Traction.QQ

Documentation

savepoint :: QuasiQuoter

schema :: QuasiQuoter

sql :: QuasiQuoter

sql is a quasiquoter that eases the syntactic burden of writing big sql statements in Haskell source code. For example:

{-# LANGUAGE QuasiQuotes #-}

query conn [sql| SELECT column_a, column_b
                   FROM table1 NATURAL JOIN table2
                  WHERE ? <= time AND time < ?
                    AND name LIKE ?
                  ORDER BY size DESC
                  LIMIT 100                        |]
           (beginTime,endTime,string)

This quasiquoter returns a literal string expression of type Query, and attempts to mimimize whitespace; otherwise the above query would consist of approximately half whitespace when sent to the database backend. It also recognizes and strips out standard sql comments "--".

The implementation of the whitespace reducer is currently incomplete. Thus it can mess up your syntax in cases where whitespace should be preserved as-is. It does preserve whitespace inside standard SQL string literals. But it can get confused by the non-standard PostgreSQL string literal syntax (which is the default setting in PostgreSQL 8 and below), the extended escape string syntax, quoted identifiers, and other similar constructs.

Of course, this caveat only applies to text written inside the SQL quasiquoter; whitespace reduction is a compile-time computation and thus will not touch the string parameter above, which is a run-time value.

Also note that this will not work if the substring |] is contained in the query.