Lists values in an entity according to the value of previous entity.

[sujithraalink]

I have 3 entities school, panchayath and wards. schools have one to many relationships with panchayath and wards .Panchayath has one to many relationship with wards.
In school entity i have listed panchayaths and wards. when i choose specific panchayath, I have to list wards according to that panchayath.
when i choose specific panchayath, it lists all existing wards now, not according to the selected panchayath. Please help me to resolve the issue.