Cart Transform: Update Lines Operation

The Update Lines transform allows you to modify the properties of cart line items, including their price, title, and image.

Overview

The Update Lines transform allows you to modify the properties of cart line items, including their price, title, and image. This is particularly useful for:

Dynamic pricing: Apply custom prices based on cart line attributes or metafields
Product customization: Change titles and images based on customer selections
Personalization: Display customized product information in the cart
Conditional pricing: Apply different prices based on product attributes

When cart lines are updated, the modifications appear immediately in the customer’s cart, providing a dynamic and personalized shopping experience.

Note: this operation is supported on the Shopify Plus stores only.

How to Configure Updates

You can configure line updates in two ways:

Manual Configuration: Set fixed values for price, title, and image in the Function Studio interface
Attribute-Based Configuration: Load all values dynamically from a cart line attribute

Both methods provide powerful ways to customize the cart experience based on your business needs.

Method 1: Manual Configuration

Adding the Update Action

In your cart transform function, click Add Action
Select Update Lines from the action list
Configure the action settings in the panel

Configuration Options

Cart Line Groups

Select which groups of cart lines should be updated
Groups must be defined earlier in your function using “Define Cart Line Groups”
Example: Select “CUSTOM_PRODUCTS” or “PERSONALIZED_ITEMS”

Price Configuration

You have two options for setting the price:

Option A: Fixed Price

Enter a specific price amount
This price will be applied to all matching cart lines
Useful for promotional pricing or fixed-rate customizations

Option B: Load Price from Field

Enable “Load price from field” toggle
Select a field source:
- Cart Line Attribute: Use an attribute value from the cart line
- Standard Field: Use a built-in product/variant field
The field value will be used as the price for each cart line

Title Configuration

Enter a custom title for the cart line
This replaces the default product/variant title
Useful for personalized products or custom configurations
Leave empty to keep the original title

Image Configuration

Select or enter an image URL (must be hosted on Shopify CDN)
This replaces the default product/variant image
Useful for showing customized products or variations
Leave empty to keep the original image

Method 2: Attribute-Based Configuration

Overview

For maximum flexibility, you can load all fields (price, title, and image) from a single cart line attribute. This is ideal for highly dynamic scenarios where values are set programmatically.

Enabling Attribute-Based Loading

In the Update Lines action, enable “Load all fields from attribute”
Specify the Attribute key (defaults to _update)
Set the attribute value on your cart lines with a JSON object

Attribute JSON Structure

The cart line attribute should contain a JSON object with these properties:

{
  "price": "34.56",
  "title": "Custom Product Title",
  "image": "https://cdn.shopify.com/path/to/image.png"
}

Attribute Object Properties

price (String, Optional)

The new price per unit for this cart line
Must be a string representation of a decimal number
Example: "29.99" or "125.50"
If omitted, the price is not changed

title (String, Optional)

The new title for this cart line
Replaces the default product/variant title
Example: "Personalized T-Shirt - John"
If omitted, the title is not changed

image (String, Optional)

The new image URL for this cart line
Must be a valid URL to an image file
Example: "https://cdn.shopify.com/s/files/1/0896/4138/6248/files/custom-image.png"
If omitted, the image is not changed

Setting the Attribute

The attribute can be set through various methods:

In Product Forms (Liquid Templates)

<input type="hidden" name="properties[_update]" value='{"price":"34.56","title":"Custom Product"}'>

Via Ajax Cart API

{
  "id": "12345",
  "qty": 1,
  "properties": {
    "_update": '{"price":"34.56","title":"Custom Product","image":"https://example.com/image.png"}'
  }
}

Through Shopify Scripts or Apps

Set the property when adding items to cart programmatically
Useful for product configurators or customization tools
Can be dynamically generated based on customer selections

Configuration Examples

Example 1: Fixed Price Override

Scenario: Apply a promotional price to all items in a specific collection

Function Studio Setup:

Create a “Define Cart Line Groups” action:
- Group name: PROMO_ITEMS
- Condition: Product is in collection “Summer Sale”
Add an “Update Lines” action:
- Cart Line Groups: Select PROMO_ITEMS
- Price: Enter 19.99
- Title: Leave empty (keep original)
- Image: Leave empty (keep original)

Result: All items in the “Summer Sale” collection are repriced to $19.99

Example 2: Load Price from Metafield

Scenario: Use a custom price stored in a product metafield

Product Setup:

Add a metafield to products: custom.special_price (type: Number)
Set value: 24.99

Function Studio Setup:

Create a “Define Cart Line Groups” action with group name CUSTOM_PRICED
Add an “Update Lines” action:
- Cart Line Groups: Select CUSTOM_PRICED
- Enable “Load price from field”
- Select Product Metafield
- Choose namespace: custom, key: special_price

Result: Each product uses its custom.special_price metafield value as the price

Example 3: Dynamic Customization with Attributes

Scenario: Customer personalizes a product with custom text and image

Cart Line Setup: Add this when the customer adds to cart:

{
  "id": "12345",
  "quantity": 1,
  "properties": {
    "_update": '{"price":"45.00","title":"Personalized Mug - Sarah","image":"https://cdn.shopify.com/generated/sarah-mug.png"}'
  }
}

Function Studio Setup:

Create a “Define Cart Line Groups” action:
- Group name: PERSONALIZED
- Condition: Has attribute _update
Add an “Update Lines” action:
- Cart Line Groups: Select PERSONALIZED
- Enable “Load all fields from attribute”
- Attribute key: _update

Result: Cart line displays custom title, image, and price based on the personalization

Example 4: Variant-Specific Pricing

Scenario: Different variants have different promotional prices stored in variant metafields

Variant Setup:

Variant A: metafield custom.promo_price = 29.99
Variant B: metafield custom.promo_price = 39.99

Function Studio Setup:

Create a “Define Cart Line Groups” action with group name ON_SALE
Add an “Update Lines” action:
- Cart Line Groups: Select ON_SALE
- Enable “Load price from field”
- Select Variant Metafield
- Choose namespace: custom, key: promo_price

Result: Each variant uses its own promotional price from the metafield

Example 5: Custom Title for Bundles

Scenario: Show a custom title for bundle products

Function Studio Setup:

Create a “Define Cart Line Groups” action:
- Group name: BUNDLES
- Condition: Product type is “Bundle”
Add an “Update Lines” action:
- Cart Line Groups: Select BUNDLES
- Title: Complete Bundle - Special Offer
- Leave price and image empty

Result: All bundle products display “Complete Bundle - Special Offer” as their title

Advanced Use Cases

Conditional Pricing Based on Quantity

Combine with conditions to apply different pricing based on cart line quantity:

Setup:

Define multiple cart line groups based on quantity ranges
Apply different update actions to each group with appropriate pricing

Multi-Tier Pricing from Attributes

Use attributes to implement complex pricing logic:

{
  "price": "19.99",
  "title": "Bulk Discount Applied - 20% OFF",
  "image": "https://cdn.shopify.com/sale-badge.png"
}

Product Configurator Integration

For products with complex configurations:

Use a product configurator app or custom form
Generate the _update attribute with calculated price and custom title
Include a preview image URL showing the configured product
Add to cart with all customization data