T4模版

T4模版

这讲适合所有的MVC程序

很荣幸，我们的系统有了体验的地址了。演示地址

之前我们发布了一个简单的代码生成器，其原理就是读取数据库的表结构，生成文本的一个方式来生成代码！

为了替代重复的劳动，微软自己有一套T4模版，我不想把T4模版说得那么的复杂，因为这个复杂我自己也不知道。

原理跟市面的代码生成器一个道理，但是T4的扩展比代码生成器更灵活，可以更方便根据类生成代码等操作。

T4代码模式是没有颜色高亮了，但是我们的VS支持插件 T4 Editor

下载安装之后就可以跟我们写C#一样有智能高亮和提示了。

新建一个项目，专门用于T4的存放。

首先我们要让T4连接我们的数据库

新建一个DbHelper.ttinclude模版包含文件

 DbHelper.ttinclude

<#+
public class DbHelper
{
#region GetDbTables

public 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 SQL
string sql = string.Format(@"SELECT
obj.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 1
ELSE 0
END
AS BIT) HasPrimaryKey
from {0}.sys.objects obj
inner join {0}.dbo.sysindexes idx on obj.object_id=idx.id and idx.indid<=1
INNER JOIN {0}.sys.schemas schem ON obj.schema_id=schem.schema_id
where type='U' {1}
order by obj.name", database, tables);
#endregion
DataTable 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 GetDbColumns

public static List<DbColumn> GetDbColumns(string connectionString, string database, string tableName, string schema = "dbo")
{
#region SQL
string sql = string.Format(@"
WITH indexCTE AS
(
SELECT
ic.column_id,
ic.index_column_id,
ic.object_id
FROM {0}.sys.indexes idx
INNER JOIN {0}.sys.index_columns ic ON idx.index_id = ic.index_id AND idx.object_id = ic.object_id
WHERE idx.object_id =OBJECT_ID(@tableName) AND idx.is_primary_key=1
)
select
colm.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/2
when systype.name='ntext' and colm.max_length>0 then colm.max_length/2
else colm.max_length
end
) CharLength,
cast(colm.precision as int) Precision,
cast(colm.scale as int) Scale,
prop.value Remark
from {0}.sys.columns colm
inner join {0}.sys.types systype on colm.system_type_id=systype.system_type_id and colm.user_type_id=systype.user_type_id
left join {0}.sys.extended_properties prop on colm.object_id=prop.major_id and colm.column_id=prop.minor_id
LEFT 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);
#endregion
SqlParameter 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 GetDataTable

public 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 SqlServerDbTypeMap

public 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

#>

DbHelper.ttinclude

这里面包含了一些转换的方法和访问数据库的SQL语句

其中GetDbTables方法就是根据数据库的链接，表名来读取字段数据

怎么用呢？就是让模版包含这个文件，就可以访问方法了

举一个Model为例吧，新建Model文件夹。并新建文件，模版文件为tt结尾的扩展

我们新建Test.tt之后

复制代码
<#@ template debug="false" hostspecific="false" language="C#" #>
<#@ assembly name="System.Core" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.Text" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ output extension=".txt" #>
复制代码

最后一行<#@ output extension=".txt" #>

为模版生成的文件，可以是.cs可以是其他。我们就不改了，就是txt

如果是cs类，生成会编译，如果代码是对的，但是系统不知道是对的，会编译出错，虽然这不影响结果，但是不爽

我们为Test.tt添加如下代码

复制代码
<#@ template debug="false" hostspecific="false" language="C#" #>
<#@ output extension=".txt" #>
<#@ 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 YmNets
//     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>
//------------------------------------------------------------------------------
复制代码

我们引入了一些命名空间，因为我们要将读到的表结构进行一系列的处理，比如for循环等操作

其中<#@ include file="$(ProjectDir)DbHelper.ttinclude"  #>就是包含了刚刚简历的访问数据库文件

T4模版的语法通过上面我们可以看出是<#@#>,<#=#>,<##>,<#+#>结构跟原生的asp.net一个鸟样，不是Razor语法，这里要注意

我们添加一些代码

复制代码
<#@ template debug="false" hostspecific="false" language="C#" #>
<#@ output extension=".txt" #>
<#@ 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 YmNets
//     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;
using System.ComponentModel.DataAnnotations;
namespace <#=config.nameSpace#>
{    

    public class <#=config.TableName#>Model
    {
        <# foreach(DbColumn column in DbHelper.GetDbColumns(config.ConnectionString, config.DbDatabase, config.TableName)){#>
        public <#= column.CSharpType#><# if(column.CommonType.IsValueType && column.IsNullable){#>?<#}#> <#=column.ColumnName#> { get; set; }
        <#}#> 
    }
}
<#+
    public class config
    {
        public static readonly string ConnectionString="Data Source=(local);Initial Catalog=AppDB;User ID=sa;Password=zhaoyun123!@#;";
        public static readonly string DbDatabase="AppDB";
        public static readonly string TableName="SysSample";
        public static readonly string nameSpace="App.Sys";
    }
#>
复制代码

有一些通用的我建了一个类config，访问config只需要config.TableName即可

访问DbHelper.ttinclude，值需要DbHelper.***即可

所以同道理，通用的类我们可以建造 Common.ttinclude来完善模版生成库

OK。配置好之后，值需要展开Test.tt就可以看到Test.txt文件，文件生成情况如下

复制代码
//------------------------------------------------------------------------------
// <auto-generated>
//     此代码由T4模板自动生成
//       生成时间 2014-03-03 17:34:45 by YmNets
//     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;
using System.ComponentModel.DataAnnotations;
namespace App.Sys
{    

    public class SysSampleModel
    {
                public string Id { get; set; }
                public string Name { get; set; }
                public int? Age { get; set; }
                public DateTime? Bir { get; set; }
                public string Photo { get; set; }
                public string Note { get; set; }
                public DateTime? CreateTime { get; set; }
         
    }
}
复制代码

非常快速，所以，你可以很快建立自己项目的模版文件了。

以上只是基础，我们更加关心的是更多的扩展，比如判断数据库类型啊等等，做逻辑处理，获取字段的长度做处理啊。

所以我给大家提供一个备注：下面这条语句可以得到表的结构

 <# foreach(DbColumn column in DbHelper.GetDbColumns(config.ConnectionString, config.DbDatabase, config.TableName)){#>
       <#}#>

其中：

column.CSharpType              字段的类型

column.IsNullable                  是否为空

column.IsPrimaryKey             是否是主键

column.CharLength               字段的长度，如varchar(50)那么column.CharLength=50

column.ColumnName             字段的名称

样例：判断是否DataTime类型

<#if(column.CSharpType=="DateTime"){#>

<# } #>

一个小小的例子，我们就能看懂MVC的T4模版，并能熟练运用它

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原文地址：https://www.cnblogs.com/Leo_wl/p/3579461.html