Re: Eventual consistency and 1 to n relationships

"Greg Young [email protected] [domaindrivendesign]" <[email protected]> Thu, 11 Jan 2018 15:16:03 +0000
Newsgroups gmane.comp.programming.domain-driven-design
Message-ID <CAC9RQtjbf1wOwB1xK_0rAOE__VXvkChDKh=q0v3feOKNuUbOuA@mail.gmail.com> 
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This is more a rabbitmq discussion than a ddd question but when dealing
with a system like rabbitmq you must make operations idempotent. The
message will be delivered at-least-once. As such you need to handle the
possibility that you may receive it 5 times and be able to realize you have
already done the action (to ignore the message). If you are using a
transactional data storage it will do this handling for you providing a
reasonable level of isolation.

On Wed, Jan 10, 2018 at 5:32 PM, dirk g [email protected]
[domaindrivendesign] <[email protected]> wrote:

>
>
> Hi,
>
> In my domain I have Product and Order aggregates. Orders reference
> Products.
> This is a 1 to n relationship, so a Product has many Orders and Orders
> belong to a Product. When a Product is discontinued a ProductDiscontinued
> event is published and all Orders that belong to this Product must be
> cancelled. So there's an adapter that receives the ProductDiscontinued
> event
> via RabbitMQ. The adapters then delegates cancelling Orders to an
> application service. How can I achieve that a single Order is cancelled i=
n
> a
> single transaction? Should the adapter iterate over all Orders for the
> discontinued Product and call the application service for every single
> Order? Should I just ignore that I modify more than one aggregate in a
> single transaction and call the application service just once with a list
> of
> all affected OrderIds? Or is there a better solution?
>
> Many thanks,
>
> Dirk
>
> --
> Sent from: http://domain-driven-design.3010926.n2.nabble.com/
>=20
>



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<div dir=3D"ltr">This is more a rabbitmq discussion than a ddd question but=
 when dealing with a system like rabbitmq you must make operations idempote=
nt. The message will be delivered at-least-once. As such you need to handle=
 the possibility that you may receive it 5 times and be able to realize you=
 have already done the action (to ignore the message). If you are using a t=
ransactional data storage it will do this handling for you providing a reas=
onable level of isolation.</div><div class=3D"gmail_extra"><br><div class=
=3D"gmail_quote">On Wed, Jan 10, 2018 at 5:32 PM, dirk g <a href=3D"mailto:=
[email protected]">[email protected]</a> [domaindrivendesign] <span dir=3D"=
ltr">&lt;<a href=3D"mailto:[email protected]" target=3D"_b=
lank">[email protected]</a>&gt;</span> wrote:<br><blockquo=
te class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc so=
lid;padding-left:1ex">


<u></u>









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=20=20=20=20=20=20
=20=20=20=20=20=20
      <p>Hi,<br>
<br>
In my domain I have Product and Order aggregates. Orders reference Products=
..<br>
This is a 1 to n relationship, so a Product has many Orders and Orders<br>
belong to a Product. When a Product is discontinued a ProductDiscontinued<b=
r>
event is published and all Orders that belong to this Product must be<br>
cancelled. So there&#39;s an adapter that receives the ProductDiscontinued =
event<br>
via RabbitMQ. The adapters then delegates cancelling Orders to an<br>
application service. How can I achieve that a single Order is cancelled in =
a<br>
single transaction? Should the adapter iterate over all Orders for the<br>
discontinued Product and call the application service for every single<br>
Order? Should I just ignore that I modify more than one aggregate in a<br>
single transaction and call the application service just once with a list o=
f<br>
all affected OrderIds? Or is there a better solution?<br>
<br>
Many thanks,<br>
<br>
Dirk<br>
<br>
--<br>
Sent from: <a href=3D"http://domain-driven-design.3010926.n2.nabble.com/" t=
arget=3D"_blank">http://domain-driven-design.<wbr>3010926.n2.nabble.com/</a=
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</p>

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</blockquote></div><br><br clear=3D"all"><div><br></div>-- <br><div class=
=3D"gmail_signature" data-smartmail=3D"gmail_signature"><div dir=3D"ltr">St=
udying for the Turing test</div></div>
</div>




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         Posted by: Greg Young &lt;[email protected]&gt;         <hr =
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