如何防止在使用实体框架更新单列时将其他列值更改为表？

Question

Here i have a method in ASP.NET MVC. What i am doing is to update single column checking every column of table is not null. If null then IsModified property changing to false. I have to write statement for every column.

My Sample Method -

public int ServicesEdit(helplineservice _helplineservice)
        {
            int result = 0;
            try
            {
                db.Entry(_helplineservice).State = EntityState.Modified;
                if (string.IsNullOrEmpty(_helplineservice.description))
                {
                    db.Entry(_helplineservice).Property(p => p.description).IsModified = false;
                }
                else
                {
                    db.Entry(_helplineservice).Property(p => p.description).IsModified = true;
                }
                if (string.IsNullOrEmpty(_helplineservice.title))
                {
                    db.Entry(_helplineservice).Property(p => p.title).IsModified = false;
                }
                else
                {
                    db.Entry(_helplineservice).Property(p => p.title).IsModified = true;
                }
                if (string.IsNullOrEmpty(_helplineservice.contactnumber))
                {
                    db.Entry(_helplineservice).Property(p => p.contactnumber).IsModified = false;
                }
                else
                {
                    db.Entry(_helplineservice).Property(p => p.contactnumber).IsModified = true;
                }
                //if (string.IsNullOrEmpty(_helplineservice.active.ToString()))
                //{
                //    db.Entry(_helplineservice).Property(p => p.active).IsModified = false;
                //}
                //else
                //{
                //    db.Entry(_helplineservice).Property(p => p.active).IsModified = true;
                //}
                db.SaveChanges();
                result = 1;
            }
            catch (Exception ex)
            {
                result = 0;
            }
            return result;
        }

Calling Above Method -

helplineservice _helplineservice = new helplineservice();
_helplineservice.helplineid =sectionid;
_helplineservice.allowedtoapp = allow;
result = _ftwCommonMethods.ServicesEdit(_helplineservice);

This code not look logical i think. Tell me better way to do this. How Can i Update Single Column of Table by not writing this much code? Thanks in Advance.

Answer 1

You can avoid all of the checking by loading the entity you want to update first.

var context = new DbContext();

// Load entity via whatever Id parameter you have.
var entityToUpdate = context.Set<Type>().FirstOrDefault(x => x.Id == idToUpdate);

if(entityToUpdate != null)
{
    entityToUpdate.Value1 = newValue1;
    entityToUpdate.Value2 = newValue2;

    context.SaveChanges();
}

Only Value1 and Value2 will be updated. All other existing values will remain unchanged.

In your case, what you are doing is creating a new empty entity, then setting its Key to something that already exists in the database. When you attach that entity to the context, EF has no choice but to assume that all the values in that entity are the new updated values. This is standard behavior for EF.