combobox - C# Passing Values between dependent Comboboxes -

i'm relatively new i've been researching issue on 2 days, think i've done due diligence ... if has been answered before apologize. basic issue i'm trying create dependent combo boxes. wrinkle displayed value typically not lookup value next query/combo box (i'm using oledb compliant data base) example: table1 (t1) contains id (int) & nm (string), table2 (t2) contains id (int) & status (string). run query1 (q1) display t1.nm in combobox1 (cb1), when selected run query1a lookup/get selected table1.id pass query2 populates combobox2. connection string , q1 work fine, cb1 displays properly, once select error thrown: "oledbexception .. sql passthru expression ... using equals (=) has components of different data types"

// ** initial connection & populate cb1 - works fine **

public void comboboxload()       {             string conn3str = <connection string >;             string query1 = "select nm table1 refvalue=1 ; ";             oledbconnection conn3 = new oledbconnection(conn3str);             oledbcommand tblrow1 = new oledbcommand(query1, conn3);             oledbdatareader rdrow1;             try             {                 conn3.open();                 lblconnstate.text = "connection successful";                 rdrow1 = tblrow1.executereader();                 while (rdrow1.read())                 {                     int colindx1 = rdrow1.getordinal("nm");                     string sitbl = rdrow1.getstring(colindx1);                     cb1.items.add(sitbl);                 }             }             catch (exception ex)             {                 messagebox.show("error  " + ex);             }         } 

// ** value cb1, create query populate cb2 **

private void cb1_selectedindexchanged(object sender, eventargs e)         {             string conn3str = <connection string >;             oledbconnection conn3 = new oledbconnection(conn3str);              conn3.open();              // pass selected value cb1 (string) equal table1.nm (string)                        string query1a = "select id table1 nm = '" + cb1.text + "' ; ";             oledbcommand tabid = new oledbcommand(query1a, conn3);             int tabid2 = convert.toint32(tabid.executescalar());             // pass variable tabid2 (int) equal table2.id (int)                                    string query2 = "select status table2 id = '" + tabid2 + "'; ";              oledbcommand tblrow2 = new oledbcommand(query2, conn3);             // oledbdatareader rdtabid;             // oledbdatareader rdrow2;              try             {                 oledbdatareader rdrow2 = tabid.executereader();                 oledbdatareader rdtabid = tblrow2.executereader(); // ** error points line **                  while (rdrow2.read())                 {                     int tabididx = rdtabid.getordinal("id");                     string tabidval = rdtabid.getstring(tabididx); // pass reference id label on form                     lblbtableid.text = tabid2.tostring();                      int colindx1 = rdrow2.getordinal("status");                      string sintval = rdrow2.getstring(colindx1);                     cmblowlvl.items.add(sintval);                 }             }             catch (exception ex)             {                 messagebox.show("error  " + ex);             }         } 

are positive you're getting value on line int tabid2 = convert.toint32(tabid.executescalar());?

convert.toint32 doesn't throw argumentnullexception int.parse it's possible variable not getting set.

also may want consider changing queries use parameterized sql rather concatenation security purposes. https://msdn.microsoft.com/en-us/library/system.data.oledb.oledbcommand.parameters(v=vs.110).aspx