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digitalmars.D.learn - I want to transmit the class name and the member name in the method

reply Brian <zoujiaqing gmail.com> writes:
I think code style like:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

struct User
{
     int id;
     string name;
     string email;
}

class ORM
{
}

auto db = new ORM;
auto users = 
db.select(User).where(email.like("* hotmail.com")).limit(10);

foreach(user; users)
{
     writeln("user: " + user.name + "\n");
}

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

this rust code is support it:
https://github.com/diesel-rs/diesel/blob/master/examples/postgres/all_about_updates/src/lib.rs
Jan 04
next sibling parent reply user789 <user789 789.fi> writes:
On Friday, 5 January 2018 at 07:40:14 UTC, Brian wrote:
 I think code style like:
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 struct User
 {
     int id;
     string name;
     string email;
 }

 class ORM
 {
 }

 auto db = new ORM;
 auto users = 
 db.select(User).where(email.like("* hotmail.com")).limit(10);

 foreach(user; users)
 {
     writeln("user: " + user.name + "\n");
 }

 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 this rust code is support it:
 https://github.com/diesel-rs/diesel/blob/master/examples/postgres/all_about_updates/src/lib.rs
Well in D this would be more something like that: auto users = db.select!(User).map!(a => a.email.like("* hotmail.com")).take(10);
Jan 05
parent user789 <user789 789.fi> writes:
On Friday, 5 January 2018 at 08:34:00 UTC, user789 wrote:
 On Friday, 5 January 2018 at 07:40:14 UTC, Brian wrote:
 I think code style like:
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 struct User
 {
     int id;
     string name;
     string email;
 }

 class ORM
 {
 }

 auto db = new ORM;
 auto users = 
 db.select(User).where(email.like("* hotmail.com")).limit(10);

 foreach(user; users)
 {
     writeln("user: " + user.name + "\n");
 }

 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 this rust code is support it:
 https://github.com/diesel-rs/diesel/blob/master/examples/postgres/all_about_updates/src/lib.rs
Well in D this would be more something like that: auto users = db.select!(User).map!(a => a.email.like("* hotmail.com")).take(10);
Oh, I realize that your Q was more: "which package should i use to write this way ?"
Jan 05
prev sibling next sibling parent reply thedeemon <dlang thedeemon.com> writes:
On Friday, 5 January 2018 at 07:40:14 UTC, Brian wrote:
 I think code style like:
 db.select(User).where(email.like("* hotmail.com")).limit(10);
You need to read about templates in D, here's a good guide: https://github.com/PhilippeSigaud/D-templates-tutorial Basically you can write a function like auto select(Class, string fieldName)(Class value) { ... and call it later as select!(User, "name")(u); Here User and "name" are compile-time arguments, you can pass there types, values and more exotic stuff like other templates. And inside the function you can use __traits(getMember, u, fieldName) to get field by its name from the passed value. See: https://dlang.org/spec/traits.html
Jan 05
next sibling parent Michael <michael toohuman.io> writes:
On Friday, 5 January 2018 at 12:19:11 UTC, thedeemon wrote:
 On Friday, 5 January 2018 at 07:40:14 UTC, Brian wrote:
 I think code style like:
 db.select(User).where(email.like("* hotmail.com")).limit(10);
You need to read about templates in D, here's a good guide: https://github.com/PhilippeSigaud/D-templates-tutorial Basically you can write a function like auto select(Class, string fieldName)(Class value) { ... and call it later as select!(User, "name")(u); Here User and "name" are compile-time arguments, you can pass there types, values and more exotic stuff like other templates. And inside the function you can use __traits(getMember, u, fieldName) to get field by its name from the passed value. See: https://dlang.org/spec/traits.html
This was a really nice, short example btw. I'm not OP, but thanks for that.
Jan 05
prev sibling parent Brian <zoujiaqing gmail.com> writes:
On Friday, 5 January 2018 at 12:19:11 UTC, thedeemon wrote:
 On Friday, 5 January 2018 at 07:40:14 UTC, Brian wrote:
 I think code style like:
 db.select(User).where(email.like("* hotmail.com")).limit(10);
You need to read about templates in D, here's a good guide: https://github.com/PhilippeSigaud/D-templates-tutorial Basically you can write a function like auto select(Class, string fieldName)(Class value) { ... and call it later as select!(User, "name")(u); Here User and "name" are compile-time arguments, you can pass there types, values and more exotic stuff like other templates. And inside the function you can use __traits(getMember, u, fieldName) to get field by its name from the passed value. See: https://dlang.org/spec/traits.html
I can try it?: auto users = db.select!(User).where(User.email.like("* hotmail.com")).limit(10);
Jan 05
prev sibling next sibling parent reply Binghoo Dang <dangbinghoo gmail.com> writes:
On Friday, 5 January 2018 at 07:40:14 UTC, Brian wrote:
 I think code style like:
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 struct User
 {
     int id;
     string name;
     string email;
 }

 class ORM
 {
 }

 auto db = new ORM;
 auto users = 
 db.select(User).where(email.like("* hotmail.com")).limit(10);

 foreach(user; users)
 {
     writeln("user: " + user.name + "\n");
 }

 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 this rust code is support it:
 https://github.com/diesel-rs/diesel/blob/master/examples/postgres/all_about_updates/src/lib.rs
there's entity library exist in D Dub, which is an ORM framework, you may read the code for reference: https://code.dlang.org/packages/entity
Jan 05
parent Brian <zoujiaqing gmail.com> writes:
On Friday, 5 January 2018 at 15:38:17 UTC, Binghoo Dang wrote:
 On Friday, 5 January 2018 at 07:40:14 UTC, Brian wrote:
 I think code style like:
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 struct User
 {
     int id;
     string name;
     string email;
 }

 class ORM
 {
 }

 auto db = new ORM;
 auto users = 
 db.select(User).where(email.like("* hotmail.com")).limit(10);

 foreach(user; users)
 {
     writeln("user: " + user.name + "\n");
 }

 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 this rust code is support it:
 https://github.com/diesel-rs/diesel/blob/master/examples/postgres/all_about_updates/src/lib.rs
there's entity library exist in D Dub, which is an ORM framework, you may read the code for reference: https://code.dlang.org/packages/entity
Yes, [entity] is my team's project, I want it to be simpler :)
Jan 05
prev sibling parent reply Martin Nowak <code dawg.eu> writes:
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.
Jan 15
parent Martin Nowak <code dawg.eu> writes:
On Monday, 15 January 2018 at 15:28:19 UTC, Martin Nowak wrote:
 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.
If someone wants to see this happen, but doesn't have enough time to contribute, you could help to crowdfund this work, so I could afford to spent more time working on this. Get in contact with us for more details. https://dlang.org/donate.html
Jan 15