c# - 如何检查我的数据库中是否已存在一个值并显示验证消息

Question

我有下面的代码，它连接到一个 Sql 数据库并将数据插入到一个表中:

string firstNameV = txtFname.Text;
string surnameV = txtSname.Text;
string emailV = txtEmail.Text;

SqlConnection conn = new   SqlConnection(ConfigurationManager.ConnectionStrings["myConnectionString"].ToString());

SqlCommand cmd = new SqlCommand();

cmd.CommandText = "INSERT INTO EmailSignUp (Title,FirstName,Surname,Email,EstablishmentType,Interests) VALUES (@Title,@FirstName,@Surname,@Email,@EstablishmentType,@Interests)";

cmd.Parameters.Add("@Title", SqlDbType.NVarChar).Value = title;
cmd.Parameters.Add("@FirstName", SqlDbType.NVarChar).Value = firstNameV;
cmd.Parameters.Add("@Surname", SqlDbType.NVarChar).Value = surnameV;
cmd.Parameters.Add("@Email", SqlDbType.NVarChar).Value = emailV;
cmd.Parameters.Add("@EstablishmentType", SqlDbType.NVarChar).Value = eType;
cmd.Parameters.Add("@Interests", SqlDbType.NVarChar).Value = ins;

cmd.Connection = conn;

conn.Open();

cmd.ExecuteNonQuery();
conn.Close();

我如何检查在“txtEmail”文本框中输入的电子邮件是否已经存在于我的数据库中，在电子邮件列中，然后警告消息说电子邮件已经存在，所以它不会被插入到我的数据库中？

Answer 1

在需要的文本框或区域调用此方法

public void EmailCheck()
    {
        string constring = ConfigurationManager.ConnectionStrings["ConnData"].ConnectionString;
        SqlConnection con = new SqlConnection(constring);
        SqlCommand cmd = new SqlCommand("Select * from EmailSignUp where EmailId= @EmailId", con);
        cmd.Parameters.AddWithValue("@EmailId", this.txtEmail.Text);
        con.Open();
        SqlDataReader dr = cmd.ExecuteReader();
        while (dr.Read())
        {
            if (dr.HasRows == true)
            {
                MessageBox.Show("EmailId = " + dr[5].ToString() + " Already exist");
                txtEmail.Clear();
                break;
            }
        }

    }