Shopify Metafields

Metafields allow you to store additional data on Shopify resources (Products, Orders, Customers, Shops) that aren't included in the default schema (e.g., "washing instructions" for a product).

1. Concepts

• Namespace: Grouping folder (e.g., my_app, global).
• Key: Specific field name (e.g., washing_instructions).
• Type: Data type (e.g., single_line_text_field, number_integer, json).
• Owner: The resource attaching the data (Product ID, Shop ID).

2. Metafield Definitions (Standard)

Always use Metafield Definitions (pinned metafields) when possible. This integrates them into the Admin UI and ensures standard processing.

• Create: Settings > Custom Data > [Resource] > Add definition.
• Access: namespace.key

3. Accessing in Liquid

To display metafield data on the Storefront:

<!-- Accessing a product metafield -->
<p>Washing: {{ product.metafields.my_app.washing_instructions }}</p>

<!-- Accessing a file/image metafield -->
{% assign file = product.metafields.my_app.size_chart.value %}
<img src="{{ file | image_url: width: 500 }}" />

<!-- Checking existence -->
{% if product.metafields.my_app.instructions != blank %}
   ...
{% endif %}

4. Reading via API (GraphQL)

query {
  product(id: "gid://shopify/Product/123") {
    title
    metafield(namespace: "my_app", key: "instructions") {
      value
      type
    }
  }
}

5. Writing via API (GraphQL)

To create or update a metafield, use metafieldsSet.

mutation metafieldsSet($metafields: [MetafieldsSetInput!]!) {
  metafieldsSet(metafields: $metafields) {
    metafields {
      id
      namespace
      key
      value
    }
    userErrors {
      field
      message
    }
  }
}

/* Variables */
{
  "metafields": [
    {
      "ownerId": "gid://shopify/Product/123",
      "namespace": "my_app",
      "key": "instructions",
      "type": "single_line_text_field",
      "value": "Wash cold, tumble dry."
    }
  ]
}

6. Private Metafields

If you want data to be hidden from other apps and the storefront, use Private Metafields. Note: These cannot be accessed via Liquid directly.

• Use privateMetafield queries/mutations.
• Requires explicit read_private_metafields / write_private_metafields scope (rarely used now, app_data metafields are preferred for app-specific valid storage).