control-flow-set-variable-activity.md

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Set Variable Activity	Azure Data Factory & Azure Synapse	Learn how to use the Set Variable activity to set the value of an existing variable defined in an Azure Data Factory or Azure Synapse Analytics pipeline or to set a pipeline return value.	data-factory	orchestration	synapse	01/05/2024	conceptual	kromerm	makromer	jburchel

Set Variable Activity in Azure Data Factory and Azure Synapse Analytics

[!INCLUDEappliesto-adf-asa-md]

Use the Set Variable activity to set the value of an existing variable of type String, Bool, or Array defined in a Data Factory or Synapse pipeline or use the Set Variable activity to set a pipeline return value (preview).

Create a Set Variable activity with UI

To use a Set Variable activity in a pipeline, complete the following steps:

1. Select the background of the pipeline canvas and use the Variables tab to add a variable:

:::image type="content" source="media/control-flow-activities-common/add-pipeline-array-variable.png" alt-text="Screenshot of an empty pipeline canvas with the Variables tab selected with an array type variable named TestVariable.":::

2. Search for Set Variable in the pipeline Activities pane, and drag a Set Variable activity to the pipeline canvas.

3. Select the Set Variable activity on the canvas if it isn't already selected, and then select the Settings tab to edit its details.

4. Select Pipeline variable for your Variable type.

5. Select the variable for the Name property.

6. Enter an expression to set the value for the variables. This expression can be a literal string expression, or any combination of dynamic expressions, functions, system variables, or outputs from other activities.

:::image type="content" source="media/control-flow-set-variable-activity/set-variable-activity.png" alt-text="Screenshot of the UI for a Set variable activity.":::

Setting a pipeline return value with UI

We have expanded Set Variable activity to include a special system variable, named Pipeline Return Value, allowing communication from the child pipeline to the calling pipeline, in the following scenario.

You don't need to define the variable, before using it. For more information, see Pipeline Return Value

:::image type="content" source="media/pipeline-return-value/pipeline-return-value-00-paradigm.png" alt-text="Screenshot with ExecutePipeline Activity.":::

Type properties

Property	Description	Required
name	Name of the activity in pipeline	yes
description	Text describing what the activity does	no
type	Must be set to SetVariable	yes
variableName	Name of the variable that is set by this activity	yes
value	String literal or expression object value that the variable is assigned to	yes

Incrementing a variable

A common scenario involving variable is to use a variable as an iterator within an Until or ForEach activity. In a Set variable activity, you can't reference the variable being set in the value field, that is, no self-referencing. To work around this limitation, set a temporary variable and then create a second Set variable activity. The second Set variable activity sets the value of the iterator to the temporary variable. Here's an example of this pattern:

• First you define two variables: one for the iterator, and one for temporary storage.

:::image type="content" source="media/control-flow-set-variable-activity/set-variable-integer.png" alt-text="Screenshot shows defining variables.":::

• Then you use two activities to increment values

:::image type="content" source="media/control-flow-set-variable-activity/increment-variable.png" alt-text="Screenshot shows increment variable.":::

{
    "name": "pipeline1",
    "properties": {
        "activities": [
            {
                "name": "Increment J",
                "type": "SetVariable",
                "dependsOn": [],
                "policy": {
                    "secureOutput": false,
                    "secureInput": false
                },
                "userProperties": [],
                "typeProperties": {
                    "variableName": "temp_j",
                    "value": {
                        "value": "@add(variables('counter_i'),1)",
                        "type": "Expression"
                    }
                }
            },
            {
                "name": "Set I",
                "type": "SetVariable",
                "dependsOn": [
                    {
                        "activity": "Increment J",
                        "dependencyConditions": [
                            "Succeeded"
                        ]
                    }
                ],
                "policy": {
                    "secureOutput": false,
                    "secureInput": false
                },
                "userProperties": [],
                "typeProperties": {
                    "variableName": "counter_i",
                    "value": {
                        "value": "@variables('temp_j')",
                        "type": "Expression"
                    }
                }
            }
        ],
        "variables": {
            "counter_i": {
                "type": "Integer",
                "defaultValue": 0
            },
            "temp_j": {
                "type": "Integer",
                "defaultValue": 0
            }
        },
        "annotations": []
    }
}

Variables are scoped at the pipeline level. This means that they're not thread safe and can cause unexpected and undesired behavior if they're accessed from within a parallel iteration activity such as a ForEach loop, especially when the value is also being modified within that foreach activity.

Related content

Learn about another related control flow activity:

• Append Variable Activity