C# 按摩盒不显示实体框架核心

您好，我是Microsoft entity framework core的新手我使用（net core 3.1和Microsoft entity framework core）创建了一个简单的windows窗体应用程序我已成功创建了一个如下所示的表

    using AplicationDbContext DbContext = new AplicationDbContext();
            Wholesaler tabPage = new Wholesaler()
            {
                NameOwner = NameOwner.Text,
                NameCompany = NameCompany.Text,
                Address = Address.Text,
                MobilePhoneNumber1 =  MobilePhoneNumber1.Text,
                MobilePhoneNumber2 =  MobliePhoneNumber2.Text,
                linePhone1 = LinePhone1.Text,
                linePhone2 = LinePhone2.Text,
                Email = Email.Text,
                Fax = Fax.Text
            };
DbContext.Wholesalers.Add(tabPage);
            DbContext.SaveChanges();

问题是NameCompany是PK，我想向用户显示按摩框“Name company已经存在”，并防止出现此错误（SqlException:违反主键约束“PK\U批发商”。无法在对象“dbo.whistalers”中插入重复的键。重复的键值为（）

在这里找到了答案

using AplicationDbContext DbContext = new AplicationDbContext();
        
            Wholesaler tabPage = new Wholesaler()           
        {
            NameOwner = NameOwner.Text,
            NameCompany = NameCompany.Text,
            Address = Address.Text,
            MobilePhoneNumber1 =  MobilePhoneNumber1.Text,
            MobilePhoneNumber2 =  MobliePhoneNumber2.Text,
            linePhone1 = LinePhone1.Text,
            linePhone2 = LinePhone2.Text,
            Email = Email.Text,
            Fax = Fax.Text
        };
        if (DbContext.Wholesalers.Any(s => s.NameCompany == NameCompany.Text))
        {
            MessageBox.Show($"Wholesaler: {NameCompany.Text} already exist ", "Name Company", MessageBoxButtons.OK, MessageBoxIcon.Information);
            return;
        }
        DbContext.Wholesalers.Add(tabPage);
        DbContext.SaveChanges();
    }