How to validate data reader in C#

Question

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SQL

Select * from student

Rollno      Studname   Age    DOB            Address   Active    Status
   1          Ajay      6     12.10.2010      Chennai   A          Male
   2          Suresh    5     5.7.2011        Chennai   A          Male
   3          Priya     6     10.6.2010       Chennai   A         FeMale
   4          Revathy   5     8.9.2011        Chennai   A         FeMale

from the above table i am validating as follows

C#

using (SqlConnection newCon = new SqlConnection(db.GetConnectionString))
            {
                SqlCommand newCmd = new SqlCommand(Select * from student)", newCon);
                newCmd.Parameters.Add()
                newCon.Open();
                SqlDataReader rdr = newCmd.ExecuteReader();
                rdr.Read();

                if(reader[6].ToString() == "Male");
                    {
                          //In that i am displaying Male Image
                    }
                 if(reader[6].Tostring() == "FeMale");
                    
                     {
                          //In that i am displaying FeMale Image
                     }
                   
           }

When i exeute the above code shows error as follows

Invalid attempt to read when no data is present.

The above error shows in below line as follows

C#

if(reader[6].ToString() == "Male")

What is the mistake in my above code. please help me

i tried lot but shows error.

Posted 13-Aug-16 22:08pm

sudhakarthikeyan

Updated 14-Aug-16 23:08pm

Maciej Los

v2

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Comments

Patrice T 14-Aug-16 4:13am

Which word you don't understand in the error message ?

Maciej Los 15-Aug-16 4:52am

Do not repost!
http://www.codeproject.com/Questions/1118317/Using-foreach-loop-get-data-and-save-into-excel-fi

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OriginalGriff · Answer 1 · 2016-08-13T22:36:00

You read from the DataReader, but you don't check that any rows are returned: so when they aren't you get an error which explicitly tells you just that!
Start by checking the return value:

C#

if (rdr.Read();
   {
   if(reader[6].ToString() == "Male");
      {
   ...

And the immediate error will go away.

But...the code you show isn't the code you are running, because this won't compile:

C#

SqlCommand newCmd = new SqlCommand(Select * from student)", newCon);

And I suspect that your "real" code is using a WHERE clause to select which student to return info for. And that WHERE clause doesn't work...so no rows are returned.

Maciej Los · Answer 2 · 2016-08-14T23:08:00

I'd suggest to create Dictionary[^] object for such of functionality:

C#

Dictionary <string, string> images = new Dictionary<string, string>();
images.Add("Male", "C:\Pictures\Male.jpg");
images.Add("FeMale", "C:\Pictures\FeMale.jpg");

Then you'll be able to simply assign path to image depending on student's gender.

C#

PictureBox1.Image = Image.FromFile(images[reader[6]]);

For further details, please see:
Setting Pictures at Run Time (Windows Forms)[^]
Image.FromFile Method (String) (System.Drawing)[^]

How to validate data reader in C#

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