integrated skin code gor generating Sql Query (only left to execute it)

postgrest.cabal

@@ -52,6 +52,8 @@ executable postgrest
                      , mtl
                      , cassava
                      , jwt
+                     , parsec
+                     , errors
   hs-source-dirs:      src
 
 library
@@ -88,8 +90,12 @@ library
                      , mtl
                      , cassava
                      , jwt
+                     , parsec
+                     , errors
   Exposed-Modules:     PostgREST.App
                      , PostgREST.Types
+                     , PostgREST.Parsers
+                     , PostgREST.Functions
                      , PostgREST.Auth
                      , PostgREST.Config
                      , PostgREST.Error
@@ -111,6 +117,8 @@ Test-Suite spec
   Main-Is:             Main.hs
   Other-Modules:       PostgREST.App
                      , PostgREST.Types
+                     , PostgREST.Parsers
+                     , PostgREST.Functions
                      , PostgREST.Auth
                      , PostgREST.Config
                      , PostgREST.Error
@@ -150,3 +158,5 @@ Test-Suite spec
                      , process
                      , heredoc
                      , jwt
+                     , parsec
+                     , errors

src/PostgREST/App.hs

@@ -9,7 +9,7 @@ module PostgREST.App (app, sqlError, isSqlError, contentTypeForAccept
 import Control.Monad (join)
 import Control.Arrow ((***), second)
 import Control.Applicative
-
+import           Data.Bifunctor             (first)
 import Data.Text hiding (map, find, filter)
 import Data.Maybe (fromMaybe, mapMaybe, isJust, isNothing)
 import Text.Regex.TDFA ((=~))
@@ -47,6 +47,8 @@ import PostgREST.Auth
 import PostgREST.PgQuery
 import PostgREST.RangeQuery
 import PostgREST.PgStructure
+import PostgREST.Parsers
+import PostgREST.Functions
 
 import Prelude
 
@@ -66,20 +68,31 @@ app dbstructure conf reqBody role req =
 
     ([], _) -> do
       let body = encode $ filter (filterTableAcl role) $ filter (((cs schema)==).tableSchema) allTables
-      return $ responseLBS status200 [jsonH, ("Custom", "header")] $ cs body
+      return $ responseLBS status200 [jsonH] $ cs body
 
     ([table], "OPTIONS") -> do
       let qt = Table schema table
       let cols = filter (filterCol schema table) allColumns
       let pkey = map pkName $ filter (filterPk schema table) allPrimaryKeys
       let body = encode (TableOptions cols pkey)
-      return $ responseLBS status200 [jsonH, allOrigins, ("Custom", "header2")] $ cs body
+      return $ responseLBS status200 [jsonH, allOrigins] $ cs body
 
 
     ([table], "GET") ->
       if range == Just emptyRange
       then return $ responseLBS status416 [] "HTTP Range error"
       else do
+        let apiRequest = parseGetRequest req
+            dbRequest = first formatParserError apiRequest
+                >>= traverse (requestNodeToQuery schema allTables allColumns)
+                >>= addRelations allRelations Nothing
+                >>= addJoinConditions allColumns
+                where formatParserError = pack.show
+            query = dbRequestToQuery <$> dbRequest
+            body = show query
+        return $ responseLBS status200 [] $ cs body
+
+      {--
         let qt = qualify table
             from = fromMaybe 0 $ rangeOffset <$> range
             query = B.Stmt "select " V.empty True <>
@@ -110,6 +123,7 @@ app dbstructure conf reqBody role req =
                 if Prelude.null canonical then "" else "?" <> cs canonical
             )
           ] (cs $ fromMaybe "[]" body)
+      --}
 
     (["postgrest", "users"], "POST") -> do
       let user = decode reqBody :: Maybe AuthUser

src/PostgREST/Functions.hs

@@ -0,0 +1,168 @@
+{-# LANGUAGE OverloadedStrings #-}
+module PostgREST.Functions
+where
+
+import PostgREST.Types
+import           Control.Error
+import Data.List (find)
+import Data.Tree
+import Data.Text hiding (find, foldr, map, null, last)
+import Data.Monoid
+import PostgREST.PgQuery (pgFmtOperator, pgFmtValue, pgFmtIdent, pgFmtLit, fromQi, QualifiedIdentifier(..))
+
+
+findColumn :: [Column] -> Text -> Text -> Text -> Either Text Column
+findColumn allColumns s t c = note ("no such column: "<>t<>"."<>c) $
+    find (\ col -> colSchema col == s && colTable col == t && colName col == c ) allColumns
+
+findTable :: [Table] -> Text -> Text -> Either Text Table
+findTable allTables s t = note ("no such table: "<>t) $
+    find (\tb-> s == tableSchema tb && t == tableName tb ) allTables
+
+findRelation :: [Relation] -> Text -> Text -> Text -> Maybe Relation
+findRelation allRelations s t1 t2 =
+    find (\r -> s == relSchema r && t1 == relTable r && t2 == relFTable r) allRelations
+
+
+filterToCondition :: Text -> [Column] -> Text -> Filter -> Either Text Condition
+filterToCondition schema allColumns table (Filter fld op val) =
+    Condition <$> c <*> pure op <*> pure (VText (pack val))
+    where
+        c = (,) <$> column <*> pure (snd fld)
+        column = findColumn allColumns schema table $ pack $ fst fld
+
+
+requestNodeToQuery ::Text -> [Table] -> [Column] -> RequestNode -> Either Text Query
+requestNodeToQuery schema allTables allColumns (RequestNode tblNameS flds fltrs) =
+    Select <$> mainTable <*> select <*> joinTables <*> qwhere <*> rel
+    where
+        tblName = pack tblNameS
+        mainTable = findTable allTables schema tblName
+        select = mapM toDbSelectItem flds --besides specific columns, we allow * here also
+            where
+                -- it's ok not to check that the table exists here, mainTable will do the checking
+                toDbSelectItem :: SelectItem -> Either Text DbSelectItem
+                toDbSelectItem (("*", Nothing), Nothing) = Right $ ((Star{colSchema = schema, colTable = tblName}, Nothing), Nothing)
+                toDbSelectItem ((c,jp), cast) = (,) <$> dbFld <*> pure cast
+                    where
+                        col = findColumn allColumns schema tblName $ pack c
+                        dbFld = (,) <$> col <*> pure jp
+
+        qwhere = mapM (filterToCondition schema allColumns tblName) fltrs
+        joinTables = pure []
+        rel = pure Nothing
+
+addRelations :: [Relation] -> Maybe DbRequest -> DbRequest -> Either Text DbRequest
+addRelations allRelations parentNode node@(Node query@(Select {qMainTable=table}) forest) =
+    case parentNode of
+        Nothing -> Node query{qRelation=Nothing} <$> updatedForest
+        (Just (Node (Select{qMainTable=parentTable}) _)) -> Node <$> (addRel query <$> rel) <*> updatedForest
+            where
+                rel = note ("no relation between " <> (tableName table) <> " and " <> (tableName parentTable)) $
+                    findRelation allRelations (tableSchema table) (tableName table) (tableName parentTable)
+                addRel :: Query -> Relation -> Query
+                addRel q r = q{qRelation = Just r}
+    where
+        updatedForest = mapM (addRelations allRelations (Just node)) forest
+
+
+addJoinConditions :: [Column] -> Tree Query -> Either Text DbRequest
+addJoinConditions allColumns (Node query@(Select{qRelation=relation}) forest) =
+    case relation of
+        Nothing -> Node <$> updatedQuery <*> updatedForest -- this is the root node
+        Just rel@(Relation{relType="child"}) -> Node <$> (addCond <$> updatedQuery <*> getJoinCondition rel) <*> updatedForest
+        Just (Relation{relType="parent"}) -> Node <$> updatedQuery <*> updatedForest
+        -- Just (Many relationColumn1 relationColumn2) -> Node <$> pure updatedQuery{qJoinTables=linkTable:qJoinTables updatedQuery, qWhere=cond1:cond2:qWhere updatedQuery} <*> updatedForest
+            -- where
+            --     cond1 = getJoinCondition relationColumn1
+            --     cond2 = getJoinCondition relationColumn2
+            --     linkTable = Table "public" (colTable relationColumn1) True
+        _ -> Left "unknow relation"
+    where
+        -- add parentTable and parentJoinConditions to the query
+        updatedQuery = foldr (flip addCond) (query{qJoinTables = parentTables ++ (qJoinTables query)}) <$> parentJoinConditions
+            where
+                parentJoinConditions = mapM (getJoinCondition.snd) parents
+                parentTables = map fst parents
+                parents = mapMaybe (getParents.rootLabel) forest
+                getParents qq@(Select{qRelation=(Just rel@(Relation{relType="parent"}))}) = Just (qMainTable qq, rel)
+                getParents _ = Nothing
+        updatedForest = mapM (addJoinConditions allColumns) forest
+        getJoinCondition rel@(Relation s t c _ _ _) = Condition <$> cc <*> pure "=" <*> pure (VForeignKey rel)
+            where
+                col = findColumn allColumns s t c
+                cc = (,) <$> col <*> pure Nothing
+        addCond q con = q{qWhere=con:qWhere q}
+
+
+dbRequestToQuery :: DbRequest -> Text
+dbRequestToQuery (Node (Select mainTable columns tables conditions relation) forest) =
+    case relation of
+        Nothing -> "SELECT "
+                  <> "pg_catalog.count(t),"
+                  <> "array_to_json(array_agg(row_to_json(t)))::CHARACTER VARYING AS json "
+                  <> "FROM ("
+                  <> query
+                  <> ") t;"
+
+        _         -> query
+    where
+        query = Data.Text.unwords [
+            ("WITH " <> intercalate ", " withs) `emptyOnNull` withs,
+            "SELECT ", intercalate ", " (map selectItemToStr columns ++ selects),
+            "FROM ", intercalate ", " (map pgFmtTable (mainTable:tables)),
+            ("WHERE " <> intercalate " AND " ( map pgFmtCondition conditions )) `emptyOnNull` conditions
+            ]
+        emptyOnNull val x = if null x then "" else val
+        (withs, selects) = foldr getQueryParts ([],[]) forest
+        --getQueryParts is not total but dbRequestToQuery is called only after addJoinConditions which ensures the only
+        --posible relations are Child Parent Many
+        getQueryParts :: Tree Query -> ([Text], [Text]) -> ([Text], [Text])
+        getQueryParts (Node q@(Select{qMainTable=table, qRelation=(Just (Relation {relType="child"}))}) forst) (w,s) = (w,sel:s)
+            where name = tableName table
+                  sel = "("
+                     <> "SELECT array_to_json(array_agg(row_to_json("<>name<>"))) "
+                     <> "FROM (" <> dbRequestToQuery (Node q forst) <> ") " <> name
+                     <> ") AS " <> name
+        getQueryParts (Node q@(Select{qMainTable=table, qRelation=(Just (Relation{relType="parent"}))}) forst) (w,s) = (wit:w,sel:s)
+            where name = tableName table
+                  sel = "row_to_json(" <> name <> ".*) AS "<>name --TODO must be singular
+                  wit = name <> " AS ( " <> dbRequestToQuery (Node q forst) <> " )"
+        -- getQueryParts (Node q@(Select{qMainTable=table, qRelation=(Just (Many _ _))}) forst) (w,s) = (w,sel:s)
+        --     where name = tableName table
+        --           sel = "("
+        --              <> "SELECT array_to_json(array_agg(row_to_json("<>name<>"))) "
+        --              <> "FROM (" <> dbRequestToQuery (Node q forst) <> ") " <> name
+        --              <> ") AS " <> name
+        -- the following is just to remove the warning, maybe relType should not be String?
+        getQueryParts (Node (Select{qRelation=Nothing}) _) _ = undefined
+        getQueryParts (Node (Select{qRelation=(Just (Relation {relType=_}))}) _) _ = undefined
+
+pgFmtCondition :: Condition -> Text
+pgFmtCondition (Condition (col,jp) ops val) = pgFmtColumn col <> pgFmtJsonPath jp  <> opToStr op <> valToStr val
+    where
+        op = pack ops
+        opToStr o = pgFmtOperator o
+        valToStr v = case v of
+            VText s -> pgFmtValue op s
+            VForeignKey (Relation{relFTable=table, relFColumn=column}) -> table <> "." <> column
+
+pgFmtColumn :: Column -> Text
+pgFmtColumn Column {colSchema=s, colTable=t, colName=c} = pgFmtIdent s <> "." <> pgFmtIdent t <> "." <> pgFmtIdent c
+pgFmtColumn Star {colSchema=s, colTable=t} = pgFmtIdent s <> "." <> pgFmtIdent t <> ".*"
+
+pgFmtJsonPath :: Maybe JsonPath -> Text
+pgFmtJsonPath (Just [x]) = "->>" <> (pgFmtLit $ pack x)
+pgFmtJsonPath (Just (x:xs)) = "->" <> pgFmtLit (pack x) <> pgFmtJsonPath ( Just xs )
+pgFmtJsonPath _ = ""
+
+pgFmtTable :: Table -> Text
+pgFmtTable Table{tableSchema=s, tableName=n} = fromQi $ QualifiedIdentifier s n
+
+selectItemToStr :: DbSelectItem -> Text
+selectItemToStr ((c, jp), Nothing) = pgFmtColumn c <> pgFmtJsonPath jp <> asJsonPath jp
+selectItemToStr ((c, jp), Just cast ) = "CAST (" <> pgFmtColumn c <> pgFmtJsonPath jp <> " AS " <> pack cast <> " )" <> asJsonPath jp
+
+asJsonPath :: Maybe JsonPath -> Text
+asJsonPath Nothing = ""
+asJsonPath (Just xx) = " AS " <> (pack $ last xx)

src/PostgREST/Parsers.hs

@@ -0,0 +1,154 @@
+--{-# LANGUAGE QuasiQuotes, ScopedTypeVariables, OverloadedStrings, FlexibleContexts #-}
+module PostgREST.Parsers
+-- ( parseGetRequest
+-- , pSelect
+-- , pField
+-- , pRequestSelect
+-- )
+
+where
+import           Text.ParserCombinators.Parsec hiding (many, (<|>))
+--import Text.Parsec.Text
+--import Text.Parsec hiding (many, (<|>))
+--import Text.Parsec.Prim hiding (many, (<|>))
+import           Control.Applicative
+--import Control.Monad
+--import qualified Data.Text                     as T
+import           Data.Tree
+import           Network.Wai                   (Request, pathInfo, queryString)
+import           PostgREST.Types
+--import qualified Data.ByteString.Char8 as C
+--import           Control.Monad
+--import           Data.Foldable                 (foldrM)
+import           Data.List                     (delete, find)
+import           Data.Maybe
+import           Data.String.Conversions       (cs)
+--import qualified Data.ByteString.Char8 as C
+
+--buildRequest :: String -> String -> [(String, String)] -> Either P.ParseError Request
+parseGetRequest :: Request -> Either ParseError ApiRequest
+parseGetRequest httpRequest =
+    foldr addFilter <$> apiRequest <*> flts
+    where
+        apiRequest = parse (pRequestSelect rootTableName) ("failed to parse select ("++selectStr++")") $ cs selectStr
+        flts = mapM pRequestFilter whereFilters
+        rootTableName = cs $ head $ pathInfo httpRequest -- TODO unsafe head
+        qString = [(cs k, cs <$> v)|(k,v) <- queryString httpRequest]
+        selectStr = fromMaybe "*" $ fromMaybe (Just "*") $ lookup "select" qString --in case the parametre is missing or empty we default to *
+        whereFilters = [ (k, fromJust v) | (k,v) <- qString, k `notElem` ["select"], isJust v ]
+
+pRequestSelect :: String -> Parser ApiRequest
+pRequestSelect rootNodeName = do
+    fieldTree <- pFieldForest
+    return $ foldr treeEntry (Node (RequestNode rootNodeName [] []) []) fieldTree
+    where
+        treeEntry :: Tree SelectItem -> Tree RequestNode -> Tree RequestNode
+        treeEntry (Node fld@((fn, _),_) fldForest) (Node rNode rForest) =
+            case fldForest of
+                [] -> Node (rNode {fields=fld:fields rNode}) rForest
+                _  -> Node rNode (foldr treeEntry (Node (RequestNode fn [] []) []) fldForest:rForest)
+
+pRequestFilter :: (String, String) -> Either ParseError (Path, Filter)
+pRequestFilter (k, v) = (,) <$> path <*> (Filter <$> fld <*> op <*> val)
+    where
+        treePath = parse pTreePath ("failed to parser tree path ("++k++")") k
+        opVal = parse pOpValueExp ("failed to parse filter ("++v++")") v
+        path = fst <$> treePath
+        fld = snd <$> treePath
+        op = fst <$> opVal
+        val = snd <$> opVal
+
+addFilter :: (Path, Filter) -> ApiRequest -> ApiRequest
+addFilter ([], flt) (Node rn@(RequestNode {filters=flts}) forest) = Node (rn {filters=flt:flts}) forest
+addFilter (path, flt) (Node rn forest) =
+    case targetNode of
+        Nothing -> Node rn forest -- the filter is silenty dropped in the Request does not contain the required path
+        Just tn -> Node rn (addFilter (remainingPath, flt) tn:restForest)
+    where
+        targetNodeName:remainingPath = path
+        (targetNode,restForest) = splitForest targetNodeName forest
+        splitForest name forst =
+            case maybeNode of
+                Nothing -> (Nothing,forest)
+                Just node -> (Just node, delete node forest)
+            where maybeNode = find ((name==).nodeName.rootLabel) forst
+
+ws :: Parser String
+ws = many (oneOf " \t")
+
+--lexeme :: Parser String -> Parser String
+--lexeme :: Text.Parsec.Prim.ParsecT String () Data.Functor.Identity.Identity a -> Text.Parsec.Prim.ParsecT String () Data.Functor.Identity.Identity a
+--lexeme :: Text.Parsec.Prim.ParsecT String () Data.Functor.Identity.Identity Char -> Text.Parsec.Prim.ParsecT String () Data.Functor.Identity.Identity Char
+lexeme p = ws *> p <* ws
+
+pTreePath :: Parser (Path,Field)
+pTreePath = do
+    p <- (pFieldName `sepBy1` pDelimiter)
+    --f <- pField
+    jp <- optionMaybe ( string "->" >>  pJsonPath)
+    return (init p, (last p, jp))
+
+
+pFieldForest :: Parser [Tree SelectItem]
+pFieldForest = pFieldTree `sepBy1` lexeme (char ',')
+
+pFieldTree :: Parser (Tree SelectItem)
+pFieldTree =
+    try ( do
+        fld <- pSelect
+        char '('
+        subforest <- pFieldForest
+        char ')'
+        return (Node fld subforest)
+        )
+    <|> do
+        fld <- pSelect
+        return (Node fld [])
+
+pStar :: Parser String
+pStar = string "*" *> pure "*"
+
+pFieldName :: Parser String
+pFieldName =  many1 (letter <|> digit <|> oneOf "_")
+          <?> "field name (* or [a..z0..9_])"
+
+pJsonPath :: Parser [String]
+pJsonPath = pFieldName `sepBy1` (try (string "->>") <|> string "->")
+
+pField :: Parser Field
+pField = lexeme $ do
+    f <- pFieldName
+    jp <- optionMaybe ( (try (string "->>") <|> string "->") >>  pJsonPath)
+    return (f, jp)
+
+pSelect :: Parser SelectItem
+pSelect = lexeme $
+    try (do
+        n <- pField
+        v <- optionMaybe (string "::" >> many letter)
+        return (n, v)
+        )
+    <|> do
+        s <- pStar
+        return ((s, Nothing), Nothing)
+
+pOperator :: Parser Operator
+pOperator =  try (string "eq")
+         <|> try (string "gt")
+         <|> try (string "lt")
+         <?> "operator (eq, gt, ...)"
+
+pInt :: Parser Int
+pInt = try (liftA read (many1 digit)) <?> "integer"
+
+--pValue :: Parser Value
+--pValue = (VInt <$> try (pInt <* eof))
+--      <|>(VString <$> many anyChar)
+pValue :: Parser FValue
+pValue = many anyChar
+
+pDelimiter :: Parser Char
+pDelimiter = char '.' <?> "delimiter (.)"
+
+pOpValueExp :: Parser (Operator, FValue)
+pOpValueExp = liftA2 (,) pOperator (pDelimiter *> pValue)

src/PostgREST/PgQuery.hs

@@ -222,35 +222,46 @@ wherePred table (col, predicate) =
     opCode        = hasNot (head rest) headPredicate
     notOp         = hasNot headPredicate ""
     value         = hasNot (T.intercalate "." $ tail rest) (T.intercalate "." rest)
-    whiteList val = fromMaybe
-      (cs (pgFmtLit val) <> "::unknown ")
-      (L.find ((==) . T.toLower $ val) ["null","true","false"])
+    sqlValue = pgFmtValue opCode value
+    op = pgFmtOperator opCode
+
+
+whiteList :: T.Text -> T.Text
+whiteList val = fromMaybe
+  (cs (pgFmtLit val) <> "::unknown ")
+  (L.find ((==) . T.toLower $ val) ["null","true","false"])
+
+pgFmtValue :: T.Text -> T.Text -> T.Text
+pgFmtValue opCode value =
+  case opCode of
+    "like" -> unknownLiteral $ T.map star value
+    "ilike" -> unknownLiteral $ T.map star value
+    "in" -> "(" <> T.intercalate ", " (map unknownLiteral $ T.split (==',') value) <> ") "
+    "notin" -> "(" <> T.intercalate ", " (map unknownLiteral $ T.split (==',') value) <> ") "
+    "@@" -> "to_tsquery(" <> unknownLiteral value <> ") "
+    _    -> unknownLiteral value
+  where
     star c = if c == '*' then '%' else c
     unknownLiteral = (<> "::unknown ") . pgFmtLit
 
-    sqlValue = case opCode of
-      "like" -> unknownLiteral $ T.map star value
-      "ilike" -> unknownLiteral $ T.map star value
-      "in" -> "(" <> T.intercalate ", " (map unknownLiteral $ T.split (==',') value) <> ") "
-      "notin" -> "(" <> T.intercalate ", " (map unknownLiteral $ T.split (==',') value) <> ") "
-      "@@" -> "to_tsquery(" <> unknownLiteral value <> ") "
-      _    -> unknownLiteral value
+pgFmtOperator :: T.Text -> T.Text
+pgFmtOperator opCode =
+  case opCode of
+    "eq"  -> "="
+    "gt"  -> ">"
+    "lt"  -> "<"
+    "gte" -> ">="
+    "lte" -> "<="
+    "neq" -> "<>"
+    "like"-> "like"
+    "ilike"-> "ilike"
+    "in"  -> "in"
+    "notin" -> "not in"
+    "is"    -> "is"
+    "isnot" -> "is not"
+    "@@" -> "@@"
+    _     -> "="
 
-    op = case opCode of
-      "eq"  -> "="
-      "gt"  -> ">"
-      "lt"  -> "<"
-      "gte" -> ">="
-      "lte" -> "<="
-      "neq" -> "<>"
-      "like"-> "like"
-      "ilike"-> "ilike"
-      "in"  -> "in"
-      "notin" -> "not in"
-      "is"    -> "is"
-      "isnot" -> "is not"
-      "@@" -> "@@"
-      _     -> "="
 
 orderParse :: Net.Query -> [OrderTerm]
 orderParse q =

src/PostgREST/Types.hs

@@ -1,5 +1,6 @@
 module PostgREST.Types where
 import Data.Text
+import Data.Tree
 
 data DbStructure = DbStructure {
   tables :: [Table]
@@ -34,7 +35,7 @@ data Column = Column {
 , colDefault :: Maybe Text
 , colEnum :: [Text]
 , colFK :: Maybe ForeignKey
-} deriving (Show)
+} | Star {colSchema :: Text, colTable :: Text } deriving (Show)
 
 data PrimaryKey = PrimaryKey {
   pkSchema::Text, pkTable::Text, pkName::Text
@@ -48,3 +49,26 @@ data Relation = Relation {
 , relFColumn :: Text
 , relType    :: Text
 } deriving (Show, Eq)
+
+
+--------
+-- Request Types
+type Operator = String
+type FValue = String
+type ApiRequest = Tree RequestNode
+type FieldName = String
+type JsonPath = [String]
+type Field = (FieldName, Maybe JsonPath)
+type Cast = String
+type SelectItem = (Field, Maybe Cast)
+type Path = [String]
+data RequestNode = RequestNode {nodeName::String, fields::[SelectItem], filters::[Filter]} deriving (Show, Eq)
+data Filter = Filter {field::Field, operator::Operator, value::FValue} deriving (Show, Eq)
+
+-- Db Request Types
+type DbField = (Column, Maybe JsonPath)
+type DbSelectItem = (DbField, Maybe Cast)
+data DbValue = VText Text | VForeignKey Relation deriving (Show)
+data Condition = Condition {conColumn::DbField, conOperator::Operator, conValue::DbValue} deriving (Show)
+data Query = Select {qMainTable::Table, qSelect::[DbSelectItem], qJoinTables::[Table], qWhere::[Condition], qRelation::Maybe Relation} deriving (Show)
+type DbRequest = Tree Query