前面几节，使用的都是通过EF Code First创建的新数据库，接下来，将开始使用已存在的数据库。

　　1、使用配置文件设置数据库连接

　　App.config

　　数据库连接字符串的name与Data中NorthwindContext.cs类名相同

　　Data中NorthwindContext.cs

1 using System;  2 using System.Collections.Generic;  3 using System.Linq;  4 using System.Text;  5  6 using System.Data.Entity;  7  8 using Northwind.Domain.Entities;  9 using Northwind.Domain.Mapping; 10 11 namespace Northwind.Data 12 {
   13     public class NorthwindContext : DbContext 14     {
   15         public DbSet
     
       Categories { get; set; } 16         public DbSet
      
        Products { get; set; } 17         public DbSet
       
         Suppliers { get; set; } 18 19         protected override void OnModelCreating(DbModelBuilder modelBuilder) 20         {
   21             modelBuilder.Configurations.Add(new CategoryMap()); 22             modelBuilder.Configurations.Add(new ProductMap()); 23             modelBuilder.Configurations.Add(new SupplierMap()); 24         } 25     } 26 }
       
      
     

　　执行成功后，创建的数据库如下图：

　　2、使用构造函数指定数据库

　　NorthwindContext.cs

1 using System;  2 using System.Collections.Generic;  3 using System.Linq;  4 using System.Text;  5  6 using System.Data.Entity;  7  8 using Northwind.Domain.Entities;  9 using Northwind.Domain.Mapping; 10 11 namespace Northwind.Data 12 {
   13     public class NorthwindContext : DbContext 14     {
   15         public NorthwindContext() 16         { } 17 18         public NorthwindContext(string databaseName) 19             : base(databaseName) 20         {
   21 22         } 23 24         public DbSet
     
       Categories { get; set; } 25         public DbSet
      
        Products { get; set; } 26         public DbSet
       
         Suppliers { get; set; } 27         public DbSet
        
          Users { get; set; } 28         public DbSet
         
           Roles { get; set; } 29 30         protected override void OnModelCreating(DbModelBuilder modelBuilder) 31         {
   32             modelBuilder.Configurations.Add(new CategoryMap()); 33             modelBuilder.Configurations.Add(new ProductMap()); 34             modelBuilder.Configurations.Add(new SupplierMap()); 35             modelBuilder.Configurations.Add(new UserMap()); 36             modelBuilder.Configurations.Add(new RoleMap()); 37         } 38     } 39 }
         
        
       
      
     

　　Program.cs

using (NorthwindContext db = new NorthwindContext("Northwind")) {
   }

　　3、使用构造函数指定数据库连接字符串

　　App.config

1 
       2 
     
        3   
      
         4     
         5     
       
  6   
        7   
      
         8     
         9   
       10 
     

　　NorthwindContext.cs

1 using System;  2 using System.Collections.Generic;  3 using System.Linq;  4 using System.Text;  5  6 using System.Data.Entity;  7  8 using Northwind.Domain.Entities;  9 using Northwind.Domain.Mapping; 10 11 namespace Northwind.Data 12 {
   13     public class NorthwindContext : DbContext 14     {
   15         public NorthwindContext() 16             : base("name=NorthwindConnectionString") 17         { } 18 19         public DbSet
     
       Categories { get; set; } 20         public DbSet
      
        Products { get; set; } 21         public DbSet
       
         Suppliers { get; set; } 22         public DbSet
        
          Users { get; set; } 23         public DbSet
         
           Roles { get; set; } 24 25         protected override void OnModelCreating(DbModelBuilder modelBuilder) 26         {
   27             modelBuilder.Configurations.Add(new CategoryMap()); 28             modelBuilder.Configurations.Add(new ProductMap()); 29             modelBuilder.Configurations.Add(new SupplierMap()); 30             modelBuilder.Configurations.Add(new UserMap()); 31             modelBuilder.Configurations.Add(new RoleMap()); 32         } 33     } 34 }