Flow variables

  • Release version: Yokohama
  • Updated January 30, 2025
  • 2 minutes to read
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    Summary of Flow variables

    Flow variables in ServiceNow allow you to create, modify, and use variables directly within a flow, similar to Workflow scratchpad variables. They provide a way to set and retrieve values throughout the entire flow execution, offering more flexibility compared to subflow inputs and outputs, which are limited to the start or completion of subflows.

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    Key Features

    • Creation: Flow variables can be created via the Flow Variables option in the More Actions menu, allowing you to define multiple variables at once with specific names and data types.
    • Access and Modification: Flow variables are accessible as data pills in the Data panel and can be assigned or updated anytime during the flow using the Set Flow Variables action.
    • Mutability: Values assigned to flow variables are mutable and can be overridden multiple times within the flow; the last assigned value is the one used at runtime.
    • Dependency and Order: When assigning variable values by referencing other data pills or variables, maintaining the assignment order is crucial to avoid null values.
    • Data Types Supported: ServiceNow supports Date/Time, Decimal, Floating-point number, Integer, JSON, Reference, String, and True/False data types for flow variables.
    • Execution Details: The flow execution logs provide detailed summaries of flow variables, including their names, types, configurations, and runtime values, which aids in debugging and validation.

    Practical Use for ServiceNow Customers

    By using flow variables, you can efficiently store and manipulate data throughout your flow processes, improving the flow's flexibility and control. This capability is essential for scenarios where values need to be updated dynamically during execution or shared across multiple flow actions. Understanding how to define, assign, and reference flow variables ensures that your flows run predictably and allow for complex data handling without resorting to subflows.

    Similar to Workflow scratchpad variables, create variables that you can use and modify directly in your flow. Access flow variables as data pills directly in the Data panel.

    Use flow variables to set and retrieve values throughout a flow. Flow variables are similar to subflow inputs and outputs. Both define data available to a flow or subflow. The main difference between them is when they are accessible. Flow variables are accessible throughout a flow. Inputs are only accessible at the start of a subflow, and outputs are only accessible when a subflow completes.

    Creating flow variables

    Create variables with the Flow Variables option on the More Actions menu. You can create several variables at a time by choosing a name and data type for each one. Flow variables appear as data pills in the Flow Variables section of the Data panel.

    Assigning values to flow variables

    Assign values to variables with the Set Flow Variables flow logic. Set Flow Variables has the following inputs:
    • The name of the variable.
    • The data value for the variable.

    You can assign values to all of your variables with a single use of Set Flow Variables. Unlike other data pills, the values assigned to flow variables are mutable and can be changed at any time. Using Set Flow Variables overrides the current value of the variable. If no value is assigned to a variable, the default value is null.

    Flow variable values are set in the order in which they're assigned from top to bottom. If you set the value of the same variable multiple times, the flow only uses the last value set. For example, these three variable definitions result in the variable having the runtime value of last value set.

    Table 1. Last value set defines flow variable value
    Order Variable Configuration
    1 variable first value set
    2 variable second value set
    3 variable last value set

    Variable values can reference any data pill from earlier in the flow, including other variables. If you set variable values by reference to other data pills, you must maintain the order of the variable assignments. The referenced value must always come before the variable that uses the referenced value. Changing the order may produce null values. For example, these variable definitions only produce the expected runtime values when you maintain the order of the variable definitions.

    Table 2. Setting variable values by reference
    Order Variable Configuration Runtime Value
    1 variable1 One One
    2 variable2 {variable1}, Two One, Two
    3 variable3 {variable1}, {variable2}, Three One, Two, Three

    Flow execution details

    A summary of the Set Flow Variables flow logic appears in the execution details. The details show the name, type, configuration, and runtime values for all the variables set with the action. Execution details also provide information about the variables when they're used in actions or flow logic. In that case, it shows the type, configuration, and runtime values.

    Supported data types

    Workflow Studio supports the following data types for flow variables:
    • Date/Time
    • Decimal
    • Floating-point number
    • Integer
    • JSON
    • Reference
    • String
    • True/False