[odb-users] Feature request: relationships not in pointers

[Feiyun Wang]

Hi Boris,
Thanks for your info. That's really awesome!I tried the "points_to" feature and there are some problems:
Produce.h:````#pragma once
namespace orm{#pragma db object struct produce {#pragma db id auto int id;#pragma db points_to(factory) int id_factory;#pragma db points_to(product) int id_product; };
// #pragma db view object(produce) object(factory) object(product)#pragma db view object(produce) object(factory: produce::id_factory) object(product: produce::id_product) struct factory_produce_product {#pragma db column(produce::id) int id; int id_factory;#pragma db column(factory::name) std::string factory_name; int id_product;#pragma db column(product::name) std::string product_name; };}````
Building.h:````#pragma once#include <string>
#include "orm-pre.h"
namespace orm{#pragma db object abstract struct building {#pragma db id auto int id;#pragma db unique std::string name; int purchase_price; int base_costs_per_month; int demolition_costs;#pragma db default(1900) int start_year; };
#pragma db object struct factory : public building { int worker_costs_per_month; };// ... unrelated stuff omitted}````
Product.h:````#pragma once#include <string>
#include "orm-pre.h"
namespace orm{#pragma db object struct product {#pragma db id auto int id; std::string name; int costs_per_unit; int sell_price; int production_time;#pragma db default(1900) int start_year; };}````
orm-pre.h:````#pragma once#pragma db value(std::string) type("VARCHAR(45)")
````
runodb.bat:````set PATH=C:\build2\bin;%PATH%cd /d %~dp0where odb.exeECHO ===== Running odb.exe for MySQL MyISAModb.exe -d mysql --mysql-engine MyISAM --generate-schema --at-once --input-name AllTable --generate-query --generate-session --std c++14 Building.h Product.h Produce.h````
Output:````1>------ Build started: Project: TestApp, Configuration: Debug x64 ------1>C:\build2\bin\odb.exe1>===== Running odb.exe for MySQL MyISAM1>AllTable-odb.cxx1>g:\prj\industrygiant\src\orm\alltable-odb.cxx(4583): error C2679: binary '+=': no operator found which takes a right-hand operand of type 'const odb::query_columns<orm::produce,odb::id_mysql,A>::id_factory_type_' (or there is no acceptable conversion)1>        with1>        [1>            A=odb::access::object_traits_impl<orm::produce,odb::id_mysql>1>        ]1>g:\prj\industrygiant\src\include\odb\mysql\query.hxx(339): note: could be 'odb::mysql::query_base &odb::mysql::query_base::operator +=(const std::string &)'1>g:\prj\industrygiant\src\include\odb\mysql\query.hxx(336): note: or       'odb::mysql::query_base &odb::mysql::query_base::operator +=(const odb::mysql::query_base &)'1>g:\prj\industrygiant\src\orm\alltable-odb.cxx(4583): note: while trying to match the argument list '(odb::access::view_traits_impl<orm::factory_produce_product,odb::id_mysql>::query_base_type, const odb::query_columns<orm::produce,odb::id_mysql,A>::id_factory_type_)'1>        with1>        [1>            A=odb::access::object_traits_impl<orm::produce,odb::id_mysql>1>        ]1>g:\prj\industrygiant\src\orm\alltable-odb.cxx(4587): error C2679: binary '+=': no operator found which takes a right-hand operand of type 'const odb::query_columns<orm::produce,odb::id_mysql,A>::id_product_type_' (or there is no acceptable conversion)1>        with1>        [1>            A=odb::access::object_traits_impl<orm::produce,odb::id_mysql>1>        ]1>g:\prj\industrygiant\src\include\odb\mysql\query.hxx(339): note: could be 'odb::mysql::query_base &odb::mysql::query_base::operator +=(const std::string &)'1>g:\prj\industrygiant\src\include\odb\mysql\query.hxx(336): note: or       'odb::mysql::query_base &odb::mysql::query_base::operator +=(const odb::mysql::query_base &)'1>g:\prj\industrygiant\src\orm\alltable-odb.cxx(4587): note: while trying to match the argument list '(odb::access::view_traits_impl<orm::factory_produce_product,odb::id_mysql>::query_base_type, const odb::query_columns<orm::produce,odb::id_mysql,A>::id_product_type_)'1>        with1>        [1>            A=odb::access::object_traits_impl<orm::produce,odb::id_mysql>1>        ]1>Done building project "TestApp.vcxproj" -- FAILED.========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========````
AllTable-odb.cxx snippet:````  access::view_traits_impl< ::orm::factory_produce_product, id_mysql >::query_base_type  access::view_traits_impl< ::orm::factory_produce_product, id_mysql >::  query_statement (const query_base_type& q)  {    query_base_type r (      "SELECT "      "`produce`.`id`, "      "`produce`.`id_factory`, "      "`factory`.`name`, "      "`produce`.`id_product`, "      "`product`.`name` ");
    r += "FROM `produce`";
    r += " LEFT JOIN `factory` ON";    // From Produce.h:17:33    r += query_columns::produce::id_factory;
    r += " LEFT JOIN `product` ON";    // From Produce.h:17:70    r += query_columns::produce::id_product;
    if (!q.empty ())    {      r += " ";      r += q.clause_prefix ();      r += q;    }
    return r;  }````
Is there a special way to use "points_to" with "db view" (except using native view), or did I do something wrong?BTW, "#pragma db view object(produce) object(factory) object(product)" should have provided enough clues for the ODB compiler to work.
Sincerely,Feiyun Wang
P.S.As for lazy_ptr, "unload all the pointer before passing" will ease the burden somehow, but it is still risky as somebody could miss it.
   On Tuesday, July 24, 2018, 6:02:36 PM GMT+8, Boris Kolpackov <boris at codesynthesis.com> wrote:  
 
 Feiyun Wang <feiyunw at yahoo.com> writes:

> In the ODB manual, Chapter 6 Relationships:> Relationships between
> persistent objects are expressed with pointers or containers of pointers. I
> suggest to add the support for relationships expressed in the ODB pragma
> language.

This has already been implemented:

https://git.codesynthesis.com/cgit/odb/odb/commit/?id=e78db08d98d5adb4dee3006eea8c3569e383c562

It is not yet documented in the manual, but the basic usage is:

#pragma db object
class obj1
{
  #pragma db id
  int id;

  ...
};

#pragma db object
class obj2
{
  ...

  #pragma db points_to(obj1)
  int o1;
};


Note also that in your case you may also consider lazy object pointers. You
could just unload all the pointer before passing things to another thread.