struct Product {
        string concept;
        uint256 quantity;
}
mapping (uint => Product) allProducts;
uint[] public productDates;
function setProduct(string _concept, uint256 _quantity, uint _date) public {
     var newproduct = allProducts[_date];
     newproduct.concept = _concept;
     newproduct.quantity = _quantity;
     productDates.push(_date) -1;
 }
function getProducts() view public returns (uint[]) {
     return productDates;
}
function getProduct(uint date) view public returns (string, uint256) {
    return (allProducts[date].concept, allProducts[date].quantity);
}