在通过T4模版引擎之基础入门 对T4有了初步印象后，我们开始实战篇。T4模板引擎可以当做一个代码生成器，代码生成器的职责当然是用来生成代码(这不是废话吗)。而这其中我们使用的最普遍的是根据数据库生成实体类。

　　工欲善其事必先利其器，在这之前先来介绍一款T4编辑器T4 Editor，我们可以点击链接去下载然后安装，不过还是推荐大家直接在VS扩展管理器里直接安装来的方便 工具->扩展管理器->联机库 搜索 "T4 Editor"，选择第一项 "tangible T4 Editor 2.0 plus modeling tools for VS2010" 进行安装即可，如下图所示:

安装上T4 Editor后，编辑T4模板是就有代码着色和智能提示了，下图为安装T4 Editor后的代码着色效果，怎么样是不是耳目一新

接下来开始正式进入我们的主题，从数据库自动生成实体类

1. 新建一个控制台项目，然后添加T4模板，这里我们起名字为Customers.tt
2. 修改输出文件扩展名为.cs

   <#@ output extension=".cs" #>

3. 添加常用的程序集和命名空间引用

   <#@ assembly name="System.Core.dll" #>
   <#@ assembly name="System.Data.dll" #>
   <#@ assembly name="System.Data.DataSetExtensions.dll" #>
   <#@ assembly name="System.Xml.dll" #>
   <#@ import namespace="System" #>
   <#@ import namespace="System.Xml" #>
   <#@ import namespace="System.Linq" #>
   <#@ import namespace="System.Data" #>
   <#@ import namespace="System.Data.SqlClient" #>
   <#@ import namespace="System.Collections.Generic" #>
   <#@ import namespace="System.IO" #>

4. 添加数据库操作DbHelper引用
   

   DbHelper.ttinclude<#+public class DbHelper{#region GetDbTablespublic static List<DbTable> GetDbTables(string connectionString, string database, string tables = null){if (!string.IsNullOrEmpty(tables)){tables = string.Format(" and obj.name in ('{0}')", tables.Replace(",", "','"));}#region SQLstring sql = string.Format(@"SELECTobj.name tablename,schem.name schemname,idx.rows,CAST(CASE WHEN (SELECT COUNT(1) FROM sys.indexes WHERE object_id= obj.OBJECT_ID AND is_primary_key=1) >=1 THEN 1ELSE 0END AS BIT) HasPrimaryKey                                         from {0}.sys.objects obj inner join {0}.dbo.sysindexes idx on obj.object_id=idx.id and idx.indid<=1INNER JOIN {0}.sys.schemas schem ON obj.schema_id=schem.schema_idwhere type='U' {1}order by obj.name", database, tables);#endregionDataTable dt = GetDataTable(connectionString, sql);return dt.Rows.Cast<DataRow>().Select(row => new DbTable{TableName = row.Field<string>("tablename"),SchemaName = row.Field<string>("schemname"),Rows = row.Field<int>("rows"),HasPrimaryKey = row.Field<bool>("HasPrimaryKey")}).ToList();}#endregion#region GetDbColumnspublic static List<DbColumn> GetDbColumns(string connectionString, string database, string tableName, string schema = "dbo"){#region SQLstring sql = string.Format(@"WITH indexCTE AS(SELECT ic.column_id,ic.index_column_id,ic.object_id    FROM {0}.sys.indexes idxINNER JOIN {0}.sys.index_columns ic ON idx.index_id = ic.index_id AND idx.object_id = ic.object_idWHERE  idx.object_id =OBJECT_ID(@tableName) AND idx.is_primary_key=1)selectcolm.column_id ColumnID,CAST(CASE WHEN indexCTE.column_id IS NULL THEN 0 ELSE 1 END AS BIT) IsPrimaryKey,colm.name ColumnName,systype.name ColumnType,colm.is_identity IsIdentity,colm.is_nullable IsNullable,cast(colm.max_length as int) ByteLength,(case when systype.name='nvarchar' and colm.max_length>0 then colm.max_length/2 when systype.name='nchar' and colm.max_length>0 then colm.max_length/2when systype.name='ntext' and colm.max_length>0 then colm.max_length/2 else colm.max_lengthend) CharLength,cast(colm.precision as int) Precision,cast(colm.scale as int) Scale,prop.value Remarkfrom {0}.sys.columns colminner join {0}.sys.types systype on colm.system_type_id=systype.system_type_id and colm.user_type_id=systype.user_type_idleft join {0}.sys.extended_properties prop on colm.object_id=prop.major_id and colm.column_id=prop.minor_idLEFT JOIN indexCTE ON colm.column_id=indexCTE.column_id AND colm.object_id=indexCTE.object_id                                        where colm.object_id=OBJECT_ID(@tableName)order by colm.column_id", database);#endregionSqlParameter param = new SqlParameter("@tableName", SqlDbType.NVarChar, 100) { Value = string.Format("{0}.{1}.{2}", database, schema, tableName) };DataTable dt = GetDataTable(connectionString, sql, param);return dt.Rows.Cast<DataRow>().Select(row => new DbColumn(){ColumnID = row.Field<int>("ColumnID"),IsPrimaryKey = row.Field<bool>("IsPrimaryKey"),ColumnName = row.Field<string>("ColumnName"),ColumnType = row.Field<string>("ColumnType"),IsIdentity = row.Field<bool>("IsIdentity"),IsNullable = row.Field<bool>("IsNullable"),ByteLength = row.Field<int>("ByteLength"),CharLength = row.Field<int>("CharLength"),Scale = row.Field<int>("Scale"),Remark = row["Remark"].ToString()}).ToList();}#endregion     #region GetDataTablepublic static DataTable GetDataTable(string connectionString, string commandText, params SqlParameter[] parms){using (SqlConnection connection = new SqlConnection(connectionString)){SqlCommand command = connection.CreateCommand();command.CommandText = commandText;command.Parameters.AddRange(parms);SqlDataAdapter adapter = new SqlDataAdapter(command);DataTable dt = new DataTable();adapter.Fill(dt);return dt;}}#endregion}#region DbTable/// <summary>/// 表结构/// </summary>public sealed class DbTable{/// <summary>/// 表名称/// </summary>public string TableName { get; set; }/// <summary>/// 表的架构/// </summary>public string SchemaName { get; set; }/// <summary>/// 表的记录数/// </summary>public int Rows { get; set; }/// <summary>/// 是否含有主键/// </summary>public bool HasPrimaryKey { get; set; }}#endregion#region DbColumn/// <summary>/// 表字段结构/// </summary>public sealed class DbColumn{/// <summary>/// 字段ID/// </summary>public int ColumnID { get; set; }/// <summary>/// 是否主键/// </summary>public bool IsPrimaryKey { get; set; }/// <summary>/// 字段名称/// </summary>public string ColumnName { get; set; }/// <summary>/// 字段类型/// </summary>public string ColumnType { get; set; }/// <summary>/// 数据库类型对应的C#类型/// </summary>public string CSharpType{get{return SqlServerDbTypeMap.MapCsharpType(ColumnType);}}/// <summary>/// /// </summary>public Type CommonType{get{return SqlServerDbTypeMap.MapCommonType(ColumnType);}}/// <summary>/// 字节长度/// </summary>public int ByteLength { get; set; }/// <summary>/// 字符长度/// </summary>public int CharLength { get; set; }/// <summary>/// 小数位/// </summary>public int Scale { get; set; }/// <summary>/// 是否自增列/// </summary>public bool IsIdentity { get; set; }/// <summary>/// 是否允许空/// </summary>public bool IsNullable { get; set; }/// <summary>/// 描述/// </summary>public string Remark { get; set; }}#endregion#region SqlServerDbTypeMappublic class SqlServerDbTypeMap{public static string MapCsharpType(string dbtype){if (string.IsNullOrEmpty(dbtype)) return dbtype;dbtype = dbtype.ToLower();string csharpType = "object";switch (dbtype){case "bigint": csharpType = "long"; break;case "binary": csharpType = "byte[]"; break;case "bit": csharpType = "bool"; break;case "char": csharpType = "string"; break;case "date": csharpType = "DateTime"; break;case "datetime": csharpType = "DateTime"; break;case "datetime2": csharpType = "DateTime"; break;case "datetimeoffset": csharpType = "DateTimeOffset"; break;case "decimal": csharpType = "decimal"; break;case "float": csharpType = "double"; break;case "image": csharpType = "byte[]"; break;case "int": csharpType = "int"; break;case "money": csharpType = "decimal"; break;case "nchar": csharpType = "string"; break;case "ntext": csharpType = "string"; break;case "numeric": csharpType = "decimal"; break;case "nvarchar": csharpType = "string"; break;case "real": csharpType = "Single"; break;case "smalldatetime": csharpType = "DateTime"; break;case "smallint": csharpType = "short"; break;case "smallmoney": csharpType = "decimal"; break;case "sql_variant": csharpType = "object"; break;case "sysname": csharpType = "object"; break;case "text": csharpType = "string"; break;case "time": csharpType = "TimeSpan"; break;case "timestamp": csharpType = "byte[]"; break;case "tinyint": csharpType = "byte"; break;case "uniqueidentifier": csharpType = "Guid"; break;case "varbinary": csharpType = "byte[]"; break;case "varchar": csharpType = "string"; break;case "xml": csharpType = "string"; break;default: csharpType = "object"; break;}return csharpType;}public static Type MapCommonType(string dbtype){if (string.IsNullOrEmpty(dbtype)) return Type.Missing.GetType();dbtype = dbtype.ToLower();Type commonType = typeof(object);switch (dbtype){case "bigint": commonType = typeof(long); break;case "binary": commonType = typeof(byte[]); break;case "bit": commonType = typeof(bool); break;case "char": commonType = typeof(string); break;case "date": commonType = typeof(DateTime); break;case "datetime": commonType = typeof(DateTime); break;case "datetime2": commonType = typeof(DateTime); break;case "datetimeoffset": commonType = typeof(DateTimeOffset); break;case "decimal": commonType = typeof(decimal); break;case "float": commonType = typeof(double); break;case "image": commonType = typeof(byte[]); break;case "int": commonType = typeof(int); break;case "money": commonType = typeof(decimal); break;case "nchar": commonType = typeof(string); break;case "ntext": commonType = typeof(string); break;case "numeric": commonType = typeof(decimal); break;case "nvarchar": commonType = typeof(string); break;case "real": commonType = typeof(Single); break;case "smalldatetime": commonType = typeof(DateTime); break;case "smallint": commonType = typeof(short); break;case "smallmoney": commonType = typeof(decimal); break;case "sql_variant": commonType = typeof(object); break;case "sysname": commonType = typeof(object); break;case "text": commonType = typeof(string); break;case "time": commonType = typeof(TimeSpan); break;case "timestamp": commonType = typeof(byte[]); break;case "tinyint": commonType = typeof(byte); break;case "uniqueidentifier": commonType = typeof(Guid); break;case "varbinary": commonType = typeof(byte[]); break;case "varchar": commonType = typeof(string); break;case "xml": commonType = typeof(string); break;default: commonType = typeof(object); break;}return commonType;}}#endregion#>

   View Code

   <#@ include file="$(ProjectDir)DbHelper.ttinclude"  #>

   DbHelper相对比较复杂，把一些常用操作进行了简单封装，因此放到一个单独的文件里面进行引用，可以方便的进行复用，这里DbHelper的后缀名使用ttinclude，这里的后缀名可以随便起，按照微软的建议：用于include的文件尽量不要使用.tt做后缀名

5. 在页面底部定义一些常用变量，以方便操作
   

   <#+public class config{public static readonly string ConnectionString="Data Source=(local);Integrated Security=true;Initial Catalog=Northwind;";public static readonly string DbDatabase="Northwind";public static readonly string TableName="Customers";}
   #>

   View Code

   这里我们把数据库连接串和数据库、表名字定义一下，方便修改和使用

6. 最后来编写用于实体类生成的代码

   //------------------------------------------------------------------------------
   // <auto-generated>
   //     此代码由T4模板自动生成
   //       生成时间 <#=DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss")#> by 懒惰的肥兔
   //     对此文件的更改可能会导致不正确的行为，并且如果
   //     重新生成代码，这些更改将会丢失。
   // </auto-generated>
   //------------------------------------------------------------------------------using System;
   namespace T4ConsoleApplication.Entities
   {    public class <#=config.TableName#>{<# foreach(DbColumn column in DbHelper.GetDbColumns(config.ConnectionString, config.DbDatabase, config.TableName)){#>/// <summary>/// <#=column.Remark#>/// </summary>        public <#= column.CSharpType#><# if(column.CommonType.IsValueType && column.IsNullable){#>?<#}#> <#=column.ColumnName#> { get; set; }<#}#> }
   }

7. 全部完成后我们的Customers.tt文件就编写好了
   

   Customers.tt<#@ template debug="false" hostspecific="false" language="C#" #>
   <#@ output extension=".cs" #>
   <#@ assembly name="System.Core.dll" #>
   <#@ assembly name="System.Data.dll" #>
   <#@ assembly name="System.Data.DataSetExtensions.dll" #>
   <#@ assembly name="System.Xml.dll" #>
   <#@ import namespace="System" #>
   <#@ import namespace="System.Xml" #>
   <#@ import namespace="System.Linq" #>
   <#@ import namespace="System.Data" #>
   <#@ import namespace="System.Data.SqlClient" #>
   <#@ import namespace="System.Collections.Generic" #>
   <#@ import namespace="System.IO" #>
   <#@ include file="$(ProjectDir)DbHelper.ttinclude"  #>
   //------------------------------------------------------------------------------
   // <auto-generated>
   //     此代码由T4模板自动生成
   //       生成时间 <#=DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss")#> by 懒惰的肥兔
   //     对此文件的更改可能会导致不正确的行为，并且如果
   //     重新生成代码，这些更改将会丢失。
   // </auto-generated>
   //------------------------------------------------------------------------------using System;
   namespace T4ConsoleApplication.Entities
   {    public class <#=config.TableName#>{<# foreach(DbColumn column in DbHelper.GetDbColumns(config.ConnectionString, config.DbDatabase, config.TableName)){#>/// <summary>/// <#=column.Remark#>/// </summary>        public <#= column.CSharpType#><# if(column.CommonType.IsValueType && column.IsNullable){#>?<#}#> <#=column.ColumnName#> { get; set; }<#}#> }
   }<#+public class config{public static readonly string ConnectionString="Data Source=(local);Integrated Security=true;Initial Catalog=Northwind;";public static readonly string DbDatabase="Northwind";public static readonly string TableName="Customers";}
   #>

   View Code

   进行保存后会自动生成Customers.cs文件

   Customers.cs//------------------------------------------------------------------------------
   // <auto-generated>
   //     此代码由T4模板自动生成
   //       生成时间 2012-07-18 17:51:26 by 懒惰的肥兔
   //     对此文件的更改可能会导致不正确的行为，并且如果
   //     重新生成代码，这些更改将会丢失。
   // </auto-generated>
   //------------------------------------------------------------------------------using System;
   namespace T4ConsoleApplication.Entities
   {    public class Customers{/// <summary>/// /// </summary>        public string CustomerID { get; set; }/// <summary>/// /// </summary>        public string CompanyName { get; set; }/// <summary>/// /// </summary>        public string ContactName { get; set; }/// <summary>/// /// </summary>        public string ContactTitle { get; set; }/// <summary>/// /// </summary>        public string Address { get; set; }/// <summary>/// /// </summary>        public string City { get; set; }/// <summary>/// /// </summary>        public string Region { get; set; }/// <summary>/// /// </summary>        public string PostalCode { get; set; }/// <summary>/// /// </summary>        public string Country { get; set; }/// <summary>/// /// </summary>        public string Phone { get; set; }/// <summary>/// /// </summary>        public string Fax { get; set; }}
   }

原文：http://www.cnblogs.com/lzrabbit/archive/2012/07/18/2597953.html