ADO.NET的記憶碎片（九）

這一篇是講復雜更新數據，在講復雜更新之前，我們要先將參數化查詢，今天我猛然發現，參數化查詢我真的之前沒有提到過，
不過在上篇中有用到參數化查詢，那我今天就正好把參數化的查詢這一塊內容整理出來，不要留下什么盲點。
參數化查詢
假設一種場景，希望獲得一位特定的用戶訂單信息，希望執行下面的SQL查詢：

**select OrderID,CustomerID,OrderDate,EmployeeID from Orders where CustomerID = @CustomerID

要在ADO.NET對象模型中執行一個參數化查詢，需要向Command對象的Parameters集合中添加Parameter對象。
參考代碼如下：

SqlCommand cmd = new SqlCommand();
cmd.Connection = new SqlConnection("連接字符串");
cmd.CommandText = "select OrderID,CustomerID,OrderDate,EmployeeID from Orders where CustomerID = @CustomerID";
SqlParameter p;
p = new SqlParameter();
p.ParameterName = "@CustomerID";
p.Value = "ALFKI";
cmd.Parameters.Add(p);

**使用語法糖

p = cmd.Parameters.AddWithValue("@CustomerID", "ALFKI");

*顯式設置數據類型
*有兩種方法可以對參數的類型進行設置：設置SqlParameter對象的SqlDbType屬性，或者在SqlParameter的構造函數中設置
*參考代碼如下：
構造函數中設置

p = new SqlParameter("@CustomerID",SqlDbType.NVarChar,5);
p.Value = "ALFKI";
cmd.Parameters.Add(p);

設置SqlParameter對象的SqlDbType屬性

p.SqlDbType = SqlDbType.NVarChar;
p.Size = 5;

*參數的方向
*在上面的類子中我們設置的參數都是輸入參數，還可以使用參數從數據庫中獲取數據。即是：使用輸出參數，返回結果，而且性能會更好
*假設使用輸入參數根據ProductName來查詢數據，並通過輸出參數來返回Price和InStock的值，SQL語句如下：
*select @Price = Price,@InStock = InStock from Products where ProductName = @ProductName
*參考代碼如下：

SqlCommand cmd2 = new SqlCommand();
cmd2.Connection = new SqlConnection("連接字符串");
cmd2.CommandText = "select @Price = Price,@InStock = InStock from Products where ProductName = @ProductName";
SqlParameter price,instock,productname;
price = cmd.Parameters.Add("@Price",SqlDbType.Money);
price.Direction = ParameterDirection.Output;
instock = cmd.Parameters.Add("@InStock", SqlDbType.NVarChar,20);
instock.Direction = ParameterDirection.Output;
productname = cmd.Parameters.Add("@ProductName", SqlDbType.NVarChar, 40);
productname.Value = "Chai";
cmd2.ExecuteNonQuery();
if (price.Value == DBNull.Value)
{
    Console.WriteLine("No found named {0}", productname.Value);
}
else
{
    Console.WriteLine("{0}--{1}", price.Value, instock.Value);
}

 復雜更新：提交更新后刷新一行
 在提交更新后刷新一行，因為有時間截列，可以保證數據不會被亂改，所以在提交更新后刷新一行是非常有必要的，
 我們的解決方法就是用輸出參數獲取新行數據，使用SQL語句是：

 update OrderDetailsWithTimestamp
    set OrderID = @OrderIDNew, ProductID = @ProductIDNew, Quantity = @QuantityNew, Price = @PriceNew
 where OrderID = @OrderIDOld and ProductID = @ProductIDOld and Timestamp = @TimestampOld
 if @@ROWCOUNT <> 0 then
 select @QuantityNew = Quantity,@PriceNew = Price, @TimestampNew = Timestamp
 from OrderDetailsWithTimestamp
 where OrderID = @OrderIDNew and ProductID=@ProductIDNew

 參考代碼如下：

cmd2.CommandText = "update OrderDetailsWithTimestamp" +
     "set OrderID = @OrderIDNew, ProductID = @ProductIDNew, Quantity = @QuantityNew, Price = @PriceNew" +
  "where OrderID = @OrderIDOld and ProductID = @ProductIDOld and Timestamp = @TimestampOld" +
  "if @@ROWCOUNT <> 0 then" +
  "select @QuantityNew = Quantity,@PriceNew = Price, @TimestampNew = Timestamp" +
  "from OrderDetailsWithTimestamp" +
  "where OrderID = @OrderIDNew and ProductID=@ProductIDNew";
SqlParameter QuantityNew, PriceNew, TimestampNew;

cmd2.Parameters.AddWithValue("@OrderIDNew", "OrderIDNew");
cmd2.Parameters.AddWithValue("@ProductIDNew", "ProductIDNew");
QuantityNew = cmd2.Parameters.AddWithValue("@QuantityNew", "QuantityNew");
QuantityNew.Direction = ParameterDirection.InputOutput;
PriceNew = cmd2.Parameters.AddWithValue("@PriceNew", "PriceNew");
PriceNew.Direction = ParameterDirection.InputOutput;
TimestampNew = cmd2.Parameters.AddWithValue("@TimestampNew", "TimestampNew");
TimestampNew.Direction = ParameterDirection.Output;
cmd2.Parameters.AddWithValue("@OrderIDOld", "OrderIDOld");
cmd2.Parameters.AddWithValue("@ProductIDOld", "ProductIDOld");
cmd2.Parameters.AddWithValue("@TimestampOld", "TimestampOld");

 QuantityNew, PriceNew, TimestampNew這三個輸出參數可以作為刷新數據來使用
 復雜更新：一次插入多條數據，使用SqlBulkCopy對象
 參考代碼：

 <summary>
向表插入數據
 <summary>
 <param name="table">在內存中的數據，即將要插入數據庫的數據<param>
 <param name="database">對應數據庫的名稱<param>
 <param name="database">對應數據庫的表名稱<param>

public static void InsertTableData(DataTable table, string database,string tableName)
{
    using (SqlBulkCopy bcp = new SqlBulkCopy("Server=.;database=;user id=;Password=;connection reset=false;"))
    {
        bcp.BatchSize = 100;//每次傳輸的行數
        bcp.DestinationTableName = tableName;//目標表
        bcp.WriteToServer(table);
    }
}