The whole database is a Monoid.

[sjoerdvisscher]

I had a bit of fun turning the whole database into a Monoid:

data Db f = Db
    { datumRows   :: f (TableEntity DatumRowT)
    , scriptRows  :: f (TableEntity ScriptRowT)
    , txRows      :: f (TableEntity TxRowT)
    , addressRows :: f (TableEntity AddressRowT)
    }
    deriving (Generic, Database be)

type AllTables (c :: * -> Constraint) f = (c (f (TableEntity DatumRowT)), c (f (TableEntity ScriptRowT)), c (f (TableEntity TxRowT)), c (f (TableEntity AddressRowT)))
deriving via (GenericSemigroupMonoid (Db f)) instance AllTables Semigroup f => Semigroup (Db f)
deriving via (GenericSemigroupMonoid (Db f)) instance AllTables Monoid f => Monoid (Db f)

It’s useful for generating batch inserts. You can mconcat together inserts into various tables, and using zipTables to generate batch inserts per table:

data InsertRows te where
    InsertRows :: BeamableSqlite t => [t Identity] -> InsertRows (TableEntity t)

instance Semigroup (InsertRows te) where
    InsertRows l <> InsertRows r = InsertRows (l <> r)
instance BeamableSqlite t => Monoid (InsertRows (TableEntity t)) where
    mempty = InsertRows []

insertRows :: Db InsertRows -> SqliteM ()
insertRows = getAp . getConst . zipTables (Proxy :: Proxy Sqlite) (\tbl (InsertRows rows) -> Const . Ap . runInsert . insert tbl $ insertValues rows) db

I posted this on Twitter and someone replied that this should go in the documentation somewhere. I think that's a good idea, but I'm not sure what would be the right place, and if some of the code should be part of a beam package. If we can decide on the right place for this I'm more than willing to create a PR.