Question

Friends,
I have a dynamic sql query that I would like to execute and return a list.
From most of my internet searches on goole, I found that the type of the list has to be known to convert the sqldatareader to a list.
How can I do that when I do not know what query will be executed.

Execute(String query)
{
  SqlConnection con=new SqlConnection(connection);//connection from elsewhere
  SqlCommand cmd = new SqlCommand(query);
  cmd.connection=con;
  con.Open();
  SqlDataReader result=cmd.ExecuteReader();
  //How to convert result to a list when i do not know the table structure 
} 

Now I want to convert the result to a list.
However I do not know the details of the table which the query works on.The query can vary, it can query any table.
So under these conditions how can I convert the result to a list. Is it possible?

This leaves me with one simple question, if I do not know the table details, then what will be the entries of the list or it will be a list of what?

To answer that question, I ask myself another question, is it possible to have a list where each list entry will correspond to one row of the SqlDataReader result?

So I can use a List < DataRow > x =result.Select().ToList(), but I do not want to use this either.

I want each entry of the list to map to each row of the result and at the same time be composed of the atomic datatypes which make a row.

Eg Select studentname,studentid from student;
This will return me a SqlDataReader result and I want to construct a list whose type contains a string and an int and then populate the list with the rows of the result.

When the query changes to select marks,subject,grade from marks where studentid=1432, then I want to construct a list whose type contains int,string,char and then fill the list with the rows of the result.

Is there a way to do it?

PS The user knows how to pick the values if I return a list as detailed above, since he created the query and he knows how many columns to expect.

Answer 1

If the caller will know the type, make is a generic method, and create a T per row…

Or, since dapper-dot-net already does that:

var list = connection.Query<T>(command [, args]).ToList();

If the caller can’t know the T either, you could use ExpandoObject to populate a List<dynamic>, casting the expando to IDictionary<string,object> to populate it with key/value pairs.

Or, since dapper-dot-net already does that:

var list = connection.Query(command [, args]).ToList();

Then the caller can use:

foreach(var item in list) {
    Console.WriteList("{0}, {1}, {2}", item.marks, item.subject, item.grade);
}