[odb-users] Re: Recursive Loading Issue with Mutual Aggregation in ODB Classes

[xuewen wang]

I fixed the mistake mentioned in the previous email, but the recursive
querying still exists.
here are odb class headers and SQL log.
Best regards...
---- Sean Wang (Xuewen Wang), Beijing, China.


On Sat, Aug 3, 2024 at 11:23 AM xuewen wang <xuewen.ok at gmail.com> wrote:

> Sorry, all,
> It is my fault that I used the wrong inverse(id) keyword; it used the
> second class's id but not the inverse member id.
> Best regards...
> ---- Sean Wang (Xuewen Wang), Beijing, China.
>
>
> On Fri, Aug 2, 2024 at 11:21 PM xuewen wang <xuewen.ok at gmail.com> wrote:
>
>> Dear ODB Development Team,
>>
>> I am writing to report a potential issue with the ODB ORM system when two
>> model classes include or aggregate each other. This mutual aggregation can
>> lead to recursive loading problems when querying records from the database.
>>
>> ### Example Scenario
>>
>> Consider the following two classes, `Person` and `Address`, where each
>> `Person` has an `Address` and each `Address` has a `Person`.
>>
>> #### Person.hxx
>> cpp
>> #pragma once
>>
>> #include <memory>
>> #include <odb/core.hxx>
>> #include "Address.hxx"
>>
>> #pragma db object
>> class Person
>> {
>> public:
>>     Person() = default;
>>     Person(const std::string& name, std::shared_ptr<Address> address)
>>         : name_(name), address_(address) {}
>>
>>     const std::string& name() const { return name_; }
>>     std::shared_ptr<Address> address() const { return address_; }
>>
>> private:
>>     friend class odb::access;
>>
>>     #pragma db id auto
>>     unsigned long id_;
>>     std::string name_;
>>
>>     #pragma db not_null
>>     std::shared_ptr<Address> address_;
>> };
>> #### Address.hxx
>> cpp
>> #pragma once
>>
>> #include <memory>
>> #include <odb/core.hxx>
>> #include "Person.hxx"
>>
>> #pragma db object
>> class Address
>> {
>> public:
>>     Address() = default;
>>     Address(const std::string& street, std::shared_ptr<Person> person)
>>         : street_(street), person_(person) {}
>>
>>     const std::string& street() const { return street_; }
>>     std::shared_ptr<Person> person() const { return person_; }
>>
>> private:
>>     friend class odb::access;
>>
>>     #pragma db id auto
>>     unsigned long id_;
>>     std::string street_;
>>
>>     #pragma db not_null
>>     std::shared_ptr<Person> person_;
>> };
>> ### Issue
>>
>> When querying a `Person` from the database, ODB will try to load the
>> associated `Address`. While loading the `Address`, ODB will again try to
>> load the associated `Person`, leading to a recursive loop.
>>
>> ### Query Example
>> cpp
>> #include <odb/database.hxx>
>> #include <odb/transaction.hxx>
>> #include <odb/sqlite/database.hxx>
>> #include "Person.hxx"
>> #include "Person-odb.hxx"
>> #include "Address.hxx"
>> #include "Address-odb.hxx"
>>
>> int main()
>> {
>>     std::shared_ptr<odb::database> db(new
>> odb::sqlite::database("test.db", SQLITE_OPEN_READWRITE |
>> SQLITE_OPEN_CREATE));
>>
>>     // Start a transaction
>>     odb::transaction t(db->begin());
>>
>>     // Query a person by id
>>     std::shared_ptr<Person> person(db->load<Person>(1));
>>
>>     // Commit the transaction
>>     t.commit();
>>
>>     // Access the person's address
>>     std::shared_ptr<Address> address = person->address();
>>
>>     return 0;
>> }
>> In this example, loading a `Person` will recursively load the `Address`,
>> which will again try to load the `Person`, causing a recursive call.
>>
>> ### Request
>>
>> Could you please look into this issue and provide a resolution or
>> workaround?
>>
>> Thank you for your attention to this matter.
>>
>> Best regards,
>>
>
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