In CQRS (event-sourced), do you need a global sequence counter in the event store?

Posted by Jon M on Stack Overflow See other posts from Stack Overflow or by Jon M
Published on 2010-06-01T09:21:35Z Indexed on 2010/06/01 9:23 UTC
Read the original article Hit count: 221

Filed under:
|

In trying to get my head around CQRS (and DDD in general) I have come across situations when two events occur on different aggregates but the order of them has domain meaning. If so then they could happen so close together that a timestamp (as used by the sample implementations I have seen) cannot differentiate them, meaning the event store doesn't contain a 'complete' representation of the domain as there is ambiguity over the order in which events occurred.

As an example, the domain could fire a CustomerCreatedEvent which applies to the Customer aggregate, and then a CustomerAssignedToAgent event on the Agent aggregate. The CustomerAssignedToAgent event doesn't make sense if it occurs before the CustomerCreatedEvent, but typically both of these might be fired as a result of one operation which makes it likely that the timestamps would effectively be the same.

So am I just modelling things badly? Should there ever be a situation where the sequence of events across different aggregates is important? Or should you keep a global sequence number on your event store, so that you can identify the exact sequence in which events occurred?

© Stack Overflow or respective owner

Related posts about ddd

Related posts about cqrs

  • CQRS at Jax Code Camp 2012

    as seen on ASP.net Weblogs - Search for 'ASP.net Weblogs'
    Continuing my CQRS world tour...I gave my CQRS presentation at the Jax Code Camp 2012 this past Saturday.  It was a great crowd with lots of representation from the wicked smart engineers at Feature[23] and others from the Jacksonville developer community. If you'd like to take a… >>> More

  • CQRS without using others patterns

    as seen on Programmers - Search for 'Programmers'
    I would like to explain CQRS to my team of developers. I just can't figure out how to explain it in the simplest way so they can implement the pattern rapidly without any others frameworks. I've read a lot of resources including video and articles but I don't find how to implement CQRS without using… >>> More

  • Domain queries in CQRS

    as seen on Stack Overflow - Search for 'Stack Overflow'
    We are trying out CQRS. We have a validation situation where a CustomerService (domain service) needs to know whether or not a Customer exists. Customers are unique by their email address. Our Customer repository (a generic repository) only has Get(id) and Add(customer). How should the CustomerService… >>> More

  • CQRS - The query side

    as seen on Stack Overflow - Search for 'Stack Overflow'
    A lot of the blogsphere articles related to CQRS (command query repsonsibility) seperation seem to imply that all screens/viewmodels are flat. e.g. Name, Age, Location Of Birth etc.. and thus the suggestion that implementation wise we stick them into fast read source etc.. single table per view mySQL… >>> More

  • CQRS event versioning

    as seen on Stack Overflow - Search for 'Stack Overflow'
    Versioning If your events changes you would create a new version of that event, and keep the old ones. To keep your domain code form being bloated with handling of all versions of events you would basically introduce a component that converts your events from previous to newer versions, and then… >>> More