我在实体框架中有一个 SQL Server 表,其名称employ
为一个名为ID
.
如何使用实体框架从表中删除一条记录?
不必先查询对象,您可以通过其 id 将其附加到上下文中。像这样:
var employer = new Employ { Id = 1 };
ctx.Employ.Attach(employer);
ctx.Employ.Remove(employer);
ctx.SaveChanges();
或者,您可以将附加条目的状态设置为已删除:
var employer = new Employ { Id = 1 };
ctx.Entry(employer).State = EntityState.Deleted;
ctx.SaveChanges();
您可以使用SingleOrDefault
获取与您的条件匹配的单个对象,然后将其传递给Remove
EF 表的方法。
var itemToRemove = Context.Employ.SingleOrDefault(x => x.id == 1); //returns a single item.
if (itemToRemove != null) {
Context.Employ.Remove(itemToRemove);
Context.SaveChanges();
}
var stud = (from s1 in entities.Students
where s1.ID== student.ID
select s1).SingleOrDefault();
//Delete it from memory
entities.DeleteObject(stud);
//Save to database
entities.SaveChanges();
Employer employer = context.Employers.First(x => x.EmployerId == 1);
context.Customers.DeleteObject(employer);
context.SaveChanges();
我正在使用带有 LINQ 的实体框架。以下代码对我有帮助;
1- 对于多条记录
using (var dbContext = new Chat_ServerEntities())
{
var allRec= dbContext.myEntities;
dbContext.myEntities.RemoveRange(allRec);
dbContext.SaveChanges();
}
2- 对于单条记录
using (var dbContext = new Chat_ServerEntities())
{
var singleRec = dbContext.ChatUserConnections.FirstOrDefault( x => x.ID ==1);// object your want to delete
dbContext.ChatUserConnections.Remove(singleRec);
dbContext.SaveChanges();
}
更通用的方法
public virtual void Delete<T>(int id) where T : BaseEntity, new()
{
T instance = Activator.CreateInstance<T>();
instance.Id = id;
if (dbContext.Entry<T>(entity).State == EntityState.Detached)
{
dbContext.Set<T>().Attach(entity);
}
dbContext.Set<T>().Remove(entity);
}
使用 Entity Framework 6,您可以使用Remove
. using
这也是确保您的连接关闭的好策略。
using (var context = new EmployDbContext())
{
Employ emp = context.Employ.Where(x => x.Id == id).Single<Employ>();
context.Employ.Remove(emp);
context.SaveChanges();
}
只是想贡献我反复使用的三种方法。
方法一:
var record = ctx.Records.FirstOrDefault();
ctx.Records.Remove(record);
ctx.SaveChanges();
方法二:
var record = ctx.Records.FirstOfDefault();
ctx.Entry(record).State = EntityState.Deleted;
ctx.SaveChanges();
ctx.Entry(record).State = EntityState.Detached;
我更喜欢使用方法 2的原因之一是因为在将 EF 或 EFCore 设置为 的情况下QueryTrackingBehavior.NoTracking
,这样做更安全。
然后是方法3:
var record = ctx.Records.FirstOrDefault();
var entry = ctx.Entry(record);
record.DeletedOn = DateTimeOffset.Now;
entry.State = EntityState.Modified;
ctx.SaveChanges();
entry.State = EntityState.Detached;
这通过设置记录的属性来利用软删除方法DeletedOn
,并且仍然能够保留记录以供将来使用,无论可能是什么。基本上,将其放入回收站。
此外,关于Method 3,而不是将整个记录设置为被修改:
entry.State = EntityState.Modified;
您还可以仅将列设置DeletedOn
为已修改:
entry.Property(x => x.DeletedOn).IsModified = true;
[HttpPost]
public JsonResult DeleteCotnact(int id)
{
using (MycasedbEntities dbde = new MycasedbEntities())
{
Contact rowcontact = (from c in dbde.Contact
where c.Id == id
select c).FirstOrDefault();
dbde.Contact.Remove(rowcontact);
dbde.SaveChanges();
return Json(id);
}
}
你怎么看这个,简单与否,你也可以试试这个:
var productrow = cnn.Product.Find(id);
cnn.Product.Remove(productrow);
cnn.SaveChanges();
For a generic DAO this worked:
public void Delete(T entity)
{
db.Entry(entity).State = EntityState.Deleted;
db.SaveChanges();
}
您可以在网格的 click 或 celldoubleclick 事件中执行类似的操作(如果您使用过)
if(dgEmp.CurrentRow.Index != -1)
{
employ.Id = (Int32)dgEmp.CurrentRow.Cells["Id"].Value;
//Some other stuff here
}
然后在您的删除按钮中执行以下操作:
using(Context context = new Context())
{
var entry = context.Entry(employ);
if(entry.State == EntityState.Detached)
{
//Attached it since the record is already being tracked
context.Employee.Attach(employ);
}
//Use Remove method to remove it virtually from the memory
context.Employee.Remove(employ);
//Finally, execute SaveChanges method to finalized the delete command
//to the actual table
context.SaveChanges();
//Some stuff here
}
或者,您可以使用 LINQ 查询而不是使用 LINQ To Entities 查询:
var query = (from emp in db.Employee
where emp.Id == employ.Id
select emp).Single();
employ.Id用作过滤参数,该参数已从 DataGridView 的 CellDoubleClick 事件传递。
你可以像这样简单地做到这一点
public ActionResult Delete(int? id)
{
using (var db = new RegistrationEntities())
{
Models.RegisterTable Obj = new Models.RegisterTable();
Registration.DAL.RegisterDbTable personalDetail = db.RegisterDbTable.Find(id);
if (personalDetail == null)
{
return HttpNotFound();
}
else
{
Obj.UserID = personalDetail.UserID;
Obj.FirstName = personalDetail.FName;
Obj.LastName = personalDetail.LName;
Obj.City = personalDetail.City;
}
return View(Obj);
}
}
[HttpPost, ActionName("Delete")]
public ActionResult DeleteConfirmed(int? id)
{
using (var db = new RegistrationEntities())
{
Registration.DAL.RegisterDbTable personalDetail = db.RegisterDbTable.Find(id);
db.RegisterDbTable.Remove(personalDetail);
db.SaveChanges();
return RedirectToAction("where u want it to redirect");
}
}
模型
public class RegisterTable
{
public int UserID
{ get; set; }
public string FirstName
{ get; set; }
public string LastName
{ get; set; }
public string Password
{ get; set; }
public string City
{ get; set; }
}
从哪个视图你会调用它
<table class="table">
<tr>
<th>
FirstName
</th>
<th>
LastName
</th>
<th>
City
</th>
<th></th>
</tr>
@foreach (var item in Model)
{
<tr>
<td> @item.FirstName </td>
<td> @item.LastName </td>
<td> @item.City</td>
<td>
<a href="@Url.Action("Edit", "Registeration", new { id = item.UserID })">Edit</a> |
<a href="@Url.Action("Details", "Registeration", new { id = item.UserID })">Details</a> |
<a href="@Url.Action("Delete", "Registeration", new { id = item.UserID })">Delete</a>
</td>
</tr>
}
</table>
我希望这对你来说很容易理解
这是一个安全的方法:
using (var transitron = ctx.Database.BeginTransaction())
{
try
{
var employer = new Employ { Id = 1 };
ctx.Entry(employer).State = EntityState.Deleted;
ctx.SaveChanges();
transitron.Commit();
}
catch (Exception ex)
{
transitron.Rollback();
//capture exception like: entity does not exist, Id property does not exist, etc...
}
}
在这里你可以把你想要的所有更改都堆起来,这样你就可以在 SaveChanges 和 Commit 之前做一系列的删除,所以只有全部成功才会应用。
最好的方法是检查然后删除
if (ctx.Employ.Any(r=>r.Id == entity.Id))
{
Employ rec = new Employ() { Id = entity.Id };
ctx.Entry(rec).State = EntityState.Deleted;
ctx.SaveChanges();
}