更新數據庫 - 刪除現有的數據和的EntityFramework

Question

添加新的數據我有StudentRegistration模型類如下

public partial class StudentRegistration 
{ 
    public StudentRegistration() 
    {    
     this.StudentReceipts = new HashSet<StudentReceipt>();    
    } 

    public int Id { get; set; } 
    public Nullable<int> StudentWalkInnID { get; set; } 
    ... 
    ... 

    public virtual ICollection<StudentReceipt> StudentReceipts { get; set; } 

} 
public partial class StudentReceipt 
{ 
    public int Id { get; set; } 
    public Nullable<int> StudentRegistrationID { get; set; } 
    ... 
    ...  

    public virtual StudentRegistration StudentRegistration { get; set; } 
} 

我試圖刪除現有studentreceipt列表和添加新list.The new studentreceipt list在數據庫中適當添加但是existing studentreceipt list未從數據庫中刪除，並且existing studentreceipt list的StudentRegistrationId設置爲null。

我想從數據庫中刪除現有的studentreceipt list並添加新的列表。我該如何做？

這是我曾嘗試

using (TransactionScope _ts = new TransactionScope()) 
{ 
    _dbRegn = _db.StudentRegistrations 
    .Where(r => r.Id == Id).FirstOrDefault(); 
    if (_dbRegn != null) 
    {      
    //Remove existing receipts 
    foreach (var _existingReceipt in _dbRegn.StudentReceipts.ToList()) 
    { 
     _dbRegn.StudentReceipts.Remove(_existingReceipt); 
    }       

    //adding new receipt 
    foreach (var _receipt in mdlCourseInterchange.StudentReceiptList) 
    { 
     StudentReceipt _studReceipt = new StudentReceipt(); 
     //... 
     //... 
     _dbRegn.StudentReceipts.Add(_studReceipt); 
    } 
    //... 
    //.. 

    db.Entry(_dbRegn).State = EntityState.Modified; 
    int j = _db.SaveChanges(); 
    if (j > 0) 
    { 
     _ts.Complete(); 
     return Json(new { message = "success" }, JsonRequestBehavior.AllowGet); 
    } 
    } 
} 

Answer 1

你可以嘗試如下圖所示。

using (TransactionScope _ts = new TransactionScope()) 
{ 
    _dbRegn = _db.StudentRegistrations.Where(r => r.Id == Id).FirstOrDefault(); 

    if (_dbRegn != null) 
    {      
    //Remove existing receipts 
    foreach (var _existingReceipt in _dbRegn.StudentReceipts.ToList()) 
    { 
     __db.StudentReceipts.Remove(_existingReceipt); 
    }       

    //adding new receipt 
    foreach (var _receipt in mdlCourseInterchange.StudentReceiptList) 
    { 
     StudentReceipt _studReceipt = new StudentReceipt(); 
     //... 
     //... 
     _db.StudentReceipts.Add(_studReceipt); 
    } 
    //... 
    //.. 

    int j = _db.SaveChanges(); 
    if (j > 0) 
    { 
     _ts.Complete(); 
     return Json(new { message = "success" }, JsonRequestBehavior.AllowGet); 
    } 
    } 
}