Ruby on Rails

On 30 May 2011 04:51, Matt Harrison <iwasinnamuknow@genestate.com> wrote:
> I'm working on a community app that allows the residents of a village to log and
> monitor the traffic going past their houses.
>
> There are multiple locations which have many log entries with a traffic count and a
> time block.
>
> I want to let users view a location and see the average vehicles per day, as well as
> the average for a given month.
>
> I'm thinking it won't be very efficient to run though every log entry and calculate a
> running average every time a user views the statistics page. I've never dealt with
> data in this manner before so I'm not sure the best practice. I suppose I could
> maintain a table with a record for each location. On creation or modification of a log
> entry I could calculate the average and store it there for viewing. Again, not sure if
> I'm heading the right direction.

Rails has several schemes for handling this sort of problem using
caching. Have a good look at the Rails Guide on caching. It is quite
complex so make sure you understand how the various methods work in
order to work out which one is right for your particular problem.
Come back and ask again if you are still not sure after understanding
the guide.

>
> The second part is calculating average for a give month, or indeed a year. I could
> present the appropriate year/month select box but how can I pull records that only
> relate to the given options?
>
> I could probably pull every single record and compare the entry date to the given
> parameters, then act on it if it fits the time period. Once more I'm thinking this
> isn't the most efficient way to proceed.

Asssuming your records have a column called measured_at, for example,
then you can query with comparison operators for these. So you can
fetch records in a time range using something like the following in
the query
:conditions => ['measured_at >= ? and measured_at < ?', start_time, end_time]
where start_time and end_time are derived from the values from the form.

Colin

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