Database.PostgreSQL.Transact

Documentation

newtype DBT m a

Constructors

DBT

Fields

• unDBT :: ReaderT Connection m a

Instances

MonadTrans DBT

Methods

lift :: Monad m => m a -> DBT m a

Monad m => Monad (DBT m)

Methods

(>>=) :: DBT m a -> (a -> DBT m b) -> DBT m b

(>>) :: DBT m a -> DBT m b -> DBT m b

return :: a -> DBT m a

fail :: String -> DBT m a

Functor m => Functor (DBT m)

Methods

fmap :: (a -> b) -> DBT m a -> DBT m b

(<$) :: a -> DBT m b -> DBT m a

Applicative m => Applicative (DBT m)

Methods

pure :: a -> DBT m a

(<*>) :: DBT m (a -> b) -> DBT m a -> DBT m b

(*>) :: DBT m a -> DBT m b -> DBT m b

(<*) :: DBT m a -> DBT m b -> DBT m a

MonadIO m => MonadIO (DBT m)

Methods

liftIO :: IO a -> DBT m a

MonadThrow m => MonadThrow (DBT m)

Methods

throwM :: Exception e => e -> DBT m a

(MonadIO m, MonadMask m) => MonadCatch (DBT m)

Methods

catch :: Exception e => DBT m a -> (e -> DBT m a) -> DBT m a

type DB = DBT IO

isClass25 :: SqlError -> Bool

getConnection :: Monad m => DBT m Connection

runDBT :: MonadBaseControl IO m => DBT m a -> IsolationLevel -> Connection -> m a

runDBTSerializable :: MonadBaseControl IO m => DBT m a -> Connection -> m a

query :: (ToRow a, FromRow b, MonadIO m) => Query -> a -> DBT m [b]

Perform a SELECT or other SQL query that is expected to return results. All results are retrieved and converted before this function returns.

When processing large results, this function will consume a lot of client-side memory. Consider using fold instead.

Exceptions that may be thrown:

• FormatError: the query string could not be formatted correctly.
• QueryError: the result contains no columns (i.e. you should be using execute instead of query).
• ResultError: result conversion failed.
• SqlError: the postgresql backend returned an error, e.g. a syntax or type error, or an incorrect table or column name.

query_ :: (FromRow b, MonadIO m) => Query -> DBT m [b]

A version of query that does not perform query substitution.

execute :: (ToRow q, MonadIO m) => Query -> q -> DBT m Int64

Execute an INSERT, UPDATE, or other SQL query that is not expected to return results.

Returns the number of rows affected.

Throws FormatError if the query could not be formatted correctly, or a SqlError exception if the backend returns an error.

execute_ :: MonadIO m => Query -> DBT m Int64

A version of execute that does not perform query substitution.

executeMany :: (ToRow q, MonadIO m) => Query -> [q] -> DBT m Int64

Execute a multi-row INSERT, UPDATE, or other SQL query that is not expected to return results.

Returns the number of rows affected. If the list of parameters is empty, this function will simply return 0 without issuing the query to the backend. If this is not desired, consider using the Values constructor instead.

Throws FormatError if the query could not be formatted correctly, or a SqlError exception if the backend returns an error.

For example, here's a command that inserts two rows into a table with two columns:

executeMany [sql|
    INSERT INTO sometable VALUES (?,?)
 |] [(1, "hello"),(2, "world")]

Here's an canonical example of a multi-row update command:

executeMany [sql|
    UPDATE sometable
       SET sometable.y = upd.y
      FROM (VALUES (?,?)) as upd(x,y)
     WHERE sometable.x = upd.x
 |] [(1, "hello"),(2, "world")]

returning :: (ToRow q, FromRow r, MonadIO m) => Query -> [q] -> DBT m [r]

Execute INSERT ... RETURNING, UPDATE ... RETURNING, or other SQL query that accepts multi-row input and is expected to return results. Note that it is possible to write query conn "INSERT ... RETURNING ..." ... in cases where you are only inserting a single row, and do not need functionality analogous to executeMany.

If the list of parameters is empty, this function will simply return [] without issuing the query to the backend. If this is not desired, consider using the Values constructor instead.

Throws FormatError if the query could not be formatted correctly.