Retrieving data from GORM Raw() Query

I am trying to learn Golang via project based learning. The problem I have placed before myself to simulate customers adding products to their cart. Currently, I have the Cart.go model as such..

type Cart struct {
     ID         string    
     Customer   Customer  
     CustomerID string    
     Product    Product   
     ProductID  string    
     CreatedAt  time.Time 
     UpdatedAt  time.Time
}

On the Cart model, I have a function defined as

func (c *Cart) GetAllItemsInCart(db *gorm.DB, customer_id string) (*gorm.DB, error) {
    items := db.Raw("SELECT id, product_id FROM carts WHERE customer_id = ?", customer_id).Scan(&c)

    return items, nil
}

This function is called in a controller

func (server *Server) GetAllCartItems(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)

    id := vars["id"]

    cart := models.Cart{}

    items, err := cart.GetAllItemsInCart(server.DB, id)

    if err != nil {
	    responses.ERROR(w, http.StatusInternalServerError, err)
	    return
    }

    responses.JSON(w, http.StatusOK, items)
}

As I understand it currently is that Scan() will scan the value of a struct, or in this case load the data found into the specified struct. However, the response I am seeing come back is

 {
    "Value": null,
    "Error": null,
    "RowsAffected": 2
 }

Which gives me 50% hope because "RowsAffected": 2 would be correct. However, the payload response is obviously not what I am looking for. Any guidance would be greatly appreciated, thank you.

Scan places the value into the pointer to a variable you've given it (via &c), and returns a database transaction object. You're calling that transaction object items, which it isn't. The items (ie, the contents of your cart) are in c *Cart, not in the thing returned by Scan.

Your method modifies c by filling it, it doesn't have to return anything, unless you want to return the error that Scan may return.

Instead of this...

    items, err := cart.GetAllItemsInCart(server.DB, id)

    // ... 

    responses.JSON(w, http.StatusOK, items)

You should be doing this:

    err := cart.GetAllItemsInCart(server.DB, id)

    // ...

    responses.JSON(w, http.StatusOK, cart)

You will need to fix a couple of things:

• You will need to use Scan(c) instead of Scan(&c) since c is already a pointer.
• You should always check for errors. In your GetAllItemsInCart method, you don't pass or check the error. Technically, you do pass it (inside the items object), but you do not check it anywhere.
• There is no need to pass the *gorm.DB pointer higher up.

If you want to preserve the structure of the code the way you already started, it could look something like this:

func (c *Cart) GetAllItemsInCart(db *gorm.DB, customer_id string) error {
    return db.Raw("SELECT id, product_id FROM carts WHERE customer_id = ?", customer_id).Scan(c).Error
}

// controller
func (server *Server) GetAllCartItems(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)

    id := vars["id"]

    cart := models.Cart{}

    err := cart.GetAllItemsInCart(server.DB, id)
    if err != nil {
        responses.ERROR(w, http.StatusInternalServerError, err)
        return
    }

    responses.JSON(w, http.StatusOK, cart)
}