On Fri, Apr 6, 2012 at 11:28 AM, Jan-Henrik Haukeland
<hauk@tildeslash.com> wrote:
On Apr 6, 2012, at 7:21 PM, Joe Flemmings wrote:
> That would be nice but in lua you create a table in C that you pass to lua.
If you don't mind continue the discussion a little bit longer? I was curious and went and looked at lua and C integration (http://www.lua.org/pil/26.1.html) and came across this example for reading a directory which kind of maps conceptually to a result set.
static int l_dir (lua_State *L) {
DIR *dir;
struct dirent *entry;
int i;
const char *path = luaL_checkstring(L, 1);
/* open directory */
dir = opendir(path);
if (dir == NULL) { /* error opening the directory? */
lua_pushnil(L); /* return nil and ... */
lua_pushstring(L, strerror(errno)); /* error message */
return 2; /* number of results */
}
/* create result table */
lua_newtable(L);
i = 1;
while ((entry = readdir(dir)) != NULL) {
lua_pushnumber(L, i++); /* push key */
lua_pushstring(L, entry->d_name); /* push value */
lua_settable(L, -3);
}
closedir(dir);
return 1; /* table is already on top */
}
As far as I can see, lua tables are dynamic hash tables and from the example above there is no need to know the number of entries beforehand.
I simply rewrote the above example to this general C method that can be called from lua and will return any result set given any sql select statement. I have no idea if it will it will compile or has errors, but according to the documentation something like this should be possible. Maybe useful?
static int l_select (lua_State *L) {
int result = 1; /* table is on top if all goes well */
const char *select = luaL_checkstring(L, 1);
Connection_T c = ConnectionPool_getConnection(pool); // pool is usually global
TRY
{
ResultSet_T r = Connection_executeQuery(c, select);
/* create result table */
lua_newtable(L);
int columnCount = ResultSet_getColumnCount(r);
while (ResultSet_next(r)) {
for (int i = 1; i < columnCount; i++) {
lua_pushstring(L, ResultSet_getColumnName(r, i)); /* push column name */
lua_pushstring(L, ResultSet_getString(r, i)); /* push value as a string */
lua_settable(L, -3);
}
}
}
ELSE
{
lua_pushnil(L); /* return nil and ... */
lua_pushstring(L, Exception_frame.message); /* error message */
result = 2; /* number of results */
}
FINALLY
{
Connection_close(c);
}
END_TRY;
return result;