Error on calculate counts of rows (for a table)

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hello

i write a webservice.
in the cs file i write bellow lines. after run, it returns 1.
but there are many rows in mytable.

SqlConnection con = new SqlConnection("Data Source=mypc;Initial Catalog=myDB;User ID=admin;Password=admin123");
    SqlCommand cmd;
    SqlDataReader dr;
    DatatableToJson dts = new DatatableToJson();
    long id = 0;
    string Table_Name = "";


    [WebMethod]
    public void OnlineUsers_Counts()
    {
        DataTable dt = new DataTable();
        SqlCommand myCMD = new SqlCommand();
        myCMD.CommandText = "select count(*) from OnlineUsers  ";  
        
        con.Close();
        con.Open();

        myCMD.Connection = con;
        dr = myCMD.ExecuteReader();

        dt.Clear();
        dt.Load(dr);
                
        if (dt.Rows.Count > 0)
        {
            Context.Response.Write(dt.Rows.Count.ToString());
        }

thanks

What I have tried:

i couldn't do any things for solve the problems.

help

Posted 9-Nov-18 7:39am

Member 13522501

Updated 9-Nov-18 11:35am

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OriginalGriff · Answer 1 · 2018-11-09T08:03:00

Solution 1

Um. You get 1, don't you?

That's because

SQL

SELECT COUNT(*) FROM MyTable

Returns a single row, with a single field in, which contains the number of rows in the original table...

I'd use ExecuteScalar which returns a single value - the number of rows - instead of ExecuteReader.

Posted 9-Nov-18 8:03am

OriginalGriff

MadMyche · Answer 2 · 2018-11-09T08:08:00

SQL

select count(*) from OnlineUsers

The ExecuteReader() method is going to retrieve this data as a table. There will be one row with one field.

What you can do is to change the method; use ExecuteScalar();. The needed code is a few lines shorter as well.

C#

        int RowCount = myCMD.ExecuteScalar();
        Context.Response.Write(RowCount);
//      dr = myCMD.ExecuteReader();
//
//      dt.Clear();
//      dt.Load(dr);
                
//      if (dt.Rows.Count > 0)
//      {
//            Context.Response.Write(dt.Rows.Count.ToString());
//       }

Vincent Maverick Durano · Answer 3 · 2018-11-09T11:36:00

If I may add to the solution provided, I would strongly recommend you do the following:

(1) Always put app level configuration such as your connection string in your web.config file so you won't have to recompile and redeploy your code when you modify your connection string.

(2) Wrap objects that eat resources such as SqlConenction and SqlCommand within a using block so objects will be automatically disposed after using them. Here's a quick example:

C#

[WebMethod]
public void OnlineUsers_Counts()
{
	int rowCount = 0;
        using(SqlConnection connection = new SqlConnection("YOUR CONNECTION STRING HERE")){
           using(SqlCommand cmd = new SqlCommand("SELECT count(*) FROM OnlineUsers" , connection)){
               	 cmd.CommandType = CommandType.Text;
                 rowCount = cmd.ExecuteScalar();
        	
        }
        
	Context.Response.Write(rowCount);
}

Error on calculate counts of rows (for a table)

3 solutions

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