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connecting-tasks-programmatically.md

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title description author ms.author ms.date ms.service ms.subservice ms.topic helpviewer_keywords dev_langs
Connecting Tasks Programmatically
Connecting Tasks Programmatically
chugugrace
chugu
03/04/2017
sql
integration-services
reference
tasks [Integration Services], precedence constraints
precedence constraints [Integration Services], connecting tasks
constraints [Integration Services]
VB
CSharp

Connecting Tasks Programmatically

[!INCLUDEsqlserver-ssis]

A precedence constraint, represented in the object model by the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint class, establishes the order in which xref:Microsoft.SqlServer.Dts.Runtime.Executable objects run in a package. The precedence constraint allows the execution of the containers and tasks in a package to be dependent on the result of the execution of a previous task or container. Precedence constraints are established between pairs of xref:Microsoft.SqlServer.Dts.Runtime.Executable objects by calling the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraints.Add%2A method of the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraints collection on the container object. After you create a constraint between two executable objects, you set the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint.Value%2A property to establish the criteria for executing the second executable defined in the constraint.

You can use both a constraint and an expression in a single precedence constraint, depending on the value that you specify for the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint.EvalOp%2A property, as described in the following table:

Value of the EvalOp property Description
xref:Microsoft.SqlServer.Dts.Runtime.DTSPrecedenceEvalOp.Constraint Specifies that the execution outcome determines whether the constrained container or task runs. Set the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint.Value%2A property of the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint to the desired value from the xref:Microsoft.SqlServer.Dts.Runtime.DTSExecResult enumeration.
xref:Microsoft.SqlServer.Dts.Runtime.DTSPrecedenceEvalOp.Expression Specifies that the value of an expression determines whether the constrained container or task runs. Set the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint.Expression%2A property of the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint.
xref:Microsoft.SqlServer.Dts.Runtime.DTSPrecedenceEvalOp.ExpressionAndConstraint Specifies that the constraint outcome must occur and the expression must evaluate for the constrained container or task to run. Set both the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint.Value%2A and the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint.Expression%2A properties of the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint, and set its xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint.LogicalAnd%2A property to true.
xref:Microsoft.SqlServer.Dts.Runtime.DTSPrecedenceEvalOp.ExpressionOrConstraint Specifies that either the constraint outcome must occur, or the expression must evaluate, for the constrained container or task to run. Set both the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint.Value%2A and the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint.Expression%2A properties of the xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint, and set its xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint.LogicalAnd%2A property to false.

The following code sample demonstrates adding two tasks to a package. A xref:Microsoft.SqlServer.Dts.Runtime.PrecedenceConstraint is created between them that prevents the second task from running until the first task finishes.

using System;  
using Microsoft.SqlServer.Dts.Runtime;  
  
namespace Microsoft.SqlServer.Dts.Samples  
{  
  class Program  
  {  
    static void Main(string[] args)  
    {  
      Package p = new Package();  
  
      // Add a File System task.  
      Executable eFileTask1 = p.Executables.Add("STOCK:FileSystemTask");  
      TaskHost thFileHost1 = eFileTask1 as TaskHost;  
  
      // Add a second File System task.  
      Executable eFileTask2 = p.Executables.Add("STOCK:FileSystemTask");  
      TaskHost thFileHost2 = eFileTask2 as TaskHost;  
  
      // Put a precedence constraint between the tasks.  
      // Set the constraint to specify that the second File System task cannot run  
      // until the first File System task finishes.  
      PrecedenceConstraint pcFileTasks =   
        p.PrecedenceConstraints.Add((Executable)thFileHost1, (Executable)thFileHost2);  
      pcFileTasks.Value = DTSExecResult.Completion;  
    }  
  }  
}  
Imports Microsoft.SqlServer.Dts.Runtime  
  
Module Module1  
  
  Sub Main()  
  
    Dim p As Package = New Package()  
    ' Add a File System task.  
    Dim eFileTask1 As Executable = p.Executables.Add("STOCK:FileSystemTask")  
    Dim thFileHost1 As TaskHost = CType(eFileTask1, TaskHost)  
  
    ' Add a second File System task.  
    Dim eFileTask2 As Executable = p.Executables.Add("STOCK:FileSystemTask")  
    Dim thFileHost2 As TaskHost = CType(eFileTask2, TaskHost)  
  
    ' Put a precedence constraint between the tasks.  
    ' Set the constraint to specify that the second File System task cannot run  
    ' until the first File System task finishes.  
    Dim pcFileTasks As PrecedenceConstraint = _  
      p.PrecedenceConstraints.Add(CType(thFileHost1, Executable), CType(thFileHost2, Executable))  
    pcFileTasks.Value = DTSExecResult.Completion  
  
  End Sub  
  
End Module

See Also

Adding the Data Flow Task Programmatically