feat: Create cart with line items (#6449)

**What**
- Add support for creating a cart with items
- Add endpoint `POST /store/carts/:id/line-items`
- Add `CreateCartWorkflow`
- Add `AddToCartWorkflow`
- Add steps for both workflows

**Testing**
- Endpoints
- Workflows

I would still call this a first iteration, as we are missing a few pieces of the full flow, such as payment sessions, discounts, and taxes.

Co-authored-by: Adrien de Peretti <25098370+adrien2p@users.noreply.github.com>

packages/medusa/src/api-v2/store/carts/[id]/line-items/route.ts

@@ -0,0 +1,44 @@
+import { addToCartWorkflow } from "@medusajs/core-flows"
+import { ModuleRegistrationName } from "@medusajs/modules-sdk"
+import { ICartModuleService } from "@medusajs/types"
+import { remoteQueryObjectFromString } from "@medusajs/utils"
+import { MedusaRequest, MedusaResponse } from "../../../../../types/routing"
+import { defaultStoreCartFields } from "../../query-config"
+import { StorePostCartsCartLineItemsReq } from "./validators"
+
+export const POST = async (req: MedusaRequest, res: MedusaResponse) => {
+  const cartModuleService = req.scope.resolve<ICartModuleService>(
+    ModuleRegistrationName.CART
+  )
+
+  const cart = await cartModuleService.retrieve(req.params.id, {
+    select: ["id", "region_id", "currency_code"],
+  })
+
+  const workflowInput = {
+    items: [req.validatedBody as StorePostCartsCartLineItemsReq],
+    cart,
+  }
+
+  const { errors } = await addToCartWorkflow(req.scope).run({
+    input: workflowInput,
+    throwOnError: false,
+  })
+
+  if (Array.isArray(errors) && errors[0]) {
+    throw errors[0].error
+  }
+
+  const remoteQuery = req.scope.resolve("remoteQuery")
+
+  const query = remoteQueryObjectFromString({
+    entryPoint: "cart",
+    fields: defaultStoreCartFields,
+  })
+
+  const [updatedCart] = await remoteQuery(query, {
+    cart: { id: req.params.id },
+  })
+
+  res.status(200).json({ cart: updatedCart })
+}

packages/medusa/src/api-v2/store/carts/[id]/line-items/validators.ts

@@ -0,0 +1,12 @@
+import { IsInt, IsOptional, IsString } from "class-validator"
+
+export class StorePostCartsCartLineItemsReq {
+  @IsString()
+  variant_id: string
+
+  @IsInt()
+  quantity: number
+
+  @IsOptional()
+  metadata?: Record<string, unknown> | undefined
+}

packages/medusa/src/api-v2/store/carts/middlewares.ts

@@ -1,6 +1,7 @@
 import { transformBody, transformQuery } from "../../../api/middlewares"
 import { MiddlewareRoute } from "../../../loaders/helpers/routing/types"
 import { authenticate } from "../../../utils/authenticate-middleware"
+import { StorePostCartsCartLineItemsReq } from "./[id]/line-items/validators"
 import * as QueryConfig from "./query-config"
 import {
   StoreDeleteCartsCartPromotionsReq,
@@ -40,6 +41,11 @@ export const storeCartRoutesMiddlewares: MiddlewareRoute[] = [
     matcher: "/store/carts/:id",
     middlewares: [transformBody(StorePostCartsCartReq)],
   },
+  {
+    method: ["POST"],
+    matcher: "/store/carts/:id/line-items",
+    middlewares: [transformBody(StorePostCartsCartLineItemsReq)],
+  },
   {
     method: ["POST"],
     matcher: "/store/carts/:id/promotions",

packages/medusa/src/api-v2/store/carts/route.ts

@@ -3,13 +3,9 @@ import { CreateCartWorkflowInputDTO } from "@medusajs/types"
 import { remoteQueryObjectFromString } from "@medusajs/utils"
 import { MedusaRequest, MedusaResponse } from "../../../types/routing"
 import { defaultStoreCartFields } from "../carts/query-config"
-import { StorePostCartReq } from "./validators"
 
 export const POST = async (req: MedusaRequest, res: MedusaResponse) => {
-  const input = req.validatedBody as StorePostCartReq
-  const workflowInput: CreateCartWorkflowInputDTO = {
-    ...input,
-  }
+  const workflowInput = req.validatedBody as CreateCartWorkflowInputDTO
 
   // If the customer is logged in, we auto-assign them to the cart
   if (req.auth_user?.app_metadata?.customer_id) {