the 'creation' changes.
+   */
+  protected void addNewTable(MTable newTable) {
+
+    createChanges.add(newTable.createTable());
+//    createChanges.add(newTable.createForeignKeys());
+  }
+
+  /**
+   * Compare tables looking for add/drop/modify columns etc.
+   */
+  protected void compareTables(MTable currentTable, MTable newTable) {
+
+    //TODO: compareTables()
+    // changed columns
+    // find additional columns
+    // find removed columns
+    // changes to indexes?
+    // changes to primary key
+    // changes to foreign key
+    // changes to unique constraints?
+
+  }
+}