memorel

Load relational data into memory.

Example usage:

create table companies(id serial primary key, name varchar);
create table users(id serial primary key, name varchar, company_id integer);
insert into companies (name) VALUES ('ndrive'), ('github'), ('google');
insert into users (name, company_id) VALUES ('hugo', 1), ('john', 2), ('jane', 3), ('kate', 2), ('khan', NULL);

#include "memorel/has_many.h"
#include "memorel/belongs_to.h"
#include "memorel/relation.h"
#include "memorel/postgresql.h"

#include "hugopeixoto/enumerable_ostream.h"

#include <iostream>

struct User {
  uint64_t id;
  std::string name;
  Optional<uint64_t> company_id;
};

struct Company {
  uint64_t id;
  std::string name;
};

struct Users : public memorel::Relation<User> {
  OptionalBelongsTo<Company, &User::company_id> company;
};

struct Companies : public memorel::Relation<Company> {
  OptionalHasMany<User, &User::company_id> users;
};

template <> memorel::LoadInformation<User> memorel::Info() {
  return {"select id, name, company_id from users order by id;",
          [](auto result, auto &resource) {
    return Fetch(result, resource.id, resource.name, resource.company_id);
  }};
}

template <> memorel::LoadInformation<Company> memorel::Info() {
  return {"select id, name from companies order by id;",
          [](auto result, auto &resource) {
    return Fetch(result, resource.id, resource.name);
  }};
}

int main() {
  Users users;
  Companies companies;

  PGconn *connection = PQconnectdb("dbname=memorel host=localhost");

  Load(connection, users);
  Load(connection, companies);

  users.company.Load(companies);
  companies.users.Load(users);

  std::cout << "users: " << users.map(&User::name) << std::endl;
  std::cout << "companies: " << companies.map(&Company::name) << std::endl;

  for (auto u : users) {
    std::cout << u.name << " works for "
              << users.company(u).map(&Company::name).orDefault("no one")
              << std::endl;
  }

  for (auto c : companies) {
    std::cout << c.name << " employs "
              << companies.users.get(c).map(&User::name)
              << std::endl;
  }

  return 0;
}

Output:

users: (hugo, john, jane, kate, khan)
companies: (ndrive, github, google)
hugo works for ndrive
john works for github
jane works for google
kate works for github
khan works for no one
ndrive employs (hugo)
github employs (john, kate)
google employs (jane)