with_transaction #2

[dominicletz]

On the original pull request there is unfortunately not much traction. But here is the grown version that I'm using in the mean time since. It has a couple of improvements on top of the initial with_transaction pull request.

• Server.with_transaction() becomes reentrancy safe. Instead of passing a pure Sqlitex db instance, it is passing it's own pid as parameters, and it's safe to call all Server.* methods on it without getting stuck in a GenServer self-call

• This allows faster query() within with_transaction() calls because the StatementCache of the Sqlitex.Server instance is now used.

BEFORE
      iex> Sqlitex.Server.with_transaction(server, fn(db) ->
      ...>   Sqlitex.exec(db, "create table foo(id integer)")
      ...>   Sqlitex.exec(db, "insert into foo (id) values(42)")
      ...> end)
NOW
      iex> Sqlitex.Server.with_transaction(server, fn(pid) ->
      ...>   Sqlitex.Server.query(pid, "create table foo(id integer)")
      ...>   Sqlitex.Server.query(pid, "insert into foo (id) values(42)")
      ...> end)

• This also allows calling Server.with_transaction() within a transaction -- double wrapping of the statement is avoided. So you can write small functions that execute transactions but reuse them in other transaction creating functions.

      iex> Sqlitex.Server.with_transaction(server, fn(pid) ->
      ...>   Sqlitex.Server.with_transaction(pid, fn(pid2) ->
      ...>     Sqlitex.Server.query(pid2, "create table foo(id integer)")
      ...>     Sqlitex.Server.query(pid2, "insert into foo (id) values(42)")
      ...>   end)
      ...> end)

• Errors in SQL statements within the Servers with_transaction are rescued as before but then rethrown in the context of the caller for easier debugging and locating of errors.

[coveralls]

Coverage increased (+0.3%) to 93.45% when pulling 6e79d79 on diodechain:with_tx into 1d47a6b on elixir-sqlite:master.

[ConnorRigby]

A very much welcome addition. Thanks for the hard work!

[dominicletz]

Ha, so the nicer debug output actually only compiles with Elixir > 1.7 because of __STACKTRACE__ not sure what to do about that. Is there away to have a compatibility switch?

[ConnorRigby]

This fails on CI for elixir 1.6 and older. I don't really mind breaking incompatibility with those versions, since i think this will be an API breaking change anyway. When this is released, i will remove CI and make note of the breakage in the changelog.