存儲過程

在我們編寫程式中,往往需要一些存儲過程,在LINQ to SQL中怎麼使用呢?也許比原來的更簡單些。

下面我們以NORTHWND.MDF資料庫中自帶的幾個存儲過程來理解一下。

1.標量返回

在資料庫中,有名為Customers Count By Region的存儲過程。該存儲過程返回顧客所在"WA"區域的數量。

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

我們只要把這個存儲過程拖到O/R設計器內,它自動生成了以下程式碼片段:

[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));
}

我們需要時,直接調用就可以了,例如:

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

語句描述:這個實例使用存儲過程返回在“WA”地區的客戶數。

2.單一結果集

從資料庫中返回行集合,並包含用於篩選結果的輸入參數。 當我們執行返回行集合的存儲過程時,會用到結果類,它存儲從存儲過程中返回的結果。

下面的示例表示一個存儲過程,該存儲過程返回客戶行並使用輸入參數來僅返回將“London”列為客戶城市的那些行的固定幾列。

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設計器內,它自動生成了以下程式碼片段:

[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));
}

我們用下面的代碼調用:

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);
}

語句描述:這個實例使用存儲過程返回在倫敦的客戶的 CustomerID和City。

3.多個可能形狀的單一結果集

當存儲過程可以返回多個結果形狀時,返回類型無法強類型化為單個投影形狀。儘管 LINQ to SQL 可以生成所有可能的投影類型,但它無法獲知將以何種順序返回它們。 ResultTypeAttribute 屬性適用於返回多個結果類型的存儲過程,用以指定該過程可以返回的類型的集合。

在下面的 SQL 代碼示例中,結果形狀取決於輸入(param1 = 1或param1 = 2)。我們不知道先返回哪個投影。

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設計器內,它自動生成了以下程式碼片段:

[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會把多結果集存儲過程識別為單結果集的存儲過程,預設生成的代碼我們要手動修改一下,要求返回多個結果集,像這樣:

[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)); }

我們分別定義了兩個分部類,用於指定返回的類型。

WholeCustomersSetResult類 如下:

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類如下:

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;
        }
    }
}

這樣就可以使用了,下面代碼直接調用,分別返回各自的結果集合。

//返回全部Customer結果集
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結果集
result = db.Whole_Or_Partial_Customers_Set(2);
IEnumerable<PartialCustomersSetResult> shape2 =
  result.GetResult<PartialCustomersSetResult>();
foreach (PartialCustomersSetResult con in shape2)
{
  Console.WriteLine(con.ContactName);
}

語句描述:這個實例使用存儲過程返回“WA”地區中的一組客戶。返回的結果集形狀取決於傳入的參數。如果參數等於 1,則返回所有客戶屬性。如果參數等於2,則返回ContactName屬性。

4.多個結果集

這種存儲過程可以生成多個結果形狀,但我們已經知道結果的返回順序。

下面是一個按順序返回多個結果集的存儲過程Get Customer And Orders。 返回顧客ID為"SEVES"的顧客和他們所有的訂單。

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

拖到設計器代碼如下:

[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));
}

同樣,我們要修改自動生成的代碼:

[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));
}

同樣,自己手寫類,讓其存儲過程返回各自的結果集。

CustomerResultSet類

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類

public partial class OrdersResultSet
{
    private System.Nullable _OrderID;
    private string _CustomerID;
    private System.Nullable _EmployeeID;
    private System.Nullable _OrderDate;
    private System.Nullable _RequiredDate;
    private System.Nullable _ShippedDate;
    private System.Nullable _ShipVia;
    private System.Nullable _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 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 EmployeeID
    {
        get { return this._EmployeeID; }
        set
        {
            if ((this._EmployeeID != value))
                this._EmployeeID = value;
        }
    }
    [Column(Storage = "_OrderDate", DbType = "DateTime")]
    public System.Nullable OrderDate
    {
        get { return this._OrderDate; }
        set
        {
            if ((this._OrderDate != value))
                this._OrderDate = value;
        }
    }
    [Column(Storage = "_RequiredDate", DbType = "DateTime")]
    public System.Nullable RequiredDate
    {
        get { return this._RequiredDate; }
        set
        {
            if ((this._RequiredDate != value))
                this._RequiredDate = value;
        }
    }
    [Column(Storage = "_ShippedDate", DbType = "DateTime")]
    public System.Nullable ShippedDate
    {
        get { return this._ShippedDate; }
        set
        {
            if ((this._ShippedDate != value))
                this._ShippedDate = value;
        }
    }
    [Column(Storage = "_ShipVia", DbType = "Int")]
    public System.Nullable ShipVia
    {
        get { return this._ShipVia; }
        set
        {
            if ((this._ShipVia != value))
                this._ShipVia = value;
        }
    }
    [Column(Storage = "_Freight", DbType = "Money")]
    public System.Nullable 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;
        }
    }
}

這時,只要調用就可以了。

IMultipleResults result = db.Get_Customer_And_Orders("SEVES");
//返回Customer結果集
IEnumerable<CustomerResultSet> customer = 
  result.GetResult<CustomerResultSet>();
//返回Orders結果集
IEnumerable<OrdersResultSet> orders = 
  result.GetResult<OrdersResultSet>();
//在這裡,我們讀取CustomerResultSet中的資料
foreach (CustomerResultSet cust in customer)
{
  Console.WriteLine(cust.CustomerID);
}

語句描述:這個實例使用存儲過程返回客戶“SEVES”及其所有訂單。

5.帶輸出參數

LINQ to SQL 將輸出參數映射到傳址參數,並且對於數值型別,它將參數聲明為可以為 null。

下面的示例帶有單個輸入參數(客戶 ID)並返回一個輸出參數(該客戶的總銷售額)。

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

把這個存儲過程拖到設計器中,圖片如下:

StoreProcesser  

其生成代碼如下:

[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));
}

我們使用下面的語句調用此存儲過程:注意:輸出參數是按引用傳遞的,以支持參數為“in/out”的方案。在這種情況下,參數僅為“out”。

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

語句描述:這個實例使用返回 Out 參數的存儲過程。

好了,就說到這裡了,其增刪改操作同理。相信大家通過這5個實例理解了存儲過程。

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