如何在ASP.NET MVC 4 Web应用程序中使用LINQ更新两个表

Question

I'm making Library Management System project in which I have a Deposit Controller which deposits the earlier issued books. Two tables are used:

1. BooksData
2. BookDepositIssue

BooksData has all book info with a BookStatus Flag which sets 'A' for Available and 'I' for Issued. BookDepositIssue has BookID which is common in both tables and IssueDate, DepositDate, and DueDate .

Now in my deposit controller I'm checking if the BookStatus flag is "I"; which means Issued. And also DueDate<= DateTime .Today so that no fine is incurred. But I'm unable to make the correct code pls help. As shown by the debugger var v is getting null, thus not going into the if condition. The database has issued books whose flag is "I" then why it is not executing the condition?

Controller part

    [HttpPost]
    public ActionResult Deposit (BookDepositIssue deposit)
    {
      if (ModelState.IsValid)
      {
        using (LibraryEntities dc = new LibraryEntities())
        {
            var v = dc.BooksDatas.Where(a=> a.BookStatus.Equals("I") && a.BookID.Equals(deposit.BookID) && deposit.DueDate<=DateTime.Today).FirstOrDefault();
            if(v!=null)
             {
                v.BookStatus="A";
                deposit.depositDate = DateTime.Today;
             }
            UpdateModel(dc.BooksDatas);
            UpdateModel(dc.BookDepositIssues);
            dc.SaveChanges();
        }
      }
    }

Model Part

      Model class 1:
      public partial class BookDepositIssue
      {
      public int SequenceNo {get; set;}
      public string BookID {get; set;}
      public string ID {get; set;}
      public Nullable<System.DateTime> IssueDate {get; set;}
      public Nullable<System.DateTime> DueDate {get; set;}
      public Nullable<System.DateTime> DepositDate {get; set;}
      }

     Model Class 2:
     public partial class BooksData
     {
     public string BookID {get; set;}
     public BookName {get; set;}
     public BookGenre {get; set;}
     public BookStatus {get; set;}
     public Author {get; set;}
     }

Answer 1

try this - assuming you have a navigation property between BookDepositIssue to 'BookDepositIssue' named bookData . if you don't have one, you should.

replace this part:

var v = dc.BooksDatas.Where(a=> a.BookStatus.Equals("I") && a.BookID.Equals(deposit.BookID) && deposit.DueDate<=DateTime.Today).FirstOrDefault();
            if(v!=null)
             {
                v.BookStatus="A";
                deposit.depositDate = DateTime.Today;
             }
            UpdateModel(dc.BooksDatas);
            UpdateModel(dc.BookDepositIssues);
            dc.SaveChanges();

with this:

if(deposit.bookData.BookStatus == "I" && deposit.DueDate<=DateTime.Today){
    deposit.bookData.BookStatus = "A";
    deposit.depositDate = DateTime.Today;
}
dc.SaveChanges();

let me know if that worked for you. if not please be specific on what is not working.