private void StandardEFUpdateApproach()
{
GC.Collect();
BookLibraryEntities ctx = new BookLibraryEntities();
//First trip to SQL Server:executes select statement if run for the first time
Book book = ctx.Books.First(bk => bk.ID == 1);
book.Author = "new Updated Author Name";
//Second trip to SQL Server:Update the author
ctx.SaveChanges();
}
private void UpdateApproachThatWillCrash()
{
try
{
GC.Collect();
BookLibraryEntities ctx = new BookLibraryEntities();
Book b = new Book();
b.ID = 1;
ctx.Books.Attach(b);
DbEntityEntry entry = ctx.Entry(b);
//The commented lines represent the entry state right after attaching
//entry.State = EntityState.Unchanged;
//entry.Property("ID").IsModified = false;
//entry.Property("Author").IsModified = false;
//entry.Property("Name").IsModified = false;
//entry.Property("Category").IsModified = false;
b.Author = "New Author";
ctx.ChangeTracker.DetectChanges();
entry = ctx.Entry(b);
//This is how the entry will look like now
//entry.State = EntityState.Modified;
//entry.Property("ID").IsModified = false;
//entry.Property("Author").IsModified = true;
//entry.Property("Name").IsModified = false;
//entry.Property("Category").IsModified = false;
ctx.SaveChanges();
}
catch (System.Data.Entity.Validation.DbEntityValidationException ex)
{
// Will crash in EF and wil not even reach SQL server since Name prop is null while it is mandatory in Metadata
}
}
