C# 检查数据是否已经存在

Question

I have a product record table in the database, it will save the following: ID, product code, product name, size, and price. A product can have the same size and price right? In my code, I am trying to check if the data already exists, if it already exists it won't save but if not it will save. I already tried saving a different name and size of the product but with the same price but it would say that it already exists. I am new to c# and this is in WinForms, I searched it up here but I don't understand it and it is on other language. I only know java so far. I guess this error is a logical error, but I don't know what to do.

This is what I tried so far,

cmd = new SqlCommand("select Product_Code from ProductRecord where Product_Code = @Product_Code", con);
cmd.Parameters.AddWithValue("@Product_Code", tbpcCode.Text);
DataTable dt = new DataTable();
adapt.Fill(dt);
if ( dt.Rows.Count >= 1 )
{
  MessageBox.Show("Record Already Existing");
}
else
{
  // Do save
}

Answer 1

You don't have to open connection to the database each time you create a product. In fact you can rely on the Product_Code field in your database and change it to a unique key constraint see Microsoft docs here so its going to block the insertion of duplicate products.