# Customise event field mappings

Field mappings control how Littledata maps Shopify data to destination parameters.

You can override defaults, add custom parameters, and preview the result before saving.

## Open the editor

{% stepper %}
{% step %}

### Open the destination Events tab

Start in the [Events tab](/event-customiser/events-tab.md) for the destination you want to customise.
{% endstep %}

{% step %}

### Select an event

Click any event row to open its editor.
{% endstep %}

{% step %}

### Review the editor sections

The editor has three parts:

* **Event Trigger** — the Shopify event that powers the customisation.
* **Field Mappings** — the source-to-destination field relationships.
* **Event Preview** — a preview of the destination payload.

<figure><img src="/files/2b8GtgXTu7rFOe7A5TJp" alt=""><figcaption></figcaption></figure>
{% endstep %}
{% endstepper %}

## Mapping types

### Locked mappings

These mappings are required by the destination platform.

Both the source and destination are read-only.

<figure><img src="/files/pJ720fejIYsd8PPqnq2E" alt=""><figcaption></figcaption></figure>

### Editable standard mappings

These mappings use Littledata defaults.

You can change the source field, but not the destination field.

For example, GA4 maps `products[*].productId` to `items[*].item_id` by default.

You can switch the source to `products[*].sku` instead.

<figure><img src="/files/3iUNJdJiKcAWRkGNi0zP" alt=""><figcaption></figcaption></figure>

### Custom parameters

Custom parameters let you add fields outside the default schema.

Each one has a **source dropdown** and a destination name field.

The source dropdown includes standard Shopify fields and configured [Custom Data Sources](/event-customiser/custom-data-sources.md).

<figure><img src="/files/EGHqW4p0HbyDP8AtPEO7" alt=""><figcaption></figcaption></figure>

{% hint style="info" %}
Each event has a custom parameter limit. The **Add parameter** button disables at the limit.
{% endhint %}

## Add a custom parameter

{% stepper %}
{% step %}

### Go to Field Mappings

Scroll to the bottom of the **Field Mappings** section.
{% endstep %}

{% step %}

### Add a new row

Click **Add parameter**.
{% endstep %}

{% step %}

### Choose the source

Select the Shopify field you want to send.
{% endstep %}

{% step %}

### Name the destination parameter

Enter the destination parameter name, such as `material`.

<figure><img src="/files/lRHRjCBHRQzGi6uqb3vy" alt=""><figcaption></figcaption></figure>
{% endstep %}
{% endstepper %}

To remove a custom parameter, click the **X** beside that row.

Standard and locked mappings cannot be removed.

## Save or delete a customisation

{% stepper %}
{% step %}

### Review the preview

Use [Event preview](/event-customiser/event-preview.md) to confirm your output.
{% endstep %}

{% step %}

### Save or discard

Click **Save** to apply the customisation.

Click **Discard** to undo unsaved changes.
{% endstep %}

{% step %}

### Delete if needed

To remove the customisation entirely, open the overflow menu and click **Delete**.
{% endstep %}
{% endstepper %}

{% hint style="info" %}
Changes only affect future events. Historical events stay unchanged.
{% endhint %}


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