# `MyXQL`
[🔗](https://github.com/elixir-ecto/myxql/blob/v0.8.1/lib/myxql.ex#L1)

MySQL driver for Elixir.

# `conn`

```elixir
@type conn() :: DBConnection.conn()
```

# `option`

```elixir
@type option() :: DBConnection.option()
```

# `query_option`

```elixir
@type query_option() ::
  option()
  | {:query_type, :binary | :binary_then_text | :text}
  | {:cache_statement, iodata()}
```

# `start_option`

```elixir
@type start_option() ::
  {:protocol, :socket | :tcp}
  | {:socket, Path.t()}
  | {:socket_options, [:gen_tcp.connect_option()]}
  | {:hostname, String.t()}
  | {:port, :inet.port_number()}
  | {:database, String.t() | nil}
  | {:username, String.t()}
  | {:password, String.t() | nil}
  | {:charset, String.t() | nil}
  | {:collation, String.t() | nil}
  | {:ssl, boolean() | [:ssl.tls_client_option()]}
  | {:connect_timeout, timeout()}
  | {:handshake_timeout, timeout()}
  | {:ping_timeout, timeout()}
  | {:prepare, :force_named | :named | :unnamed}
  | {:disconnect_on_error_codes, [atom()]}
  | {:enable_cleartext_plugin, boolean()}
  | DBConnection.start_option()
```

# `stream_option`

```elixir
@type stream_option() :: option() | {:max_rows, pos_integer()}
```

# `child_spec`

```elixir
@spec child_spec([start_option()]) :: :supervisor.child_spec()
```

Returns a supervisor child specification for a DBConnection pool.

# `close`

```elixir
@spec close(conn(), MyXQL.Query.t() | MyXQL.Queries.t(), [option()]) :: :ok
```

Closes a prepared query.

Returns `:ok` on success, or raises an exception if there was an error.

## Options

Options are passed to `DBConnection.close/3`, see it's documentation for
all available options.

# `execute`

```elixir
@spec execute(conn(), MyXQL.Query.t(), list(), [option()]) ::
  {:ok, MyXQL.Query.t(), MyXQL.Result.t()} | {:error, Exception.t()}
```

Executes a prepared query that returns a single result.

## Options

Options are passed to `DBConnection.execute/4`, see it's documentation for
all available options.

## Examples

    iex> {:ok, query} = MyXQL.prepare(conn, "", "SELECT ? * ?")
    iex> {:ok, %MyXQL.Result{rows: [row]}} = MyXQL.execute(conn, query, [2, 3])
    iex> row
    [6]

# `execute!`

```elixir
@spec execute!(conn(), MyXQL.Query.t(), list(), keyword()) :: MyXQL.Result.t()
```

Executes a prepared query that returns a single result.

Returns `%MyXQL.Result{}` on success, or raises an exception if there was an error.

See: `execute/4`.

# `execute_many`

```elixir
@spec execute_many(conn(), MyXQL.Queries.t(), list(), [option()]) ::
  {:ok, MyXQL.Queries.t(), [MyXQL.Result.t()]} | {:error, Exception.t()}
```

Executes a prepared query that returns multiple results.

## Options

Options are passed to `DBConnection.execute/4`, see it's documentation for
all available options.

## Examples

    iex> {:ok, query} = MyXQL.prepare_many(conn, "", "CALL multi_procedure()")
    iex> {:ok, [%MyXQL.Result{rows: [row1]}, %MyXQL.Result{rows: [row2]}]} = MyXQL.execute_many(conn, query)
    iex> row1
    [2]
    iex> row2
    [3]

# `execute_many!`

```elixir
@spec execute_many!(conn(), MyXQL.Queries.t(), list(), keyword()) :: [
  MyXQL.Result.t()
]
```

Executes a prepared query that returns multiple results.

Returns `[%MyXQL.Result{}]` on success, or raises an exception if there was an error.

See: `execute_many/4`.

# `json_library`

```elixir
@spec json_library() :: module()
```

Returns the configured JSON library.

To customize the JSON library, include the following in your `config/config.exs`:

    config :myxql, json_library: SomeJSONModule

Defaults to `Jason`.

# `prepare`

```elixir
@spec prepare(conn(), iodata(), iodata(), [option()]) ::
  {:ok, MyXQL.Query.t()} | {:error, Exception.t()}
```

Prepares a query that returns a single result to be later executed.

To execute the query, call `execute/4`. To close the query, call `close/3`.
If a name is given, the name must be unique per query, as the name is cached
but the statement isn't. If a new statement is given to an old name, the old
statement will be the one effectively used.

## Options

Options are passed to `DBConnection.prepare/3`, see it's documentation for
all available options.

## Examples

    iex> {:ok, query} = MyXQL.prepare(conn, "", "SELECT ? * ?")
    iex> {:ok, %MyXQL.Result{rows: [row]}} = MyXQL.execute(conn, query, [2, 3])
    iex> row
    [6]

# `prepare!`

```elixir
@spec prepare!(conn(), iodata(), iodata(), [option()]) :: MyXQL.Query.t()
```

Prepares a query that returns a single result.

Returns `%MyXQL.Query{}` on success, or raises an exception if there was an error.

See `prepare/4`.

# `prepare_execute`

```elixir
@spec prepare_execute(conn(), iodata(), iodata(), list(), keyword()) ::
  {:ok, MyXQL.Query.t(), MyXQL.Result.t()} | {:error, Exception.t()}
```

Prepares and executes a query that returns a single result, in a single step.

## Options

Options are passed to `DBConnection.prepare_execute/4`, see it's documentation for
all available options.

## Examples

    iex> {:ok, _query, %MyXQL.Result{rows: [row]}} = MyXQL.prepare_execute(conn, "", "SELECT ? * ?", [2, 3])
    iex> row
    [6]

# `prepare_execute!`

```elixir
@spec prepare_execute!(conn(), iodata(), iodata(), list(), [option()]) ::
  {MyXQL.Query.t(), MyXQL.Result.t()}
```

Prepares and executes a query that returns a single result, in a single step.

Returns `{%MyXQL.Query{}, %MyXQL.Result{}}` on success, or raises an exception if there was
an error.

See: `prepare_execute/5`.

# `prepare_execute_many`

```elixir
@spec prepare_execute_many(conn(), iodata(), iodata(), list(), keyword()) ::
  {:ok, MyXQL.Queries.t(), [MyXQL.Result.t()]} | {:error, Exception.t()}
```

Prepares and executes a query that returns multiple results, in a single step.

A prepared statement may return multiple results if it is a stored procedure.
Any other type of prepared statement is not allowed to return multiple results
and will return an error.

## Options

Options are passed to `DBConnection.prepare_execute/4`, see it's documentation for
all available options.

## Examples

    iex> {:ok, _, [%MyXQL.Result{rows: [row1]}, %MyXQL.Result{rows: [row2]}]} = MyXQL.prepare_execute(conn, "", "CALL multi_procedure()")
    iex> row1
    [2]
    iex> row2
    [3]

# `prepare_execute_many!`

```elixir
@spec prepare_execute_many!(conn(), iodata(), iodata(), list(), [option()]) ::
  {MyXQL.Queries.t(), [MyXQL.Result.t()]}
```

Prepares and executes a query that returns multiple results, in a single step.

Returns `{%MyXQL.Queries{}, [%MyXQL.Result{}]}` on success, or raises an exception if there was
an error.

See: `prepare_execute_many/5`.

# `prepare_many`

```elixir
@spec prepare_many(conn(), iodata(), iodata(), [option()]) ::
  {:ok, MyXQL.Queries.t()} | {:error, Exception.t()}
```

Prepares a query that returns multiple results to be later executed.

A prepared statement may return multiple results if it is a stored procedure.
Any other type of prepared statement is not allowed to return multiple results
and will return an error.

To execute the query, call `execute_many/4`. To close the query, call `close/3`.
If a name is given, the name must be unique per query, as the name is cached.
If a new statement uses an old name, the old statement will be closed.

## Options

Options are passed to `DBConnection.prepare/3`, see it's documentation for
all available options.

## Examples

    iex> {:ok, query} = MyXQL.prepare_many(conn, "", "CALL multi_procedure()")
    iex> {:ok, [%MyXQL.Result{rows: [row1]}, %MyXQL.Result{rows: [row2]}]} = MyXQL.execute_many(conn, query, [2, 3])
    iex> row1
    [2]
    iex> row2
    [3]

# `prepare_many!`

```elixir
@spec prepare_many!(conn(), iodata(), iodata(), [option()]) :: MyXQL.Queries.t()
```

Prepares a query that returns multiple results.

Returns `%MyXQL.Queries{}` on success, or raises an exception if there was an error.

See `prepare_many/4`.

# `query`

```elixir
@spec query(conn(), iodata(), list(), [query_option()]) ::
  {:ok, MyXQL.Result.t()} | {:error, Exception.t()}
```

Runs a query that returns a single result.

## Text queries and prepared statements

MyXQL supports MySQL's two ways of executing queries:

  * text protocol - queries are sent as text

  * binary protocol - used by prepared statements

    The query statement is still sent as text, however it may contain placeholders for parameter
    values.

    Prepared statements have following benefits:

      * better performance: less overhead when parsing the query by the DB engine
      * better performance: binary protocol for encoding parameters and decoding result sets is more efficient
      * protection against SQL injection attacks

    The drawbacks of prepared statements are:

      * not all statements are preparable
      * requires two roundtrips to the DB server: one for preparing the statement and one for executing it.
        This can be alleviated by holding on to prepared statement and executing it multiple times.

## Options

  * `:query_type` - use `:binary` for binary protocol (prepared statements), `:binary_then_text` to attempt
    executing a binary query and if that fails fallback to executing a text query, and `:text` for text protocol
    (default: `:binary`)

  * `:cache_statement` - caches the query with the given name. Opposite to the `name` option
    given to `prepare/4`, if the cache statement name is reused with a different, the previous
    query is automatically closed

Options are passed to `DBConnection.execute/4` for text protocol, and
`DBConnection.prepare_execute/4` for binary protocol. See their documentation for all available
options.

## Examples

    iex> MyXQL.query(conn, "CREATE TABLE posts (id serial, title text)")
    {:ok, %MyXQL.Result{}}

    iex> MyXQL.query(conn, "INSERT INTO posts (title) VALUES ('title 1')")
    {:ok, %MyXQL.Result{last_insert_id: 1, num_rows: 1}}

    iex> MyXQL.query(conn, "INSERT INTO posts (title) VALUES (?)", ["title 2"])
    {:ok, %MyXQL.Result{last_insert_id: 2, num_rows: 1}}

# `query!`

```elixir
@spec query!(conn(), iodata(), list(), [query_option()]) :: MyXQL.Result.t()
```

Runs a query that returns a single result.

Returns `%MyXQL.Result{}` on success, or raises an exception if there was an error.

See `query/4`.

# `query_many`

```elixir
@spec query_many(conn(), iodata(), list(), [query_option()]) ::
  {:ok, [MyXQL.Result.t()]} | {:error, Exception.t()}
```

Runs a query that returns multiple results.

A query may return multiple results if it is a text
query with statements separated by semicolons or a stored
procedure. Any prepared statement that is not a stored
procedure is not allowed to return multiple results and will
return an error.

For more information on text queries and prepared statements,
see `query/4`.

## Options

  * `:query_type` - Use `:binary` for binary protocol (prepared statements), `:binary_then_text` to attempt
    executing a binary query and if that fails fallback to executing a text query, and `:text` for text protocol
    (default: `:binary`).

  * `:cache_statement` - Caches the query with the given name. If the cache statement
    name is reused with a different statement, the previous query is automatically closed.

Options are passed to `DBConnection.execute/4` for text protocol, and
`DBConnection.prepare_execute/4` for binary protocol. See their documentation for all available
options.

## Examples

    iex> MyXQL.query_many(conn, "SELECT 1; SELECT 2;", [], query_type: :text)
    {:ok, [%MyXQL.Result{rows: [[1]]}, %MyXQL.Result{rows: [[2]]}]}

# `query_many!`

```elixir
@spec query_many!(conn(), iodata(), list(), [query_option()]) :: [MyXQL.Result.t()]
```

Runs a query that returns multiple results.

Returns `[%MyXQL.Result{}]` on success, or raises an exception if there was an error.

See `query_many/4`.

# `rollback`

```elixir
@spec rollback(DBConnection.t(), any()) :: no_return()
```

Rollback a transaction, does not return.

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

## Example

    {:error, :oops} =
      MyXQL.transaction(pid, fn conn  ->
        MyXQL.rollback(conn, :oops)
        IO.puts "never reaches here!"
      end)

# `start_link`

```elixir
@spec start_link([start_option()]) :: GenServer.on_start()
```

Starts the connection process and connects to a MySQL server.

## Options

  * `:protocol` - Set to `:socket` for using UNIX domain socket, or `:tcp` for TCP
    (default: `:socket`)

    Connecting using UNIX domain socket is the preferred method. If `:hostname` or `:port` is
    set, protocol defaults to `:tcp` unless `:socket` is set too.

  * `:socket` - Connect to MySQL via UNIX domain socket in the given path
    (default: `MYSQL_UNIX_PORT` env variable, then `"/tmp/mysql.sock"`)

  * `:socket_options` - Options to be given to the underlying socket, applies to both TCP and
    UNIX sockets. See `:gen_tcp.connect/3` for more information.  (default: `[]`)

  * `:hostname` - Server hostname (default: `MYSQL_HOST` env variable, then `"localhost"`)

  * `:port` - Server port (default: `MYSQL_TCP_PORT` env variable, then `3306`)

  * `:database` - Database (default: `nil`)

  * `:username` - Username (default: `USER` env variable)

  * `:password` - Password (default: `MYSQL_PWD` env variable, then `nil`)

  * `:charset` - A connection charset. On connection handshake, the charset is set to `utf8mb4`,
    but if this option is set, an additional `SET NAMES <charset> [COLLATE <collation>]` query
    will be executed after establishing the connection. `COLLATE` will be added if `:collation`
    is set. (default: `nil`)

  * `:collation` - A connection collation. Must be given with `:charset` option, and if set
    it overwrites the default collation for the given charset. (default: `nil`)

  * `:ssl` - Enables SSL. Setting it to `true` enables SSL without server certificate verification,
    which emits a warning. Instead, prefer to set it to a keyword list, with either
    `:cacerts` or `:cacertfile` set to a CA trust store, to enable server certificate
    verification. (default: `false`)

  * `:connect_timeout` - Socket connect timeout in milliseconds (default:
    `15_000`)

  * `:handshake_timeout` - Connection handshake timeout in milliseconds (default: `15_000`)

  * `:ping_timeout` - Socket receive timeout when idle in milliseconds (default:
    `15_000`). See `c:DBConnection.ping/1` for more information

  * `:prepare` - How to cache prepared queries. Queries can be named or unnamed. Named
    queries are cached, unnamed queries are never cache by default. The possible values
    for this option are:

      * `:named` - cache only named queries
      * `:unnamed` - treat all queries as unnamed (i.e. nothing is ever cached)
      * `:force_named` - treat all queries as named (i.e. everything is cached)

    Note that MySQL has a global limit on the number of prepared queries. So if you
    enable `:force_named` in production, you may cache more queries than allowed by
    MySQL, leading to disconnections and user errors. Use `:force_named` only in a
    controlled environment, such as `:test`, and in `:prod` only if you are monitoring
    the prepare statement count of your databases (such as using a dashboard or
    setting alarm handlers)

  * `:disconnect_on_error_codes` - List of error code integers or atoms that when encountered
    will disconnect the connection. See "Disconnecting on Errors" section below for more
    information.

  * `:enable_cleartext_plugin` - Set to `true` to send password as cleartext (default: `false`)

 The given options are passed down to DBConnection, some of the most commonly used ones are
 documented below:

  * `:after_connect` - A function to run after the connection has been established, either a
    1-arity fun, a `{module, function, args}` tuple, or `nil` (default: `nil`)

  * `:pool` - The pool module to use, defaults to built-in pool provided by DBconnection

  * `:pool_size` - The size of the pool

See `DBConnection.start_link/2` for more information and a full list of available options.

## Examples

Start connection using the default configuration (UNIX domain socket):

    iex> {:ok, pid} = MyXQL.start_link([])
    {:ok, #PID<0.69.0>}

Start connection over TCP:

    iex> {:ok, pid} = MyXQL.start_link(protocol: :tcp)
    {:ok, #PID<0.69.0>}

Start connection with SSL using CA certificate file:

    iex> {:ok, pid} = MyXQL.start_link(ssl: [cacertfile: System.fetch_env!("DB_CA_CERT_FILE")])
    {:ok, #PID<0.69.0>}

Run a query after connection has been established:

    iex> {:ok, pid} = MyXQL.start_link(after_connect: &MyXQL.query!(&1, "SET time_zone = '+00:00'"))
    {:ok, #PID<0.69.0>}

## Disconnecting on errors

Sometimes the connection becomes unusable. For example, services such as AWS Aurora support
failover which means the database you are currently connected to may suddenly become
read-only. An attempt to do any write operation, such as INSERT/UPDATE/DELETE will lead to
errors such as:

    ** (MyXQL.Error) (1792) (ER_CANT_EXECUTE_IN_READ_ONLY_TRANSACTION) Cannot execute statement in a READ ONLY transaction.

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

    disconnect_on_error_codes: [:ER_CANT_EXECUTE_IN_READ_ONLY_TRANSACTION]

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

MyXQL automatically disconnects the connection on the following error codes and they don't have
to be configured:

  * `:ER_MAX_PREPARED_STMT_COUNT_REACHED`

You can pass error codes as integers too:

    disconnect_on_error_codes: [1792]

## Error codes

MyXQL maintains a mapping of integers/atoms for commonly used errors. You can add additional
ones by adding the following compile-time configuration:

    config :myxql, :extra_error_codes, [
      {1048, :ER_BAD_NULL_ERROR}
    ]

After adding the configuration, MyXQL needs to be recompiled. It can be done with:

    $ mix deps.clean myxql --build

To convert error code integers to names you can use `perror` command-line utility that ships
with MySQL client installation, e.g.:

    bash$ perror 1792
    MySQL error code 1792 (ER_CANT_EXECUTE_IN_READ_ONLY_TRANSACTION): Cannot execute statement in a READ ONLY transaction.

# `stream`

```elixir
@spec stream(DBConnection.t(), iodata() | MyXQL.Query.t(), list(), [stream_option()]) ::
  DBConnection.PrepareStream.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`.

## Options

  * `:max_rows` - Maximum numbers of rows in a result (default: `500`)

Options are passed to `DBConnection.stream/4`, see it's documentation for
other available options.

## Examples

    {:ok, results} =
      MyXQL.transaction(pid, fn conn ->
        stream = MyXQL.stream(conn, "SELECT * FROM integers", [], max_rows: max_rows)
        Enum.to_list(stream)
      end)

Suppose the `integers` table contains rows: 1, 2, 3, 4 and `max_rows` is set to `2`.
We'll get following results:

    # The first item is result of executing the query and has no rows data
    Enum.at(results, 0)
    #=> %MyXQL.Result{num_rows: 0, ...}

    # The second item is result of fetching rows 1 & 2
    Enum.at(results, 1)
    #=> %MyXQL.Result{num_rows: 2, rows: [[1], [2]]}

    # The third item is result of fetching rows 3 & 4
    Enum.at(results, 2)
    #=> %MyXQL.Result{num_rows: 2, rows: [[3], [4]]}

Because the total number of fetched rows happens to be divisible by our chosen `max_rows`,
there might be more data on the server so another fetch attempt is made.
Because in this case there weren't any more rows, the final result has 0 rows:

    Enum.at(results, 3)
    #=> %MyXQL.Result{num_rows: 0}

However, if the table contained only 3 rows, the 3rd result would contain:

    Enum.at(results, 2)
    #=> %MyXQL.Result{num_rows: 1, rows: [[3]]}

And that would be the last result in the stream.

# `transaction`

```elixir
@spec transaction(conn(), (DBConnection.t() -&gt; result), [option()]) ::
  {: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

Options are passed to `DBConnection.transaction/3`, see it's documentation for
all available options.

## Examples

    {:ok, result} =
      MyXQL.transaction(pid, fn conn  ->
        MyXQL.query!(conn, "SELECT title FROM posts")
      end)

---

*Consult [api-reference.md](api-reference.md) for complete listing*