updating table in entity framework 4 /mvc 3! - entity-framework

Question

could you help with this? I bet this isn't any tough one..but am new to EF and facing a weekend deadline. I want to update a table with values.. but the primary key is identity column. So my task is like this.. if it exists, update.. if it doesn't add to the
table.. this is my code..and am stuck in this else part..!
Table structure is like this
Primary Key table - System: SystemId, SystemName
Foreign Key table - SystemConfiguration: SystemConfigurationId, SystemId, SystemRAM, SystemHard-Disk
public void SaveSystemConfigurations(SystemConfiguration systemConfig)
{
var config = (from s in Context.SystemConfiguration
where s.SystemId == systemConfig.SystemId
select s).FirstOrDefault();
if (config == null)
{
Context.SystemConfigurations.AddObject(systemConfig);
Context.SaveChanges();
}
else
{
// EntityKey systemConfigKey= new EntityKey("systemConfig", "systemConfigId", config.SystemConfigurationId);
Context.SystemConfigurations.Attach(systemConfig);
Context.SaveChanges();
}
}

Answer 1

Try this:
public void SaveSystemConfigurations(SystemConfiguration systemConfig)
{
var config = (from s in Context.SystemConfiguration
where s.SystemId == systemConfig.SystemId
select s).FirstOrDefault();
if (config == null)
{
Context.SystemConfigurations.AddObject(systemConfig);
}
else
{
config.Attribute = value; // Do your update here
}
Context.SaveChanges();
}
Edit. It should be config not systemConfig.

Answer 2

The ApplyCurrentValues method will apply scalar attributes to an entity that matches the same key. My assumption is that you are modifying a real entity (an object that has a valid entity key).
This would work:
var eSet = config.EntityKey.EntitySetName;
Context.ApplyCurrentValues(eSet, systemConfig);
Context.SaveChanges();

Answer 3

public void SaveSystemConfigurations(SystemConfiguration systemConfig)
{
var context = new EntitiesModel();
//here is the name of the partial class created on the Context area of the edmx designer.cs
var config = (from s in context.SystemConfiguration
where s.SystemId == systemConfig.SystemId
select s).FirstOrDefault();
context.ApplyCurrentValues(config.EntityKey.EntitySetName, systemConfig);
// systemConfig comes from the view with values set by the user
// you dont have to manually need to map one value at the time
context.SaveChanges();
}