Can I update my employee record as given in the function below or do I have to make a query of the employee collection first and then update the data?
public int updateEmployee(App3_EMPLOYEE employee)
{
DBContextDataContext db = new DBContextDataContext();
db.App3_EMPLOYEEs.Attach(employee);
db.SubmitChanges();
return employee.PKEY;
}
Or do I have to do the following?
public int updateEmployee(App3_EMPLOYEE employee)
{
DBContextDataContext db = new DBContextDataContext();
App3_EMPLOYEE emp = db.App3_EMPLOYEEs
.Single(e => e.PKEY == employee.PKEY);
db.App3_EMPLOYEEs.Attach(employee, emp);
db.SubmitChanges();
return employee.PKEY;
}
But I don't want to use the second option. Is there any efficient way to update data?
I am getting this error by using both ways:
An attempt has been made to Attach or Add an entity that is not new, perhaps having been loaded from another DataContext. This is not supported.
More importantly: when it comes to querying databases, LINQ is in most cases a significantly more productive querying language than SQL. Compared to SQL, LINQ is simpler, tidier, and higher-level.
"As long as LINQ to SQL lives under Entity Framework, it's dead.
You can update rows in a database by modifying member values of the objects associated with the LINQ to SQL Table<TEntity> collection and then submitting the changes to the database. LINQ to SQL translates your changes into the appropriate SQL UPDATE commands.
I find following work around to this problem :
1) fetch and update entity (I am going to use this way because it's ok for me )
public int updateEmployee(App3_EMPLOYEE employee)
{
AppEmployeeDataContext db = new AppEmployeeDataContext();
App3_EMPLOYEE emp = db.App3_EMPLOYEEs.Single(e => e.PKEY == employee.PKEY);
emp.FIRSTNAME = employee.FIRSTNAME;//copy property one by one
db.SubmitChanges();
return employee.PKEY;
}
2) disable ObjectTrackingEnabled as following
// but in this case lazy loading is not supported
public AppEmployeeDataContext() :
base(global::LinqLibrary.Properties.Settings.Default.AppConnect3DBConnectionString, mappingSource)
{
this.ObjectTrackingEnabled = false;
OnCreated();
}
3) Detach all the related objects
partial class App3_EMPLOYEE
{
public void Detach()
{
this._APP3_EMPLOYEE_EXTs = default(EntityRef<APP3_EMPLOYEE_EXT>);
}
}
public int updateEmployee(App3_EMPLOYEE employee)
{
AppEmployeeDataContext db = new AppEmployeeDataContext();
employee.Detach();
db.App3_EMPLOYEEs.Attach(employee,true);
db.SubmitChanges();
return employee.PKEY;
}
4) use Time stamp in the column
http://www.west-wind.com/weblog/posts/135659.aspx
5) Create stored procedure for updating your data and call it by db context
You cannot attach a modified entity to a DataContext when there is no RowVersion column. Instead you could store original entity in your application as long as maintaining a copy for data changes. Then when changes need to be saved you could attach original entity to a DataContext, change its values to match the modified entity values and submit changes.
Here is an example:
public int updateEmployee(App3_EMPLOYEE employee, App3_EMPLOYEE originalEmployee)
{
DBContextDataContext db = new DBContextDataContext();
db.App3_EMPLOYEEs.Attach(originalEmployee);
// TODO: Copy values from employee to original employee
db.SubmitChanges();
return employee.PKEY;
}
Update:
There is a table in the database with columns ID, Name, Notes
// fetch an employee which will not be changed in the application
Employee original;
using(var db = new TestDbDataContext())
{
original = db.Employees.First(e => e.ID == 2);
}
// create an instance to work with
var modified = new Employee {ID = original.ID, Name = original.Name, Notes = original.Notes};
// change some info
modified.Notes = string.Format("new notes as of {0}", DateTime.Now.ToShortTimeString());
// update
using(var db = new TestDbDataContext())
{
db.Employees.Attach(original);
original.Notes = modified.Notes;
db.SubmitChanges();
}
There is a discussion on this topic here at MSDN s recommend you to use an IsVersion field and the Attach method
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