Question

I am using Entity Framework & LINQ to retrieve data. I am having a problem with the following:

var customer= db.customers.where(c=>c.id==1);
customer.name=santhosh;
customer.city=hyd;

The fields are changing in the database before I call:

db.SaveChanges();

How do I avoid this?

Answer 1

The fields are changing in the database before I call

If you mean changing as in changing outside of application, changes in SQL Management Studio for example. Entity Framework cannot detect those changes, so as a result you might get stale objects that was cached by Entity Framework. To prevent receiving cached object and get the up-to-date values from database, use AsNoTracking.

Try putting AsNoTracking():

var customer= db.customers.AsNoTracking().where(c=>c.id==1);
customer.name=santhosh;
customer.city=hyd;
db.SaveChanges();

Or if your problem is to detect concurrent updates(unfortunate terminology, it doesn’t apply to UPDATE only) to same row, use rowversion(aka timestamp) field type; then on your .NET code add Timestamp attribute on the property. Example: http://www.ienablemuch.com/2011/07/entity-framework-concurrency-checking.html

public class Song
{
    [Key]
    public int SongId { get; set; }
    public string SongName { get; set; }
    public string AlbumName { get; set; }

    [Timestamp]
    public virtual byte[] Version { get; set; }
}

UPDATE (after your comment):

If you really has no intent to persist your object changes to database. Try detaching the object.

Try this:

var customer= db.customers.where(c=>c.id==1);
db.Entry(customer).State = System.Data.EntityState.Detached; // add this
customer.name=santhosh;
customer.city=hyd;    
db.SaveChanges();

That won’t save your changes on name and city to database.

If you want something more robust(the above will fail an exception if the object was not yet attached), create a helper:

private static void Evict(DbContext ctx, Type t, 
    string primaryKeyName, object id)
{            
    var cachedEnt =
        ctx.ChangeTracker.Entries().Where(x =>   
            ObjectContext.GetObjectType(x.Entity.GetType()) == t)
            .SingleOrDefault(x =>
        {
            Type entType = x.Entity.GetType();
            object value = entType.InvokeMember(primaryKeyName, 
                                System.Reflection.BindingFlags.GetProperty, 
                                null, x.Entity, new object[] { });
 
            return value.Equals(id);
        });
 
    if (cachedEnt != null)
        ctx.Entry(cachedEnt.Entity).State = EntityState.Detached;
}

To use: Evict(yourDbContextHere, typeof(Product), "ProductId", 1);

http://www.ienablemuch.com/2011/08/entity-frameworks-nhibernate.html