refactor: Split up Types.hs and logically organize modules (#1793)

src/PostgREST/DbStructure/Identifiers.hs

@@ -0,0 +1,28 @@
+{-# LANGUAGE DeriveAnyClass #-}
+{-# LANGUAGE DeriveGeneric  #-}
+
+module PostgREST.DbStructure.Identifiers
+  ( QualifiedIdentifier(..)
+  , Schema
+  , TableName
+  , FieldName
+  ) where
+
+import qualified Data.Aeson as JSON
+
+import Protolude
+
+
+-- | Represents a pg identifier with a prepended schema name "schema.table".
+-- When qiSchema is "", the schema is defined by the pg search_path.
+data QualifiedIdentifier = QualifiedIdentifier
+  { qiSchema :: Schema
+  , qiName   :: TableName
+  }
+  deriving (Eq, Ord, Generic, JSON.ToJSON, JSON.ToJSONKey)
+
+instance Hashable QualifiedIdentifier
+
+type Schema = Text
+type TableName = Text
+type FieldName = Text