On Friday, 5 January 2018 at 07:40:14 UTC, Brian wrote:
auto db = new ORM;
auto users =
db.select(User).where(email.like("*@hotmail.com")).limit(10);
Expression templates are a dead-end for any non-trivial queries.
You have to embrace SQL to properly use RDMS, at the cost of
beginners having to learn it.
There is no free lunch and the inefficient queries ppl. are
running with Rails examplify what happens, when you pretend it's
possible to use technology without understanding it.
I'm actively working towards a design that allows full
compile-time typing with plain SQL commands. This will still take
a while, but I hope we can see an alpha in 2018H1.
http://dconf.org/2016/talks/nowak.html
alias schema = AliasSeq!(User, MailAddress, Book, Lending);
DB!schema db = DB!schema(SQLite("local.db")); // connecting
checks for missing/additional migrations
db = DB!schema(MySQL("localhost", 3306)); // DB wrapper is driver
agnostic
// Full ANSI SQL
// driver-specific functions when picking the driver at compile
time
// You can always exec dynamic queries on the underlying driver
foreach (r; db.exec!(q"SQL
SELECT u.name, m.addr, CONCAT(b.title, ';') books
FROM users u
JOIN mail_addresses m ON m.user_id = u.id AND NOT
u.can_overdraw
JOIN lendings l ON l.user_id = u.id AND DATEDIFF(NOW(),
l.end_date) >= 7
JOIN books b ON b.lending_id = l.id
WHERE b.amount < 20
GROUP BY u.id
SQL
)
sendMail(r.name, r.addr, r.books.splitter(';'));
More concise stuff is possible with heavy compile-time trickery
(https://dpaste.dzfl.pl/cd375ac594cf) without incurring dreaded
1+N queries or even any unnecessary SELECT fields.
foreach (u; db.select!User.where!"NOT can_overdraw")
{
sendMail(u.name, u.mail.addr, u.lendings // no 1+N here
.where!"DATEDIFF(NOW(), end_date) >= 7 AND book.amount <
20")
.map!(l => l.book.Reminder)); // client side range API
}
This has become even more of a challenge since we plan to make it
a @safe @nogc poster child.
If anyone wants to help with this project please contact me.
At the moment reworked @safe @nogc database drivers would be most
helpful.
I'll soon publish a small RC, Uniq, Weak library.
Unbuffered IO foundations are already here
https://github.com/MartinNowak/io, but not yet practically
proven, and still lacking vibe-core scheduler/eventcore
integration.
