How to update only one field using Entity Framework?

Question

Here\'s the table

Users

UserId
UserName
Password
EmailAddress

and the code..

Answer 1

While searching for a solution to this problem, I found a variation on GONeale's answer through Patrick Desjardins' blog:

public int Update(T entity, Expression>[] properties)
{
  DatabaseContext.Entry(entity).State = EntityState.Unchanged;
  foreach (var property in properties)
  {
    var propertyName = ExpressionHelper.GetExpressionText(property);
    DatabaseContext.Entry(entity).Property(propertyName).IsModified = true;
  }
  return DatabaseContext.SaveChangesWithoutValidation();
}

"As you can see, it takes as its second parameter an expression of a function. This will let use this method by specifying in a Lambda expression which property to update."

...Update(Model, d=>d.Name);
//or
...Update(Model, d=>d.Name, d=>d.SecondProperty, d=>d.AndSoOn);

( A somewhat similar solution is also given here: https://stackoverflow.com/a/5749469/2115384 )

The method I am currently using in my own code, extended to handle also (Linq) Expressions of type ExpressionType.Convert. This was necessary in my case, for example with Guid and other object properties. Those were 'wrapped' in a Convert() and therefore not handled by System.Web.Mvc.ExpressionHelper.GetExpressionText.

public int Update(T entity, Expression>[] properties)
{
    DbEntityEntry entry = dataContext.Entry(entity);
    entry.State = EntityState.Unchanged;
    foreach (var property in properties)
    {
        string propertyName = "";
        Expression bodyExpression = property.Body;
        if (bodyExpression.NodeType == ExpressionType.Convert && bodyExpression is UnaryExpression)
        {
            Expression operand = ((UnaryExpression)property.Body).Operand;
            propertyName = ((MemberExpression)operand).Member.Name;
        }
        else
        {
            propertyName = System.Web.Mvc.ExpressionHelper.GetExpressionText(property);
        }
        entry.Property(propertyName).IsModified = true;
    }

    dataContext.Configuration.ValidateOnSaveEnabled = false;
    return dataContext.SaveChanges();
}