Difference.java

/*
** Module   : Difference.java
** Abstract : Representation of any detected difference in schema.
**
** Copyright (c) 2022, Golden Code Development Corporation.
**
** -#- -I- --Date-- ---------------------------------------Description---------------------------------------
** 001 BS  20221103 Created initial version.
*/

/*
** This program is free software: you can redistribute it and/or modify
** it under the terms of the GNU Affero General Public License as
** published by the Free Software Foundation, either version 3 of the
** License, or (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
** GNU Affero General Public License for more details.
**
** You may find a copy of the GNU Affero GPL version 3 at the following
** location: https://www.gnu.org/licenses/agpl-3.0.en.html
**
** Additional terms under GNU Affero GPL version 3 section 7:
**
**   Under Section 7 of the GNU Affero GPL version 3, the following additional
**   terms apply to the works covered under the License.  These additional terms
**   are non-permissive additional terms allowed under Section 7 of the GNU
**   Affero GPL version 3 and may not be removed by you.
**
**   0. Attribution Requirement.
**
**     You must preserve all legal notices or author attributions in the covered
**     work or Appropriate Legal Notices displayed by works containing the covered
**     work.  You may not remove from the covered work any author or developer
**     credit already included within the covered work.
**
**   1. No License To Use Trademarks.
**
**     This license does not grant any license or rights to use the trademarks
**     Golden Code, FWD, any Golden Code or FWD logo, or any other trademarks
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**     name Golden Code, FWD, or the names of any author or contributor, for
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*/

package com.goldencode.p2j.persist.orm.schema;

import com.goldencode.p2j.persist.orm.schema.element.*;

/**
 * Representation of any detected difference. Both old and new element references may be null. The idea is
 * simple:
 *
 *  - oldElement NULL, newElement NOT NULL => Added new element
 *  - oldElement NOT NULL, newElement NULL => Deleted old element
 *  - oldElement NOT NULL, newElement NOT NULL => Element was changed (any other property except name)
 *
 */
public class Difference
{
   /**
    * Updated table representation. Should be used as a reference to the updated state.
    */
   private final Table updatedTable;
   
   /**
    * Old element reference. Nullable.
    */
   private final Element oldElement;
   
   /**
    * New element reference. Nullable.
    */
   private final Element newElement;
   
   /**
    * Default constructor.
    *
    * @param  updatedTable
    *         Updated table reference
    * @param  oldElement
    *         Old element reference
    * @param  newElement
    *         New element reference
    * @throws IllegalArgumentException if both old and new elements are null
    */
   public Difference(Table updatedTable, Element oldElement, Element newElement)
   {
      this.updatedTable = updatedTable;
      this.oldElement = oldElement;
      this.newElement = newElement;
      
      if (oldElement == null && newElement == null)
      {
         throw new IllegalArgumentException("New state and old state cannot be both null");
      }
   }
   
   /**
    * Getter for updated table.
    *
    * @return Updated table reference
    */
   public Table getUpdatedTable()
   {
      return updatedTable;
   }
   
   /**
    * Getter for old element.
    *
    * @return Old element reference
    */
   public Element getOldElement()
   {
      return oldElement;
   }
   
   /**
    * Getter for new element.
    *
    * @return New element reference
    */
   public Element getNewElement()
   {
      return newElement;
   }
   
   /**
    * For simplicity of debugging, this override implements the logic behind added/removed/modified change states.
    */
   @Override
   public String toString()
   {
      if (getOldElement() == null)
      {
         return "Added " + getNewElement().getName();
      }
      else if (getNewElement() == null)
      {
         return "Removed " + getOldElement().getName();
      }
      return getOldElement().getName() + " -> " + getNewElement().getName();
   }
}