Connecting Tasks Programmatically

A precedence constraint, represented in the object model by the PrecedenceConstraint class, establishes the order in which 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 Executable objects by calling the Add method of the PrecedenceConstraints collection on the container object. After you create a constraint between two executable objects, you set the Value 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 EvalOp property, as described in the following table:

The following code sample demonstrates adding two tasks to a package. A 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

Concepts

Adding the Data Flow Task Programmatically