Each container has its own Variables collection. When a new variable is created, it is within the scope of its parent container. Because the package container is at the top of the container hierarchy, variables with package scope function like global variables, and are visible to all containers within the package. The collection of variables for the container can also be accessed by the children of the container through the Variables collection, by using either the variable name or the variable's index in the collection.

Because the visibility of a variable is scoped from the top down, variables declared at the package level are visible to all the containers in the package. Therefore, the Variables collection on a container includes all the variables that belong to its parent in addition to its own variables

Conversely, the variables that are contained in a task are limited in scope and visibility, and are only visible to the task.

If a package runs other packages, the variables defined in the scope of the calling package are available to the called package. The only exception occurs when a same-named variable exists in the called package. When this collision occurs, the variable value in the called package overrides the value from the calling package. Variables defined in the scope of the called package are never available back to the calling package.

The following code example programmatically creates a variable, myCustomVar, at the package scope, and then iterates through all the variables visible to the package, printing their name, data type, and value.

using System;
using Microsoft.SqlServer.Dts.Runtime;

namespace Microsoft.SqlServer.Dts.Samples
{
  class Program
  {
    static void Main(string[] args)
    {
      Application app = new Application();
      // Load a sample package that contains a variable that sets the file name.
      Package pkg = app.LoadPackage(
        @"C:\Program Files\Microsoft SQL Server\100\Samples\Integration Services" +
        @"\Package Samples\CaptureDataLineage Sample\CaptureDataLineage\CaptureDataLineage.dtsx",
        null);
      Variables pkgVars = pkg.Variables;
      Variable myVar = pkg.Variables.Add("myCustomVar", false, "User", "3");
      foreach (Variable pkgVar in pkgVars)
      {
        Console.WriteLine("Variable: {0}, {1}, {2}", pkgVar.Name,
          pkgVar.DataType, pkgVar.Value.ToString());
      }
      Console.Read();
    }
  }
}

Imports Microsoft.SqlServer.Dts.Runtime

Module Module1

  Sub Main()

    Dim app As Application = New Application()
    ' Load a sample package that contains a variable that sets the file name.
    Dim pkg As Package = app.LoadPackage( _
      "C:\Program Files\Microsoft SQL Server\100\Samples\Integration Services" & _
      "\Package Samples\CaptureDataLineage Sample\CaptureDataLineage\CaptureDataLineage.dtsx", _
      Nothing)
    Dim pkgVars As Variables = pkg.Variables
    Dim myVar As Variable = pkg.Variables.Add("myCustomVar", False, "User", "3")
    Dim pkgVar As Variable
    For Each pkgVar In pkgVars
      Console.WriteLine("Variable: {0}, {1}, {2}", pkgVar.Name, _
        pkgVar.DataType, pkgVar.Value.ToString())
    Next
    Console.Read()

  End Sub

End Module

Sample Output:

Variable: CancelEvent, Int32, 0

Variable: CreationDate, DateTime, 4/18/2003 11:57:00 AM

Variable: CreatorComputerName, String,

Variable: CreatorName, String,

Variable: ExecutionInstanceGUID, String, {237AB5A4-7E59-4FC9-8D61-E8F20363DF25}

Variable: FileName, String, Junk

Variable: InteractiveMode, Boolean, False

Variable: LocaleID, Int32, 1033

Variable: MachineName, String, MYCOMPUTERNAME

Variable: myCustomVar, String, 3

Variable: OfflineMode, Boolean, False

Variable: PackageID, String, {F0D2E396-A6A5-42AE-9467-04CE946A810C}

Variable: PackageName, String, DTSPackage1

Variable: StartTime, DateTime, 1/28/2005 7:55:39 AM

Variable: UserName, String, <domain>\<userid>

Variable: VersionBuild, Int32, 198

Variable: VersionComments, String,

Variable: VersionGUID, String, {90E105B4-B4AF-4263-9CBD-C2050C2D6148}

Variable: VersionMajor, Int32, 1

Variable: VersionMinor, Int32, 0

Notice that all the variables scoped in the System namespace are available to the package. For more information, see System Variables.

Microsoft SQL Server Integration Services (SSIS) provides two default namespaces where variables reside; User and System namespaces. By default, any custom variable created by the developer is added to the User namespace. System variables reside in the System namespace. You can create additional namespaces other than the User namespace to hold custom variables, and you can change the name of the User namespace, but you cannot add or modify variables in the System namespace, or assign system variables to a different namespace.

The system variables that are available differ depending on the container type. For a list of the system variables available to packages, containers, tasks, and event handlers, see System Variables.

The value of a custom variable can be a literal or an expression:

• If you want the variable to contain a literal value, set the value of its Value property.
  
• If you want the variable to contain an expression, so that you can use the results of the expression as its value, set the EvaluateAsExpression property of the variable to true, and provide an expression in the Expression property. At run time, the expression is evaluated, and the result of the expression is used as the value of the variable. For example, if the expression property of a variable is "100 * 2""100 * 2", the variable evaluates to a value of 200.
  

For a variable, you cannot explicitly set the value of its DataType. The DataType value is inferred from the initial value assigned to the variable, and cannot be changed afterward. For more information about variable data types, see Integration Services Data Types.

The following code example creates a new variable, sets EvaluateAsExpression to true, assigns the expression "100 * 2" to the expression property of the variable, and then outputs the value of the variable.

using System;
using Microsoft.SqlServer.Dts.Runtime;

namespace Microsoft.SqlServer.Dts.Samples
{
  class Program
  {
    static void Main(string[] args)
    {
      Package pkg = new Package();
      Variable v100 = pkg.Variables.Add("myVar", false, "", 1);
      v100.EvaluateAsExpression = true;
      v100.Expression = "100 * 2";
      Console.WriteLine("Expression for myVar: {0}", 
        v100.Properties["Expression"].GetValue(v100));
      Console.WriteLine("Value of myVar: {0}", v100.Value.ToString());
      Console.Read();
    }
  }
}

Imports Microsoft.SqlServer.Dts.Runtime

Module Module1

  Sub Main()

    Dim pkg As Package = New Package
    Dim v100 As Variable = pkg.Variables.Add("myVar", False, "", 1)
    v100.EvaluateAsExpression = True
    v100.Expression = "100 * 2"
    Console.WriteLine("Expression for myVar: {0}", _
      v100.Properties("Expression").GetValue(v100))
    Console.WriteLine("Value of myVar: {0}", v100.Value.ToString)
    Console.Read()

  End Sub

End Module

Sample Output:

Expression for myVar: 100 * 2

Value of myVar: 200

The expression must be a valid expression that uses the SSIS expression syntax. Literals are permitted in variable expressions, in addition to the operators and functions that the expression syntax provides, but expressions cannot reference other variables or columns. For more information, see Integration Services Expression Reference.

If a configuration file includes a custom variable, the variable can be updated at run time. What this means is that when the package runs, the value of the variable originally in the package is replaced with a new value from the configuration file. This replacement technique is useful when a package is deployed to multiple servers that require different variable values. For example, a variable can specify the number of times a Foreach Loop container repeats its workflow, or list the recipients that an event handler sends e-mail to when an error is raised, or change the number of errors that can occur before the package fails. These variables are dynamically provided in configuration files for each environment. Therefore, only variables that are read/write are allowed in configuration files. For more information, see Creating Package Configurations.

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