How to delete an object by id with entity framework

It seems to me that I have to retrieve an object before I delete it with entity framework like below

var customer = context.Customers.First(c => c.Id == 1);

context.DeleteObject(customer);

context.Savechanges();

So I need to hit database twice. Is ther开发者_如何学运维e a easier way?

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In Entity Framework 6 the delete action is Remove. Here is an example

Customer customer = new Customer () { Id = id };
context.Customers.Attach(customer);
context.Customers.Remove(customer);
context.SaveChanges();

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The same as @Nix with a small change to be strongly typed:

If you don't want to query for it just create an entity, and then delete it.

Customer customer = new Customer () { Id = id };
context.Customers.Attach(customer);
context.Customers.DeleteObject(customer);
context.SaveChanges();

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Similar question here.

With Entity Framework there is EntityFramework-Plus (extensions library).
Available on NuGet. Then you can write something like:

// DELETE all users which has been inactive for 2 years
ctx.Users.Where(x => x.LastLoginDate < DateTime.Now.AddYears(-2))
     .Delete();

It is also useful for bulk deletes.

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If you dont want to query for it just create an entity, and then delete it.

Customer customer  = new Customer() {  Id = 1   } ; 
context.AttachTo("Customers", customer);
context.DeleteObject(customer);
context.Savechanges();

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I am using the following code in one of my projects:

    using (var _context = new DBContext(new DbContextOptions<DBContext>()))
    {
        try
        {
            _context.MyItems.Remove(new MyItem() { MyItemId = id });
            await _context.SaveChangesAsync();
        }
        catch (Exception ex)
        {
            if (!_context.MyItems.Any(i => i.MyItemId == id))
            {
                return NotFound();
            }
            else
            {
                throw ex;
            }
        }
    }

This way, it will query the database twice only if an exception occurs when trying to remove the item with the specified ID. Then if the item is not found, it returns a meaningful message; otherwise, it just throws the exception back (you can handle this in a way more fit to your case using different catch blocks for different exception types, add more custom checks using if blocks etc.).

[I am using this code in a MVC .Net Core/.Net Core project with Entity Framework Core.]

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This answer is actually taken from Scott Allen's course titled ASP.NET MVC 5 Fundamentals. I thought I'd share because I think it is slightly simpler and more intuitive than any of the answers here already. Also note according to Scott Allen and other trainings I've done, find method is an optimized way to retrieve a resource from database that can use caching if it already has been retrieved. In this code, collection refers to a DBSet of objects. Object can be any generic object type.

        var object = context.collection.Find(id);  
        context.collection.Remove(object);
        context.SaveChanges();

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dwkd's answer mostly worked for me in Entity Framework core, except when I saw this exception:

InvalidOperationException: The instance of entity type 'Customer' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values.

To avoid the exception, I updated the code:

Customer customer = context.Customers.Local.First(c => c.Id == id);
if (customer == null) {
    customer = new Customer () { Id = id };
    context.Customers.Attach(customer);
}
context.Customers.Remove(customer);
context.SaveChanges();

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A smaller version (when compared to previous ones):

var customer = context.Find(id);
context.Delete(customer);
context.SaveChanges();

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Raw sql query is fastest way I suppose

public void DeleteCustomer(int id)
{
   using (var context = new Context())
   {
      const string query = "DELETE FROM [dbo].[Customers] WHERE [id]={0}";
      var rows = context.Database.ExecuteSqlCommand(query,id);
      // rows >= 1 - count of deleted rows,
      // rows = 0 - nothing to delete.
   }
}

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From official documentation (and the most efficient one I have found so far):

Student studentToDelete = new Student() { ID = id };
_context.Entry(studentToDelete).State = EntityState.Deleted;
await _context.SaveChangesAsync();

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In EF Core, if you don't care if the object exists or not, and you just care that it will not be in the DB, the simplest would be:

context.Remove(new Customer(Id: id));  // adds the object in "Deleted" state
context.SaveChanges();                 // commits the removal

You don't really need Attach() - it adds the object to the change tracker in the Unchanged state and Remove() adds the object to the tracker in the Deleted state. The most important thing, however, is that you do only one roundtrip to the backend.

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Easier and more understandable version.

var customer = context.Find<Customer>(id);
context.Remove(customer);
context.SaveChanges();