CODEWITHSUNDEEP
restidempotent
M. Dabulskis
M. Dabulskis

Reputation: 97

When can you call operation idempotent?

The definition of idempotent in wikipedia is:Idempotence is the property of certain operations in mathematics and computer science, that can be applied multiple times without changing the result beyond the initial application.

The problem is: I have REST API PUT call, which updates properties of domain aggregate. Also, it fires event for each property, which was updated. Now if we have two exact the same PUT calls one after the other to our backend:

  1. First PUT call updates the properties of aggregate and fires lets say 5 events.
  2. Second PUT call updates the properties of aggregate, but do not fire any event, because the properties of aggregate did not change (first PUT call updated the values of aggregate properties).

The question is: is this operation idempotent?

Upvotes: 1

Views: 219

Answers (4)

Drathier
Drathier

Reputation: 14539

It depends on your definition. Since you have side-effects (fiering off some events if there is a difference), multiple calls might cause more side-effects than desired. However, the state of the application, ignoring the side-effects, with no concurrency, will be idempotent. Remember that REST calls are made over an asynchronous network, so this is a distributed system.

If you have two concurrent processes, they may fire a different number of side-effects. For example:

a = 2
a = 3
a = 2 
a = 3

will fire twice as many events as 

a = 2
a = 2 
a = 3
a = 3

which might cause some trouble.

Upvotes: 0

ACV
ACV

Reputation: 10560

Yes and No. It is idempotent from the data point of view. The data in the database won't change no matter how many times you execute the call. But it is not idempotent in the sense that some logging or other events might occur that would change the "Entropy" of the system :)

Upvotes: 0

DarkDust
DarkDust

Reputation: 92384

This question and its answers explain what an idempotent operation is. In short: repeated calls do not change the outcome.

So from your description of this operation, it seems it qualifies as idempotent.

Upvotes: 1

Alexander Guz
Alexander Guz

Reputation: 1364

Yes, it is: no matter how many times you send the same PUT request, it leaves your system (your aggregate) in the same state.

Upvotes: 0

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