SaveChanges()仅影响一行

我想删除一些记录,并尝试使用以下代码:

if (objDetail != null) 
{
    objContext.DetailVouchers.RemoveRange(
        objContext.DetailVouchers.Where(t => t.REFNO == strRefNo));
    objContext.SaveChanges();
}

但它只删除了最后一条记录,而不是全部。

我的上下文类是

class MainContext : DbContext
    {
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            //base.OnModelCreating(modelBuilder);

            Database.SetInitializer<MainContext>(null);

        modelBuilder.Entity<MainVoucher>().ToTable("TBL_ACC_VOUCHER_MAIN");
        modelBuilder.Entity<MainVoucher>().HasKey(t => new { t.REFNO });

        modelBuilder.Entity<DetailVoucher>().ToTable("TBL_ACC_VOUCHER_DETAIL");
        modelBuilder.Entity<DetailVoucher>().HasKey(t => new { t.REFNO });
}
}

并创建上下文类对象,如

MainContext objContext = new MainContext();