Update a record without first querying?

Question

Lets say I query the database and load a list of items. Then I open one of the items in a detail view form, and instead of re-querying the item out of the database, I create

Answer 1

The code:

ExampleEntity exampleEntity = dbcontext.ExampleEntities.Attach(new ExampleEntity { Id = 1 });
exampleEntity.ExampleProperty = "abc";
dbcontext.Entry(exampleEntity).Property(ee => ee.ExampleProperty).IsModified = true;
dbcontext.Configuration.ValidateOnSaveEnabled = false;
dbcontext.SaveChanges();

The result TSQL:

exec sp_executesql N'UPDATE [dbo].[ExampleEntities]
SET [ExampleProperty ] = @0
WHERE ([Id] = @1)
',N'@0 nvarchar(32),@1 bigint',@0='abc',@1=1

Note:

The "IsModified = true" line, is needed because when you create the new ExampleEntity object (only with the Id property populated) all the other properties has their default values (0, null, etc). If you want to update the DB with a "default value", the change will not be detected by entity framework, and then DB will not be updated.

In example:

exampleEntity.ExampleProperty = null;

will not work without the line "IsModified = true", because the property ExampleProperty, is already null when you created the empty ExampleEntity object, you needs to say to EF that this column must be updated, and this is the purpose of this line.