From 9cc2d958684b7c567018f9d4ae6567b96f36199a Mon Sep 17 00:00:00 2001
From: Maas-Maarten Zeeman <maas@channel.me>
Date: Sat, 5 Nov 2011 23:43:53 +0100
Subject: [PATCH] Exploring a pluggable generic sql database api

---
 src/gen_db.erl | 41 +++++++++++++++++++++++++++++++++++++++++
 src/sqlite.erl | 45 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 86 insertions(+)
 create mode 100644 src/gen_db.erl
 create mode 100644 src/sqlite.erl

diff --git a/src/gen_db.erl b/src/gen_db.erl
new file mode 100644
index 0000000..779a0af
--- /dev/null
+++ b/src/gen_db.erl
@@ -0,0 +1,41 @@
+%%
+%% Generic database interface. Sort of...
+%%
+%% Inspired by python's db api
+%%
+
+-module(gen_db).
+
+-export([behaviour_info/1]).
+
+-export([open/2, execute/2, execute/3, close/1]).
+
+behaviour_info(callbacks) ->
+    [{handle_open, 1},
+     {handle_execute, 3}, 
+     {handle_close, 1}];
+behaviour_info(_Other) ->
+    undefined.
+
+-record(gen_connection, {module, connection}).
+
+%% @doc Open a connection to a new database
+%%
+open(Module, ModuleArgs) ->
+    {ok, Conn} = Module:handle_open(ModuleArgs),
+    {ok, #gen_connection{module=Module, connection=Conn}}.
+    
+%% @doc Prepare and execute a database operation
+%%
+execute(Operation, Connection) ->
+    execute(Operation, [], Connection).
+
+%% @doc Prepare and execute a database operation
+%%
+execute(Operation, Args, #gen_connection{module=Module, connection=Connection}) ->    
+    Module:handle_execute(Operation, Args, Connection).
+
+%% @doc Close a database connection.
+%%
+close(#gen_connection{module=Module, connection=Connection}) ->
+    Module:handle_close(Connection).
diff --git a/src/sqlite.erl b/src/sqlite.erl
new file mode 100644
index 0000000..6e9eaec
--- /dev/null
+++ b/src/sqlite.erl
@@ -0,0 +1,45 @@
+-module(sqlite).
+
+-behaviour(gen_db).
+
+-export([handle_open/1, handle_execute/3, handle_close/1]).
+
+%% @doc Open a database connection
+%%
+handle_open(DatabaseName) ->
+    esqlite:open(DatabaseName).
+
+%% @doc Execute a query and return the results
+%%
+handle_execute(Operation, Args, Connection) ->
+    {ok, Stmt} = esqlite:prepare(Connection, Operation),
+    ok = esqlite:bind(Stmt, Args),
+    Answer = execute(Stmt),
+    %% TODO Finalize the statement.
+    Answer.
+
+
+%% @doc Close the connection
+%%
+handle_close(Connection) ->
+    esqlite:close(Connection).
+
+%% @doc
+%%
+execute(Statement) ->
+    execute(Statement, [], 0).
+
+%% @doc
+%%
+execute(_Statement, _Acc, Tries) when Tries > 5 ->
+    throw(too_many_tries);
+execute(Statement, Acc, Tries) ->
+    case esqlite:step(Statement) of
+	'$done' ->
+	    lists:reverse(Acc);
+	'$busy' ->
+	    timer:sleep(100), %% This is a bit lame... there is a trigger api for this.
+	    execute(Statement, Acc, Tries + 1);
+	V when is_tuple(V) ->
+	    execute(Statement, [V | Acc], 0)
+    end.