Consider we have Main User Defined Object named “Mahi_H” and It’s child table is “Mahi_D1”. If You want to Add / Updated records in Child table “Mahi_D1”. We can do using SAP B1 General Service as follows.

SAPbobsCOM.GeneralService oGeneralService = null;
SAPbobsCOM.GeneralData oGeneralData = null;
SAPbobsCOM.GeneralDataParams oGeneralParams = null;
SAPbobsCOM.CompanyService sCmp = null;
SAPbobsCOM.GeneralData oChild = null;
SAPbobsCOM.GeneralDataCollection oChildren = null;
sCmp = Main.Mahi_Company.GetCompanyService(); 

oRs = ((SAPbobsCOM.Recordset)(Main.Mahi_Company.GetBusinessObject(SAPbobsCOM.BoObjectTypes.BoRecordset)));
string selquery = "select " + '"' + "DocEntry" + '"' + ",'1' as " + '"' + "LineId" + '"' + ",'0' as " + '"' + "VisOrder" + '"' + ",'SQ_AC' as " + '"' + "Object" + '"' + ",null as " + '"' + "LogInst" + '"' + ",'Y' as " + '"' + "U_Checked" + '"' + "," + '"' + "U_DocNum" + '"' + "," + '"' + "U_SQSeries" + '"' + "," + '"' + "U_SQLineId" + '"' + "," + '"' + "U_iCode" + '"' + "," + '"' + "U_iName" + '"' + "," + '"' + "U_LineId" + '"' + " from " + '"' + "@SQAC_H" + '"';

oRs.DoQuery(selquery);

try
{                                
 oGeneralService = sCmp.GetGeneralService("Mahi_H");  // Main UDO Name
 for (int i = 1; i <= 6; i++)
 {
 // Get UDO record                
 oGeneralParams = ((SAPbobsCOM.GeneralDataParams)(oGeneralService.GetDataInterface(SAPbobsCOM.GeneralServiceDataInterfaces.gsGeneralDataParams)));
 oGeneralParams.SetProperty("DocEntry", oRs.Fields.Item("DocEntry").Value);      //Primary Key
 oGeneralData = oGeneralService.GetByParams(oGeneralParams);
 
// Add lines on UDO Child Table                
 oChildren = oGeneralData.Child("Mahi_D1");  // Child Table Of Main UDO

// Create data for rows in the child table                
oChild = oChildren.Add();      	// Adds Blank Line in Child Table          
oChild.SetProperty("U_SQLineId", oRs.Fields.Item("U_SQLineId").Value);
//oChild.SetProperty("VisOrder", oRs.Fields.Item("VisOrder").Value);
oChild.SetProperty("U_Checked", oRs.Fields.Item("U_Checked").Value);
oChild.SetProperty("U_DocNum", oRs.Fields.Item("U_DocNum").Value);
oChild.SetProperty("U_SQSeries", oRs.Fields.Item("U_SQSeries").Value);
oChild.SetProperty("U_SQLineId", oRs.Fields.Item("U_SQLineId").Value);
oChild.SetProperty("U_iCode", oRs.Fields.Item("U_iCode").Value);
oChild.SetProperty("U_iName", oRs.Fields.Item("U_iName").Value);
                                    
//Update the UDO Record                
oGeneralService.Update(oGeneralData);   // If Child Table doesnot have any record it will create else update the existing one
oRs.MoveNext();
}
}
catch (Exception ex)
{
Main.Mahi_Application.MessageBox(ex.Message, 1, "OK", null, null);
}

Thanks,

Mahendrakumar