CQRS, Task Based UIs, Event Sourcing agh!

Original address: CQRS, Task Based UIs, Event Sourcing agh!

Many people has been getting confused over what CQRS is. They look at CQRS as being a architecture; It is not. CQRS is a very, simple pattern, enables many opportunities for architecture, so may otherwise not exist. CQRS is isn't eventual consistency, it's not eventing, it's not messaging, it's not has separated models for reading a nd writing, nor is it using event sourcing. I want to take a few paragraphs to describe first exactly what CQRS are and then how it relates to other patterns.

Many people have confused what CQRS is. They look at CQRS as a schema, but it's not. CQRS is a very simple pattern that makes many opportunities that may not exist in the architecture. CQRS is not a final consistency, it is not an event, it is not a message, it does not have a read-write separation pattern, nor does it use an event source. I want to describe a few paragraphs describing what is first CQRS and then how to relate to other patterns.

CQRS command and query Responsibility segregation CQRS commands and querying duty separation

Starting with CQRS, CQRS is simply the creation of both objects where there was previously only one. The separation occurs based upon whether the methods was a command or a query (the same definition that was used by Meyer I n Command and Query separation, a command is any method, the Mutates state and a query are any method that returns a value) .

From CQRS,CQRS just two objects there was only one creation before. Depending on whether the method of separation is a command or a query (the same definition is used by Meyer in commands and queries, any method that alters the state and the query uses a method of any return value).

When most people talk about CQRS they is really speaking about applying the CQRS pattern to the object that represents th E service boundary of the application. Consider the following Pseudo-code service definition.

When most people talk about CQRS they are really talking about the object that applies the CQRS pattern, representing the application's service boundary object. Consider the following pseudo-code service definition. CustomerService Customer Service

void Makecustomerpreferred (CUSTOMERID)
Customer GetCustomer (CustomerId)
Customerset Getcustomerswithname (Name)
Customerset Getpreferredcustomers ()
void Changecustomerlocale (CustomerId, Newlocale)
void CreateCustomer (Customer)
void Editcustomerdetails (customerdetails) applying CQRS on the This would result in two services application CQRS This will result in two service CUSTOMERWR Iteservice

void Makecustomerpreferred (CUSTOMERID)
void Changecustomerlocale (CustomerId, Newlocale)
void CreateCustomer (Customer)
void Editcustomerdetails (customerdetails) Customerreadservice

Customer GetCustomer (CustomerId)
Customerset Getcustomerswithname (Name)
Customerset Getpreferredcustomers ()

That's it. That's the entirety of the CQRS pattern. There is nothing more than it than that ... Doesn ' t seem nearly as interesting when we explain it is this to does it? This separation however enables us to do many interesting things architecturally, the largest was that it forces a break of The mental retardation that because the "the" the same data they should also use the same data model.

This is the entirety of the CQRS pattern. There is nothing more interesting than this, when we explain it, there seems to be nothing interesting? This separation makes our architecture do a lot of interesting things, the biggest is that it forces separation, because both uses should also use the same data model as the same data.

The largest possible benefit though is this it recognizes that their be different architectural properties when dealing W ith commands and queries ... for example it allows us to host the services differently Eg:we can host the Read service On servers and the write service on the. The processing of commands and queries is fundamentally asymmetrical, and scaling the services symmetrically does do A lot of sense.

The most likely benefit is that you can have different architectural features when processing commands and queries, for example, it allows us to host these two different services: we can read and write services on 25 servers, and do the writing service on 2 servers. The processing of commands and queries is fundamentally asymmetric, and scaling the service symmetrically does not make a lot of sense. Task Based UI-based user interface for tasks

A task based UI is the quite different from a CRUD based UI. In a task based UI, the user is doing, and you push forward commands representing the intent. I would like to the state once and for all that CQRS does not require a task based UI. We could apply CQRS to a CRUD based interface (though things like creating separated data models would is much harder).

The task-based user interface is a CRUD-based user interface that is completely different. In the task-based user interface, you can track what the user is doing and then push the command to the user to indicate the user's intentions. I think once and for all, CQRS does not need a task-based user interface. We can use CQRS to the Crud interface (although it is more difficult to create a separate data model).

There is however one thing that does really require a task based UI ... That's Domain driven Design.

However, there is one thing that requires a task-based user interface ... This is a domain-driven design.

The application Service Layer in Domain driven Design represents the tasks the system can perform. It does not just copy data to domain objects and save them ... It should is dealing with behaviors on the objects ... Before going further let's look at what happened if we do;  There would is no verbs in we ubiquitous language except for "Create", "Delete", and "change". While there exist many domains where the "what's the Ubiquitous Language is actually like" you probably should not being usi Ng Domain driven Design for such systems.

The application service layer represents the tasks that the system can perform in a domain-driven design. It does not just copy data to the domain objects and save them ... It should handle the behavior on the object ... Then let's see what happens if we do, our ubiquitous language, except "create", "delete", and "change". While there are many areas where the ubiquitous language is actually the same, you probably shouldn't use domain-driven design for such systems.

The concept of a task based UI is more often than not assumed to being part of CQRS, it's not, it's there so the domain can The verbs but also capturing the intent of the user are important in general. Is this a managerial override or a normal update? Does It make a difference? It depends on what question you want to ask ...

A user-interface-based task concept is often not considered part of the CQRS, it is not, it is so domain can have verbs also capture the user's intentions, in general is important. Is this an administrative override or a normal update? Does it have a difference? It depends on what you want to ask the question ...

Moving the next pattern that gets confused into CQRS

Event Sourcing Events Source

For the-I want to was clear, when I use the-term I am not encompassing all of the written on the Bliki. I am referring to storing current state as a series of events and rebuilding state within the system by replaying that Ser IES of events.

This to be clear, when I use the word I do not include all of what is written in Bliki. I am referring to a series of events that store the current state and the replay of this series of events in the system to reconstruct the state.

On the command side of the equation, since reads is no longer on the domain, storing events can be a great the The current state. The value increases more if you decide to has a separate models (a write model and a read model) and you had a need to Integrate between the them as you'll likely be doing that through events. Since You is building the eventing anyway, why isn't just use the one model to manage your state?
On this side of the command way, because the read is no longer on the domain, storing events can be a great way to keep the current state. If you decide to have 2 independent models (a write model and a read model), you have a need to integrate between the two, because you are likely to do these things through events. Now that you're building an event, why not just use a model to manage the state?

Messaging Patterns Message Mode

There is no need to use messaging patterns with CQRS. That's said, if you separate your data models you'll more likely than don't use messaging in the integration between the MoD Els because it offers interesting possibilities.

There is no need to use message mode with CQRS. That is, if you separate your data model, you are more likely than not to use a message-passing model because it provides interesting possibilities.

Finally I come to the last ' pattern ' I hate to call it a pattern when it's really a concept that people tend to put into Their definitions of CQRS and it goes hand in hand with messaging.
Finally I got to the last "mode", I hate to call it a pattern when it's a real concept, people tend to be more inclined to define it as CQRS, and the message goes hand in hand.

Eventual consistency final consistency

Eventual consistency is also quite often introduced between the services. It is do for many architectural reasons but the largest are that it allows you to increase your scalability and Availabil ity. If you remember caps theorem consistency if given up allows increases in the other. Eventual consistency is extremely useful in between the models if you had them in a separated fashion it's in no A property of CQRS itself.

The final consistency is also very often introduced between the two services. It is the reason to serve many architectures, but the biggest reason is that it allows you to increase scalability and availability. If you remember the consistency of the cap theorem, if you give up allow to add the other two. Eventual consistency is very useful between models, if you use them in terms of separation, but it is by no means the Cqrs property itself.

Going through all the these we can see this CQRS itself is actually a fairly trivial pattern. What is interesting around CQRS are not CQRS itself and the architectural properties in the integration of the services . In other words the interesting stuff are not really the CQRS pattern itself and in the architectural decisions so can be Made around it. Don ' t get me wrong there is a lot of interesting decisions so can be made around a system it has had CQRS AP Plied. Just don ' t confuse all of the those architectural decisions with CQRS itself.

Through these we can see that CQRS itself is actually a fairly common pattern. Interestingly, the CQRS does not cqrs itself, but in both of these services the integration architecture features. In other words, the interesting thing is not really the CQRS pattern itself, but it can be decided around the building. Don't get me wrong. I have a lot of interesting decisions that can be made in a system that has CQRS applications ... Just don't put all of these building decisions CQRS themselves.

On a personal note it feels so weird-to is writing to a blog again. Writing for a book are hard, and Writing for a blog are easy. Pages in the book average me a hour or more and this took me just over minutes to write. The less formal style allows one-to-write in a more stream of consciousness manner. Anyways, hope everyone enjoys the blog posts that'll be pouring on over the next short period.

In personal notes, blogging feels strange. It's hard to write a book, it's easy to write a blog. This book averages me one hours or more per hour, and it only took me 30 minutes to write. The less formal style allows people to write more consciousness in a conscious way. In any case, hopefully everyone will love a blog post that can be put into the next short period.

CQRS, Task Based UIs, Event Sourcing agh!