Serializing Cyclical Objects

To serialize objects that contains Cyclical References it would be needed to use the annotation @cyclical. If this annotation is present and the depth variable is not set then the non-primitive objects are not going to be parsed and only the id or hashmap is going to be present. Let's see next to objects:

    library example;
    
    import 'package:dson/dson.dart';
    
    @MirrorsUsed(targets:const['example'],override:'*')
    import 'dart:mirrors';
    
    @cyclical
    class Employee {
      int id;
      String firstName;
      String lastName;
      
      Address address;
      
      Employee manager;
    }
    
    @cyclical
    class Address {
      int id;
      String street;
      String city;
      String country;
      String postalCode;
      
      Employee owner;
    }
    
    
    void main() {
  
      var manager = new Employee()
        ..id = 1
        ..firstName = 'Jhon'
        ..lastName = 'Doe';
      manager.address = new Address()
          ..id = 1
          ..street = 'some street'
          ..city = 'Miami'
          ..country = 'USA'
          ..owner = manager;
    
      var employee = new Employee()
        ..id = 2
        ..firstName = 'Luis'
        ..lastName = 'Vargas'
        ..manager = manager;
      employee.address = new Address()
        ..id = 2
        ..street = 'some street'
        ..city = 'Miami'
        ..country = 'USA'
        ..owner = employee;
        
      print(serialize(employee)); //will print: '{"id":2,"firstName":"Luis","lastName":"Vargas","address":{"id":2},"manager":{"id":1}}'
      
      print(serialize(employee.address)); // will print: '{"id":2,"street":"some street","city":"Miami","country":"USA","owner":{"id":2}}'
      
      // depth is a optional parameter that could be a list that should contains strings or Maps<String, Map>
      print(serialize(employee, depth: ['address']));
      /* will print:
               '{"id":2,"firstName":"Luis","lastName":"Vargas",'
                  '"address":{"id":2,"street":"some street","city":"Miami","country":"USA","owner":{"id":2}},'
                  '"manager":{"id":1}}'
      */
      
      print(serialize(employee, depth: [{'manager': ['address']}, 'address']));
      /* will print:
             '{"id":2,"firstName":"Luis","lastName":"Vargas",'
                '"address":{"id":2,"street":"some street","city":"Miami","country":"USA",'
                  '"owner":{"id":2}},'
                '"manager":{"id":1,"firstName":"Jhon","lastName":"Doe",'
                  '"address":{"id":1,"street":"some street","city":"Miami","country":"USA","owner":{"id":1}}}}');
      */
    }

as you can see employee has an address and the address has the employee as owner. If the property id is not present in the object then it is going to take the hashcode value from the object as reference. And finally, the depth parameter passed to serialize function tells serializer how deep you want to go throw the reference. This help us not only to avoid cyclical reference, but to determine what referenced objects should be serialized.

The same applies for lists:

    library example;

    import 'package:dson/dson.dart';
    
    @MirrorsUsed(targets:const['example'],override:'*')
    import 'dart:mirrors';
    
    @cyclical
    class Student {
      int id;
      String name;
      
      List<Course> courses;
    }
    
    @cyclical
    class Course {
      int id;
      
      DateTime beginDate;
      
      List<Student> students;
    }
    
    void main() {
    
      print(serialize(student1)); // will print: '{"id":1,"name":"student1","courses":[{"id":1},{"id":3}]}'
    
      print(serialize(student1, depth: ['courses']));
      /* will print:
          '{'
            '"id":1,'
            '"name":"student1",'
            '"courses":['
              '{"id":1,"beginDate":"2015-01-01T00:00:00.000Z","students":[{"id":1},{"id":2}]},'
              '{"id":3,"beginDate":"2015-01-03T00:00:00.000Z","students":[{"id":1},{"id":3}]}'
            ']'
          '}');
       */
    
      print(serialize(student1.courses)); 
      /* will print:
          '['
            '{"id":1,"beginDate":"2015-01-01T00:00:00.000Z","students":[{"id":1},{"id":2}]},'
            '{"id":3,"beginDate":"2015-01-03T00:00:00.000Z","students":[{"id":1},{"id":3}]}'
          ']');
      */
      
      print(serialize(student2.courses, depth: ['students']));
      /* will print: 
          '['
            '{"id":1,"beginDate":"2015-01-01T00:00:00.000Z","students":['
              '{"id":1,"name":"student1","courses":[{"id":1},{"id":3}]},'
              '{"id":2,"name":"student2","courses":[{"id":1},{"id":2}]}'
            ']},'
            '{"id":2,"beginDate":"2015-01-02T00:00:00.000Z","students":['
              '{"id":2,"name":"student2","courses":[{"id":1},{"id":2}]},'
              '{"id":3,"name":"student3","courses":[{"id":2},{"id":3}]}'
            ']}'
          ']'
       */
   }

Without the annotation @cyclical the program is going to throw a stack overflow error caused by the serializing of cyclical objects.