Bridges polytropos open records with the Yesod ecosystem's persistent relational database framework.

Architectural Overview & Rationale

PersistRow provides fast marshalling of records to and from [PersistValue] rows: toPersistFieldsRecord serializes the flat payload in row order, and fromPersistValuesRecord reconstructs the record by filling the payload slots directly, in \(O(N)\), with no intermediate tuples. The walk is heterogeneous: each field uses its own PersistField instance.

'PersistField (Record r)' lets a whole record travel through persistent's value machinery as a PersistList (a nested-column analogue), and PolyRowEntity pairs an integer key with a record in the shape of persistent's Entity, marshalling to the key-then-fields row layout backends use for Entity rows.

When to Use This Module

• When persisting polytropos open records with Yesod and the persistent ORM.

Worked Example

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeApplications #-}
{-# OPTIONS_GHC -fplugin=Polytropos.Plugin #-}

import Database.Persist
import Polytropos
import Polytropos.Persistent

type PersonRow = Record '["name" ':= Text, "age" ':= Int]

person :: PersonRow
person = REC { name = "Alice", age = 30 }

-- Convert to persistent values:
vals :: [PersistValue]
vals = toPersistFieldsRecord person