LINQ体验(14)——LINQ to SQL语句之存储过程

其他 2018-08-10 05:26:41 阅读次数: 0
原文地址为： LINQ体验(14)——LINQ to SQL语句之存储过程

存储过程

在我们编写程序中，往往需要一些存储过程，在LINQ to SQL中怎么使用呢？也许比原来的更简单些。下面我们以NORTHWND.MDF数据库中自带的几个存储过程来理解一下。

1.标量返回

在数据库中，有名为Customers Count By Region的存储过程。该存储过程返回顾客所在"WA"区域的数量。

ALTER PROCEDURE [dbo].[NonRowset]
    (@param1 NVARCHAR(15))
AS
BEGIN
    SET NOCOUNT ON;
DECLARE @count int
     SELECT @count = COUNT(*)FROM Customers 
     WHERECustomers.Region = @Param1
RETURN @count
END

我们只要把这个存储过程拖到O/R设计器内，它自动生成了以下代码段：

[Function(Name = "dbo.[Customers Count By Region]")]
public int Customers_Count_By_Region([Parameter
(DbType = "NVarChar(15)")] string param1)
{
IExecuteResult result = this.ExecuteMethodCall(this,
    ((MethodInfo)(MethodInfo.GetCurrentMethod())), param1);
return ((int)(result.ReturnValue));
}

我们需要时，直接调用就可以了，例如：

int count = db.CustomersCountByRegion("WA");
Console.WriteLine(count);

语句描述：这个实例使用存储过程返回在“WA”地区的客户数。

2.单一结果集

从数据库中返回行集合，并包含用于筛选结果的输入参数。 当我们执行返回行集合的存储过程时，会用到结果类，它存储从存储过程中返回的结果。

下面的示例表示一个存储过程，该存储过程返回客户行并使用输入参数来仅返回将“London”列为客户城市的那些行的固定几列。  

ALTER PROCEDURE [dbo].[Customers By City]
-- Add the parameters for the stored procedure here
(@param1 NVARCHAR(20))
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
     -- interfering with SELECT statements.
SET NOCOUNT ON;
SELECT CustomerID, ContactName, CompanyName, City from 
Customers as c where c.City=@param1
END

拖到O/R设计器内，它自动生成了以下代码段：

[Function(Name="dbo.[Customers By City]")]
public ISingleResult<Customers_By_CityResult> Customers_By_City(
[Parameter(DbType="NVarChar(20)")] string param1)
{
IExecuteResult result = this.ExecuteMethodCall(this, (
    (MethodInfo)(MethodInfo.GetCurrentMethod())), param1);
return ((ISingleResult<Customers_By_CityResult>)
    (result.ReturnValue));
}

我们用下面的代码调用：

ISingleResult<Customers_By_CityResult> result =
 db.Customers_By_City("London");
foreach (Customers_By_CityResult cust in result)
{
Console.WriteLine("CustID={0}; City={1}", cust.CustomerID,
        cust.City);
}

语句描述：这个实例使用存储过程返回在伦敦的客户的 CustomerID和City。

3.多个可能形状的单一结果集

当存储过程可以返回多个结果形状时，返回类型无法强类型化为单个投影形状。尽管 LINQ to SQL 可以生成所有可能的投影类型，但它无法获知将以何种顺序返回它们。 ResultTypeAttribute 属性适用于返回多个结果类型的存储过程，用以指定该过程可以返回的类型的集合。

在下面的 SQL 代码示例中，结果形状取决于输入（param1 = 1或param1 = 2）。我们不知道先返回哪个投影。 

ALTER PROCEDURE [dbo].[SingleRowset_MultiShape]
-- Add the parameters for the stored procedure here
(@param1 int )
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
     -- interfering with SELECT statements.
SET NOCOUNT ON;
if(@param1 = 1)
SELECT * from Customers as c where c.Region = 'WA'
else if (@param1 = 2)
SELECT CustomerID, ContactName, CompanyName from 
Customers as c where c.Region = 'WA'
END

拖到O/R设计器内，它自动生成了以下代码段：

[Function(Name="dbo.[Whole Or Partial Customers Set]")]
public ISingleResult<Whole_Or_Partial_Customers_SetResult> 
Whole_Or_Partial_Customers_Set([Parameter(DbType="Int")] 
System.Nullable<int> param1)
{
IExecuteResult result = this.ExecuteMethodCall(this, 
    ((MethodInfo)(MethodInfo.GetCurrentMethod())), param1);
return ((ISingleResult<Whole_Or_Partial_Customers_SetResult>)
    (result.ReturnValue));
}

但是，VS2008会把多结果集存储过程识别为单结果集的存储过程，默认生成的代码我们要手动修改一下，要求返回多个结果集，像这样：

[Function(Name="dbo.[Whole Or Partial Customers Set]")]
[ResultType(typeof(WholeCustomersSetResult))]
[ResultType(typeof(PartialCustomersSetResult))]
public IMultipleResults Whole_Or_Partial_Customers_Set([Parameter
(DbType="Int")] System.Nullable<int> param1)
{
IExecuteResult result = this.ExecuteMethodCall(this, 
    ((MethodInfo)(MethodInfo.GetCurrentMethod())), param1);
return ((IMultipleResults)(result.ReturnValue));
}

我们分别定义了两个分部类，用于指定返回的类型。WholeCustomersSetResult类 如下：（点击展开）

代码在这里展开 
public partial class WholeCustomersSetResult
{
private string _CustomerID;
private string _CompanyName;
private string _ContactName;
private string _ContactTitle;
private string _Address;
private string _City;
private string _Region;
private string _PostalCode;
private string _Country;
private string _Phone;
private string _Fax;
public WholeCustomersSetResult()
    {
    }
    [Column(Storage = "_CustomerID", DbType = "NChar(5)")]
public string CustomerID
    {
get { return this._CustomerID; }
set
{
if ((this._CustomerID != value))
this._CustomerID = value;
        }
    }
    [Column(Storage = "_CompanyName", DbType = "NVarChar(40)")]
public string CompanyName
    {
get { return this._CompanyName; }
set
{
if ((this._CompanyName != value))
this._CompanyName = value;
        }
    }
    [Column(Storage = "_ContactName", DbType = "NVarChar(30)")]
public string ContactName
    {
get { return this._ContactName; }
set
{
if ((this._ContactName != value))
this._ContactName = value;
        }
    }
    [Column(Storage = "_ContactTitle", DbType = "NVarChar(30)")]
public string ContactTitle
    {
get { return this._ContactTitle; }
set
{
if ((this._ContactTitle != value))
this._ContactTitle = value;
        }
    }
    [Column(Storage = "_Address", DbType = "NVarChar(60)")]
public string Address
    {
get { return this._Address; }
set
{
if ((this._Address != value))
this._Address = value;
        }
    }
    [Column(Storage = "_City", DbType = "NVarChar(15)")]
public string City
    {
get { return this._City; }
set
{
if ((this._City != value))
this._City = value;
        }
    }
    [Column(Storage = "_Region", DbType = "NVarChar(15)")]
public string Region
    {
get { return this._Region; }
set
{
if ((this._Region != value))
this._Region = value;
        }
    }
    [Column(Storage = "_PostalCode", DbType = "NVarChar(10)")]
public string PostalCode
    {
get { return this._PostalCode; }
set
{
if ((this._PostalCode != value))
this._PostalCode = value;
        }
    }
    [Column(Storage = "_Country", DbType = "NVarChar(15)")]
public string Country
    {
get { return this._Country; }
set
{
if ((this._Country != value))
this._Country = value;
        }
    }
    [Column(Storage = "_Phone", DbType = "NVarChar(24)")]
public string Phone
    {
get { return this._Phone; }
set
{
if ((this._Phone != value))
this._Phone = value;
        }
    }
    [Column(Storage = "_Fax", DbType = "NVarChar(24)")]
public string Fax
    {
get { return this._Fax; }
set
{
if ((this._Fax != value))
this._Fax = value;
        }
    }
}

PartialCustomersSetResult类 如下：（点击展开）

代码在这里展开 
public partial class PartialCustomersSetResult
{
private string _CustomerID;
private string _ContactName;
private string _CompanyName;
public PartialCustomersSetResult()
    {
    }
    [Column(Storage = "_CustomerID", DbType = "NChar(5)")]
public string CustomerID
    {
get { return this._CustomerID; }
set
{
if ((this._CustomerID != value))
this._CustomerID = value;
        }
    }
    [Column(Storage = "_ContactName", DbType = "NVarChar(30)")]
public string ContactName
    {
get { return this._ContactName; }
set
{
if ((this._ContactName != value))
this._ContactName = value;
        }
    }
    [Column(Storage = "_CompanyName", DbType = "NVarChar(40)")]
public string CompanyName
    {
get { return this._CompanyName; }
set
{
if ((this._CompanyName != value))
this._CompanyName = value;
        }
    }
}

这样就可以使用了，下面代码直接调用，分别返回各自的结果集合。

//返回全部Customer结果集
IMultipleResults result = db.Whole_Or_Partial_Customers_Set(1);
IEnumerable<WholeCustomersSetResult> shape1 =
 result.GetResult<WholeCustomersSetResult>();
foreach (WholeCustomersSetResult compName in shape1)
{
Console.WriteLine(compName.CompanyName);
}
//返回部分Customer结果集
result = db.Whole_Or_Partial_Customers_Set(2);
IEnumerable<PartialCustomersSetResult> shape2 =
 result.GetResult<PartialCustomersSetResult>();
foreach (PartialCustomersSetResult con in shape2)
{
Console.WriteLine(con.ContactName);
}

语句描述：这个实例使用存储过程返回“WA”地区中的一组客户。返回的结果集形状取决于传入的参数。如果参数等于 1，则返回所有客户属性。如果参数等于 2，则返回ContactName属性。

4.多个结果集

这种存储过程可以生成多个结果形状，但我们已经知道结果的返回顺序。

下面是一个按顺序返回多个结果集的存储过程Get Customer And Orders。 返回顾客ID为"SEVES"的顾客和他们所有的订单。

ALTER PROCEDURE [dbo].[Get Customer And Orders]
(@CustomerID nchar(5))
-- Add the parameters for the stored procedure here
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
SET NOCOUNT ON;
SELECT * FROM Customers AS c WHERE c.CustomerID = @CustomerID  
SELECT * FROM Orders AS o WHERE o.CustomerID = @CustomerID
END

拖到设计器代码如下：

[Function(Name="dbo.[Get Customer And Orders]")]
public ISingleResult<Get_Customer_And_OrdersResult>
Get_Customer_And_Orders([Parameter(Name="CustomerID",
DbType="NChar(5)")] string customerID)
{
IExecuteResult result = this.ExecuteMethodCall(this,
     ((MethodInfo)(MethodInfo.GetCurrentMethod())), customerID);
return ((ISingleResult<Get_Customer_And_OrdersResult>)
     (result.ReturnValue));
}

同样，我们要修改自动生成的代码：

[Function(Name="dbo.[Get Customer And Orders]")]
[ResultType(typeof(CustomerResultSet))]
[ResultType(typeof(OrdersResultSet))]
public IMultipleResults Get_Customer_And_Orders
([Parameter(Name="CustomerID",DbType="NChar(5)")]
string customerID)
{
IExecuteResult result = this.ExecuteMethodCall(this,
    ((MethodInfo)(MethodInfo.GetCurrentMethod())), customerID);
return ((IMultipleResults)(result.ReturnValue));
}

同样，自己手写类，让其存储过程返回各自的结果集。

CustomerResultSet类

代码在这里展开 
public partial class CustomerResultSet
{

private string _CustomerID;
private string _CompanyName;
private string _ContactName;
private string _ContactTitle;
private string _Address;
private string _City;
private string _Region;
private string _PostalCode;
private string _Country;
private string _Phone;
private string _Fax;
public CustomerResultSet()
    {
    }
    [Column(Storage = "_CustomerID", DbType = "NChar(5)")]
public string CustomerID
    {
get { return this._CustomerID; }
set
{
if ((this._CustomerID != value))
this._CustomerID = value;
        }
    }
    [Column(Storage = "_CompanyName", DbType = "NVarChar(40)")]
public string CompanyName
    {
get { return this._CompanyName; }
set
{
if ((this._CompanyName != value))
this._CompanyName = value;
        }
    }
    [Column(Storage = "_ContactName", DbType = "NVarChar(30)")]
public string ContactName
    {
get { return this._ContactName; }
set
{
if ((this._ContactName != value))
this._ContactName = value;
        }
    }
    [Column(Storage = "_ContactTitle", DbType = "NVarChar(30)")]
public string ContactTitle
    {
get { return this._ContactTitle; }
set
{
if ((this._ContactTitle != value))
this._ContactTitle = value;
        }
    }
    [Column(Storage = "_Address", DbType = "NVarChar(60)")]
public string Address
    {
get { return this._Address; }
set
{
if ((this._Address != value))
this._Address = value;
        }
    }
    [Column(Storage = "_City", DbType = "NVarChar(15)")]
public string City
    {
get { return this._City; }
set
{
if ((this._City != value))
this._City = value;
        }
    }
    [Column(Storage = "_Region", DbType = "NVarChar(15)")]
public string Region
    {
get { return this._Region; }
set
{
if ((this._Region != value))
this._Region = value;
        }
    }
    [Column(Storage = "_PostalCode", DbType = "NVarChar(10)")]
public string PostalCode
    {
get { return this._PostalCode; }
set
{
if ((this._PostalCode != value))
this._PostalCode = value;
        }
    }
    [Column(Storage = "_Country", DbType = "NVarChar(15)")]
public string Country
    {
get { return this._Country; }
set
{
if ((this._Country != value))
this._Country = value;
        }
    }
    [Column(Storage = "_Phone", DbType = "NVarChar(24)")]
public string Phone
    {
get { return this._Phone; }
set
{
if ((this._Phone != value))
this._Phone = value;
        }
    }

    [Column(Storage = "_Fax", DbType = "NVarChar(24)")]
public string Fax
    {
get { return this._Fax; }
set
{
if ((this._Fax != value))
this._Fax = value;
        }
    }
}

OrdersResultSet类

代码在这里展开 
public partial class OrdersResultSet
{
private System.Nullable<int> _OrderID;
private string _CustomerID;
private System.Nullable<int> _EmployeeID;
private System.Nullable<System.DateTime> _OrderDate;
private System.Nullable<System.DateTime> _RequiredDate;
private System.Nullable<System.DateTime> _ShippedDate;
private System.Nullable<int> _ShipVia;
private System.Nullable<decimal> _Freight;
private string _ShipName;
private string _ShipAddress;
private string _ShipCity;
private string _ShipRegion;
private string _ShipPostalCode;
private string _ShipCountry;
public OrdersResultSet()
    {
    }
    [Column(Storage = "_OrderID", DbType = "Int")]
public System.Nullable<int> OrderID
    {
get { return this._OrderID; }
set
{
if ((this._OrderID != value))
this._OrderID = value;
        }
    }
    [Column(Storage = "_CustomerID", DbType = "NChar(5)")]
public string CustomerID
    {
get { return this._CustomerID; }
set
{
if ((this._CustomerID != value))
this._CustomerID = value;
        }
    }
    [Column(Storage = "_EmployeeID", DbType = "Int")]
public System.Nullable<int> EmployeeID
    {
get { return this._EmployeeID; }
set
{
if ((this._EmployeeID != value))
this._EmployeeID = value;
        }
    }
    [Column(Storage = "_OrderDate", DbType = "DateTime")]
public System.Nullable<System.DateTime> OrderDate
    {
get { return this._OrderDate; }
set
{
if ((this._OrderDate != value))
this._OrderDate = value;
        }
    }
    [Column(Storage = "_RequiredDate", DbType = "DateTime")]
public System.Nullable<System.DateTime> RequiredDate
    {
get { return this._RequiredDate; }
set
{
if ((this._RequiredDate != value))
this._RequiredDate = value;
        }
    }
    [Column(Storage = "_ShippedDate", DbType = "DateTime")]
public System.Nullable<System.DateTime> ShippedDate
    {
get { return this._ShippedDate; }
set
{
if ((this._ShippedDate != value))
this._ShippedDate = value;
        }
    }
    [Column(Storage = "_ShipVia", DbType = "Int")]
public System.Nullable<int> ShipVia
    {
get { return this._ShipVia; }
set
{
if ((this._ShipVia != value))
this._ShipVia = value;
        }
    }
    [Column(Storage = "_Freight", DbType = "Money")]
public System.Nullable<decimal> Freight
    {
get { return this._Freight; }
set
{
if ((this._Freight != value))
this._Freight = value;
        }
    }
    [Column(Storage = "_ShipName", DbType = "NVarChar(40)")]
public string ShipName
    {
get { return this._ShipName; }
set
{
if ((this._ShipName != value))
this._ShipName = value;
        }
    }
    [Column(Storage = "_ShipAddress", DbType = "NVarChar(60)")]
public string ShipAddress
    {
get { return this._ShipAddress; }
set
{
if ((this._ShipAddress != value))
this._ShipAddress = value;
        }
    }
    [Column(Storage = "_ShipCity", DbType = "NVarChar(15)")]
public string ShipCity
    {
get { return this._ShipCity; }
set
{
if ((this._ShipCity != value))
this._ShipCity = value;
        }
    }
    [Column(Storage = "_ShipRegion", DbType = "NVarChar(15)")]
public string ShipRegion
    {
get { return this._ShipRegion; }
set
{
if ((this._ShipRegion != value))
this._ShipRegion = value;
        }
    }
    [Column(Storage = "_ShipPostalCode", DbType = "NVarChar(10)")]
public string ShipPostalCode
    {
get { return this._ShipPostalCode; }
set
{
if ((this._ShipPostalCode != value))
this._ShipPostalCode = value;
        }
    }

    [Column(Storage = "_ShipCountry", DbType = "NVarChar(15)")]
public string ShipCountry
    {
get { return this._ShipCountry; }
set
{
if ((this._ShipCountry != value))
this._ShipCountry = value;
        }
    }
}

这时，只要调用就可以了。

IMultipleResults result = db.Get_Customer_And_Orders("SEVES");
//返回Customer结果集
IEnumerable<CustomerResultSet> customer = 
result.GetResult<CustomerResultSet>();
//返回Orders结果集
IEnumerable<OrdersResultSet> orders = 
 result.GetResult<OrdersResultSet>();
//在这里，我们读取CustomerResultSet中的数据
foreach (CustomerResultSet cust in customer)
{
Console.WriteLine(cust.CustomerID);
}

语句描述：这个实例使用存储过程返回客户“SEVES”及其所有订单。

5.带输出参数

LINQ to SQL 将输出参数映射到引用参数，并且对于值类型，它将参数声明为可以为 null。

下面的示例带有单个输入参数（客户 ID）并返回一个输出参数（该客户的总销售额）。 

ALTER PROCEDURE [dbo].[CustOrderTotal] 
@CustomerID nchar(5),
@TotalSales money OUTPUT
AS
SELECT @TotalSales = SUM(OD.UNITPRICE*(1-OD.DISCOUNT) * OD.QUANTITY)
FROM ORDERS O, "ORDER DETAILS" OD
where O.CUSTOMERID = @CustomerID AND O.ORDERID = OD.ORDERID

把这个存储过程拖到设计器中，图片如下：

存储过程

其生成代码如下：

[Function(Name="dbo.CustOrderTotal")]
public int CustOrderTotal(
[Parameter(Name="CustomerID", DbType="NChar(5)")]string customerID,
[Parameter(Name="TotalSales", DbType="Money")]
ref System.Nullable<decimal> totalSales)
{
IExecuteResult result = this.ExecuteMethodCall(this,
    ((MethodInfo)(MethodInfo.GetCurrentMethod())),
    customerID, totalSales);
    totalSales = ((System.Nullable<decimal>)
    (result.GetParameterValue(1)));
return ((int)(result.ReturnValue));
}

我们使用下面的语句调用此存储过程：注意：输出参数是按引用传递的，以支持参数为“in/out”的方案。在这种情况下，参数仅为“out”。  

decimal? totalSales = 0;
string customerID = "ALFKI";
db.CustOrderTotal(customerID, ref totalSales);
Console.WriteLine("Total Sales for Customer '{0}' = {1:C}", 
customerID, totalSales);

语句描述：这个实例使用返回 Out 参数的存储过程。

好了，就说到这里了，其增删改操作同理。相信大家通过这5个实例理解了存储过程。

本系列链接：LINQ体验系列文章导航

LINQ推荐资源

LINQ专题：http://kb.cnblogs.com/zt/linq/ 关于LINQ方方面面的入门、进阶、深入的文章。
LINQ小组：http://space.cnblogs.com/group/linq/学习中遇到什么问题或者疑问提问的好地方。


转载请注明本文地址： LINQ体验(14)——LINQ to SQL语句之存储过程

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