NVelocity实现代码生成器

实现一款简单的代码生成器，需要先定义好代码结构。这里仅生成三层模式中的实体层，后续复杂结构代码生成大家可以自己动手写一下。

1、模版定义

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Mysoft.Code.Entity
{
#foreach($p in $T.Rows)##
#if($velocityCount==1)##
///
$p.get_item("table_name_c")

public class $p.get_item("table_name")
{
#end

///
#if($p.get_item("field_name_c")!="")$p.get_item("field_name_c") #else $p.get_item("field_name") #end

public#if($p.get_item("date_type")=="bigint") double#else string#end $p.get_item("field_name")
{
get;
set;
}
#end
}
}

可以看到模版很简单,最终生成的代码类似下面

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Mysoft.Code.Entity
{
///
阶段设置表

public class Pack_Stage
{

///
更新包GUID

public string StageGUID
{
get;
set;
}

///
更新包名称

public string StageName
{
get;
set;
}

///
阶段序号

public string OrderNo
{
get;
set;
}

///
是否开始合并包

public string IsHBPackage
{
get;
set;
}
}
}

2、从数据库中读取所有表和表的相关信息
SQL Sever的内置表和视图提供了许多有用信息，比如查询所有的用户表和表列信息说明。

sys.tables：用户表相关信息

sys.extended_properties：表的和列的相关描述信息

SELECT T.name AS table_name ,T.OBJECT_ID,
ISNULL(CONVERT(VARCHAR(MAX), E.value), '') AS table_name_c ,
C.name AS field_name ,
ISNULL(CONVERT(VARCHAR(MAX), D.value), '') AS field_name_c ,
ROW_NUMBER() OVER(PARTITION BY T.name ORDER BY C.colid) AS field_sequence ,
TYPE_NAME(C.xtype) AS date_type ,
(CASE WHEN EXISTS ( SELECT 1
FROM sysobjects
WHERE xtype = 'PK'
AND name IN (
SELECT name
FROM sysindexes
WHERE id = C.id
AND indid IN (
SELECT indid
FROM sysindexkeys
WHERE id = C.id
AND colid = C.colid ) ) )
THEN 1
ELSE 0
END) AS pk ,
ISNULL(C.isnullable, 1) AS isnullable ,
ISNULL(COLUMNPROPERTY(c.id, c.name, 'IsIdentity'), 0) AS isidentity
FROM sys.tables AS T
LEFT JOIN syscolumns AS C ON c.id = T.object_id
LEFT JOIN sys.extended_properties AS D ON D.major_id = T.object_id
AND D.minor_id = C.colid
AND D.major_id = C.id
LEFT JOIN sys.extended_properties AS E ON E.major_id = T.object_id
AND E.minor_id = 0

大家可以看下上面的SQL，基本上把表的相关信息都查询出来了，下章将着重讲解这个知识点。
3、代码生成

有了模版和数据源就可以生成最终代码了，有不懂的可以参考上篇，这里上最终效果图。大家可以下载示例代码自行查看。