gistfile1.txt

Создал свой товар "samolet" с количеством = 5

[
  {
    "changing_state" : "changed",
    "id" : "534e7a0f61646d7ba8000000",
    "total_price" : {
      "cents" : 0,
      "currency" : "RUB"
    },
    "updated_at" : 1397652370,
    "items" : [
      {
        "product_id" : null,
        "price" : {
          "cents" : 0,
          "currency" : "RUB"
        },
        "products_list_id" : "534e7a0f61646d7ba8000000",
        "changing_state" : "changed",
        "id" : null,
        "updated_at" : 1397652370,
        "version" : 0,
        "stricken" : 0,
        "count" : 5,
        "title" : "samolet"
      }
    ],
    "version" : 0,
    "items_count" : 2,
    "title" : "e"
  }
]
2014-04-16 16:46:13.927 FairPrice[12139:907] JSON answer: 
(
        {
        id = 534e7a0f61646d7ba8000000;
        items =         (
                        {
                count = 5;
                id = 534e7b9561646d7b89000000;
                "product_id" = "<null>";
                "products_list_id" = 534e7a0f61646d7ba8000000;
                stricken = 0;
                title = samolet;
                "updated_at" = 1397652373;
            }
        );
        "items_count" = 2;
        title = e;
        "total_price" =         {
            cents = 0;
            currency = RUB;
        };
        "updated_at" = 1397651983;
    }
)
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Ну и соответсвенно при вычеркивании товара или при любых действиях product_id уже = 0 и получаем ошибку 404
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[
  {
    "changing_state" : "changed",
    "id" : "534e7a0f61646d7ba8000000",
    "total_price" : {
      "cents" : 0,
      "currency" : "RUB"
    },
    "updated_at" : 1397652381,
    "items" : [
      {
        "product_id" : 0,
        "price" : {
          "cents" : 0,
          "currency" : null
        },
        "products_list_id" : "534e7a0f61646d7ba8000000",
        "changing_state" : "changed",
        "id" : "534e7b9561646d7b89000000",
        "updated_at" : 1397652381,
        "version" : 0,
        "stricken" : 1,
        "count" : 5,
        "title" : "samolet"
      }
    ],
    "version" : 0,
    "items_count" : 2,
    "title" : "e"
  }
]



P.S. Удаление работает.