From c4ddf1853cd767e14715721d9839ec7516fb4568 Mon Sep 17 00:00:00 2001
From: Michael Bayne <mdb@samskivert.com>
Date: Wed, 10 Sep 2008 02:00:19 +0000
Subject: [PATCH] Created an explicit EntityMigration.Add for when you want to
 add a column to a database and need to provide a defaultValue at the time
 that you add it, but don't want to have to define a permanent default value
 on the field.

---
 .../jdbc/depot/EntityMigration.java           | 46 +++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/src/java/com/samskivert/jdbc/depot/EntityMigration.java b/src/java/com/samskivert/jdbc/depot/EntityMigration.java
index 41fc15c..b802f02 100644
--- a/src/java/com/samskivert/jdbc/depot/EntityMigration.java
+++ b/src/java/com/samskivert/jdbc/depot/EntityMigration.java
@@ -150,6 +150,52 @@ public abstract class EntityMigration extends Modifier
         protected ColumnDefinition _newColumnDef;
     }
 
+    /**
+     * A convenient migration for adding a new column that requires a default value to be specified
+     * during the addition. Normally Depot will automatically handle column addition, but if you
+     * have a column that normally does not have a default value but needs one when it is added to
+     * a table with existing rows, you can use this migration.
+     *
+     * @see Column#defaultValue
+     */
+    public static class Add extends EntityMigration
+    {
+        public Add (int targetVersion, String fieldName, String defaultValue) {
+            super(targetVersion);
+            _fieldName = fieldName;
+            _defaultValue = defaultValue;
+        }
+
+        @Override public int invoke (Connection conn, DatabaseLiaison liaison) throws SQLException {
+            // override the default value in the column definition with the one provided
+            ColumnDefinition defColumnDef = new ColumnDefinition(
+                _newColumnDef.getType(), _newColumnDef.isNullable(),
+                _newColumnDef.isUnique(), _defaultValue);
+            // first add the column with the overridden default value
+            if (liaison.addColumn(conn, _tableName, _fieldName, defColumnDef, true)) {
+                // then change the column to the permanent default value
+                liaison.changeColumn(conn, _tableName, _fieldName, _newColumnDef.getType(),
+                                     null, null, _newColumnDef.getDefaultValue());
+                return 1;
+            }
+            return 0;
+        }
+
+        @Override public boolean runBeforeDefault () {
+            return true;
+        }
+
+        @Override
+        protected void init (String tableName, Map<String, FieldMarshaller<?>> marshallers) {
+            super.init(tableName, marshallers);
+            _columnName = marshallers.get(_fieldName).getColumnName();
+            _newColumnDef = marshallers.get(_fieldName).getColumnDefinition();
+        }
+
+        protected String _fieldName, _columnName, _defaultValue;
+        protected ColumnDefinition _newColumnDef;
+    }
+
     /**
      * If this method returns true, this migration will be run <b>before</b> the default
      * migrations, if false it will be run after.