UPDATE statement conflict with FOREIGN KEY constraint in ASP.NET MVC4

I am actually working on an ASP.NET MVC4 application where we used the entity framework and the Model-View-View-Model approach and 7-layered architecture. We have one page where we need to insert or update "Product" information. The inserted or updated Product data will be saved inside "Product" table. My database name is "DbOnix". The basic structure of Product Table is given below: ``` Column Name Data Type Allow Nulls ProductID PK int ProductName varchar(255) NO ProductCategoryID FK int Sequence int YES ActiveStatus int YES SlNo int NO ``` The ProductCategoryID column in Product table has a foreign key relationship with the ProductCategory table. The basic structure of ProductCategory table: ``` Column Name Data Type Allow Nulls ProductCategoryID PK int ProductCategoryName varchar(150) NO ``` Whenever I'm trying to insert or update data in the Product table, the following exception is thrown: ``` The UPDATE statement conflicted with the FOREIGN KEY constraint "FK_Product_ProductCategory". The conflict occurred in database "DbOnix", table "dbo.ProductCategory", column 'ProductCategoryID'.The statement has been terminated. ``` My Controller Code: ``` public HttpStatusCodeResult UpdateProductInformation(int id, ProductDTO ProductDTO) { _productManager.UpdateProductInformation(id, ProductDTO); return new HttpStatusCodeResult(HttpStatusCode.OK); } ``` My Manager Class Code: ``` public void UpdateProductInformation(int id, ProductDTO productDTO) { //if productDTO data is not valid if (productDTO == null) throw new ArgumentException(Messages.warning_CannotAddProfileWithNullInformation); //Create a new product entity var currentProduct = _ProductRepository.Get(id); var updatedProduct = new Product(); updatedProduct.ProductID = id; updatedProduct.ProductName = productDTO.ProductName; updatedProduct.ProductCategoryID = productDTO.ProductCategoryID; updatedProduct.Sequence = productDTO.Sequence; updatedProduct.ActiveStatus = productDTO.ActiveStatus; updatedProduct.SlNo = productDTO.SlNo; //Update Product updatedProduct = this.UpdateProduct(currentProduct, updatedProduct); } ``` My Core (Property) Class code: ``` public partial class Product : Entity, IValidatableObject { public Product() { } [Key] public int ProductID { get; set; } public string ProductName { get; set; } public int ProductCategoryID { get; set; } public int Sequence { get; set; } public int ActiveStatus { get; set; } public int SlNo { get; set; } } ``` and my DTO Class code: ``` public class ProductDTO { public int ProductID { get; set; } public string ProductName { get; set; } public int ProductCategoryID { get; set; } public int Sequence { get; set; } public int ActiveStatus { get; set; } public int SlNo { get; set; } } ``` Note that my Database Server is MS SQL Server 2008 R2. EDIT-1: I forgot to include my Javascript code: ``` $(function () { var Product = function (Product) { var self = this; self.ProductID = ko.observable(Product ? Product.ProductID : 0).extend({ required: true }); self.ProductName = ko.observable(Product ? Product.ProductName : '').extend({ required: true }); self.ActiveStatus = ko.observable(Product ? Product.ActiveStatus : 0); }; var ProductCollection = function () { var self = this; //if ProfileId is 0, It means Create new Profile if (ProductID == 0) { self.Product = ko.observable(new Product()); } else { $.ajax({ url: urlProduct + '/GetProductById/' + ProductID, async: false, dataType: 'json', success: function (json) { self.Product = ko.observable(new Product(json)); } }); } self.ProductErrors = ko.validation.group(self.Product()); self.saveProduct = function () { var isValid = true; if (self.ProductErrors().length != 0) { self.ProductErrors.showAllMessages(); isValid = false; } if (isValid) { self.Product().ActiveStatus = document.getElementById("stat").value; $.ajax({ type: (ProductID > 0 ? 'PUT' : 'POST'), cache: false, dataType: 'json', url: urlProduct + (ProductID > 0 ? '/UpdateProductInformation?id=' + ProductID : '/SaveProductInformation'), data: JSON.stringify(ko.toJS(self.Product())), contentType: 'application/json; charset=utf-8', async: false, success: function (data) { alert("Product saved successfully."); window.location.href = '/Product'; }, error: function (err) { var err = JSON.parse(err.responseText); var errors = ""; for (var key in err) { if (err.hasOwnProperty(key)) { errors += key.replace("Product.", "") + " : " + err[key]; } } $("<div></div>").html(errors).dialog({ modal: true, title: JSON.parse(err.responseText).Message, buttons: { "Ok": function () { $(this).dialog("close"); } } }).show(); }, complete: function () { } }); } }; }; var ProductsViewModel = function () { var self = this; var url = "/Product/GetAllProduct"; var refresh = function () { $.getJSON(url, {}, function (data) { self.Products(data); }); }; // Public data properties self.Products = ko.observableArray([]); // Public operations self.createProduct = function () { window.location.href = '/Product/ProductCreateEdit/0'; }; self.editProduct = function (product) { //alert(product.ProductID); window.location.href = '/Product/ProductCreateEdit/' + product.ProductID; }; }; ko.applyBindings(new ProductsViewModel(), document.getElementById("productlist")); ko.applyBindings(new ProductCollection(), document.getElementById("product_edit")); }); ``` Note that I used KnockoutJS v2.3.0