Entity Framework 6 Recipes 2nd Edition（10-1）译->非Code Frist方式返回一个实体集合

存储过程

存储过程一直存在于任何一种关系型数据库中，如微软的SQL Server.存储过程是包含在数据库中的一些代码,通常为数据执行一些操作，它能为数据密集型计算提高性能,也能执行一些为业务逻辑. 当你使用数据的时候，有时你会通过存储过程来获取它们.

在本章, 我们探讨一些EF在使用存储过程时，需要关注的地方。我们在本书的其它章节也使用了存储过程, 但通常都是context为执行插入、更新和删除动作。

在本章,我们将为你展示多种使用存储过程的方式。

10-1. 非Code Frist方式返回一个实体集合

问题

想用非Code Frist方式从存储过程里取得一个实体集合

解决方案

Code second (我把它译为非Code Frist)是参照 Code-First 技术，为一个已经存在的数据库建模的方式

我们假设有一个 POCO模型，如Listing 10-1所示：

Listing 10-1. The Customer POCO Model

public class Customer

{

public int CustomerId { get; set; }

public string Name { get; set; }

public string Company { get; set; }

public string ContactTitle { get; set; }

}

我们已经设置好了DbContext子类和Customer 实体集，如Listing 10-2所示：

Listing 10-2. The DbContext Subclass for Customer Entities

public class EF6RecipesContext : DbContext

{

public DbSet<Customer> Customers { get; set; }

public EF6RecipesContext() : base("name=EF6CodeFirstRecipesContext")

{

}

protected override void OnModelCreating(DbModelBuilder modelBuilder)

{

base.OnModelCreating(modelBuilder);

modelBuilder.Types<Customer>()

.Configure(c =>

{

c.HasKey(cust => cust.CustomerId);

c.Property(cust => cust.CustomerId)

.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

c.Property(cust => cust.Name)

.HasMaxLength(50);

c.Property(cust => cust.Company)

.HasMaxLength(50);

c.Property(cust => cust.ContactTitle)

.HasMaxLength(50);

c.ToTable("Customer", "Chapter10");

});

}

}

在数据库中，我们已经定义了如Listing 10-3所示的存储过程,该存储过程根据公司名称和客户标题返回符合条件的 customer

Listing 10-3. GetCustomers Returns All of the Customers with the Given Title in the Given Company.

create procedure Chapter10.GetCustomers

(@Company varchar(50),@ContactTitle varchar(50))

as

begin

select * from

chapter10.Customer where

(@Company is null or Company = @Company) and

(@ContactTitle is null or ContactTitle = @ContactTitle)

End

为了在方法中使用  GetCustomers 存储过程，操作如下：

1. 在DbContext 子类中创建一个公开的方法（命名为GetCustomers），它接受两个string参数，并返回Customer集合， 如 Listing 10-4所示.

Listing 10-4. A New Method to Return a Collection of Customer Objects

public ICollection<Customer> GetCustomers(string company, string contactTitle)

{

throw new NotImplementedException();

}

2.接下来实现这个GetCustomers() 方法，它调用DbContext.Database的SqlQuery方法DbContext.Database

 如Listing 10-5所示.

Listing 10-5. DbContext Subclass with GetCustomers() Implementation

public class EF6RecipesContext : DbContext

{

public DbSet<Customer> Customers { get; set; }

public EF6RecipesContext() : base("name=EF6CodeFirstRecipesContext")

{

}

protected override void OnModelCreating(DbModelBuilder modelBuilder)

{

base.OnModelCreating(modelBuilder);

modelBuilder.Types<Customer>()

.Configure(c =>

{

c.HasKey(cust => cust.CustomerId);

c.Property(cust => cust.CustomerId)

.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

c.Property(cust => cust.Name)

.HasMaxLength(50);

c.Property(cust => cust.Company)

.HasMaxLength(50);

c.Property(cust => cust.ContactTitle)

.HasMaxLength(50);

c.ToTable("Customer", "Chapter10");

});

}

 

public ICollection<Customer> GetCustomers(string company, string contactTitle)

{

return Database.SqlQuery<Customer>( "EXEC Chapter10.GetCustomers @Company,

@ContactTitle"

, new SqlParameter("Company", company)

, new SqlParameter("ContactTitle", contactTitle))

.ToList();

}

}

3.接下来的这个代码段Listing 10-6 就是调用GetCustomers存储过程.

Listing 10-6. Querying the Model with the GetCustomers Stored Procedure via the GetCustomers()

Method

//插入一些Customer,让存储过程查询.

using (var context = new EF6RecipesContext())

{

var c1 = new Customer {Name = "Robin Steele", Company = "GoShopNow.com",

ContactTitle="CEO"};

var c2 = new Customer {Name = "Orin Torrey", Company = "GoShopNow.com",

ContactTitle="Sales Manager"};

var c3 = new Customer {Name = "Robert Lancaster", Company = "GoShopNow.com",

ContactTitle = "Sales Manager"};

var c4 = new Customer { Name = "Julie Stevens", Company = "GoShopNow.com",

ContactTitle = "Sales Manager" };

context.Customers.Add(c1);

context.Customers.Add(c2);

context.Customers.Add(c3);

context.Customers.Add(c4);

context.SaveChanges();

}

using (var context = new EF6RecipesContext())

{

var allCustomers = context.GetCustomers("GoShopNow.com", "Sales Manager");

Console.WriteLine("Customers that are Sales Managers at GoShopNow.com");

foreach (var c in allCustomers)

{

Console.WriteLine("Customer: {0}", c.Name);

}

}

以下Listing 10-6是控制台输出结果：

============================================================================================

Customers that are Sales Managers at GoShopNow.com

Customer: Orin Torrey

Customer: Robert Lancaster

Customer: Julie Stevens

=============================================================

它是如何工作的？

为了能接收数据库中的存储过程里返回的实体集合,我们在DbContext子类中实现了 GetCustomers()方法,该方法用DbContext.Database.SqlQuery<T>() 来执行存储过程 GetCustomers（它的定义见Listing 10-3）. SqlQuery() 方法能用来执行返回一个结果集的 DML（数据操纵语言）语句. 该方法接收一个SQL语句的字符串。SqlQuery<T>() 泛型方法返回一个开发人员指定的强类型的实体集。

附：创建示例用到的数据库的脚本文件