CQRS Documents by Greg Young
Figure 10 The Query Side
The domain has been bypassed. There is now a new concept called a “Thin Read Layer�. This layer reads directly from the database and projects DTOs. There are many ways that this can be done with handwritten ADO.NET and mapping code and a full blown ORM on the high end. Which choice is right for a team depends largely on the team itself and what they are most comfortable with. Likely the best solution is something in the middle as much of what an ORM provides is not needed and large amounts of time will be lost manually creating mapping code. A possible solution would be to use a small convention based mapping utility. The Thin Read Layer need not be isolated from the database, it is not necessarily a bad thing to be tied to a database vendor from the read layer. It is also not necessarily bad to use stored procedures for reading, it again depends on the team and the non-functional requirements of the system. The Thin Read Layer is not a complex piece of code although it can be tedious to maintain. One benefit of the separate read layer is that it will not suffer from an impedance mismatch. It is connected directly to the data model, this can make queries much easier to optimize. Developers working on the Query http://cqrsinfo.com
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