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43 lines
1.5 KiB
Haskell
43 lines
1.5 KiB
Haskell
{- This file is part of Vervis.
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-
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- Written in 2016 by fr33domlover <fr33domlover@riseup.net>.
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-
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- ♡ Copying is an act of love. Please copy, reuse and share.
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-
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- The author(s) have dedicated all copyright and related and neighboring
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- rights to this software to the public domain worldwide. This software is
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- distributed without any warranty.
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-
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- You should have received a copy of the CC0 Public Domain Dedication along
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- with this software. If not, see
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- <http://creativecommons.org/publicdomain/zero/1.0/>.
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-}
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-- | Persistent graphs are specified using the 'PersistEntityGraph' typeclass,
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-- using value functions which specify fields. But the DB schema is known at
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-- development time, and a specific graph needs to be picked statically. Since
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-- the 'persistent' package doesn't have compile-time (e.g. type-level)
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-- representation of the schema (but instead converts from TH directly to
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-- datatypes), the graph related functions use a 'Proxy' which specifies the
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-- graph using the type.
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--
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-- I don't know enough about type systems and advanced type features and GHC
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-- extensions, to tell whether a better solution is possible. For now, this is
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-- how things work.
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--
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-- This module is a helper for easily specifying graphs instead of typing the
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-- proxy type directly each time, which may be long and cumbersome.
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module Vervis.GraphProxy
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( GraphProxy
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, ticketDepGraph
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)
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where
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import Data.Proxy
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import Vervis.Model
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type GraphProxy n e = Proxy (n, e)
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ticketDepGraph :: GraphProxy Ticket TicketDependency
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ticketDepGraph = Proxy
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