添加和保存时未将EF实体提交到数据库是单独的方法

Question

I am trying to create an expense report application using Razor and EF. I have two entities: 1. ExpenseReport and 2. LineItem. There is a 1:N relationship using FK b/t ExpenseReport and LineItem. I need to allow the user to fill out the properties of a ExpenseReport and add a number of LineItems.

The user should see a table of line items as they are added to the ExpenseReport.

The commit to the database should save the ExpenseReport and the LineItems together, maintaining the FK relationship.

After three days of seemingly stabbing around in the dark, I cannot seem to wrap my head around what is a very simple scenario. I've read many articles where requirements are NOT to save the child entity when saving the parent entity, but couldn't glean any insights from those resources.

    public class ExpenseReport
    {
        public Guid ID { get; set; }
        [Required]
        public Guid UserID { get; set; }
        [Required]
        public string Title { get; set; }
        ...
        public virtual List<LineItem> LineItems { get; set; } = new List<LineItem>();
    }

    public class LineItem
    {       
        public int ID { get; set; }
        [Required]
        public Guid ExpenseReportID { get; set; } // FK ExpenseReport
        [Required]
        public int LineItemTypeID { get; set; } // Also a FK
        public string Note { get; set; }
        [Required]
        [DataType(DataType.Currency)]
        public decimal Amount { get; set; }
    }

I have two buttons in the UI attached to different handlers. One hard codes a new LineItem, sets the properties on the ExpenseReport and adds the ExpenseReport to the DbContext. The other just commits the changes.

Buttons to call the two different methods: <input type="submit" value="Add Expenses" asp-page-handler="AddExpense" class="btn btn-default" /> <input type="submit" value="Create" asp-page-handler="Create" class="btn btn-default" />

    private readonly WebApp1.Data.ApplicationDbContext _context;
    // constructor
    public CreateModel(WebApp1.Data.ApplicationDbContext context)
    {
        _context = context;
    }

    public IActionResult OnPostAddExpense()
    {
        if(!ModelState.IsValid)
        {
            return Page();
        }

        ExpenseReport.ID = Guid.NewGuid();
        ExpenseReport.Status = ExpenseReportStatus.Submitted;
        ExpenseReport.Created = DateTime.Now;
        Guid userId = new Guid(HttpContext.User.FindFirstValue(ClaimTypes.NameIdentifier));
        ExpenseReport.UserID = userId;
        _context.ExpenseReport.Add(ExpenseReport);
        LineItem lineItem = new LineItem
        {
            LineItemTypeID = 1,
            ExpenseReportID = ExpenseReport.ID,
            Amount = 125.00M,
            Note = "Note"
        };
        //_context.LineItem.Add(lineItem); // Tried with and without
        ExpenseReport.LineItems.Add(lineItem); // Tried with and without
        _context.ExpenseReport.Update(ExpenseReport); // Tried with and without
        return Page();
    }

    public async Task<IActionResult> OnPostCreateAsync()
    {
        await _context.SaveChangesAsync();
        return RedirectToPage("./Index");
    }

If I place the _context.ExpenseReport.Add(ExpenseReport) method call and _context.SaveChangesAsync() in the same method the ExpenseReport and LineItem is created with the relationship intact. The goal is to allow the user to add/edit/delete the LineItems "in memory" then commit to database at once.

Any help is greatly appreciated. UPDATED: Providing code asked for in the comment.

Answer 1

Like Mojtaba Tajik has said the DBContext is being lost between the two post request. Rather than having the user create a in memory object on the server you could have the line item information stored on the client side. You could do this with a cookie or session storage assuming this is a web application. Then once the user has added all the line items they need to the report you could then submit everything at once with one post request.

Here is some information on using session storage - https://www.w3schools.com/jsref/prop_win_sessionstorage.asp

Also I developed a similar sounding application we used a shopping cart approach to our line items.

Edit- The end goal is to accomplish everything within 1 post request. From all my experience dealing with DBContext and object life times it would be easiest to do everything inside of one post request.

-Good luck.

Answer 2

Your problem is that you add some items in one HTTP post method and want to save theme in other HTTP post method for example by clicking "Save" button. if you do this the .Net Core behavior is normal because of it's architecture. The state of everything reset with each request because of your DB context life cycles.

You should use in memory databases like "Redis" and do add/edit/delete operation in it and at the end by user clicking "Save" button, join the "Redis" stored records in one request and save them to database.