试用了几天linq,感觉确实方便，而且生成的sql也还不错,下面是几点体会
1.几种常见的等效select写法
var s = from c in ctx.T_Users select new { c.F_Name, c.F_Sex, c.F_Birthday, c.F_ID }
这种写法对于初学者来说，最容易理解
var s = ctx.T_Users.Select(p => new { p.F_Name, p.F_Sex, p.F_Birthday, p.F_ID })
这种写法利用T_Users这一泛型Table集合的扩展方法
var s = ctx.T_User.Select(p => new { p.F_Name, p.F_Sex, p.F_Birthday, p.F_ID })
这种写法几乎与第二种写法完全一样，看清楚，这里T_User而不是T_Users！这是直接利用T_User的扩展方法
经调试，这三种方法生成的sql语句完全一样
2.快速更新数据库结构
如果数据库的表结构或视图结构等对象做了改动，而又不想在dbml可视化环境里，删除原来的对象，再拖拉同样的对象到可视环境中，有一个相对简单点的办法,利用sqlmetal.exe工具(开始-->程序-->Microsoft Visual Studio 2008-->Visual Studio Tools-->Visual Studio 2008 Command Prompt)
该工具可方便快速的将整个数据库的表，视图，存储过程生成cs类，完整参数如下:
Microsoft (R) Database Mapping Generator 2008 version 1.00.21022
for Microsoft (R) .NET Framework version 3.5
Copyright (C) Microsoft Corporation. All rights reserved.
SqlMetal [options] [<input file>]
Generates code and mapping for the LINQ to SQL component of the .NET framework. SqlMetal can:
- Generate source code and mapping attributes or a mapping file from a database.
- Generate an intermediate dbml file for customization from the database.
- Generate code and mapping attributes or mapping file from a dbml file.
Options:
/server:<name> Database server name.
/database:<name> Database catalog on server.
/user:<name> Login user ID (default: use Windows Authentication).
/password:<password> Login password (default: use Windows Authentication).
/conn:<connection string> Database connection string. Cannot be used with /server, /database, /user or /password options.
/timeout:<seconds> Timeout value to use when SqlMetal accesses the database (default: 0 which means infinite).
/views Extract database views.
/functions Extract database functions.
/sprocs Extract stored procedures.
/dbml[:file] Output as dbml. Cannot be used with /map option.
/code[:file] Output as source code. Cannot be used with /dbml option.
/map[:file] Generate mapping file, not attributes. Cannot be used with /dbml option.
/language:<language> Language for source code: VB or C# (default: derived from extension on code file name).
/namespace:<name> Namespace of generated code (default: no namespace).
/context:<type> Name of data context class (default: derived from database name).
/entitybase:<type> Base class of entity classes in the generated code (default: entities have no base class).
/pluralize Automatically pluralize or singularize class and member names using English language rules.
/serialization:<option> Generate serializable classes: None or Unidirectional (default: None).
/provider:<type> Provider type: SQLCompact, SQL2000, or SQL2005. (default: provider is determined at run time).
<input file> May be a SqlExpress mdf file, a SqlCE sdf file, or a dbml intermediate file.
Create code from SqlServer:
SqlMetal /server:myserver /database:northwind /code:nwind.cs /namespace:nwind
Generate intermediate dbml file from SqlServer:
SqlMetal /server:myserver /database:northwind /dbml:northwind.dbml /namespace:nwind
Generate code with external mapping from dbml:
SqlMetal /code:nwind.cs /map:nwind.map northwind.dbml
Generate dbml from a SqlCE sdf file:
SqlMetal /dbml:northwind.dbml northwind.sdf
Generate dbml from SqlExpress local server:
SqlMetal /server:.\sqlexpress /database:northwind /dbml:northwind.dbml
Generate dbml by using a connection string in the command line:
SqlMetal /conn:"server='myserver'; database='northwind'" /dbml:northwind.dbml
个人感觉，直接生成map和cs文件比较实用
比如生成LINQDB.MAP和LINQDB.CS后，如何使用呢?往下看
将LINQDB.MAP 复制到 网站根目录/DATAMAP目录下(当然DATAMAP这个名字，你可以随意指定)
将LINQDB.CS 复制到 ／APP_CODE/目录下
为了方便以后代码重用，我习惯在APP_CODE目录下建立一个公用的类文件CONFIG.CS(用来放一些常用的公共方法)
/// <summary>
/// Summary description for CONFIG
/// </summary>
public static class CONFIG
{
public static Linqdb GetDBContext(string ConnString)
{
String path = HttpContext.Current.Server.MapPath("~/DATAMAP/LINQDB.MAP");
XmlMappingSource xms = XmlMappingSource.FromXml(File.ReadAllText(path));
Linqdb ctx = new Linqdb(ConnString, xms);
return ctx;
}
public static Linqdb GetDBContext()
{
String path = HttpContext.Current.Server.MapPath("~/DATAMAP/LINQDB.MAP");
XmlMappingSource xms = XmlMappingSource.FromXml(File.ReadAllText(path));
Linqdb ctx = new Linqdb(ConfigurationManager.ConnectionStrings["ConnStr"].ToString(), xms);
return ctx;
}
}
这是二个主要方法，用来得到DataContext对象的实例
终于进到关键地方了，以下是使用的代码:
protected void Page_Load(object sender, EventArgs e)
{
ShowData();
}
void ShowData()
{
using (Linqdb ctx = CONFIG.GetDBContext())
{
var s = ctx.T_User.Select(p => new { p.F_Name, p.F_Sex, p.F_Birthday, p.F_ID });
this.GridView1.DataSource = s;
this.GridView1.DataBind();
}
}
值得注意的是:如果用metasql.exe生成的cs文件，里面不会有"表名s"这个类，而在可视化环境中，拖放出来的表，除会生成"表名"这个类外，还会同步生成一个"表名s"的类
即:假设数据库中有一个表T_User,用metasql.exe生成的cs文件中，仅包含T_User这个对应该表的类，而在可视化环境中，除生成T_User类外，还会有一个T_Users类，代码类似下面这样:
public System.Data.Linq.Table<T_User> T_Users
{
get
{
return this.GetTable<T_User>();
}
}
呵呵，今天就写这么多,以后有好的心得再接着写
