fix(utils): medusa internal service returned data should match typings (#12715)

FIXES SUP-1824

**What**
The medusa internal service update should always return the data in the expected shape described by the interface. The medusa service should not have to handle the reshapre

packages/modules/auth/src/services/auth-module.ts

@@ -129,7 +129,7 @@ export default class AuthModuleService
       populate: true,
     })
 
-    return Array.isArray(data) ? serializedUsers : serializedUsers[0]
+    return serializedUsers
   }
 
   async register(
@@ -206,7 +206,7 @@ export default class AuthModuleService
       AuthTypes.ProviderIdentityDTO[]
     >(updatedProviders)
 
-    return Array.isArray(data) ? serializedProviders : serializedProviders[0]
+    return serializedProviders
   }
 
   async updateProvider(

packages/modules/customer/src/services/customer-module.ts

@@ -218,7 +218,7 @@ export default class CustomerModuleService
       populate: true,
     })
 
-    return isString(idsOrSelector) ? serialized[0] : serialized
+    return serialized
   }
 
   // @ts-expect-error

packages/modules/fulfillment/src/services/fulfillment-module-service.ts

@@ -2021,9 +2021,11 @@ export default class FulfillmentModuleService
       })
     }
 
-    const result = await this.baseRepository_.serialize(fulfillment)
+    const result = await this.baseRepository_.serialize<FulfillmentDTO>(
+      fulfillment
+    )
 
-    return Array.isArray(result) ? result[0] : result
+    return result
   }
 
   async retrieveFulfillmentOptions(

packages/modules/inventory/src/services/inventory-module.ts

@@ -1052,7 +1052,7 @@ export default class InventoryModuleService
       context
     )
 
-    return result[0]
+    return result
   }
 
   @InjectManager()

packages/modules/payment/src/services/payment-module.ts

@@ -359,15 +359,13 @@ export default class PaymentModuleService
         }
       )
 
-      paymentSession = (
-        await this.paymentSessionService_.update(
-          {
-            id: paymentSession!.id,
-            data: { ...input.data, ...providerPaymentSession.data },
-          },
-          sharedContext
-        )
-      )[0]
+      paymentSession = await this.paymentSessionService_.update(
+        {
+          id: paymentSession!.id,
+          data: { ...input.data, ...providerPaymentSession.data },
+        },
+        sharedContext
+      )
     } catch (error) {
       if (providerPaymentSession) {
         await this.paymentProviderService_.deleteSession(input.provider_id, {
@@ -440,7 +438,7 @@ export default class PaymentModuleService
       sharedContext
     )
 
-    return await this.baseRepository_.serialize(updated[0], { populate: true })
+    return await this.baseRepository_.serialize(updated, { populate: true })
   }
 
   @InjectManager()
@@ -605,7 +603,7 @@ export default class PaymentModuleService
     // NOTE: currently there is no update with the provider but maybe data could be updated
     const result = await this.paymentService_.update(data, sharedContext)
 
-    return await this.baseRepository_.serialize<PaymentDTO>(result[0])
+    return await this.baseRepository_.serialize<PaymentDTO>(result)
   }
 
   // TODO: This method should return a capture, not a payment

packages/modules/product/integration-tests/__tests__/product.ts

@@ -285,6 +285,59 @@ moduleIntegrationTestRunner<Service>({
           )
         })
 
+        it("should update a product and its allowed relations using selector", async () => {
+          const updateData = [
+            {
+              selector: {
+                id: productOne.id,
+              },
+              data: {
+                title: "update test 1",
+              },
+            },
+          ]
+
+          const products = await service.update(updateData)
+
+          expect(products.length).toEqual(1)
+
+          let result = await service.retrieve(productOne.id)
+          let serialized = JSON.parse(JSON.stringify(result))
+
+          expect(serialized).toEqual(
+            expect.objectContaining({
+              id: productOne.id,
+              title: "update test 1",
+            })
+          )
+        })
+
+        it("should update a single product and its allowed relations", async () => {
+          const updateData = {
+            id: productOne.id,
+            title: "update test 1",
+          }
+
+          const product = await service.update(updateData)
+
+          expect(product).toEqual(
+            expect.objectContaining({
+              id: productOne.id,
+              title: "update test 1",
+            })
+          )
+
+          let result = await service.retrieve(productOne.id)
+          let serialized = JSON.parse(JSON.stringify(result))
+
+          expect(serialized).toEqual(
+            expect.objectContaining({
+              id: productOne.id,
+              title: "update test 1",
+            })
+          )
+        })
+
         it("should throw an error when id is not present", async () => {
           let error
           const updateData = [