Whether you're building a new application from scratch or enhancing an existing one with new functionality, being able to scale is very important to the life of your application. While some may say that you should just throw more hardware at the problem, designing your system up front properly will save you a number of headaches down the road. Command Query Responsibility Segregation (CQRS) is a pattern that helps you design your system to scale over time by taking messaging and applying it to commands your application issues and events that it raises. We'll see a very simple message distribution system and see how applying CQRS along with some event-driven concepts can help your application grow and scale over time. (Presented at the Rockville, MD .NET User Group on 12/11/2013.)

2. http://geekswithblogs.net/DavidHoerster
david@agileways.com

5. Business
Logic
Client
Searching
Black Box System
User Services
Data Store

6. Business
Logic
Client
Searching
Application System
User Services
Data Store

7. Client
Searching
Application System
User Services
Repository
Business
Logic
Data Store

8. Client
User Services
Repository
Repository
Business
Searching
Logic
Application System
Data Store

9. Repository
Searching
Client
Business
Logic
Application
System
User Services
Repository
Repository
Data Store

13. SearchRepo
Searching
Client
Business
Logic
Application
System
User Services
UserRepo
AppRepo
Data Store

14. Bounded Context
Search
Store
SearchRepo
Searching
Client
Business
Logic
Application
System
User Services
UserRepo
AppRepo
Data Store

17. Bounded Context
Search
Store
SearchRepo
Search Svc
Reads
Writes
Search
Queue
Handler
Client
Business
Logic
Application
System
User Services
UserRepo
AppRepo
Data Store

20. “every method should either be a command that performs an
action, or a query that returns data to the caller, but not both. In
other words, asking a question should not change the answer”
(Meyer)

25. Bounded Context
Search
Store
SearchRepo
Search Req’s
Writes
Reads
Search
Queue
Cmd
Handler
Search Domain
and Events
Cmd
Client
Business
Logic
Application
System
User Services
UserRepo
AppRepo
Data Store

26. Read Model
Command
Client
Repository /
Read Model
Command
Handler
Write Store
Domain
Read Store
Event(s)
Event
Handler(s)

27. public class CreatePlayer : CommandBase
{
public Int32 LahmanId { get; set; }
public String PlayerId { get; set; }
public String FirstName { get; set; }
public String LastName { get; set; }
public String NickName { get; set; }
public String College { get; set; }
public String Bats { get; set; }
public String Throws { get; set; }
public Int32 Height { get; set; }
public Int32 Weight { get; set; }
public DateTime? Debut { get; set; }
public DateTime? FinalGame { get; set; }
}

30. public class PlayerCreated : EventBase
{
public String FullName { get; set; }
public String PlayerId { get; set; }
}

31. public class PlayerHandler : IHandle<PlayerCreated>,
IHandle<PlayerYearAdded>
{
public void Handle(PlayerCreated theEvent)
{
//do something
}
public void Handle(PlayerYearAdded theEvent)
{
//do something else
}
}

34. SalesOrderHeader (SalesLT)
SalesOrderID
SalesOrderDetail (SalesLT)
SalesOrderID
SalesOrderDetailID
RevisionNumber
OrderQty
OrderDate
ProductID
DueDate
Product (SalesLT)
UnitPrice
ShipDate
ProductID
UnitPriceDiscount
Status
Name
LineTotal
OnlineOrderFlag
SalesOrderNumber
PurchaseOrderNumber
ProductNumber
rowguid
Color
ModifiedDate
StandardCost
AccountNumber
ListPrice
CustomerID
Size
ShipToAddressID
Weight
BillToAddressID
ProductCategoryID
ShipMethod
ProductModelID
CreditCardApprovalCode
SellStartDate
SubTotal
SellEndDate
TaxAmt
Freight
Customer (SalesLT)
ProductModel (SalesLT)
ProductCategory (SalesLT)
CustomerID
ProductModelID
NameStyle
Name
ParentProductCategoryID
Title
CatalogDescription
Name
FirstName
rowguid
rowguid
MiddleName
ModifiedDate
ModifiedDate
LastName
Suffix
CompanyName
SalesPerson
EmailAddress
ProductCategoryID

35. SELECT c.FirstName, c.MiddleName, c.LastName, soh.SalesOrderID, soh.OrderDate,
sod.UnitPrice, sod.OrderQty, sod.LineTotal,
p.Name as 'ProductName', p.Color, p.ProductNumber,
pm.Name as 'ProductModel',
pc.Name as 'ProductCategory',
pcParent.Name as 'ProductParentCategory'
FROM SalesLT.Customer c INNER JOIN SalesLT.SalesOrderHeader soh
ON c.CustomerID = soh.CustomerID
INNER JOIN SalesLT.SalesOrderDetail sod ON soh.SalesOrderID = sod.SalesOrderID
INNER JOIN SalesLT.Product p ON sod.ProductID = p.ProductID
INNER JOIN SalesLT.ProductModel pm ON p.ProductModelID = pm.ProductModelID
INNER JOIN SalesLT.ProductCategory pc ON p.ProductCategoryID = pc.ProductCategoryID
INNER JOIN SalesLT.ProductCategory pcParent ON pc.ParentProductCategoryID = pcParent.ProductCategoryID
WHERE c.FirstName = 'David'
AND soh.OrderDate > (GETDATE()-30)

36. SELECT FirstName, MiddleName, LastName, SalesOrderID, OrderDate,
UnitPrice, OrderQty, LineTotal, ProductName, Color, ProductNumber,
ProductModel, ProductCategory, ProductParentCategory
FROM CustomerSales
WHERE FirstName = 'David'
AND OrderDate > (GETDATE()-30)

38. Repository
(SolrNet)
Client
Web
Server
(Nancy)
Solr Service
Cmd
MongoDB
Event
Handler
Event
Cmd
MSMQ
Command
Handler
Domain

40. https://github.com/DavidHoerster/Conference
https://github.com/mspnp/cqrs-journey-doc
http://cqrs.wordpress.com/
http://groups.google.com/group/dddcqrs
http://www.udidahan.com/2009/12/09/clarified-cqrs/
http://abdullin.com/cqrs
http://distributedpodcast.com/

41. Query Side
Command Side
Client
Data Requested/Returned
Repository
Command Issued – ack/nack
Command Service
Domain (ARs)
Event Handler
Read Model Store
Denormalizer
Event Store