Shopify Inventory Architecture

Overview

In Shopify, inventory is not stored directly as a simple integer property on ProductVariant. Instead, Shopify uses a normalized 3-part relational structure:

ProductVariant 
   └── InventoryItem 
          └── InventoryLevel (Quantity per Location)

Core Entities

1. ProductVariant: Commercial purchasing option shown to customers.
2. InventoryItem: Internal physical item record representing cost, tracked flag, country of origin, and harmonized system (HS) codes.
3. InventoryLevel: The join record storing the actual quantity at a specific physical Location.

GraphQL API Query

To query inventory across locations in Shopify Admin GraphQL API:

query getVariantInventory($id: ID!) {
  productVariant(id: $id) {
    id
    title
    sku
    inventoryItem {
      id
      tracked
      unitCost {
        amount
      }
      inventoryLevels(first: 5) {
        edges {
          node {
            location {
              name
            }
            quantities(names: ["available", "committed", "on_hand"]) {
              name
              quantity
            }
          }
        }
      }
    }
  }
}

Inventory Quantities API

In modern Shopify GraphQL APIs, quantities are categorized explicitly by name:

• available: Stock ready for immediate purchase.
• committed: Stock allocated to unfulfilled orders.
• on_hand: Total physical units present at the location (on_hand = available + committed).
• reserved: Units set aside for drafts or active holds.

Developer Takeaway