Impelementing multi tenant database solution with Yesod persistent

[Juuso Vuorinen]

Hi!

I am trying to figure out how to rewrite/change/utilize functions such as selectList (and others), so that it would by default add a where statement such as ..."where company_id = 3". This would be applied to all tables that need to have their records being shared by multiple tenants referred to by company_id or equivalent.  

The type of the selectList function is as follows: 

selectListSecure :: forall record backend (m :: * -> *). (MonadIO m, PersistQueryRead backend,
 PersistRecordBackend record backend) => [Filter record] -> [SelectOpt record] -> ReaderT backend m [Entity record]

I was wondering if I could somehow figure out the type of the record in my own version of the function, so that I could add a new filter such as [MyId ==. myid] to the filter and let the db action happen after that? 

Somehow I have the feeling that we cannot figure out (use pattern matching) to get that type out and create the filters in a function with such a signature, but be need to do something else? How would you do it?

Regards

Juuso 

Regards

Juuso

[Juuso Vuorinen]

I ended up doing it this way but wonder if there were a more elegant solution available? 

selectList'

    :: forall record backend . (PersistQueryRead backend, PersistRecordBackend record backend)

    => EntityField record (Key Company) -> [Filter record]

    -> [SelectOpt record]

    -> ReaderT backend Handler [Entity record]

selectList' tenantIdField filts opts = do

    c <- liftHandler getCompanyId

    let g =  Filter    { filterField  = tenantIdField

                       , filterValue  = FilterValue  c

                       , filterFilter = Eq }

    selectList (g:filts) opts

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