DB graph cycle existence checking using recursive SQL query
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fr33domlover
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3 changed files with 227 additions and 1 deletions
27
src/Database/Persist/Local/Class/PersistEntityGraph.hs
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27
src/Database/Persist/Local/Class/PersistEntityGraph.hs
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@ -0,0 +1,27 @@
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{- 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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module Database.Persist.Local.Class.PersistEntityGraph
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( PersistEntityGraph (..)
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)
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where
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import Prelude
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import Database.Persist
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class (PersistEntity n, PersistEntity e) => PersistEntityGraph n e where
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parentField :: EntityField e (Key n)
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childField :: EntityField e (Key n)
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@ -16,6 +16,7 @@
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module Database.Persist.Local.Sql
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( dummyFromField
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, rawSqlWithGraph
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, containsCycle
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)
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where
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@ -24,6 +25,7 @@ import Prelude
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import Control.Monad.IO.Class (MonadIO)
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import Control.Monad.Trans.Reader (ReaderT, ask)
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import Data.Monoid ((<>))
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import Data.Proxy (Proxy)
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import Data.Text (Text)
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import Database.Persist
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import Database.Persist.Sql
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@ -31,6 +33,7 @@ import Database.Persist.Sql.Util
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import qualified Data.Text as T (intercalate)
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import Database.Persist.Local.Class.PersistEntityGraph
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import Database.Persist.Local.Class.PersistQueryForest
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import Database.Persist.Local.Sql.Orphan.Common
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@ -40,6 +43,24 @@ dummyFromKey _ = Nothing
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dummyFromField :: EntityField val t -> Maybe val
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dummyFromField _ = Nothing
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dummyFromFst :: Proxy (a, b) -> Maybe a
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dummyFromFst _ = Nothing
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dummyFromSnd :: Proxy (a, b) -> Maybe b
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dummyFromSnd _ = Nothing
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childFieldFromProxy
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:: PersistEntityGraph node edge
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=> Proxy (node, edge)
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-> EntityField edge (Key node)
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childFieldFromProxy _ = childField
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parentFieldFromProxy
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:: PersistEntityGraph node edge
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=> Proxy (node, edge)
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-> EntityField edge (Key node)
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parentFieldFromProxy _ = parentField
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rawSqlWithGraph
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:: ( RawSql a
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, MonadIO m
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@ -103,3 +124,179 @@ rawSqlWithGraph dir root parent child sub vals = do
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sql = sqlWith <> sub temp
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vals' = toPersistValue root : vals
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rawSql sql vals'
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containsCycle'
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:: ( MonadIO m
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, PersistEntity node
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, PersistEntity edge
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, PersistEntityGraph node edge
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, SqlBackend ~ PersistEntityBackend node
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, SqlBackend ~ PersistEntityBackend edge
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)
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=> Proxy (node, edge)
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-> ReaderT SqlBackend m [Single Int]
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containsCycle' proxy = do
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conn <- ask
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let tNode = entityDef $ dummyFromFst proxy
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tEdge = entityDef $ dummyFromSnd proxy
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fwd = childFieldFromProxy proxy
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bwd = parentFieldFromProxy proxy
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start = DBName "temp_start_cte"
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temp = DBName "temp_hierarchy_cte"
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tid = DBName "id"
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tpath = DBName "path"
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tcycle = DBName "cycle"
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dbname = connEscapeName conn
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sql = mconcat
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[ "WITH RECURSIVE "
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, dbname start
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, " ("
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, T.intercalate "," $ map dbname [tid, tpath, tcycle]
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, ") AS ( SELECT "
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, dbname $ entityDB tNode
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, "."
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, dbname $ fieldDB $ entityId tNode
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, ", "
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, "ARRAY["
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, dbname $ entityDB tNode
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, "."
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, dbname $ fieldDB $ entityId tNode
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, "]"
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, ", "
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, "FALSE"
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, " FROM "
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, dbname $ entityDB tNode
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, " LEFT OUTER JOIN "
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, dbname $ entityDB tEdge
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, " ON "
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, dbname $ entityDB tNode
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, "."
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, dbname $ fieldDB $ entityId tNode
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, " = "
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, dbname $ entityDB tEdge
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, "."
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, dbname $ fieldDB $ persistFieldDef fwd
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, " WHERE "
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, dbname $ entityDB tEdge
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, "."
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, dbname $ fieldDB $ persistFieldDef fwd
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, " IS NULL "
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, " ), "
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, dbname temp
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, " ("
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, T.intercalate "," $ map dbname [tid, tpath, tcycle]
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, ") AS ( SELECT "
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, "* FROM "
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, dbname start
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, " UNION ALL SELECT "
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, dbname $ entityDB tEdge
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, "."
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, dbname $ fieldDB $ persistFieldDef fwd
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, ", "
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, dbname temp
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, "."
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, dbname tpath
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, " || "
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, dbname $ entityDB tEdge
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, "."
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, dbname $ fieldDB $ persistFieldDef fwd
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, ", "
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, dbname $ entityDB tEdge
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, "."
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, dbname $ fieldDB $ persistFieldDef fwd
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, " = "
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, "ANY(", dbname temp, ".", dbname tpath, ")"
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, " FROM "
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, dbname $ entityDB tEdge
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, " INNER JOIN "
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, dbname temp
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, " ON "
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, dbname $ entityDB tEdge
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, "."
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, dbname $ fieldDB $ persistFieldDef bwd
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, " = "
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, dbname temp, ".", dbname tid
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, " WHERE NOT "
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, dbname temp, ".", dbname tcycle
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, " ) "
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, "("
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, "SELECT 1 FROM "
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, dbname start
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, " UNION ALL "
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, "SELECT 1 FROM "
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, dbname temp
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, " WHERE ", dbname tcycle, " = TRUE"
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, ") LIMIT 1"
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]
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rawSql sql []
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-- | Check whether the graph contains (directed) cycles.
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--
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-- Start with nodes which don't have in-edges, and traverse through the edges,
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-- either until we visit all the nodes, or until we find a node we visited
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-- before. If we can't find nodes without in-edges, or we found a node we
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-- visited before, then a cycle exists.
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--
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-- > WITH RECURSIVE
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-- > start (id, path, cycle) AS (
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-- > SELECT node.id, ARRAY[node.id], false
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-- > FROM node LEFT OUTER JOIN edge
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-- > ON node.id = edge.parent
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-- > WHERE edge.parent IS NULL
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-- > ),
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-- > temp (id, path, cycle) AS (
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-- > SELECT * from start
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-- > UNION ALL
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-- > SELECT edge.parent,
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-- > temp.path || edge.parent,
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-- > edge.parent = ANY(temp.path)
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-- > FROM edge INNER JOIN temp
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-- > ON edge.child = temp.id
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-- > WHERE NOT temp.cycle
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-- > )
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-- > ( SELECT 1
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-- > FROM start
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-- > UNION ALL
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-- > SELECT 1
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-- > FROM temp
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-- > WHERE cycle = true
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-- > )
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-- > LIMIT 1
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--
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-- The parent and child fields are interchangeable, which is an opportunity to
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-- optimize. Currently the recursion goes from parents to children (i.e.
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-- towards decendants), but it could be changed, or made available for the user
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-- to choose, if benchmarks reveal performace differences.
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containsCycle
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:: ( MonadIO m
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, PersistEntity node
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, PersistEntity edge
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, PersistEntityGraph node edge
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, SqlBackend ~ PersistEntityBackend node
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, SqlBackend ~ PersistEntityBackend edge
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)
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=> Proxy (node, edge)
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-> ReaderT SqlBackend m Bool
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containsCycle = fmap (not . null) . containsCycle'
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@ -53,6 +53,7 @@ library
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Data.EventTime.Local
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Data.Functor.Local
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Data.Git.Local
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Data.Graph.Inductive.Query.Cycle
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Data.Graph.Inductive.Query.Layer
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Data.HashMap.Lazy.Local
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Data.Hourglass.Local
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@ -66,6 +67,7 @@ library
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Database.Esqueleto.Local
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Database.Persist.Class.Local
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Database.Persist.Sql.Local
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Database.Persist.Local.Class.PersistEntityGraph
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Database.Persist.Local.Class.PersistQueryForest
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Database.Persist.Local.RecursionDoc
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Database.Persist.Local.Sql
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