why constraint not working in seed_fu file?

[LongLonghaoran]

I wrote a seed_fu file like this:

Privilege.seed(:school_id, :p_object, :p_action,
             {school_id: 16, p_object: "repair", p_action: "applyable"},
             {school_id: 16, p_object: "repair", p_action: "editable"}
             ...
) 

but when i run rake db:seed_fu FILTER=privilege repeatedly, it create the same records again,the constraint not work, otherwise the constraint is worked on rails console. is anyone who can help me?thank you