Postgrex v0.14.1 Postgrex View Source

PostgreSQL driver for Elixir.

This module handles the connection to Postgres, providing support for queries, transactions, connection backoff, logging, pooling and more.

Note that the notifications API (pub/sub) supported by Postgres is handled by Postgrex.Notifications. Hence, to use this feature, you need to start a separate (notifications) connection.

Link to this section Summary

Types

A connection process name, pid or reference

Functions

Returns a supervisor child specification for a DBConnection pool

Closes an (extended) prepared query and returns :ok or raises Postgrex.Error if there was an error. See close/3

Closes an (extended) prepared query and returns :ok or {:error, %Postgrex.Error{}} if there was an error. Closing a query releases any resources held by postgresql for a prepared query with that name. See Postgrex.Query for the query data

Runs an (extended) prepared query and returns the result or raises Postgrex.Error if there was an error. See execute/4

Runs an (extended) prepared query

Returns a cached map of connection parameters

Prepares an (extended) query and returns the prepared query or raises Postgrex.Error if there was an error. See prepare/4

Prepares an (extended) query and returns the result as {:ok, %Postgrex.Query{}} or {:error, %Postgrex.Error{}} if there was an error. Parameters can be set in the query as $1 embedded in the query string. To execute the query call execute/4. To close the prepared query call close/3. See Postgrex.Query for the query data

Prepares and runs a query and returns the result or raises Postgrex.Error if there was an error. See prepare_execute/5

Prepares and executes a query in a single step

Runs an (extended) query and returns the result or raises Postgrex.Error if there was an error. See query/3

Runs an (extended) query and returns the result as {:ok, %Postgrex.Result{}} or {:error, %Postgrex.Error{}} if there was a database error. Parameters can be set in the query as $1 embedded in the query string. Parameters are given as a list of elixir values. See the README for information on how Postgrex encodes and decodes Elixir values by default. See Postgrex.Result for the result data

Rollback a transaction, does not return

Start the connection process and connect to postgres

Returns a stream for a query on a connection

Acquire a lock on a connection and run a series of requests inside a transaction. The result of the transaction fun is return inside an :ok tuple: {:ok, result}

Link to this section Types

A connection process name, pid or reference.

A connection reference is used when making multiple requests to the same connection, see transaction/3.

Link to this section Functions

Returns a supervisor child specification for a DBConnection pool.

Link to this function close!(conn, query, opts \\ []) View Source
close!(conn(), Postgrex.Query.t(), Keyword.t()) :: :ok

Closes an (extended) prepared query and returns :ok or raises Postgrex.Error if there was an error. See close/3.

Link to this function close(conn, query, opts \\ []) View Source
close(conn(), Postgrex.Query.t(), Keyword.t()) :: :ok | {:error, Exception.t()}

Closes an (extended) prepared query and returns :ok or {:error, %Postgrex.Error{}} if there was an error. Closing a query releases any resources held by postgresql for a prepared query with that name. See Postgrex.Query for the query data.

This function may still raise an exception if there is an issue with types (ArgumentError), connection (DBConnection.ConnectionError), ownership (DBConnection.OwnershipError) or other error (RuntimeError).

Options

  • :queue - Whether to wait for connection in a queue (default: true);
  • :timeout - Close request timeout (default: 15000);
  • :mode - set to :savepoint to use a savepoint to rollback to before the close on error, otherwise set to :transaction (default: :transaction);

Examples

query = Postgrex.prepare!(conn, "", "CREATE TABLE posts (id serial, title text)")
Postgrex.close(conn, query)
Link to this function execute!(conn, query, params, opts \\ []) View Source

Runs an (extended) prepared query and returns the result or raises Postgrex.Error if there was an error. See execute/4.

Link to this function execute(conn, query, params, opts \\ []) View Source
execute(conn(), Postgrex.Query.t(), list(), Keyword.t()) ::
  {:ok, Postgrex.Query.t(), Postgrex.Result.t()} | {:error, Postgrex.Error.t()}

Runs an (extended) prepared query.

It returns the result as {:ok, %Postgrex.Query{}, %Postgrex.Result{}} or {:error, %Postgrex.Error{}} if there was an error. Parameters are given as part of the prepared query, %Postgrex.Query{}.

See the README for information on how Postgrex encodes and decodes Elixir values by default. See Postgrex.Query for the query data and Postgrex.Result for the result data.

Options

  • :queue - Whether to wait for connection in a queue (default: true);
  • :timeout - Execute request timeout (default: 15000);
  • :decode_mapper - Fun to map each row in the result to a term after decoding, (default: fn x -> x end);
  • :mode - set to :savepoint to use a savepoint to rollback to before the execute on error, otherwise set to :transaction (default: :transaction);

Examples

query = Postgrex.prepare!(conn, "", "CREATE TABLE posts (id serial, title text)")
Postgrex.execute(conn, query, [])

query = Postgrex.prepare!(conn, "", "SELECT id FROM posts WHERE title like $1")
Postgrex.execute(conn, query, ["%my%"])
Link to this function parameters(conn, opts \\ []) View Source
parameters(conn(), Keyword.t()) :: %{optional(binary()) => binary()}

Returns a cached map of connection parameters.

Options

  • :timeout - Call timeout (default: 15000)
Link to this function prepare!(conn, name, statement, opts \\ []) View Source
prepare!(conn(), iodata(), iodata(), Keyword.t()) :: Postgrex.Query.t()

Prepares an (extended) query and returns the prepared query or raises Postgrex.Error if there was an error. See prepare/4.

Link to this function prepare(conn, name, statement, opts \\ []) View Source
prepare(conn(), iodata(), iodata(), Keyword.t()) ::
  {:ok, Postgrex.Query.t()} | {:error, Exception.t()}

Prepares an (extended) query and returns the result as {:ok, %Postgrex.Query{}} or {:error, %Postgrex.Error{}} if there was an error. Parameters can be set in the query as $1 embedded in the query string. To execute the query call execute/4. To close the prepared query call close/3. See Postgrex.Query for the query data.

This function may still raise an exception if there is an issue with types (ArgumentError), connection (DBConnection.ConnectionError), ownership (DBConnection.OwnershipError) or other error (RuntimeError).

Options

  • :queue - Whether to wait for connection in a queue (default: true);
  • :timeout - Prepare request timeout (default: 15000);
  • :mode - set to :savepoint to use a savepoint to rollback to before the prepare on error, otherwise set to :transaction (default: :transaction);

Examples

Postgrex.prepare(conn, "", "CREATE TABLE posts (id serial, title text)")
Link to this function prepare_execute!(conn, name, statement, params, opts \\ []) View Source
prepare_execute!(conn(), iodata(), iodata(), list(), Keyword.t()) ::
  {Postgrex.Query.t(), Postgrex.Result.t()}

Prepares and runs a query and returns the result or raises Postgrex.Error if there was an error. See prepare_execute/5.

Link to this function prepare_execute(conn, name, statement, params, opts \\ []) View Source
prepare_execute(conn(), iodata(), iodata(), list(), Keyword.t()) ::
  {:ok, Postgrex.Query.t(), Postgrex.Result.t()} | {:error, Postgrex.Error.t()}

Prepares and executes a query in a single step.

It returns the result as {:ok, %Postgrex.Query{}, %Postgrex.Result{}} or {:error, %Postgrex.Error{}} if there was an error. Parameters are given as part of the prepared query, %Postgrex.Query{}.

See the README for information on how Postgrex encodes and decodes Elixir values by default. See Postgrex.Query for the query data and Postgrex.Result for the result data.

Options

  • :queue - Whether to wait for connection in a queue (default: true);
  • :timeout - Execute request timeout (default: 15000);
  • :decode_mapper - Fun to map each row in the result to a term after decoding, (default: fn x -> x end);
  • :mode - set to :savepoint to use a savepoint to rollback to before the execute on error, otherwise set to :transaction (default: :transaction);

Examples

Postgrex.prepare_and_execute(conn, "", "SELECT id FROM posts WHERE title like $1", ["%my%"])
Link to this function query!(conn, statement, params, opts \\ []) View Source
query!(conn(), iodata(), list(), Keyword.t()) :: Postgrex.Result.t()

Runs an (extended) query and returns the result or raises Postgrex.Error if there was an error. See query/3.

Link to this function query(conn, statement, params, opts \\ []) View Source
query(conn(), iodata(), list(), Keyword.t()) ::
  {:ok, Postgrex.Result.t()} | {:error, Exception.t()}

Runs an (extended) query and returns the result as {:ok, %Postgrex.Result{}} or {:error, %Postgrex.Error{}} if there was a database error. Parameters can be set in the query as $1 embedded in the query string. Parameters are given as a list of elixir values. See the README for information on how Postgrex encodes and decodes Elixir values by default. See Postgrex.Result for the result data.

This function may still raise an exception if there is an issue with types (ArgumentError), connection (DBConnection.ConnectionError), ownership (DBConnection.OwnershipError) or other error (RuntimeError).

Options

  • :queue - Whether to wait for connection in a queue (default: true);
  • :timeout - Query request timeout (default: 15000);
  • :decode_mapper - Fun to map each row in the result to a term after decoding, (default: fn x -> x end);
  • :mode - set to :savepoint to use a savepoint to rollback to before the query on error, otherwise set to :transaction (default: :transaction);

Examples

Postgrex.query(conn, "CREATE TABLE posts (id serial, title text)", [])

Postgrex.query(conn, "INSERT INTO posts (title) VALUES ('my title')", [])

Postgrex.query(conn, "SELECT title FROM posts", [])

Postgrex.query(conn, "SELECT id FROM posts WHERE title like $1", ["%my%"])

Postgrex.query(conn, "COPY posts TO STDOUT", [])
Link to this function rollback(conn, any) View Source
rollback(DBConnection.t(), any()) :: no_return()

Rollback a transaction, does not return.

Aborts the current transaction fun. If inside multiple transaction/3 functions, bubbles up to the top level.

Example

{:error, :oops} = Postgrex.transaction(pid, fn(conn) ->
  DBConnection.rollback(conn, :bar)
  IO.puts "never reaches here!"
end)
Link to this function start_link(opts) View Source
start_link(Keyword.t()) :: {:ok, pid()} | {:error, Postgrex.Error.t() | term()}

Start the connection process and connect to postgres.

Options

  • :hostname - Server hostname (default: PGHOST env variable, then localhost);
  • :socket_dir - Connect to Postgres via UNIX sockets in the given directory; The socket name is derived based on the port. This is the preferred method for configuring sockets and it takes precedence over the hostname. If you are connecting to a socket outside of the Postgres convention, use :socket instead;
  • :socket - Connect to Postgres via UNIX sockets in the given path. This option takes precedence over the :hostname and :socket_dir;
  • :port - Server port (default: PGPORT env variable, then 5432);
  • :database - Database (default: PGDATABASE env variable; otherwise required);
  • :username - Username (default: PGUSER env variable, then USER env var);
  • :password - User password (default: PGPASSWORD env variable);
  • :parameters - Keyword list of connection parameters;
  • :timeout - Socket receive timeout when idle in milliseconds (default: 15000);
  • :connect_timeout - Socket connect timeout in milliseconds (defaults to :timeout value);
  • :handshake_timeout - Connection handshake timeout in milliseconds (defaults to :timeout value);
  • :ssl - Set to true if ssl should be used (default: false);
  • :ssl_opts - A list of ssl options, see ssl docs;
  • :socket_options - Options to be given to the underlying socket (applies to both TCP and UNIX sockets);
  • :prepare - How to prepare queries, either :named to use named queries or :unnamed to force unnamed queries (default: :named);
  • :transactions - Set to :strict to error on unexpected transaction state, otherwise set to :naive (default: :strict);
  • :pool - The pool module to use, defaults to DBConnection.ConnectionPool. See the pool documentation for more options. The default :pool_size for the default pool is 1. If you set a different pool, this option must be included with all requests contacting the pool;
  • :types - The types module to use, see Postgrex.TypeModule, this option is only required when using custom encoding or decoding (default: Postgrex.DefaultTypes);
  • :disconnect_on_error_codes - List of error code atoms that when encountered will disconnect the connection (default: []);

Postgrex uses the DBConnection library and supports all DBConnection options like :idle, :after_connect etc. See DBConnection.start_link/2 for more information.

Examples

iex> {:ok, pid} = Postgrex.start_link(database: "postgres")
{:ok, #PID<0.69.0>}

Run a query after connection has been established:

iex> {:ok, pid} = Postgrex.start_link(after_connect: &Postgrex.query!(&1, "SET TIME ZONE 'UTC';", []))
{:ok, #PID<0.69.0>}

Connect to postgres instance through a unix domain socket

iex> {:ok, pid} = Postgrex.start_link(socket_dir: "/tmp", database: "postgres")
{:ok, #PID<0.69.0>}

PgBouncer

When using PgBouncer with transaction or statement pooling named prepared queries can not be used because the bouncer may route requests from the same postgrex connection to different PostgreSQL backend processes and discards named queries after the transactions closes. To force unnamed prepared queries set the :prepare option to :unnamed.

Handling failover

Some services, such as AWS Aurora, support failovers. This means the database you are currently connected to may suddenly become read-only, and an attempt to do any write operation, such as INSERT/UPDATE/DELETE will lead to errors such as:

11:11:03.089 [error] Postgrex.Protocol (#PID<0.189.0>) disconnected:
** (Postgrex.Error) ERROR 25006 (read_only_sql_transaction)
cannot execute INSERT in a read-only transaction

Luckily, you can instruct Postgrex to disconnect in such cases by using the following configuration:

disconnect_on_error_codes: [:read_only_sql_transaction]

This cause the connection process to attempt to reconnect according to the backoff configuration.

Link to this function stream(conn, query, params, options \\ []) View Source
stream(DBConnection.t(), iodata() | Postgrex.Query.t(), list(), Keyword.t()) ::
  Postgrex.Stream.t()

Returns a stream for a query on a connection.

Stream consumes memory in chunks of at most max_rows rows (see Options). This is useful for processing large datasets.

A stream must be wrapped in a transaction and may be used as an Enumerable or a Collectable.

When used as an Enumerable with a COPY .. TO STDOUT SQL query no other queries or streams can be interspersed until the copy has finished. Otherwise it is possible to intersperse enumerable streams and queries.

When used as a Collectable the values are passed as copy data with the query. No other queries or streams can be interspersed until the copy has finished. If the query is not copying to the database the copy data will still be sent but is silently discarded.

Options

  • :max_rows - Maximum numbers of rows in a result (default to 500)
  • :decode_mapper - Fun to map each row in the result to a term after decoding, (default: fn x -> x end);
  • :mode - set to :savepoint to use a savepoint to rollback to before an execute on error, otherwise set to :transaction (default: :transaction);

Examples

Postgrex.transaction(pid, fn(conn) ->
  query = Postgrex.prepare!(conn, "", "COPY posts TO STDOUT")
  stream = Postgrex.stream(conn, query, [])
  result_to_iodata = fn(%Postgrex.Result{rows: rows}) -> rows end
  Enum.into(stream, File.stream!("posts"), result_to_iodata)
end)

Postgrex.transaction(pid, fn(conn) ->
  stream = Postgrex.stream(conn, "COPY posts FROM STDIN", [])
  Enum.into(File.stream!("posts"), stream)
end)
Link to this function transaction(conn, fun, opts \\ []) View Source
transaction(conn(), (DBConnection.t() -> result), Keyword.t()) ::
  {:ok, result} | {:error, any()}
when result: var

Acquire a lock on a connection and run a series of requests inside a transaction. The result of the transaction fun is return inside an :ok tuple: {:ok, result}.

To use the locked connection call the request with the connection reference passed as the single argument to the fun. If the connection disconnects all future calls using that connection reference will fail.

rollback/2 rolls back the transaction and causes the function to return {:error, reason}.

transaction/3 can be nested multiple times if the connection reference is used to start a nested transaction. The top level transaction function is the actual transaction.

Options

  • :queue - Whether to wait for connection in a queue (default: true);
  • :timeout - Transaction timeout (default: 15000);
  • :mode - Set to :savepoint to use savepoints instead of an SQL transaction, otherwise set to :transaction (default: :transaction);

The :timeout is for the duration of the transaction and all nested transactions and requests. This timeout overrides timeouts set by internal transactions and requests. The :mode will be used for all requests inside the transaction function.

Example

{:ok, res} = Postgrex.transaction(pid, fn(conn) ->
  Postgrex.query!(conn, "SELECT title FROM posts", [])
end)