Should serialization logic be in the entity or other class

Question

Where should object serialization logic (the mapping of fields into XML or JSON names and values) be placed? Inside each entity object OR into a different set of classes onl

Answer 1

I would say the serialization logic should not be part of the POCO/data classes for many reasons:

1. Single Responsibility Principle (data classes should only define data model, note serialization logic)
2. There could be different kinds of serializers that you may require (json/xml etc. as you mentioned)
3. Serialization implementation most of the time is a generic solution or an external package. Even if you want custom implementation for some objects, still you can have a generic solution which you can extend for specific classes, so no need to have it for each class.
4. You can decorate your POCO classes with attributes to direct the serializer for special conditions (like to control sequence of properties, property names or even a customer serializer for complex type properties)

There will be other reasons as well but there are some strong arguments why you should not put the serialization logic into your POCO/Data Model.