one_to_many

children also works with a one-to-many relationship, but they are different in that children only gives you the many in the one-to-many relationship and only works with a single foreign key at a time.

Say you have a User and Role tables where each User has a role and a Role can be used by multiple users, with:

/*
This would give you all of the users with the Role `role`.
*/
auto res = role.children!(User, Role).execute(db);

However if you wanted to get the Role of a user there would be no way of doing so with children. It doesn't work the other way around.

Also the big thing that one_to_many can do and children can not do is handle multiple relationships(Multiple foreign keys pointing to the same Table for example:

import std.stdio;
import arsd.sqlite;
import arsd.database_generation;

alias FK(alias toWhat) = ForeignKey!(toWhat, null);

@DBName("Professor") struct Professor
{
    int id;
    string name;
}

@DBName("Course") struct Course
{
    int id;
    @FK!(Professor.id) int professor_id;
    @FK!(Professor.id) int assistant_id;
}

mixin(one_to_many!(Course.professor_id, "prof", "courses_taught"));
mixin(one_to_many!(Course.assistant_id, "assistant", "courses_assisted"));

void main()
{
    Database db = new Sqlite("test2.db");

    Course course = db.find!Course(1);
    Professor prof = course.get_prof(db);

    writeln(prof.get_courses_taught(db));
    writeln(prof.get_courses_assisted(db));
}

Here there are 2 relationships from Course to Professor here. One of them you can get from get_courses_taught and the other one with get_courses_assisted. If you attempt to use children like so

writeln(prof.children!(Course, Professor).execute(db));

You would get:

source/arsd/database_generation.d(489,2): Error: static assert: "Course does not have exactly one foreign key of type Professor"

In conclusion, children is nice in that its simple, doesn't require mixins to create extra symbols(functions). However it doesn't handle the one in one-to-many relationships at all, and it also doesn't work in tables with more than one relationship to a table. And finally, you might prefer the syntax of prof.get_courses(db) over prof.children!(Course, Professor).execute(db).