hasql-0.19.10: A very efficient PostgreSQL driver and a flexible mapping API

Safe HaskellNone





data Session a Source

A batch of actions to be executed in the context of a database connection.

sql :: ByteString -> Session () Source

Possibly a multi-statement query, which however cannot be parameterized or prepared, nor can any results of it be collected.

query :: a -> Query a b -> Session b Source

Parameters and a specification of the parametric query to apply them to.


data Error Source

An error of some command in the session.


ClientError !(Maybe ByteString)

An error on the client-side, with a message generated by the "libpq" library. Usually indicates problems with connection.

ResultError !ResultError

Some error with a command result.

data ResultError Source

An error with a command result.


ServerError !ByteString !ByteString !(Maybe ByteString) !(Maybe ByteString)

An error reported by the DB. Consists of the following: Code, message, details, hint.

  • Code. The SQLSTATE code for the error. It's recommended to use the "postgresql-error-codes" package to work with those.
  • Message. The primary human-readable error message (typically one line). Always present.
  • Details. An optional secondary error message carrying more detail about the problem. Might run to multiple lines.
  • Hint. An optional suggestion on what to do about the problem. This is intended to differ from detail in that it offers advice (potentially inappropriate) rather than hard facts. Might run to multiple lines.
UnexpectedResult !Text

The database returned an unexpected result. Indicates an improper statement or a schema mismatch.

RowError !Int !RowError

An error of the row reader, preceded by the index of the row.

UnexpectedAmountOfRows !Int

An unexpected amount of rows.

data RowError Source

An error during the decoding of a specific row.



Appears on the attempt to parse more columns than there are in the result.


Appears on the attempt to parse a NULL as some value.

ValueError !Text

Appears when a wrong value parser is used. Comes with the error details.

run :: Session a -> Connection -> IO (Either Error a) Source

Executes a bunch of commands on the provided connection.