Stuff About CQRS

Jak Charlton@JakCharlton

jak@thinkddd.com

Disclaimer:This Isn’t All AboutCommand Query

ResponsibilitySegregation

does anyone here even know what CQRS is anyway, or were the other sessions full?

Another Disclaimer:There won’t be any code,

I don’t do code,just opinions

My Objective Today

My Objective Todayis to Make You Think

My Objective Todayis to Make You Think

“Maybe There Is A Better Way?”

Why Don’t We Talk Like “Normal” People Do?

Why Don’t We Talk Like “Normal” People Do?

Developers are usually techy

Why Don’t We Talk Like “Normal” People Do?

Developers are usually techy

Business people usually don’t understand “techy”

Why Don’t We Talk Like “Normal” People Do?

Developers are usually techy

Business people usually don’t understand “techy”

So why do we try to make them think like we do?

Why Does Language Matter So Much?

Why Does Language Matter So Much?

Without language, we cannot convey meaning

Why Does Language Matter So Much?

Without language, we cannot convey meaning

But when we talk different languages, we lose in the translation

Why Does Language Matter So Much?

Without language, we cannot convey meaning

But when we talk different languages, we lose in the translation

Let’s agree on one

How Do “Normal” People See the World?

How Do “Normal” People See the World?

People don’t think in terms of “data”

How Do “Normal” People See the World?

People don’t think in terms of “data”

People think “tasks”

How Do “Normal” People See the World?

People don’t think in terms of “data”

People think “tasks”

People are objective based, only computers work on data

Otherwise Known As “Grid Abuse”

Otherwise Known As “Grid Abuse”

Grids are a UI problem created by developers

Otherwise Known As “Grid Abuse”

Grids are a UI problem created by developers

People don’t see information in columns and rows

Otherwise Known As “Grid Abuse”

Grids are a UI problem created by developers

People don’t see information in columns and rows

Even Excel doesn’t force you to think that way

If People Don’t Think In Grids, Why Force Data Into Grids?

If People Don’t Think In Grids, Why Force Data Into Grids?Developers are ingrained with RDBMS Rows and Columns

If People Don’t Think In Grids, Why Force Data Into Grids?Developers are ingrained with RDBMS Rows and Columns

Business information doesn’t come in rows and columns

If People Don’t Think In Grids, Why Force Data Into Grids?Developers are ingrained with RDBMS Rows and Columns

Business information doesn’t come in rows and columns

We forced them to store and use it that way

Thinking AboutNoSQL Databases

Thinking AboutNoSQL Databases

If users think about things like “my documents” maybe we should just store stuff that way?

Thinking AboutNoSQL Databases

If users think about things like “my documents” maybe we should just store stuff that way?

NoSQL databases let us concentrate on what to store, not how

Quick Summary

Quick Summary

People need to communicate

Quick Summary

People need to communicate

People think Tasks

Quick Summary

People need to communicate

People think Tasks

People think “stuff” or “documents” or “things”

What Does This Have to Do With CQRS ???

What Does This Have to Do With CQRS ???

Not much ...

What Does This Have to Do With CQRS ???

Not much ...

Yet...

What Does This Have to Do With CQRS ???

Not much ...

Yet...

One more step... now we get a bit techy

CAP Theory

CAP Theory

Consistency: The client perceives that a set of operations has occurred all at once.

CAP Theory

Consistency: The client perceives that a set of operations has occurred all at once.

Availability: Every operation must terminate in an intended response.

CAP Theory

Consistency: The client perceives that a set of operations has occurred all at once.

Availability: Every operation must terminate in an intended response.

Partition tolerance: Operations will complete, even if individual components are unavailable.

CAP Theory

Consistency: The client perceives that a set of operations has occurred all at once.

Availability: Every operation must terminate in an intended response.

Partition tolerance: Operations will complete, even if individual components are unavailable.

You cannot have all three

ACID

ACID

Atomic, Consistent, Isolated, Durable

ACID

Atomic, Consistent, Isolated, Durable

In CAP Theory terms ACID gives you:

ACID

Atomic, Consistent, Isolated, Durable

In CAP Theory terms ACID gives you:

Consistency and Availability

ACID

Atomic, Consistent, Isolated, Durable

In CAP Theory terms ACID gives you:

Consistency and Availability

But Sacrifices Partition Tolerance

BASE

BASE

Basically Available, Soft state, Eventually consistent

BASE

Basically Available, Soft state, Eventually consistent

In CAP Theory BASE gives you:

BASE

Basically Available, Soft state, Eventually consistent

In CAP Theory BASE gives you:

Availability and Partition Tolerance

BASE

Basically Available, Soft state, Eventually consistent

In CAP Theory BASE gives you:

Availability and Partition Tolerance

But Sacrifices Consistency

Command Query Responsibility Segregation

Command Query Responsibility Segregation

Bertrand Meyer principle of CQS:every method should either be a command that performs an action, or a query that returns data to the caller

Command Query Responsibility Segregation

Bertrand Meyer principle of CQS:every method should either be a command that performs an action, or a query that returns data to the caller

At an architectural level this means:either issue commands, or issue queries, but never both

Command Query Responsibility Segregation

Bertrand Meyer principle of CQS:every method should either be a command that performs an action, or a query that returns data to the caller

At an architectural level this means:either issue commands, or issue queries, but never both

And, query from a separate source from your domain commands

CQRS and BASE

CQRS and BASE

CQRS gives us BASE at an architectural level

CQRS and BASE

CQRS gives us BASE at an architectural level

We may not always be consistent

CQRS and BASE

CQRS gives us BASE at an architectural level

We may not always be consistent

But most data isn’t consistent in reality anyway, we just think it is

CQRS and BASE

CQRS gives us BASE at an architectural level

We may not always be consistent

But most data isn’t consistent in reality anyway, we just think it is

Eventually our architecture will be consistent

CQRS in a Picture

Client

Domain

Command

Persist

PublishEvent HandlersEvent Handlers

Update

Queries

(synchronous no bus)

Domain Persistence Read Model

CQRS in a Simpler Picture

Domain Read Model

Client

Comm

andsDT

Os

Events

What Did All That Beginning Stuff Have to Do With CQRS ???

What Did All That Beginning Stuff Have to Do With CQRS ???

The way people think matters

What Did All That Beginning Stuff Have to Do With CQRS ???

The way people think matters

CQRS splits actions from queries

What Did All That Beginning Stuff Have to Do With CQRS ???

The way people think matters

CQRS splits actions from queries

And people think about asking people to do things or asking them for information

Benefits of CQRS

Benefits of CQRS

Simplified Architecture

Benefits of CQRS

Simplified Architecture

Closer Alignment with Users

Benefits of CQRS

Simplified Architecture

Closer Alignment with Users

Performance

Benefits of CQRS

Simplified Architecture

Closer Alignment with Users

Performance

Scalability

Benefits of CQRS

Simplified Architecture

Closer Alignment with Users

Performance

Scalability

Eliminates a leaky abstraction

My Objective Todaywas to Make You Think

My Objective Todaywas to Make You Think

“Maybe There Is A Better Way?”

My Objective Todaywas to Make You Think

“Maybe There Is A Better Way?”

I Hope I Succeeded

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