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title: Graphically Construct a Mapping
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# Graphically Construct a Mapping

> For the full documentation index, see: https://docs.mulesoft.com/llms.txt

Use the graphical UI of the Transform Message component to map fields and structures and to set
fixed values or functions. Studio adds the necessary lines to your DataWeave code for each action.

## Map a Field

Drag an element on the input structure over to another on the output structure, this casts a line
that joins them.

![A diagram illustrates the process of converting a JSON payload to a string output](/mulesoft/current/en-us/studio/_images/using-dataweave-in-studio-8e6e0.png)

## Map a Structure

Drag a high-level structure that contains lists of elements or inner fields onto another in the
output. This creates a shaded region covering all the mapped structure. Fields that have identical
names in these structures are automatically mapped too.

![A diagram that displays the data fields for items and their respective data types](/mulesoft/current/en-us/studio/_images/using-dataweave-in-studio-6b171.png)

## Set a Fixed Value or Function

1.  Double click on a field in the output tree. This adds a function icon
    ![A  dot next to the letters f and x](/mulesoft/current/en-us/studio/_images/using-dataweave-in-studio-66cdc.png) next to it.

2.  A new line is added to the DataWeave code that assigns a default `null` value to the field. This
    line is highlighted. Change its value to anything you want.

    ![Code displaying a null text value within a JSON object](/mulesoft/current/en-us/studio/_images/dw-click.png)

    You can add:

    - A fixed string value by using " ".

    - A reference to an input field.

    - A DataWeave statement that includes functions.

## See Also

- [Transform Message Component](https://docs.mulesoft.com/studio/transform-message-component-concept-studio)

- [Workflow: Create a Mapping](https://docs.mulesoft.com/studio/workflow-create-mapping-ui-studio)

- [DataWeave language](https://docs.mulesoft.com/mule-runtime/latest/dataweave)