20 years of ERP
10.000 customers
90% cloud
Web
Scalable
CQRS
Event sourcing
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20 years of ERP
10.000 customers
90% cloud
Person
Entity
Customer
Role
Order
Agreement
party
Spending limit
Address
Organisation
Entity
Delivery
BusinessAc tivity
party
Invoice
BusinessAc tivity
party
Address
Address
Spending limit
Spending limit
Own Organisation
Workarea
workarea
Spending limit
Put all our knowledge and
experience in a model
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Customized
Web
Scalable
CQRS
Event sourcing
Person
Entity
Customer
Role
Order
Agreement
party
Spending limit
Address
Organisation
Entity
Delivery
BusinessAc tivity
party
Invoice
BusinessAc tivity
party
Address
Address
Spending limit
Spending limit
Own Organisation
Workarea
workarea
Spending limit
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(2.830 tables with 126.705 columns)
ERP software is inherently relational
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Command Query
Responsibility Segregation
Client
Command system
Query system
Eventing system
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Command Query
Responsibility Segregation
Client
Command system
Query system
Eventing system
“PlaceOrderCommand”: {
“OrderId”: “0b81b458-7671-4e9b-844b-9934255f5406”,
“CustomerName”: “Linus Torvalds”,
“OrderLines”: [ … ]
}
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Command Query
Responsibility Segregation
Client
Command system
Query system
Eventing system
“GetOrders”: {
“CustomerName”: “Linus Torvalds”,
}
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Command Query
Responsibility Segregation
Client
Command system
Query system
Eventing system
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DDD
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Aggregates - independent, self-contained business objects
that handle commands and raise events.
Aggregates - independent, self-contained business objects
that handle commands and raise events.
That sounds a lot like actors ☺
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No content
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Events – Something that has happened.
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Events
Events that need to
be processed in the
query system.
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Projectors – A process that builds a projection from events.
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Projectors
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Projectors
Needs routing to find
the correct store
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No content
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How to get the events from
the command system
to
the query system?
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CQRS
Client
Command system
Query system
Eventing system
Some kind of
message bus?
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Event push
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No content
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T
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2 phase commit Independence
Command
system
Query system
Eventing system
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Event push
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Event pull
But we need persistence. And
we still have a 2 phase commit.
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Use the emitted events as single
source of truth
Event sourcing
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CQRS
Client
Command system
Query system
Eventing system
What is the data
model used in the
command side?
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CQRS
Client
Command system
Query system
Eventing system
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Event Store
StreamId Stream
Revision
PayloadItemName Payload StreamType Sequence
Number
CommitTime AccountId
Person1 1 PersonCreatedEvent { … } Person 1 … …
Person1 2 PersonUpdatedEvent { … } Person 2 … …
Person2 1 PersonCreatedEvent { … } Person 3 … …
Order1 1 OrderCreatedEvent { … } Order 1 … …
Order2 1 OrderCreatedEvent { … } Order 2 … …
Order3 1 OrderCreatedEvent { … } Order 3 … …
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Aggregates loading
Event Store
StreamId Stream
Revision
PayloadItemName Payload StreamType Sequence
Number
CommitTime AccountId
Person1 1 PersonCreatedEvent { … } Person 1 … …
Person1 2 PersonUpdatedEvent { … } Person 2 … …
Person2 1 PersonCreatedEvent { … } Person 3 … …
Order1 1 OrderCreatedEvent { … } Order 1 … …
Order2 1 OrderCreatedEvent { … } Order 2 … …
Order3 1 OrderCreatedEvent { … } Order 3 … …
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Event processing
Event Store
StreamId Stream
Revision
PayloadItemName Payload StreamType Sequence
Number
CommitTime AccountId
Person1 1 PersonCreatedEvent { … } Person 1 … …
Person1 2 PersonUpdatedEvent { … } Person 2 … …
Person2 1 PersonCreatedEvent { … } Person 3 … …
Order1 1 OrderCreatedEvent { … } Order 1 … …
Order2 1 OrderCreatedEvent { … } Order 2 … …
Order3 1 OrderCreatedEvent { … } Order 3 … …
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Event Sourcing
A
B
A
E
C
D
D
F
B
B
A
C
C
G
H
D
A
B
C
A
D
A
A
A
A
A
A
B
B
C
C
1
2
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5
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2
3
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1
1
1
2
1
1
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1
1
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1
2
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Event Sourcing
A
B
A
E
C
D
D
F
B
B
A
C
C
G
H
D
A
B
C
A
D
A
A
A
A
A
A
B
B
C
C
1
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Sequencenumbers for
projectors
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Event Sourcing
A
B
A
E
C
D
D
F
B
B
A
C
C
G
H
D
A
B
C
A
D
A
A
A
A
A
A
B
B
C
C
1
2
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5
1
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1
2
Revisions for aggregate
loading and concurrency
control
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Event sourcing
This is both the store as
the messaging system.
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Eventual consistency
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Eventual
consistency
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Eventual
consistency
This is an async process
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Eventual consistency
Client
Command system
Query system
Eventing system
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Notifications
β
α γ
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Notifications
β
α γ
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No content
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Projector optimization
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Projection
Information from the
customer stream
Information from the
order stream
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Projection
A helper-table with customer info
A table for the projection
A customer update could
mean that we need to
update 1.000.000+ rows
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Projection:
joins
A table with customer info
A table for the projection
A query should join the
two tables.
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Projection:
duplication
A table with customer info
A table with order info
A table with customer info
A table with invoice info
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Projection:
combine
A table with customer info
A table with order info
A table with invoice info
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Projection:
chaining
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So what have we seen?
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Summary
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Summary
β
α γ
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No content
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Building an event sourced system in .NET
michiel.overeem@afas.nl
@michielovereem