fix(medusa): Account for multiple inventory items in get-inventory (#3094)

* use pvi service method instead of inventory service method to get quantity for sales channel

* save a few invocations

* rename quantity

* omit || 0

* add changeset

* extract method for retrieving variant inventory quantity

* update pr with feedback

packages/medusa/src/api/routes/admin/variants/get-inventory.ts

@@ -4,6 +4,7 @@ import {
 } from "../../../../types/inventory"
 import ProductVariantInventoryService from "../../../../services/product-variant-inventory"
 import {
+  SalesChannelInventoryService,
   SalesChannelLocationService,
   SalesChannelService,
 } from "../../../../services"
@@ -75,6 +76,8 @@ export default async (req, res) => {
   const channelLocationService: SalesChannelLocationService = req.scope.resolve(
     "salesChannelLocationService"
   )
+  const salesChannelInventoryService: SalesChannelInventoryService =
+    req.scope.resolve("salesChannelInventoryService")
   const channelService: SalesChannelService = req.scope.resolve(
     "salesChannelService"
   )
@@ -106,11 +109,13 @@ export default async (req, res) => {
     })
   )
 
+  const variantInventoryItems =
+    await productVariantInventoryService.listByVariant(variant.id)
+
   const inventory =
     await productVariantInventoryService.listInventoryItemsByVariant(variant.id)
   responseVariant.inventory = await joinLevels(inventory, [], inventoryService)
 
-  // TODO: adjust for required quantity
   if (inventory.length) {
     responseVariant.sales_channel_availability = await Promise.all(
       channels.map(async (channel) => {
@@ -122,10 +127,11 @@ export default async (req, res) => {
           }
         }
 
-        const quantity = await inventoryService.retrieveAvailableQuantity(
-          inventory[0].id,
-          channel.locations
-        )
+        const quantity =
+          await productVariantInventoryService.getVariantQuantityFromVariantInventoryItems(
+            variantInventoryItems,
+            channel.id
+          )
 
         return {
           channel_name: channel.name as string,