Merge pull request #110554 from djpmsft/docUpdates

Add set variable example

Author: Jak-MS

articles/data-factory/control-flow-set-variable-activity.md

@@ -5,28 +5,89 @@ services: data-factory
 documentationcenter: ''
 ms.service: data-factory
 ms.workload: data-services
-
 ms.topic: conceptual
-ms.date: 10/10/2018
+ms.date: 04/07/2020
 author: djpmsft
 ms.author: daperlov
 manager: jroth
 ms.reviewer: maghan
 ---
-# Set Variable Activity in Azure Data Factory
+# Set variable activity in Azure Data Factory
 
 Use the Set Variable activity to set the value of an existing variable of type String, Bool, or Array defined in a Data Factory pipeline.
 
 ## Type properties
 
 Property | Description | Required
 -------- | ----------- | --------
-name | Name of the activity in pipeline | Yes
+name | Name of the activity in pipeline | yes
 description | Text describing what the activity does | no
-type | Activity Type is SetVariable | yes
-value | String literal or expression object value used to set specified variable | yes
+type | Must be set to **SetVariable** | yes
+value | String literal or expression object value that the variable will be assigned to | yes
 variableName | Name of the variable that will be set by this activity | yes
 
+## Incrementing a variable
+
+A common scenario involving variables in Azure Data Factory is using a variable as an iterator within an until or foreach activity. In a set variable activity you cannot reference the variable being set in the `value` field. To workaround 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. 
+
+Below is an example of this pattern:
+
+![Increment variable](media/control-flow-set-variable-activity/increment-variable.png "Increment variable")
+
+``` json
+{
+    "name": "pipeline3",
+    "properties": {
+        "activities": [
+            {
+                "name": "Set I",
+                "type": "SetVariable",
+                "dependsOn": [
+                    {
+                        "activity": "Increment J",
+                        "dependencyConditions": [
+                            "Succeeded"
+                        ]
+                    }
+                ],
+                "userProperties": [],
+                "typeProperties": {
+                    "variableName": "i",
+                    "value": {
+                        "value": "@variables('j')",
+                        "type": "Expression"
+                    }
+                }
+            },
+            {
+                "name": "Increment J",
+                "type": "SetVariable",
+                "dependsOn": [],
+                "userProperties": [],
+                "typeProperties": {
+                    "variableName": "j",
+                    "value": {
+                        "value": "@string(add(int(variables('i')), 1))",
+                        "type": "Expression"
+                    }
+                }
+            }
+        ],
+        "variables": {
+            "i": {
+                "type": "String",
+                "defaultValue": "0"
+            },
+            "j": {
+                "type": "String",
+                "defaultValue": "0"
+            }
+        },
+        "annotations": []
+    }
+}
+```
+
 
 ## Next steps
 Learn about a related control flow activity supported by Data Factory: