The document discusses using MongoDB as an event store. It notes that modeling state transitions as domain events has become an important approach. The document outlines an architecture with MongoDB to store and read these domain events, showing how events are stored as documents with a timestamp and metadata. Events can be replayed to reconstruct state across multiple members for high availability.

1. Alessandro Melchiori
MongoDb as event store
alessandro@codiceplastico.com

2. MongoDb as event store
Alessandro Melchiori alessandro@codiceplastico.com
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"role": "software architect @ codiceplastico",
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{ "type": "email", "value": alessandro@codiceplastico.com },
{ "type": "twitter", "value": "@amelchiori" },
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3. MongoDb as event store
Alessandro Melchiori alessandro@codiceplastico.com
• It’s really become clear to me in the last couple of years that we need
a new building block and that is the Domain Events
(Eric Evans)
• State transition are an important part of our problem space and
should be modeled within our domain
(Greg Young)

4. MongoDb as event store
Alessandro Melchiori alessandro@codiceplastico.com
1 2 3 4 5 6 ...
snapshot

5. MongoDb as event store
Alessandro Melchiori alessandro@codiceplastico.com
Domain Model
Service Layer
Write storage
Presentation Layer
Read storage

6. MongoDb as event store
Alessandro Melchiori alessandro@codiceplastico.com
LOCAL LOCAL
MEMBER 01 MEMBER 02
MEMBER 03
LOCAL

7. MongoDb as event store
Alessandro Melchiori alessandro@codiceplastico.com
{
"ts" : Timestamp(1363605458000, 2),
"h" : NumberLong("4039405765251735075"),
"v" : 2,
"op" : "i",
"ns" : "webdebs.Streams",
"o" : {
"HeadRevision" : 1,
"SnapshotRevision" : 0,
"Unsnapshotted" : 1,
"_id" : BinData(3,"+KYFwLvnxkS8Lsuy6P562Q==")
}
}