Linq中使用存储过程作为结果集（转）

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 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：





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。