[Haskell-cafe] ANNOUNCE postgresql-query and postgresql-config

Alexey Uimanov s9gf4ult at gmail.com
Sun Mar 1 12:30:36 UTC 2015

Hi guys! Here is yet another some-level library to work with PostgreSQL DB.


This library uses `postgresql-query` and is a list of helpers/workarounds
to generate
complex queries more safely and parse result.

What it contains:

1. interplating quasiquote `sqlExp` which uses instances of `ToField`
typeclass to paste
   values inside query.
   It looks like this:

   let val = "'hello'" :: Text
       q = [sqlExp|SELECT field1 FROM tbl WHERE field2 = #{val}|]

   where `val` is an arbitrary Haskell expression which type has instance
of `ToField`
   Resulting query will be like:

   "SELECT field1 FROM tbl WHERE field2 = '''hello'''"

   Yes, proper string escaping is performed authomatically like using this
   queries with parameters.

   Resulting type of quasiquote is `SqlBuilder` which uses bytestring
builders inside and
   can be concatenated efficiently.

   There is also posibility to paste one query inside another like:

   let q2 = [sqlExp|SELECT field1 f FROM (^{q}) WHERE field1 is not null|]

   so `q2` will generate nested query.

   sqlExp also removes SQL comments and removes long sequences of space
characters. It also
   properly handles string literals and quoted identifiers inside

2. Typeclass `HasPostgres`, simple connection reader `PgMonadT` and
functions like
   `pgQuery` to perform queries.


3. TH functions to authomatically derive `FromRow` and `ToRow` instances
   (from postgresql-simple)


4. Some kind of primitive pre-ORM which generates queries for CRUD-ing
simple record types.
   It looks like:

    data User = User
      { userName              :: !Text
      , userPasswordEncrypted :: !Text
      } deriving (Show, Eq, Ord, Typeable)

    type UserId = EntityId User

    $(deriveFromRow ''User)
    $(deriveToRow ''User)

    instance Entity User where
        newtype EntityId User
            = UserId { unUserId :: UUID } -- Note that you can use any type
for id
            deriving (Show, Read, Ord, Eq,
                      FromField, ToField, PathPiece) -- To use with Yesod
        tableName _ = "users"
        fieldNames _ = [ "name"
                       , "password_encrypted" ]

    runPgMonadT con $ do
      uid <- pgInsertEntity $ User "name" "j27dna74ja784ha7"
      pgUpdateEntity uid $ MR [("name", mkValue "John")]
      pgDeleteEntity uid

There is also package http://hackage.haskell.org/package/postgresql-config
which contains trivial code
to make your postgresql-simple connection pool easily configurable.
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