qr code generator c# Lesson 2: Using SQLCLR and Filestream in C#

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Lesson 2: Using SQLCLR and Filestream
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using System.Data.SqlTypes; using Microsoft.SqlServer.Server;
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... [SqlFunction(FillRowMethodName = "SplitStringFillRow", TableDefinition = "ValueIndex INT, Value NVARCHAR(100)")] static public IEnumerator SplitString(SqlString stringToSplit) { // Exit if the string to split is NULL. if (stringToSplit.IsNull) yield break;
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int valueIndex = 0; foreach (string s in stringToSplit.Value.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries)) { yield return new KeyValuePair<int, string>(valueIndex++, s.Trim()); } }
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static public void SplitStringFillRow(object oKeyValuePair, out SqlInt32 valueIndex, out SqlString value) { // Fetch the key value pair from the first parameter. KeyValuePair<int, string> keyValuePair = (KeyValuePair<int, string>)oKeyValuePair;
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// Set each output parameter's value. valueIndex = keyValuePair.Key; value = keyValuePair.Value; } ...
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In the previous example, you can see that we created the two methods SplitString and SplitStringFillRow. When you execute the UDF from SQL Server, the SplitString method is executed first. Each yield return statement that is executed within this method calls the SplitStringFillRow method (that is, the fill row method specified in the SqlFunction attribute). As you can see, the result set that is returned by the SplitString function is defined using the TableDefinition parameter of the SqlFunction attribute. The fill row method always takes one parameter of type System.Object that contains a reference to whatever you called yield return for, as well as one out parameter for each column that should be returned by the function according to the TableDefinition parameter. In the following example, you can see the T-SQL code used to create and query the table-valued UDF:
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CREATE FUNCTION dbo.fnSplitString ( @StringToSplit NVARCHAR(max) )
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Extending Microsoft SQL Server Functionality with XML, SQLCLR, and Filestream
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RETURNS TABLE (ValueIndex INT, Value NVARCHAR(100)) AS EXTERNAL NAME TK433ClrDemo."TK433.Clr.Demo".SplitString; GO
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SELECT ValueIndex ,Value FROM dbo.fnSplitString('Hi,how,are,you ') AS a;
Here is the result:
ValueIndex Value ----------- --------0 1 2 3 Hi how are you
Creating a CLR Trigger
Creating a CLR trigger is very similar to creating a CLR stored procedure. The CLR code consists of a single method or Sub that performs the actions that you want the trigger to perform. Just like a T-SQL trigger, a CLR trigger has access to the trigger-specific inserted and deleted tables. In the following example of a CLR trigger, the transaction is rolled back if the statement that triggered the trigger deleted more than one row:
'VB: Imports System.Data.SqlClient Imports System.Text.RegularExpressions Imports Microsoft.SqlServer.Server
... Public Shared Sub ClrTrigger() ' If this wasn't a delete statement, just exit. If SqlContext.TriggerContext.TriggerAction <> TriggerAction.Delete Then Return End If
Using conn As SqlConnection = New SqlConnection("context connection=true") Dim cmd As SqlCommand = conn.CreateCommand() cmd.CommandText = "SELECT COUNT(*) FROM deleted" conn.Open()
Lesson 2: Using SQLCLR and Filestream
' Check the number of rows that were found in the deleted table. If (CType(cmd.ExecuteScalar(), Integer)) > 1 Then cmd.CommandText = _ "RAISERROR('Too many rows deleted, rolling back " & _ "transaction.', 16, 1);" & vbCrLf & _ "ROLLBACK TRAN;"
' This try/catch is needed in order to skip the error that is ' caused by the RAISERROR being executed. Try SqlContext.Pipe.ExecuteAndSend(cmd) Catch End Try End If End Using End Sub ...
//C#: using System; using System.Data.SqlClient; using Microsoft.SqlServer.Server;
... static public void ClrTrigger() { // If this wasn't a delete statement, just exit. if (SqlContext.TriggerContext.TriggerAction != TriggerAction.Delete) return;
using (SqlConnection conn = new SqlConnection("context connection=true")) { SqlCommand cmd = conn.CreateCommand(); cmd.CommandText = "SELECT COUNT(*) FROM deleted;"; conn.Open();
// Check the number of rows that were found in the deleted table. if (((int)cmd.ExecuteScalar()) > 1) { cmd.CommandText = @"RAISERROR('Too many rows deleted, " + "rolling back transaction.', 16, 1);" + "ROLLBACK TRAN;";
// This try/catch is needed in order to skip the error that is // caused by the RAISERROR being executed. try
Extending Microsoft SQL Server Functionality with XML, SQLCLR, and Filestream
{ SqlContext.Pipe.ExecuteAndSend(cmd); } catch { } } } }
The following code would be used to create the trigger:
CREATE TRIGGER dbo.ClrTrigger ON dbo.MyTable AFTER DELETE AS EXTERNAL NAME TK433ClrDemo."TK433.Clr.Demo".ClrTrigger; GO
Just as with CLR stored procedures, creating this otherwise simple trigger becomes very cumbersome compared to creating a T-SQL trigger because you need to use a SqlConnection and SqlCommand object every time that you want to execute an SQL statement. As you can see, there is a property of the SqlContext class called TriggerContext (of type SqlTriggerContext), which can be used to perform trigger-specific checks from the CLR code. CLR triggers should be used only when you need to perform tasks that cannot be performed using regular T-SQL triggers, or when the tasks are heavily calculation-intensive and the CLR trigger outperforms the T-SQL trigger.
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