---
schema_version: "1"
id: 6dce06d0ee7b2e09cbff08ddc4ddc40fee232d508bbc1e7b5c0ff52100564086
title: Validate Input Parameters and Transform Flight Data
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content_type: documentation
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latest: true
---
---
product: Anypoint Code Builder
version: master
---

# Validate Input Parameters and Transform Flight Data

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

When you scaffold an API specification into an implementation project, APIKit automatically
validates incoming requests against your API specification. This validation includes:

- **Path parameter formats**: If your API spec defines a pattern (such as
  `pattern: "^[A-Z]{2}\d+$"`), APIKit validates the format automatically.

- **Required vs. optional parameters**: APIKit ensures required parameters are present.

- **Data types**: APIKit validates that parameters match their specified types (string, integer,
  boolean, and so on).

- **Enum values**: If your spec defines allowed values, APIKit validates against that list.

If a request doesn’t match these rules, APIKit returns a `400 Bad Request` with an appropriate error
message before your flow logic even executes.

While APIKit handles format and structural validation, you need custom validation for:

- **Business logic rules**: Validating that a resource exists in your system (for example, "Does
  this flight code exist in our database?").

- **Cross-field validation**: Rules that depend on multiple parameters.

- **External system checks**: Validating against external APIs or services.

- **Database lookups**: Confirming that identifiers correspond to actual records.

In this section, you add business logic validation to check whether a flight code exists in your
database before attempting to query for it. This prevents unnecessary database calls and provides
more meaningful error messages to API consumers.

In the American Flights API, the example database stores flights with numeric IDs (1, 2, 3), but the
API exposes flight codes like `AA123`, `AA234`, and `AA345`. You need to map these codes to database
IDs and validate that the flight exists before querying.

## Create the Flight Code to Database ID Mapping

First, create a transform that stores the mapping of flight codes to database IDs.

1.  Open the `get:\flights\(flightId):american-flights-api-config` flow.

    Because MuleSoft Vibes generated the API spec, your implementation flows might have different
    names. You must locate the flow that starts with `get:\flights\(flightId)`.

    ![The Flow List with the get:\\flights\\(flightId):american-flights-api-config flow selected](/mulesoft/current/en-us/anypoint-code-builder/_images/tut-flights-flow-list-select-flow.png)

2.  If the flow already contains any **Transform Message** components, select the components and
    press **Delete**, or click **More actions…​**
    (![The More actions menu icon.](/mulesoft/current/en-us/anypoint-code-builder/_images/icon-kebab.svg)) and select **Delete Component**.

    Delete any existing **Transform Messages** to start with a clean flow.

3.  Click **Add Component** (**+**) at the start of the flow and select **Core Processors >
    Components > Transform Message**.

4.  Click the **Transform Message** component to open its properties panel.

5.  Click **Delete Target** next to **Payload**.

    ![The Transform Message General tab with Delete Target selected next to the Payload target](/mulesoft/current/en-us/anypoint-code-builder/_images/tut-flights-delete-target.png)

    This step ensures the Transform does not modify the payload.

6.  Click **Edit name** (![The Edit Name icon.](/mulesoft/current/en-us/anypoint-code-builder/_images/icon-edit.svg)), change it to **Create
    Flight Code Map**, then click **Apply** (![The Apply icon.](/mulesoft/current/en-us/anypoint-code-builder/_images/icon-apply.svg)).

7.  In the **General** tab, under **Target**, click **Add** (+) and select **Variable**.

8.  Click **Edit name** (![The Edit Name icon.](/mulesoft/current/en-us/anypoint-code-builder/_images/icon-edit.svg)) next to `vars.NewVariable1`,
    set the name to `flightCodeMap`, then click **Apply**
    (![The Apply icon.](/mulesoft/current/en-us/anypoint-code-builder/_images/icon-apply.svg)).

9.  In the **Inline Script** field, replace the content with this DataWeave script:

    ```dataweave
    %dw 2.0
    output application/java
    ---
    {
    	"AA123": 1,
    	"AA234": 2,
    	"AA345": 3,
    	"AA456": 4,
    	"AA567": 5
    }
    ```

This creates a variable `vars.flightCodeMap` that maps flight codes to their corresponding database
IDs.

> [!NOTE] In a production application, you would typically query the database directly rather than
> maintaining a hardcoded map. This tutorial uses a map to clearly demonstrate the validation logic
> without requiring additional database queries.

## Look Up the Database Flight ID

Now create a second transform to look up the flight code in the mapping you just created.

1.  After the **Create Flight Code Map** transform, click **Add Component** (**+**) and select
    **Core Processors > Components > Transform Message**.

    ![The Add Component button after the Create Flight Code Map Transform element.](/mulesoft/current/en-us/anypoint-code-builder/_images/tut-flights-flow-add-component.png)

2.  Click the **Transform Message** component to open its properties panel.

3.  Click **Edit name** (![The Edit Name icon.](/mulesoft/current/en-us/anypoint-code-builder/_images/icon-edit.svg)), change it to **Lookup DB
    Flight ID**, then click **Apply** (![The Apply icon.](/mulesoft/current/en-us/anypoint-code-builder/_images/icon-apply.svg)).

4.  Click **Delete Target** next to **Payload**.

5.  In the **General** tab, under **Target**, click **Add** (+) and select **Variable**.

6.  Click **Edit name** (![The Edit Name icon.](/mulesoft/current/en-us/anypoint-code-builder/_images/icon-edit.svg)) next to `vars.NewVariable1`,
    set the name to `dbFlightId`, then click **Apply** (![The Apply icon.](/mulesoft/current/en-us/anypoint-code-builder/_images/icon-apply.svg)).

7.  In the **Inline Script** field for this variable, paste this code:

    ```dataweave
    %dw 2.0
    output application/java
    ---
    vars.flightCodeMap[attributes.uriParams.flightId]
    ```

This script looks up the flight code from the request URL in the mapping created in the previous
transform and returns the corresponding database ID. If the flight code isn’t in the map, it returns
`null`.

> [!NOTE] You cannot reference a variable in the same Transform Message where you’re creating it.
> The variable only becomes available **after** the transform completes. By splitting the logic into
> two transforms, `vars.flightCodeMap` is available for use in the second transform.

## Add a Choice Router to Validate Flight Existence

Now add logic to check whether the flight code was found in the mapping.

1.  After the **Lookup DB Flight ID** transform, click **Add Component** (**+**) and select **Core
    Processors > Flow Control > Choice**.

2.  Click the **When** path inside the Choice router.

    ![The When path of the Choice router selected and the When element properties panel.](/mulesoft/current/en-us/anypoint-code-builder/_images/tut-flights-flow-when-config.png)

3.  In the **When** properties panel, under **Expression**, add this condition to check if the
    flight code wasn’t found:

    ```dataweave
    #[vars.dbFlightId == null]
    ```

This expression evaluates to `true` when the flight code doesn’t exist in the mapping.

## Raise an Error for Unknown Flight Codes

When a flight code isn’t found, raise a custom error instead of proceeding with the query.

1.  Inside the **When** path (where the condition is true), click **Add Component** (**+**) and
    select **Core Processors > Error Handling > Raise Error**.

2.  In the **Raise Error** properties panel, configure:

    <table><colgroup><col> <col></colgroup><thead><tr><th>Field Name</th><th>Field Value</th></tr></thead><tbody><tr><td><div><div><p><strong>Type</strong></p></div></div></td><td><div><div><p><code>VALIDATION:FLIGHT_NOT_FOUND</code></p></div></div></td></tr><tr><td><div><div><p><strong>Description</strong></p></div></div></td><td><div><div><p><code>'Flight code ' ++ attributes.uriParams.flightId ++ ' not found in our system'</code></p></div></div></td></tr></tbody></table>

This creates a custom error type that you handle in the error handler, providing a meaningful
message that includes the flight code the user attempted to look up.

## Add the Database Query to the Otherwise Path

The database query executes when the flight exists (when `vars.dbFlightId` is not null).

1.  Inside the **Otherwise** path of the Choice router, click **Add Component** (**+**) and select
    **Connectors > Database > Select**.

2.  Select the component and configure:

    <table><colgroup><col> <col></colgroup><thead><tr><th>Field Name</th><th>Field Value</th></tr></thead><tbody><tr><td><div><div><p><strong>Name</strong></p></div></div></td><td><div><div><p><code>Flight by ID</code></p></div></div></td></tr><tr><td><div><div><p><strong>Connection Config</strong></p></div></div></td><td><div><div><p><code>Config</code> (your MySQL connection)</p></div></div></td></tr><tr><td><div><div><p><strong>SQL Query Text</strong></p></div></div></td><td><div><div><p><code>SELECT * FROM american WHERE ID = :flightId</code></p></div></div></td></tr><tr><td><div><div><p><strong>Input Parameters</strong></p></div></div></td><td><div><div><p><code>{ 'flightId': vars.dbFlightId }</code></p></div></div></td></tr></tbody></table>

    ![Database - Select properties panel with Name set to Flight by ID, Connection Config set to Config, and the SQL Query Text and Input Parameters fields configured](/mulesoft/current/en-us/anypoint-code-builder/_images/tut-flights-db-flight-by-id-config.png)

Your flow should now look like this:

![The get:\\flights\\(flightId):american-flights-api-config flow with the Choice router’s When and Otherwise paths configured with Raise Error and Database Select components](/mulesoft/current/en-us/anypoint-code-builder/_images/tut-flights-choice-flow-overview.png)

## Add an Error Handler for Flight Not Found

Now configure the error handler to return a proper 404 response when a flight isn’t found.

1.  In the canvas, open the `american-flights-api-main` flow (the main flow with the HTTP listener
    and error handler).

2.  After the last **Error Handler**, click **Add Component** (**+**).

    ![The american-flights-api-main flow’s Error Handler section with Add Component clicked after the last error handler](/mulesoft/current/en-us/anypoint-code-builder/_images/tut-flights-error-handler-add-component.png)

3.  Select **On Error Propagate**.

4.  Click the **On Error Propagate** component to open its properties panel

5.  Next to **Type** click the **Text Mode** button
    (![The Text Mode icon.](/mulesoft/current/en-us/anypoint-code-builder/_images/icon-text-mode.svg)) to enable it.

    ![The On Error Propagate properties panel with the Text Mode button next to the Type field](/mulesoft/current/en-us/anypoint-code-builder/_images/tut-flights-enable-text-mode.png)

6.  In **Type**, paste `VALIDATION:FLIGHT_NOT_FOUND`.

7.  Inside this error handler, click **Add Component** (**+**) and select **Core Processors >
    Components > Logger**.

8.  Select the **Logger** and set these properties:

    <table><colgroup><col> <col></colgroup><thead><tr><th>Field Name</th><th>Field Value</th></tr></thead><tbody><tr><td><div><div><p><strong>Level</strong></p></div></div></td><td><div><div><p><code>WARN</code></p></div></div></td></tr><tr><td><div><div><p><strong>Message</strong></p></div></div></td><td><div><div><p><code>#['Flight not found: ' ++ error.description]</code></p></div></div></td></tr></tbody></table>

    This logs details about which flight was requested but not found, helping with debugging and
    monitoring.

9.  After the Logger, click **Add Component** (**+**) and add **Core Processors > Components >
    Transform Message**.

10. Configure the Transform Message:

    1.  In the **General** tab, under **Target > Payload**, set **Source** to **Inline Script**.

    2.  In the **Inline Script** field, set:

        ```dataweave
        %dw 2.0
        output application/json
        ---
        {
        	message: error.description default "Flight not found",
        	flightId: attributes.uriParams.flightId
        }
        ```

11. Click **+Add** and select **Variable**.

12. Name the variable `httpStatus` and set its value to `404`.

    ![The Transform Message properties panel with the error response script and the httpStatus variable set to 404](/mulesoft/current/en-us/anypoint-code-builder/_images/tut-flights-dw-transform-config.png)

This returns a JSON response with a meaningful error message and the flight ID that was requested,
along with a 404 HTTP status code.

## Transform Data to Meet the API Contract

When building an API implementation, it’s essential that your responses match the structure defined
in your API specification. While the database might store data in one format, your API contract
defines how that data should be presented to consumers. DataWeave transformations bridge this gap by
mapping database fields to the expected API response format.

In this section, you create a DataWeave transformation that converts database query results into the
JSON format specified in your American Flights API contract.

### Understand the Data Mapping Challenge

Your MySQL database stores flight information with these fields:

Example database record

```json
{
  "ID": 1,
  "code1": "rree",
  "code2": "0001",
  "airlineName": "American Airlines",
  "toAirport": "LAX",
  "fromAirport": "MUA",
  "takeOffDate": "2016-01-20",
  "price": 541,
  "planeType": "Boeing 787",
  "seatsAvailable": 0,
  "totalSeats": 200
}
```

Your API specification defines a different structure for the response:

```json
{
  "ID": 1,
  "code": "AA123",
  "price": 499.99,
  "departureDate": "2024-12-25T10:00:00",
  "origin": "SFO",
  "destination": "LAX",
  "emptySeats": 45,
  "plane": {
    "type": "Boeing 737",
    "totalSeats": 150
  }
}
```

Notice the transformation challenges:

1.  **Field name changes**: Database fields have different names than API fields:

    1.  `fromAirport` → `origin`

    2.  `toAirport` → `destination`

    3.  `takeOffDate` → `departureDate`

    4.  `seatsAvailable` → `emptySeats`

2.  **Field combination**: `code1` and `code2` need to be combined into a single `code` field.

3.  **Nested object creation**: `planeType` and `totalSeats` (flat fields in the database) must
    become a nested `plane` object in the API response.

4.  **Fields to exclude**: `airlineName` is in the database but not needed in the API response.

### Step 1: Add the Transform Message Component

In your implementation flow `get:\flights\(flightId):american-flights-api-config`, add a Transform
Message component after the Database Select operation.

1.  Locate the `get:\flights\(flightId):american-flights-api-config` flow in your canvas.

2.  After the **Flight by ID** database query, click **Add Component** (**+**) and select **Core
    Processors > Components > Transform Message**.

3.  Click the **Transform Message** component to open its properties panel.

4.  Click **Edit name** (![The Edit Name icon.](/mulesoft/current/en-us/anypoint-code-builder/_images/icon-edit.svg)), change it to **Transform
    Flight**, then click **Apply** (![The Apply icon.](/mulesoft/current/en-us/anypoint-code-builder/_images/icon-apply.svg)).

By default, this transform just outputs `payload`, which passes through the raw database structure
without transformation.

### Step 2: Define Input Metadata

To help DataWeave understand the structure of your database results, define input metadata.

1.  In the project explorer, right-click the `examples` folder (`src/main/resources/examples`) and
    select **New File**.

    If the `examples` folder doesn’t exist, right-click the **resources** folder
    (`src/main/resources`), select **New Folder**, and name it `examples`.

    ![The project explorer with the examples folder highlighted and New File selected from the context menu](/mulesoft/current/en-us/anypoint-code-builder/_images/tut-flights-new-file.png)

2.  Name the file `sample-database-input.json`.

3.  Open the file, populate it with this sample database record, and save the file:

    ```json
    [
      {
        "ID": 1,
        "code1": "rree",
        "code2": "0001",
        "airlineName": "American Airlines",
        "toAirport": "LAX",
        "fromAirport": "MUA",
        "takeOffDate": "2016-01-20",
        "price": 541,
        "planeType": "Boeing 787",
        "seatsAvailable": 0,
        "totalSeats": 200
      }
    ]
    ```

4.  Open the `get:\flights\(flightId):american-flights-api-config` flow in the canvas.

5.  Click the **Transform Flight** element you added previously.

6.  Click the **Metadata** tab.

7.  Inside **Input** and next to **Payload: Any**, click **(No metadata selected)** > **Set custom
    metadata**.

    ![The Input Payload metadata selector with Set custom metadata highlighted](/mulesoft/current/en-us/anypoint-code-builder/_images/tut-flights-set-custom-metadata.png)

8.  In the tab that opens, click **Create New**.

9.  In the **Add Custom Metadata** dialog, set:

    <table><colgroup><col> <col></colgroup><thead><tr><th>Field Name</th><th>Field Value</th></tr></thead><tbody><tr><td><div><div><p><strong>Name</strong></p></div></div></td><td><div><div><p><code>DatabaseFlightRecord</code></p></div></div></td></tr><tr><td><div><div><p><strong>Type</strong></p></div></div></td><td><div><div><p><strong>JSON</strong></p></div></div></td></tr><tr><td><div><div><p><strong>Source</strong></p></div></div></td><td><div><div><p><strong>Example</strong></p></div></div></td></tr><tr><td><div><div><p><strong>Example</strong></p></div></div></td><td><div><div><p><code>examples/sample-database-input.json</code><br>This is the example file you just created.</p></div></div></td></tr></tbody></table>

10. Click **Save & Close**.

11. Click **Apply & Close**.

You should now see the input payload structure in the left panel, showing all available database
fields.

### Step 3: Define Output Metadata

Now define the expected API response format based on your specification.

1.  In the project explorer, right-click the `examples` folder (`src/main/resources/examples`) and
    select **New File**.

2.  Name the file `sample-flight-response.json`.

3.  Open the file, populate it with this sample API response (from your API spec), and save the
    file:

    ```json
    {
      "ID": 1,
      "code": "AA123",
      "price": 499.99,
      "departureDate": "2024-12-25T10:00:00",
      "origin": "SFO",
      "destination": "LAX",
      "emptySeats": 45,
      "plane": {
        "type": "Boeing 737",
        "totalSeats": 150
      }
    }
    ```

4.  Open the `get:\flights\(flightId):american-flights-api-config` flow in the canvas.

5.  Click the **Transform Flight** element you added previously.

6.  Click the **Metadata** tab.

7.  Inside **Output** and next to **Payload: Any**, click **(No metadata selected)** > **Set custom
    metadata**.

8.  In the tab that opens, click **Create New**.

9.  In the **Add Custom Metadata** dialog, set:

    <table><colgroup><col> <col></colgroup><thead><tr><th>Field Name</th><th>Field Value</th></tr></thead><tbody><tr><td><div><div><p><strong>Name</strong></p></div></div></td><td><div><div><p><code>FlightResponse</code></p></div></div></td></tr><tr><td><div><div><p><strong>Type</strong></p></div></div></td><td><div><div><p><strong>JSON</strong></p></div></div></td></tr><tr><td><div><div><p><strong>Source</strong></p></div></div></td><td><div><div><p><strong>Example</strong></p></div></div></td></tr><tr><td><div><div><p><strong>Example</strong></p></div></div></td><td><div><div><p><code>examples/sample-flight-response.json</code><br>This is the example file you just created.</p></div></div></td></tr></tbody></table>

10. Click **Save & Close**.

11. Click **Apply & Close**.

The output panel now shows the expected response structure with the nested `plane` object.

### Step 4: Create the Field Mappings

With both input and output metadata defined, you can now create the transformation using DataWeave’s
mapping features.

- Use MuleSoft Vibes

- Write the DataWeave Script Manually

1.  Open MuleSoft Vibes.

2.  Send this message:

    ```command
    In the get:\flights\(flightId):american-flights-api-config flow, open the Transform Flight component and add a transformation that maps the input metadata with the output metadata. For code, use code1 ++ code2.
    ```

    > [!NOTE] If you used a different flow or component name, ensure you specify it in the message
    > so MuleSoft Vibes knows exactly which flow and components to modify.

3.  Wait until MuleSoft Vibes completes the task before making further changes.

After MuleSoft Vibes finishes adding the transformation, confirm that the DataWeave script is
similar to this:

```dataweave
%dw 2.0
output application/json
---
{
	ID: payload[0].ID,
	code: payload[0].code1 ++ payload[0].code2,
	price: payload[0].price,
	departureDate: payload[0].takeOffDate,
	origin: payload[0].fromAirport,
	destination: payload[0].toAirport,
	emptySeats: payload[0].seatsAvailable,
	plane: {
		"type": payload[0].planeType,
		totalSeats: payload[0].totalSeats
	}
}
```

You can write the complete DataWeave script in the **Script** view:

1.  Click the **Script** tab in the Transform Message component.

2.  Replace the current content with:

    ```dataweave
    %dw 2.0
    output application/json
    ---
    {
    	ID: payload[0].ID,
    	code: payload[0].code1 ++ payload[0].code2,
    	price: payload[0].price,
    	departureDate: payload[0].takeOffDate,
    	origin: payload[0].fromAirport,
    	destination: payload[0].toAirport,
    	emptySeats: payload[0].seatsAvailable,
    	plane: {
    		"type": payload[0].planeType,
    		totalSeats: payload[0].totalSeats
    	}
    }
    ```

**Explanation:**

- `code: payload[0].code1 ++ payload[0].code2` — concatenates `code1` and `code2` into a single
  `code` field.

- `departureDate: payload[0].takeOffDate` — renames the field from database to API format.

- `origin: payload[0].fromAirport` — maps `fromAirport` to `origin`.

- `destination: payload[0].toAirport` — maps `toAirport` to `destination`.

- `emptySeats: payload[0].seatsAvailable` — renames `seatsAvailable` to `emptySeats`.

- `plane: { …​ }` — creates a nested object from flat database fields.

- `output application/json` — specifies the output format.

[Implement the American Flights API](https://docs.mulesoft.com/anypoint-code-builder/tut-flights-implement-api)
[Debug the American Flights API](https://docs.mulesoft.com/anypoint-code-builder/tut-flights-debug-api)