Inserting to tables except where records already exist - asp.net-mvc

Question

I'm looking to add records to my database but not sure of the best approach.
Here are my models:
public class fList
{
public int fListID { get; set; }
public string Title { get; set; }
public int UserID { get; set; }
public ICollection<Item> Items { get; set; }
}
public class Item
{
public int ItemID { get; set; }
public string Name { get; set; }
public ICollection<fList> fLists { get; set; }
}
public class User
{
public int UserID { get; set; }
public string UserName { get; set; }
public ICollection<fList> fLists { get; set; }
}
Here is the database before performing the operation:
Here is how the database should look after performing the operation:
What I want to do is add a new fList and new User. I also want to add new Items but only where they don't already exist. And I want to join Items to the fList accordingly.
I'm hoping to achieve the above as efficiently as possible with minimal db calls.
Here's the controller so far:
var flist = new fList
{
Title = "Colors",
UserName = "Chris"
Items = new List<Item>()
};
flist.Items.Add(new Item { Name = "White" });
flist.Items.Add(new Item { Name = "Orange" });
flist.Items.Add(new Item { Name = "Purple" });
flist.Items.Add(new Item { Name = "Blue" });
flist.Items.Add(new Item { Name = "Green" });
foreach (var item in flist.Items)
{
// Check item exists in database
var existingitem = db.Items.SingleOrDefault(n => n.Name == item.Name);
// If item doesn't exist, add it to database
if (existingitem == null) {
db.Items.Add(item);
}
// ...What next?
}
db.fLists.Add(flist);
db.SaveChanges();

Answer 1

If you have time, you can download the Prodinner sample from Microsoft, it is a perfect solution include OOP, DI, IOC,etc. It also show you the generic functions for saving data.
If you need control the state during save records, you need implement state control your own. Create Interface, Enum and Implement class as show below.
public interface IDataObjectWithState
{
State State { get; set; }
}
public enum State
{
Added,
Unchanged,
Modified,
Deleted
}
public abstract class DataObjectWithState : IDataObjectWithState
{
[NotMapped]
public State State { get; set; }
}
After that any model class you want control the state you need inherit this Class, so your models have extra UnMap State columns.
In your DB Context file, make a contractor as sample below.
public Db()
: base("name=TP_HOST")
{
try
{
((IObjectContextAdapter)this).ObjectContext
.ObjectMaterialized += (sender, args) =>
{
var entity = args.Entity as IDataObjectWithState;
if (entity != null)
{
entity.State = YourEnumNamespace.State.Unchanged;
}
};
}
catch (Exception ex)
{
}
finally { }
}
// this class need include using System.Data.Entity.Infrastructure;
public static EntityState ConvertState(YourEnumNamespace.State state)
{
switch (state)
{
case YourEnumNamespace.State.Added:
return EntityState.Added;
case YourEnumNamespace.State.Deleted:
return EntityState.Deleted;
case YourEnumNamespace.State.Modified:
return EntityState.Modified;
default:
return EntityState.Unchanged;
}
}
Then before you make the call of db.SaveChanges(), you have to set the state like sample below
foreach (var entry in dbContext.ChangeTracker
.Entries<IDataObjectWithState>())
{
IDataObjectWithState stateInfo = entry.Entity;
entry.State =Functions.ConvertState(stateInfo.State);
}
I know difficult to understand mine code, what I want to mention is we define our own enum state, we tell the models what we want (Add, Unchanged, Update, Delete), using for loop change the state become knowing by System.Data.Entity.Infrastructure.