monet

MonetDB driver


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A MonetDB driver for Elixir

Warning: Early development.

Usage

In your mix.exs file, add the project dependency:

{:monet, "~> 0.0.6"}

You can start a pool by adding Monet to your supervisor tree and providing configuration options:

opts = [
    pool_size: 10,
    port: 50_000,
    host: "127.0.0.1",
    username: "monetdb",
    password: "monetdb",
    database: "monetdb",
    read_timeout: 10_000,
    send_timeout: 10_000,
    connect_timeout: 10_000,
]
children = [
  ...
  {Monet, opts} 
]

You can then use the Monet.query/1 and Monet.query/2 functions:

{:ok, result} = Monet.query("create table atreides(name text)")
{:ok, result} = Monet.query("insert into attreides (name) values (?)", ["Leto"])

You can optionally use the query! variant.

Named Pool

When you create the pool, you have the option of providing a name This is useful in the case where you want to connect to multiple instances:

opts = [
 pool_size: 10,
 ...
 name: :replica
]

When a named pool is used, the query/2 and query/3 functions must be used:

{:ok, result} = Monet.query(:replica, "create table atreides(name text)")
{:ok, result} = Monet.query(:replica, "insert into atreides (name) values (?)", ["Paul"])

Results

On success, a Monet.Result structure is returned. The rows field exposes a list of list.

Monet.Result also implements the Enumerable and Jason.Encoder protocols. By default, these simply enumerate or render rows as a list of lists. However, Monet.as_map/1 can be used to change this behavior to iterate over a list of maps.

case Monet.as_map(Monet.query("select id, name from saiyans")) do
  {:ok, result} -> ...
  {:error, err} -> ...
end

as_map/1 is safe to chain with Monet.query as it will return any {:error, _} structure passed to it as-is.

Note that result.rows does not change. It continues to be a listof lists. What does change is the Enumerable and Jason encoding behavior.

Optionally, columns: :atoms can be passed to as_map.

Transactions

Monet.transaction/1 and Monet.transaction/2 (for named pools) can be used to wrap code in a transaction:

Monet.transaction(fn tx ->
  Monet.query!(tx, "insert into table...", [args])
  Monet.query!(tx, "select * from table")
end)

The function you provide can return:

  • {:rollback, value} - to rollback the transaction and return the same 2-value tuple
  • {:commit, value} - to commit the transaction and return {:ok, value}
  • {:ok, value} - to commit the transaction and return {:ok, value}
  • value - to commit the transaction and return {:ok, value}

Prepared Statements

Any calls to query which passes arguments will use a prepared statement.

Special handling of prepared within a transaction is available. Using Monet.prepare/3, prepared statements can be registered with a given name and re-used. At the end of the transaction, the prepared statements are automatically deallocated.

Monet.transaction(fn tx ->
  Monet.prepare(tx, :test_insert, "insert into test (id) values (?)")
  with {:ok, r1} <- Monet.query(tx, :test_insert, [1]),
       {:ok, r2} <- Monet.query(tx, :test_insert, [2])
  do
    {:ok, [r1, r2]}
  else
    err -> {:rollback, err}
  end
end)

Keep in mind that MonetDB automatically deallocates prepared statements on execution error. This is why having automatically management of prepared statements at the transaction level makes sense (since a failure to execute probably means the transaction ends). It's much more complicated at the connection level (especially when you add the indirection of the pool).