插入前检查重复的条目（C＃.net）

Question

我有一个文本框表格，学生填写了他们的一般信息，如姓名，城市，州等等。有时学生不记得他们是否填写在之前的表单中，它将导致ms-access数据库中的重复条目。理想情况下，我希望代码首先在插入前在同一条记录上搜索ms-access数据库，查找匹配的名和姓。如果在输入的名字和姓氏字段上都有匹配的记录，那么脚本就会运行，并说出如下内容：“匹配记录已存在，您希望继续吗？”点击“是”将输入记录到一个新行中，点击“取消”根本不会将其输入到数据库中。

我开始这段代码，但我不确定它是否是正确的方向，任何指导将不胜感激，谢谢。

using (OleDbConnection con = new OleDbConnection(constr)) 
    using (OleDbCommand com = new OleDbCommand("SELECT COUNT(*) FROM StudentList WHERE [FName] = @FName AND [LName] = @LName", con)) 
    { 
     con.Open(); 
     using (OleDbDataReader myReader = com.ExecuteReader()) 
     { 
      (This is where I am stuck) 
     } 
    } 

下面是提交按钮当前的代码。

protected void btnSubmit_Click(object sender, EventArgs e) 
{ 
    { 
     //Preforms insert statement on click to allow additions to the database 
     DateTime CurrentDate; 
     CurrentDate = DateTime.Now; 

     string constr = @"Provider=Microsoft.Jet.OLEDB.4.0; Data Source=D:\sites\schoolinfo\students_dev\App_Data\Studentdb.mdb"; 
     string cmdstr = "INSERT into StudentList(FName, LName, BDay, Gender, School, Grade, Address, APT, City, State, Zip, Email, Phone, CellPhone, ParentFName, ParentLName, ParentEmail) values(@FName, @LName, @BDay, @Gender, @School, @Grade, @Address, @APT, @City, @State, @Zip, @Email, @Phone, @CellPhone, @ParentFName, @ParentLName, @ParentEmail)"; 



     OleDbConnection con = new OleDbConnection(constr); 
     OleDbCommand com = new OleDbCommand(cmdstr, con); 
     { 
      con.Open(); 
     } 
     //The following fields are added from the student information to the corresponding database fields 
     com.Parameters.AddWithValue("@FName", txtFirstName.Text); 
     com.Parameters.AddWithValue("@LName", txtLastName.Text); 
     com.Parameters.AddWithValue("@BDay", txtBirthDate.Text); 
     com.Parameters.AddWithValue("@Gender", ddlGender.Text); 
     com.Parameters.AddWithValue("@School", txtSchool.Text); 
     com.Parameters.AddWithValue("@Grade", txtGrade.Text); 

     //The following fields are added from the contact information to the corresponding database fields 
     com.Parameters.AddWithValue("@Address", txtAddress.Text); 
     com.Parameters.AddWithValue("@APT", txtApt.Text); 
     com.Parameters.AddWithValue("@City", txtCity.Text); 
     com.Parameters.AddWithValue("@State", ddlState.Text); 
     com.Parameters.AddWithValue("@Zip", txtZip.Text); 
     com.Parameters.AddWithValue("@Email", txtEmail.Text); 
     com.Parameters.AddWithValue("@Phone", txtPhone.Text); 
     com.Parameters.AddWithValue("@CellPhone", txtCellPhone.Text); 
     com.Parameters.AddWithValue("@ParentFName", txtParentFName.Text); 
     com.Parameters.AddWithValue("@ParentLName", txtParentLName.Text); 
     com.Parameters.AddWithValue("@ParentEmail", txtParentEmail.Text); 
     com.ExecuteNonQuery(); 
     con.Close(); 

     //End database connection 
     ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "alertMessage", "alert('Student has been successfully added!')", true); 
    } 
} 

Answer 1

using (OleDbConnection con = new OleDbConnection(constr)) 
    using (OleDbCommand com = new OleDbCommand("SELECT COUNT(*) FROM StudentList WHERE [FName] = @FName AND [LName] = @LName", con)) 
    { 
     // Add your @Fname and @LName parameters here 
     com.Parameters.AddWithValue("@FName", firstName); 
     com.Parameters.AddWithValue("@LName", lastName); 

     con.Open(); 
     using (OleDbDataReader myReader = com.ExecuteReader()) 
     { 
      myReader.Read(); 
      int count = myReader.GetInt32(0); 
      // return count > 0 or whatever to indicate that it exists 
     } 
    } 

Answer 2

几件事情：

1. 您可以在表中设定的第一个名字和姓氏为1个主键（是的，它在MS-访问可能）。这样一来，你永远不会得到任何重复的记录

2. COUNT（*）不与数据库中的最佳实践..但因为你正在处理MS-访问

   using (OleDbDataReader myReader = com.ExecuteReader()) 
   { 
       // reads the first and only column count(*) and convert it to a number 
       if (Convert.ToInt16(myReader[0]) > 0) 
       { 
        // an entry already exists 
       } 
   } 
   

Answer 3

你应该使用的ExecuteScalar时您的查询的返回值只有一列，只有一列。当然，这有参数占位符的命令文本中的OleDbCommand也需要有相应的参数集合

using (OleDbConnection con = new OleDbConnection(constr)) 
using (OleDbCommand com = new OleDbCommand("SELECT COUNT(*) FROM StudentList WHERE [FName] = @FName AND [LName] = @LName", con)) 
{ 
    con.Open(); 
    com.Parameters.AddWithValue("@FName", txtFirstName.Text); 
    com.Parameters.AddWithValue("@LName", txtLastName.Text); 
    int count = Convert.ToInt32(com.ExecuteScalar()); 
    if(count == 0) 
    { 
     ... record doesn't exist 
    } 
    else 
    { 
     ... you have got count records 
    } 

} 

但是让我说，这个逻辑是相当薄弱。如果两个学生的名字和姓氏相同，会发生什么？如果有人输错了名字，会发生什么？我认为你应该要求更独特的东西。就像学校提供的SSN或其他ID一样。 （学生号码或类似的东西）