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From tfisc...@apache.org
Subject svn commit: r1348439 - in /db/torque/torque4/trunk/torque-site/src/site/xdoc/documentation/modules/generator/reference: configuration.xml existing-target-modes.xml
Date Sat, 09 Jun 2012 16:00:33 GMT
Author: tfischer
Date: Sat Jun  9 16:00:33 2012
New Revision: 1348439

URL: http://svn.apache.org/viewvc?rev=1348439&view=rev
added merge mode docs


Modified: db/torque/torque4/trunk/torque-site/src/site/xdoc/documentation/modules/generator/reference/configuration.xml
URL: http://svn.apache.org/viewvc/db/torque/torque4/trunk/torque-site/src/site/xdoc/documentation/modules/generator/reference/configuration.xml?rev=1348439&r1=1348438&r2=1348439&view=diff
--- db/torque/torque4/trunk/torque-site/src/site/xdoc/documentation/modules/generator/reference/configuration.xml
+++ db/torque/torque4/trunk/torque-site/src/site/xdoc/documentation/modules/generator/reference/configuration.xml
Sat Jun  9 16:00:33 2012
@@ -149,7 +149,9 @@
     other modes are "skip" (skip generation and leave existing file as is),
     "append" (append generation result to the existing file)
     and "merge" (merge changes in the generation output with changed generation
-    result, see <a href="mergeMode.html" /> for a detailed documentation).
+    result, see 
+    <a href="existing-target-modes.html">the existing target modes documentation</a>
+    for details).
     The outputDirKey attribute of the output tag allows to write the
     output files to another output directory, the outputDirKey defines
     a symbolic name for this directory. On generation time, the user needs

Added: db/torque/torque4/trunk/torque-site/src/site/xdoc/documentation/modules/generator/reference/existing-target-modes.xml
URL: http://svn.apache.org/viewvc/db/torque/torque4/trunk/torque-site/src/site/xdoc/documentation/modules/generator/reference/existing-target-modes.xml?rev=1348439&view=auto
--- db/torque/torque4/trunk/torque-site/src/site/xdoc/documentation/modules/generator/reference/existing-target-modes.xml
+++ db/torque/torque4/trunk/torque-site/src/site/xdoc/documentation/modules/generator/reference/existing-target-modes.xml
Sat Jun  9 16:00:33 2012
@@ -0,0 +1,161 @@
+<?xml version="1.0" encoding="UTF-8"?>
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements.  See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership.  The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License.  You may obtain a copy of the License at
+   http://www.apache.org/licenses/LICENSE-2.0
+ Unless required by applicable law or agreed to in writing,
+ software distributed under the License is distributed on an
+ KIND, either express or implied.  See the License for the
+ specific language governing permissions and limitations
+ under the License.
+ <properties>
+  <title>Existing Target Modes</title>
+ </properties>
+ <body>
+  <section name="Existing Target Modes">
+    <p>
+      This page explains the possible modes to handle existing target files.
+      If the generator encounters a file to be generated which already exists,
+      it can be instructed to treat it the following ways:
+      <ul>
+        <li>
+          <code>replace</code> (default): 
+          The existing file is replaced by the newly generated file.
+        </li>
+        <li>
+          <code>skip</code>: Generation is skipped, the existing file is left
+          as is.
+        </li>
+        <li>
+          <code>append</code>: The generation result is appended to the
+          content of the existing file.
+        </li>
+        <li>
+          <code>merge</code>: The generation result merged with the
+          content of the existing file.
+        </li>
+      </ul>
+      The replace mode is suitable when the target file is not intended to be
+      edited.<br/>
+      The skip mode is suitable when a starting point for a file should be
+      generated, which can then subsequently be edited by the user.<br/>
+      The append mode can be useful for generating log files and similar.<br/>
+      The skip mode is suitable when a file should be generated
+      which content can then either be changed by the user and the generator.
+      <br/>
+    </p>
+  </section>
+  <section name="Allow user to change generated code">
+    <p>
+      Three of the modes above allows the user to change generated files:
+      skip, append and merge. From those, append is unlikely to appear in code
+      generation so it will not be considered further. The two other modes, 
+      skip and merge, have different merits in user-generator interaction. 
+    </p>
+    <p>
+      The mode skip should be used if the generated file is just a starting
+      point, or if the generation result is very unlikely to change,
+      e.g. if the code templates are believed to have all needed features
+      and the sources are unlikely to change.<br/>
+      It is a strategy which is simple to understand and use, so if a problem
+      can be solved by both the skip mode and the merge mode, 
+      the skip mode should be used. 
+    </p>
+    <p>
+      The mode merge should be used if the generated code is not stable yet
+      (e.g. because the generator lacks features, or the source is likely
+      to change in such a way that the contents of a generated file is changed),
+      and it is likely that user interaction is needed in the generated files.
+      <br/>
+      Even if the above is the case, it may be better to separate generated 
+      content and user-written content by using a delegation or inheritance
+      strategy (e.g. see the inheritance strategy in the Torque templates).
+      Delegation or inheritance will usually work if the user changes
+      involve changing whole methods; it will not work if changes involve only
+      parts of methods and these parts cannot (or should not) be factored out.
+      The reasons for trying to avoud merging are:
+      <ul>
+        <li>Merging is complicated to understand.</li>
+        <li>Merging is complicated to use.</li>
+      </ul>
+      That said, there are situations where merging saves a lot of pain,
+      so it should be considered whenever generated and user-written code
+      are very interwoven.
+    </p>
+    <subsection name="Merge Mode">
+      <p>
+        The merge mode works as follows:
+        If a file is generated which existingTargetStrategy is
+        <code>merge</code>is generated, the generator will store the generated

+        code in two files: one file being the nominal target, and the other
+        file is stored in another directory tree 
+        (e.g. src/unmerged-gen-output/).
+        Once this has happened, the user can change the generated file
+        (all changes should be in the nominal target file, the file in 
+        src/unmerged-gen-output/ should _NOT_ be edited),
+        Also changes can be made to the generator.<br/>
+        As an example, let us assume that in the second generator run,
+        both the file which was generated in the first generator run
+        and the generation result have changed.
+        The generator will now produce the generation output in memory
+        and will compare 
+        a) the src/unmerged-gen-output file with the new generation result and
+        b) the src/unmerged-gen-output file with the nominal target file.
+        This way the generator can determine which changes were made
+        in the generator output and which changes were made by the user.
+        Then, the generator will perform a three-way-merge with the two 
+        changesets and overwrite the nominal target file with the results
+        of the merge and the src/unmerged-gen-output file with the raw
+        (unmerged) generation result.
+        In the case that conflicts appear in the merge,
+        the merger will produce the usual &lt; and &gt; marked sections
+        with both the conflicting inputs.<br/>
+        Of course, other generation runs can follow, with either the user
+        editing the generated file, wit changed generation output, or both.
+      </p>
+      <p>
+        There are a couple of things to consider when operating in merge mode:
+        <ul>
+          <li>
+            Conflicts should be resolved before attempting a new generation
+            run. Otherwise, the &lt; and &gt; marked sections will probably
+            produce more conflicts, eventually ending in &lt; and &gt;
+            merge hell.
+          </li>
+          <li>
+            When several copies of the project exist where the generation 
+            is run, the unmerged files 
+            (in src/unmerged-gen-output in the above example)
+            should also be shared between the copies
+            (this usually implies that they are checked in version control).
+            Otherwise, the three-way-merge can produce strage results
+            because the merge basis is different in different copies.
+          </li>
+          <li>
+            If the unmerged files 
+            (in src/unmerged-gen-output in the above example)
+            are checked into version control, care should be taken to always
+            check in the nominal target files and the src/unmerged-gen-output
+            files in the same commit; otherwise different people may
+            use a different merge basis which can produce a different merge
+            result. 
+          </li>
+        </ul>
+      </p>
+    </subsection>
+  </section>
+ </body>
\ No newline at end of file

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