postgresql - Querying postgres from c# using npgsql -

i have installed postgres in windows machine , started working on poc. able connect database windows command line. but, unable connect c# application.

it seems have issues in connection string. have gone through multiple tutorials every tutorial has own way of providing connection string parameters.is there standard way of giving hostname,port,username,password , database.

i trying query using rest api. am, doing right way.

// api/values [httpget] public iactionresult get() {    test test = new test();    return ok(test.table2json()); }  using npgsql; using system;  namespace zeiss.mccneo.datamigration.utilities {   public class test   {      private readonly npgsqlconnection conn;      public test()      {       conn = new npgsqlconnection("server=127.0.0.1;user id=postgres;" +                                     "password=postgres;database=postgres;");      //also tried using      conn = new npgsqlconnection("server=127.0.0.1;port=5432;user                                                                           id=postgres;" +                                                                  "password=postgres;database=postgres;");      }       public string table2json()      {          string value = null;          npgsqlcommand command = new npgsqlcommand("select * test",                                          conn);          npgsqldatareader dr = command.executereader();          while (dr.read())          {          value = dr[0].tostring();          }          return value;          }     }  } 

exception:

-       $exception  {system.invalidoperationexception: connection not open    @ npgsql.npgsqlconnection.checkreadyandgetconnector()    @ npgsql.npgsqlcommand.<executedbdatareader>d__92.movenext() --- end of stack trace previous location exception thrown ---    @ system.runtime.exceptionservices.exceptiondispatchinfo.throw()    @ system.runtime.compilerservices.taskawaiter.handlenonsuccessanddebuggernotification(task task)    @ system.runtime.compilerservices.taskawaiter`1.getresult()    @ system.runtime.compilerservices.valuetaskawaiter`1.getresult()    @ npgsql.npgsqlcommand.executedbdatareader(commandbehavior behavior)    @ npgsql.npgsqlcommand.executereader()    @ zeiss.mccneo.datamigration.utilities.test.table2json() in c:\users\inpyadav\documents\visual studio 2017\projects\datamigration\zeiss.mccneo.datamigration.utilities\test.cs:line 19    @ datamigration.controllers.valuescontroller.get() in c:\users\inpyadav\documents\visual studio 2017\projects\datamigration\datamigration\controllers\valuescontroller.cs:line 18    @ lambda_method(closure , object , object[] )    @ microsoft.aspnetcore.mvc.internal.controlleractioninvoker.<invokeactionmethodasync>d__27.movenext()}  system.invalidoperationexception 

why don't open connection says in error message?

conn.open();