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  • CodeSmith : Merge策略

    通过代码模板来生成代码,但如果你修改了自动生成的代码,再次使用代码模板生成代码后,你修改的代码也就丢失了,CodeSmith 支持多种“合并(Merge)”来解决这个问题,以保留你自己修该过的部分。

    CodeSmith支持如下三种“合并策略”:

    不过这些策略主要是针对C#,VB这些支持Region的语言,对于其它语言可能就需要使用其它方法,比如自定义Merge策略,CodeSmith允许通过CodeSmith.Engine.IMergeStrategy 来扩展“合并”策略,本人推荐CodeSmith的一个原因就是CodeSmith提供了很多接口而不仅仅是一个工具,比如除了CodeSmith支持的属性,XML属性,你也可以通过 CodeSmith.CustomProperties来自定义属性种类,除了CodeSmith支持的数据源种类(MySQL,Oracle),你也可以通过自定义的Schema Provider 支持新的数据库类型或是其它数据类型。

    InsertRegion策略

    InsertRegion 顾名思义,就是在源码中定义一个Region,然后让CodeSmith自动生成的代码只插入到该区域,而在区域外的代码CodeSmith不会去碰它们,从而实现了自定义的代码和自动生成代码的合并。

    PreserveRegion策略

    PreserveRegion 是定义多个区域,然后通知CodeSmith保持这些区域代码不变,自动创建的代码添加到这些区域的外面,和InsertRegion作用相反。

    下面还是借用CodeSmith 自带的Merge示例说明一下这两种策略的基本用法:

    首先是InsertRegion策略,定义一个类文件InsertRegionSample.cs

        public class InsertRegionsSample  
        {  
          
            public void SomeCustomMethod()  
            {  
                // This is my custom code that I want to preserve.  
                // I can make changes to it and my changes will  
                // not be overwritten.  
            }  
         
            #region Sample Generated Region  
        // This region generated by CodeSmith on Saturday, 12 January 2013  
            #endregion  
        }  

    其中定义了一个Region,名为Sample Generated Region ,准备让CodeSmith查入代码,编写一个简单的代码模板,插入当前时间:

    <%@ Template Language="C#" TargetLanguage="C#"   Description="Demonstrates using an InsertRegion merge strategy in C#." %> 

    然后通过CodeSmith项目为模板设置Merge策略:

    20130112002

    选择InsertRegion策略, 然后设置要插入的RegionName。

    生成后的代码如下:

        public class InsertRegionsSample  
        {  
          
            public void SomeCustomMethod()  
            {  
                // This is my custom code that I want to preserve.  
                // I can make changes to it and my changes will  
                // not be overwritten.  
            }  
         
            #region Sample Generated Region  
        // This region generated by CodeSmith on Saturday, 12 January 2013  
            #endregion  
        }  

    可以看到CodeSmith只在Region 处插入代码,而该Region外的部分保持不变。

    类似的PreserveRegions策略,代码和模板定义如下:
    PreserveRegionsSample.cs

        public class PreserveRegionsSample  
        {  
         
        #region "Custom Region 1"  
          
            // This is a place holder for your custom code.  
            // It must exist so that CodeSmith knows where  
            // to put the custom code that will be parsed  
            // from the target source file.  
            // The region name is used to match up the regions  
            // and determine where each region of custom code  
            // should be inserted into the merge result.  
         
        #endregion  
          
            public void SomeGeneratedMethod()  
            {  
          
                // This section and all other non-custom code  
                // regions will be overwritten during each  
                // template execution.  
                // Current Date: Saturday, 12 January 2013  
            }  
         
        #region "Custom Region 2"  
          
            // The contents of this region will also be preserved  
            // during generation.  
         
        #endregion  
          
        }  

    模板定义如下:

        <%@ Template Language="C#" TargetLanguage="C#"    Description="Demonstrates using a PreserveRegions merge strategy in C#." %>  
        public class PreserveRegionsSample  
        {  
         
        #region "Custom Region 1"  
          
            // This is a place holder for your custom code.  
            // It must exist so that CodeSmith knows where  
            // to put the custom code that will be parsed  
            // from the target source file.  
            // The region name is used to match up the regions  
            // and determine where each region of custom code  
            // should be inserted into the merge result.  
         
        #endregion  
          
            public void SomeGeneratedMethod()  
            {  
          
                // This section and all other non-custom code  
                // regions will be overwritten during each  
                // template execution.  
                // Current Date: <%= DateTime.Now.ToLongDateString() %>  
            }  
         
        #region "Custom Region 2"  
          
            // The contents of this region will also be preserved  
            // during generation.  
         
        #endregion  
          
        }  

    模板中也定义了两个区域,然后为该模板设置Merge策略,使用PreserveRegion时可能有多个Region需要保留,因此可以使用RegX来定义要保留的Region:
    20130112003

    InsertClass 策略用在给以重载的代码中插入自动生成的代码,挺起来和InsertRegion功能很类似,的确也是如此,但InsertClass支持更多的配置,可以实现更加灵活和强大的功能。

    它支持的配置有:

    Language

    String, Required

    只支持VB和C#

    ClassName String, Required 需插入代码的类名.
    PreserveClassAttributes Boolean, defaults to False 是否保留类已有的Attributes,缺省CodeSmith替代类原来的Attributes
    OnlyInsertMatchingClass Boolean, defaults to False 是否只插入匹配的类定义中
    MergeImports Boolean, defaults to False 是否合并Import语句
    NotFoundAction Enum, defaults to None 如果指定的类没找到后的行动,可以None,InsertAtBottom,InsertInParent几种选项
    NotFoundParent String, no default 如果指定NotFoundAction为InsertInParent对应的父类名称.

    比如使用如下配置:

    Language: C#
    ClassName: “Pet”
    PreserveClassAttributes: True
    OnlyInsertMatchingClass: True
    MergeImports: True

    现有类定义:

        using System;  
        using System.ComponentModel.DataAnnotations;  
        namespace Petshop  
        {  
            [ScaffoldTable(true)]  
            public class Pet  
            {  
                public int Age { get; set; }  
                public string FirstName { get; set; }  
                public string LastName { get; set; }  
            }  
        }  

    自动生成的代码如下:

        using System;  
        using System.Text;  
        namespace Petshop  
        {  
            public class Pet  
            {  
                public string FirstName { get; set; }  
          
                public string LastName { get; set; }  
          
                public string FullName  
                {  
                    get { return String.Format("{0} {1}", FirstName, LastName); }  
          
                }  
            }  
        }  

    使用InsertClass 合并后的代码如下:

        using System;  
        using System.ComponentModel.DataAnnotations;  
        using System.Text;  
        namespace Petshop  
        {  
            [ScaffoldTable(true)]  
            public class Pet  
            {  
                public string FirstName { get; set; }  
          
                public string LastName { get; set; }  
          
                public string FullName  
                {  
                    get { return String.Format("{0} {1}", FirstName, LastName); }  
          
                }  
            }  
        }  

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  • 原文地址:https://www.cnblogs.com/ful1021/p/4804429.html
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