add documentation for assignCustomerToGuestCart mutation

src/_data/toc/graphql.yml

@@ -295,6 +295,10 @@ pages:
           url: /graphql/mutations/assign-compare-list-to-customer.html
           exclude_versions: ["2.3"]
 
+        - label: assignCustomerToGuestCart mutation
+          url: /graphql/mutations/assign-customer-to-guest-cart.html
+          exclude_versions: [ "2.3" ]
+
         - label: changeCustomerPassword mutation
           url: /graphql/mutations/change-customer-password.html
 

src/guides/v2.4/graphql/mutations/assign-customer-to-guest-cart.md

@@ -0,0 +1,108 @@
+---
+group: graphql
+title: assignCustomerToGuestCart mutation
+contributor_name: Atwix
+contributor_link: https://www.atwix.com/
+---
+
+The `assignCustomerToGuestCart` mutation assigns a logged in customer and merge customer's shopping cart items to the specified guest shopping cart.
+
+The customer must be logged in (You must specify the customer’s authorization token in the headers).
+
+If this mutation is successful, the customer's shopping cart becomes inactive and all the products it contains are added to the contents of the guest cart (the active one).
+Customer now is assigned to that active cart.
+
+*Note:*
+Customer cart becomes inactive and the guest cart remains active; but for guest cart new `masked_id` is being generated.
+`quote_id` remains same.
+
+The other similar mutation, [mergeCarts]({{page.baseurl}}/graphql/mutations/merge-carts.html), just merges cart items.
+Unlike `assignCustomerToGuestCart`, it transfers the contents of a guest cart into the customer's cart. The mutation deletes the original guest cart.
+
+## Syntax
+
+```graphql
+mutation {
+    assignCustomerToGuestCart(
+        cart_id: String!
+    ) {
+        Cart!
+    }
+}
+```
+
+## Example usage
+
+Assuming that there is a logged in customer who has an item in the cart, this call will merge customer's cart item to the specified guest shopping cart (which also contains an item).
+
+**Request:**
+
+```graphql
+mutation {
+  assignCustomerToGuestCart(
+    cart_id: "MDYKgqIdWMKr7VD1zlYwxrB7kuX8lR5s"
+  ) {
+    items {
+      quantity
+      product {
+        sku
+      }
+    }
+  }
+}
+```
+
+**Response:**
+
+```json
+{
+  "data": {
+    "assignCustomerToGuestCart": {
+      "items": [
+        {
+          "quantity": 1,
+          "product": {
+            "sku": "customer_item"
+          }
+        },
+        {
+          "quantity": 1,
+          "product": {
+            "sku": "guest_item"
+          }
+        }
+      ]
+    }
+  }
+}
+```
+
+## Input attributes
+
+Attribute |  Data Type | Description
+--- | --- | ---
+`cart_id` | String! | The unique ID that identifies the guest's cart
+
+## Output attributes
+
+The `assignCustomerToGuestCart` mutation returns a `Cart` object.
+
+Attribute |  Data Type | Description
+--- | --- | ---
+`cart` |[Cart!](#CartObject) | Describes the contents of the specified shopping cart
+
+### Cart object {#CartObject}
+
+{% include graphql/cart-object-24.md %}
+
+[Cart query output]({{page.baseurl}}/graphql/queries/cart.html#cart-output) provides more information about the `Cart` object.
+
+## Errors
+
+Error | Description
+--- | ---
+`The current customer isn't authorized.` | The current customer is not currently logged in.
+`Unable to assign the customer to the guest cart` | The current customer can't be assigned to the provided guset cart.
+`The cart isn't active` | The cart with the specified cart ID is unavailable, because the items have been purchased and the cart ID becomes inactive.
+`Could not find a cart with ID "XXX"` | The specified `cart_id` value does not exist in the `quote_id_mask` table.
+`The current user cannot perform operations on cart "XXX"` | Tried to assign the customer to the customer's cart.

src/guides/v2.4/graphql/mutations/merge-carts.md

@@ -7,6 +7,9 @@ The `mergeCarts` mutation transfers the contents of a guest cart into the cart o
 
 The mutation retains any items that were already in the logged-in customer's cart. If both the guest and customer carts contain the same item, `mergeCarts` adds the quantities. Upon success, the mutation deletes the original guest cart.
 
+There is a similar [assignCustomerToGuestCart]({{page.baseurl}}/graphql/mutations/assign-customer-to-guest-cart.html) mutation which works in a different way: it assigns a logged in customer and merge customer's shopping cart items to the guest shopping cart.
+Customer cart becomes inactive and the guest cart remains active.
+
 ## Syntax
 
 ```graphql