Mapping data between two similar structures seems to be a very common activity in the type of software I work on. Some examples:

• database to object
• DTO to object model
• XML to object
• JSON to object
• CSV to a object
• all the above the other way round

I'm not talking about serialisation, but subtle transformation with variations in naming and/or type conversion, some examples:

• ORDER_ID maps to OrderId (or just Id)
• nullable int maps to int (null is treated as zero)
• integers (or strings) are mapped to enums
• all the above the other way round

While some serialisation libraries try to have some features for transformation it does not seem to be treated as a separate concept.

In the .NET world configuration is popular, for example attributes on properties to control Entity Framework. I find configuration repetitive, as often transformations follow patterns.
Configuration is like writing a long list of "a1 maps to b1, a2 maps to b2, ...", where as convention allow you write a few rules like "map a to b like this..."

• Object of T to object of U
• IDataRecord to object of T
• IDataReader to sequence of T (common case of a single result)
• IDataReader to sequence of T1, T2, ... for multiple result data readers
• IXmlReader to object of T
• IXmlReader to sequence of T
• IJsonReader to object of T
• IJsonReader to sequence of T
• CSV reader to sequence of T
• all the above the other way round

Note: why is there no standard JSON Reader interface in .Net?