I have few UI components in an angularjs web-application. Each display data based upon same input. One shows stats which are calculated on the basis of a time period. Other shows a chart of daily progress of all of those stats in the given time period.

I have designed both the components in such a way that they make their own API call. However now I know that data that component A receives can be used to configure component B instead of it making another API call.

There is some calculation that I have to on daily data to get aggregated information. This can be done on the frontend too.

Example: If data is for a year, component A shows a graph of 10 stats based on a list of 365 entries and component B receives 10 stats based on aggregate of the same 365 entries. Component B also has to show changes in each stat in terms of percentage between last 365 days and the ones that were selected.

Shall I have it as two API calls or just one ?

2 Answers 2


It depends. When A and B obtain their data each on its own, this has the advantage that both are independent from each other, and A may be used without B, and B without A. The disadvantage is that you might need to pull the same data over the network twice, and that the data displayed by A and B might not be always consistent because the content changed between the two data requests.

If the data must be consistent, and/or you want to reduce network traffic, it will probably be a good idea to introduce a component C which works as a "data layer", makes the API call for both A and B, and provides the same data (or different views on the same data) for both. That will still allow to use A & B independently from each other (of course, not independent from C). Moreover, this provides you immediately with a place where you can put any code shared between A and B.

  • I'm pretty sure if you want the data to be consistent, as long as you are doing two API calls, you can't guarantee it. Just having client side component C making two separate API calls still has the same consistency flaw as separate components A and B. Aug 28, 2015 at 16:26
  • @RibaldEddie: I was more thinking of a component C which retrieves the data once from the Web API and delivers the same data (or different views on the same data) to A and B - a standard model-view-approach.
    – Doc Brown
    Aug 28, 2015 at 17:21
  • Sure but it just was a bit unclear from the wording in your answer. Aug 28, 2015 at 17:22
  • @RibaldEddie: see my edit, hope its clearer now.
    – Doc Brown
    Aug 28, 2015 at 17:24
  • 2
    @RibaldEddie: nitty, nitty ;-)
    – Doc Brown
    Aug 28, 2015 at 21:35

In general a ui component should not get its data itself but should be given data to display. There is very likely some other component whose job it is to get the data, closely related to the ui component.

When you say “accessing a database” - neither component should know that there is a database or what kind of database it is. You’d have a service that supplies data someone asks for. That this service accesses a database is nobody’s business.

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