Based on selected element in combo box it has to show data in grid
Based on selected enum element it has to display the data.
The enum should contain two elements.
1. Customer.
2. Vendor.

Explanation:

I created a table using common fields from cust table and vend table.
Created table is attached to newly created form datasource.
Overrided form datasource init method as below to show grid empty while opening form.

public void init()
{
    delete_from CustomerVend;
    super();
}

Required fields are added to form designs -> grid.
A new combobox is created under designs
Enum property of combobox --> customervend(Enum)
Overrided modified method of combobox to show data
based on selected element in customervend enum.

public boolean modified()
{
    CustomerVend cv;
    CustTable ct;
    VendTable vt;
    boolean ret;
    ret = super();
    delete_from cv;
    if(this.valueStr() ==(enum2str(CustVendACType::Cust)))
    {
        while select * from ct
        {
            cv.AccountNum=ct.AccountNum;
            cv.BankAccount=ct.BankAccount;
            cv.CurrencyName=ct.Currency;
            cv.insert();
        }

        CustomerVend_ds.research();
        CustomerVend_ds.refresh();
    }
   else
      {
        while select * from vt
        {
            cv.AccountNum=vt.AccountNum;
            cv.BankAccount=vt.BankAccount;
            cv.CurrencyName=vt.Currency;
            cv.insert();
        }
          CustomerVend_ds.research();
          CustomerVend_ds.refresh();
    }
    return ret;
}