title: Entityframework Core Unable to cast object of type 'System.Int32' to type 'System.Int64'
body: <p>DB first entity framework core throws this exception when SaveChanges();
  This code works just fine with Entity Framework but not with Entity Framework Core.</p>
  
  <blockquote>
    <p>Exception message: Unable to cast object of type 'System.Int32' to type 'System.Int64'.</p>
  </blockquote>
  
  <pre><code>CsProduct csProduct = new CsProduct()
  {
      CheapestPrice = 1,
      LastPrice = 1,
      LastUpdateDate = DateTime.Now,
      ProductName = "123",
      Quantity = 1,
      UploadDate = DateTime.Now
  };
  CSContext ctx = new CSContext();
  ctx.Entry(csProduct).State = EntityState.Added; 
  // ctx.CsProduct.Add(csProduct); This does not work neither
  csProduct.ProductNo = 0; // Still throws exception without this line
  ctx.SaveChanges();  
  
  ------------------------------------------------------------------ 
  CsProduct.cs
  public partial class CsProduct
  {
      public CsProduct()
      {
      }
  
      public long ProductNo { get; set; }
      public string ProductName { get; set; }
      public decimal CheapestPrice { get; set; }
      public decimal LastPrice { get; set; }
      public int Quantity { get; set; }
      public DateTime UploadDate { get; set; }
      public DateTime LastUpdateDate { get; set; }
      public string Comment { get; set; }
  }
  </code></pre>
  
  <pre>
  ------------------------------------------------------------------------------
  DDL
  CREATE TABLE CS_Product(
      productNo               bigint              IDENTITY(1,1)   NOT NULL,
      productName             nvarchar(256)                   NOT NULL,
      cheapestPrice               decimal(14,2)                   NOT NULL,
      lastPrice                   decimal(14,2)                   NOT NULL,
      quantity                    int                         NOT NULL,
      uploadDate              datetime                        NOT NULL,
      lastUpdateDate          datetime                        NOT NULL,
      comment                 nvarchar(450)                           ,
      CONSTRAINT PK_CS_Product PRIMARY KEY (productNo),
  );
  </pre>