adam@2031: table images : { Id : int, Content : blob } adam@2031: table tags : { Id : int, Tag : string } adam@2031: adam@2031: datatype mode = Present | Absent adam@2031: type condition = { Tag : string, Mode : mode } adam@2031: adam@2031: type tag_query = sql_query [] [] [] [Id = int] adam@2031: adam@2031: fun addCondition (c : condition) (q : tag_query) : tag_query = adam@2031: case c.Mode of adam@2031: Present => (SELECT I.Id AS Id adam@2031: FROM ({{q}}) AS I adam@2031: JOIN tags ON tags.Id = I.Id AND tags.Tag = {[c.Tag]}) adam@2032: | Absent => (SELECT I.Id AS Id adam@2032: FROM ({{q}}) AS I adam@2032: LEFT JOIN tags ON tags.Id = I.Id AND tags.Tag = {[c.Tag]} adam@2032: WHERE tags.Tag IS NULL) adam@2031: adam@2031: fun withConditions (cs : list condition) : tag_query = adam@2031: List.foldl addCondition (SELECT images.Id AS Id FROM images) cs adam@2031: adam@2031: fun main (cs : list condition) : transaction page = adam@2031: x <- queryX (withConditions cs) (fn r =>
  • {[r.Id]}
  • ); adam@2031: return adam@2031: {x} adam@2031: