有时候我们希望 Id 要好看一些，比如 Id=1 -> Id=T000001

refer : 

http://www.kodyaz.com/t-sql/custom-sequence-string-as-sql-identity-column.aspx

http://www.sqlteam.com/article/custom-auto-generated-sequences-with-sql-server

 

方法有很多，我目前选择的方式是使用触发器在插入之后更新 

我们把这个好看一点的Id称为 viewId 吧。

先做一个方法来格式化Id

调用 viewId = dbo.getViewId('T',CAST(inserted.Id as nvarchar(50)),6,'0'); 

drop function dbo.getViewId;create function [dbo].[getViewId] ( @Prefix nvarchar(10), @Id int, @Length int, @PaddingChar char(1) = '0')returns nvarchar(MAX)asbeginreturn ( select @Prefix + RIGHT(REPLICATE(@PaddingChar, @Length) + CAST(@Id as nvarchar(10)), @Length))end

 

针对某个表写入触发器逻辑

drop trigger OrdersAfterInsert;create trigger OrdersAfterInsert on [dbo].[Orders] for insertas     update Orders set viewId = dbo.getViewId('O', CAST(inserted.Id as nvarchar(50)),6,'0')         from Orders inner join inserted on Orders.Id= inserted.Id;     go

 

如果表已经存在数据的话，要更新哦

update Orders set viewId = dbo.getViewId('O', CAST(Id as nvarchar(50)),6,'0');

 

创建column and UNIQUE

alter table Orders add viewId nvarchar(50) null;create unique nonclustered index [UNIQUE_Orders_viewId]    on [dbo].[Orders]([viewId] asc) where ([viewId] IS NOT NULL AND [viewId] IS NOT NULL);

 

使用 Entity Framewrok的话可以把这个数据标签为 Computed.

public class Order{    [Key]    public int Id { get; set; }    [DatabaseGenerated(DatabaseGeneratedOption.Computed)]    public string viewId { get; set; }} 

 

以上.