Automapper is an "object-object mapper" for .Net, which means copying objects from a class into another class that represents the same thing.
Why is this ever useful? Is the duplication of classes ever useful/good design?
A quick google search revealed this example:
showing a perfectly valid usage of AutoMapper which is definitely not an example for a poor design. In a layered application, you may have objects in your data or business layer, and you sometimes need just a subset of the attributes of that data objects, or some kind of view to them in your UI layer. So you create a view model which contains objects with exactly the attributes you need in your UI, not more, and use AutoMapper to provide the content of that objects with less boilerplate code.
In such a situation your "view objects" are not a duplicate of the original class. They have different methods and perhaps a few duplicate attributes. But that's ok as long as you use that view objects only for UI displaying purposes and don't start to misuse them for data manipulation or business operations.
Another topic you may read to get a better understanding of this is Fowlers Command Query Responsibility Segregation pattern, in contrast to CRUD. It shows you situations where different object models for querying data and updating them in a database make sense. Here, mapping from one object model to another may also be done by a tool like AutoMapper.
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