如何从 SqlDataReader 获取 int32 和字符串。 获取错误 System.IndexOutOfRangeException: 'StudentID'

Question

I am working on a personal project that is using a Microsoft SQL DB and a web layer for Rest API calls. I am trying to get int32s and strings back from the database using a SqlDataReader. When I read in Strings there is no error, however when I attempt to read integers I get the following

`Exception: System.IndexOutOfRangeException: 'StudentID'

public StudentAccount FindStudentByID(int id)
{
    using (SqlConnection connection = new SqlConnection(connectionString))
    {
        connection.Open();
        String sql = "SELECT FirstName, LastName,StudentBiography FROM [PersonTest].[dbo].[StudentAccounts] WHERE StudentID = @p1";
        StudentAccount matchingStudent = new StudentAccount();

        using (SqlCommand cmd = new SqlCommand(sql, connection))
        {
            cmd.Parameters.Add("@p1", SqlDbType.Int).Value = id;
            cmd.CommandType = CommandType.Text;

            SqlDataReader reader = cmd.ExecuteReader();

                while (reader.Read())
                {
                    matchingStudent.StudentID = reader.GetInt32(reader.GetOrdinal("StudentID"));

                    matchingStudent.FirstName = reader["FirstName"].ToString();
                    matchingStudent.LastName = reader["LastName"].ToString();
                    matchingStudent.Biography = reader["StudentBiography"].ToString();

                    matchingStudent.CollegeID = reader.GetInt32(reader.GetOrdinal("COLLTB_CollegeID"));
                }

            reader.Close();

            return matchingStudent;
        }
    }
}

The StudentAccounts table is as following:

StudentAccounts (StudentID, FirstName, LastName, StudentBiography, CollTB_CollegeID)

The StudentID is the primary key.

I apologize ahead of time if I messsed up the format or anything, this is my first time posting on this forum. Thanks!

Answer 1

You're not returning StudentID or COLLTB_CollegeID as columns in your select statement...

String sql = "SELECT FirstName, LastName,StudentBiography FROM [PersonTest].[dbo].[StudentAccounts] WHERE StudentID = @p1";

Should be...

String sql = "SELECT StudentID, FirstName, LastName, StudentBiography, COLLTB_CollegeID FROM [PersonTest].[dbo].[StudentAccounts] WHERE StudentID = @p1";

---

Although you appear to be setting matchingStudent.CollegeID twice, so it doesn't look like you need StudentID in your return columns anyway!

Answer 2

You're using:

matchingStudent.CollegeID = reader.GetInt32(reader.GetOrdinal("StudentID"));

This means:

var columnNumber = reader.GetOrdinal("StudentID");
matchingStudent.CollegeID = reader.GetInt32(columnNumber);

Now the first call fails, because StudentID is not in your SELECT statement. Include the columns you want to read. The same goes for COLLTB_CollegeID .

So:

var sql = "SELECT FirstName, LastName, StudentBiography, StudentID, COLLTB_CollegeID FROM [PersonTest].[dbo].[StudentAccounts] WHERE StudentID = @p1";

Also, you're assigning the result to the wrong property:

matchingStudent.StudentID = reader.GetInt32(reader.GetOrdinal("StudentID"));