Keep variant inventory in sync across locations, with Mechanic.

shopify/inventory_levels/update

{% assign filter_by_these_product_types = options.filter_by_these_product_types__array %}

{% comment %}
  -- query for "available" quantites at all locations where this inventory item / variant is stocked
{% endcomment %}

{% capture query %}
  query {
    inventoryLevel(id: {{ inventory_level.admin_graphql_api_id | json }}) {
      item {
        id
        variant {
          legacyResourceId
          product {
            productType
          }
        }
        inventoryLevels(first: 100) {
          nodes {
            id
            location {
              id
            }
            quantities(names: "available") {
              quantity
            }
          }
        }
      }
    }
  }
{% endcapture %}

{% assign result = query | shopify %}

{% if event.preview %}
  {% capture result_json %}
    {
      "data": {
        "inventoryLevel": {
          "item": {
            "id": "gid://shopify/InventoryItem/1234567890",
            "variant": {
              "legacyResourceId": "1234567890",
              "product": {
                "productType": {{ filter_by_these_product_types.first | json }}
              }
            },
            "inventoryLevels": {
              "nodes": [
                {
                  "id": "gid://shopify/InventoryLevel/1234567890?inventory_item_id=1234567890",
                  "location": {
                    "id": "gid://shopify/Location/1234567890"
                  },
                  "quantities": [
                    {
                      "quantity": 1
                    }
                  ]
                },
                {
                  "id": "gid://shopify/InventoryLevel/2345678901?inventory_item_id=1234567890",
                  "location": {
                    "id": "gid://shopify/Location/2345678901"
                  },
                  "quantities": [
                    {
                      "quantity": 0
                    }
                  ]
                }
              ]
            }
          }
        }
      }
    }
  {% endcapture %}

  {% assign result = result_json | parse_json %}
{% endif %}

{% assign inventory_item = result.data.inventoryLevel.item %}
{% assign variant = inventory_item.variant %}
{% assign product = inventory_item.variant.product %}
{% assign inventory_levels = inventory_item.inventoryLevels.nodes %}

{% comment %}
  -- if product types are configured in the task, make sure this inventory level update belongs to a product with one of the configured types
{% endcomment %}

{% if filter_by_these_product_types != blank %}
  {% unless filter_by_these_product_types contains product.productType %}
    {% log
      message: "Product type is not in the configured product types; skipping.",
      variant: variant,
      filter_by_these_product_types: filter_by_these_product_types
    %}
    {% break %}
  {% endunless %}
{% endif %}

{% if inventory_levels.size < 2 %}
  {% log
    message: "This variant is only stocked at a single location; no inventory sync needed.",
    variant: variant
  %}
  {% break %}
{% endif %}

{% comment %}
  -- get the "available" quantity for the inventory level that caused the update event
{% endcomment %}

{% assign source_inventory_level
  = inventory_levels
  | where: "id", inventory_level.admin_graphql_api_id
  | first
%}
{% assign source_quantity = source_inventory_level.quantities.first.quantity %}

{% comment %}
  -- since this task updates ALL inventory levels of a variant in bulk, then a source quantity that doesn't equal the cached value for this variant indicates the change was likely not made via a prior run of this task
{% endcomment %}

{% assign cache_key = "variant-inventory-level-" | append: inventory_item.variant.legacyResourceId %}
{% assign cached_value = cache[cache_key] %}

{% if cached_value != blank %}
  {% if cached_value == source_quantity %}
    {% log
      message: "The 'available' inventory level of this variant at this location (i.e. source quantity) matches the cached value for this variant; no updates to make.",
      cached_value: cached_value,
      source_quantity: source_quantity
    %}
    {% break %}
  {% endif %}

  {% log
    message: "The 'available' inventory level of this variant at this location (i.e. source quantity) does not match the cached value for this variant; update the cache and adjust the other levels as needed.",
    cached_value: cached_value,
    source_quantity: source_quantity
  %}
{% endif %}

{% comment %}
  -- no cached value exists OR this new value does not match it, so set it and then adjust "available" quantities across locations, using the source quantity to determine deltas
{% endcomment %}

{% action "cache", "setex", cache_key, 60, source_quantity %}

{% assign adjustments = array %}

{% for inventory_level in inventory_levels %}
  {% assign delta = source_quantity | minus: inventory_level.quantities.first.quantity %}

  {% if delta != 0 %}
    {% assign adjustment = hash %}
    {% assign adjustment["inventoryItemId"] = inventory_item.id %}
    {% assign adjustment["locationId"] = inventory_level.location.id %}
    {% assign adjustment["delta"] = delta %}
    {% assign adjustments = adjustments | push: adjustment %}
  {% endif %}
{% endfor %}

{% if adjustments != blank %}
  {% action "shopify" %}
    mutation {
      inventoryAdjustQuantities(
        input: {
          name: "available"
          reason: "correction"
          changes: {{ adjustments | graphql_arguments }}
        }
      ) {
        userErrors {
          code
          field
          message
        }
      }
    }
  {% endaction %}
{% endif %}