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POCreating an observable which relies on state from an Interval
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copied!<p>I am trying to write a class which will query a set of data out of a database every x seconds.</p> <p>The issue is that this observable remembers it's previous state and that state is used to determine what is actually sent on the observable.</p> <p>For Example I want an </p> <pre><code>IObservable<SomeEntity> AddedEntities { get; private set; } IObservable<SomeEntity> ChangedEntities { get; private set; } IObservable<SomeEntity> DeletedEntities { get; private set; } </code></pre> <p>My issue is that I have been reading <a href="http://www.introtorx.com/" rel="nofollow">http://www.introtorx.com/</a> and they say that using Subject is a bad idea. Instead I should be using the Observable.Create methods.</p> <p>My issue is I only want to query the database once and then send the relevant information back to the correct observable but I dont want each subscribe to my observable start it's own timer and query the database every 5 seconds per subscription to each IObservable.</p> <p>I have played around with making just one observable which returns a new model with the changed as a set:</p> <pre><code>IObservable<EntityChangeSet> Changes {get; private set;} public class EntityChangeSet { Public IEnumerable<SomeEntity> Added {get; set;} Public IEnumerable<SomeEntity> Changed {get; set;} Public IEnumerable<SomeEntity> Deleted {get; set;} } </code></pre> <p>And I am open to any solution like this as well.</p> <p>What I have so far is:</p> <pre><code>public class IntervalChangeReader { // My state between ticks. private IEnumerable<SomeEntity> knowEntities; // Reads the data from the db and uses knowEntities to determine adds, changes, // and deletes which are exposed through properties. private DbReaderAndChangeChecker checker; IDisposeable timerCancel; public IntervalChangeReader(DbReaderAndChangeChecker checker) { this.checker = checker; } public IObservable<EntityChangeSet> Changes { get; private set; } public Start(int seconds) { this.timerCancel = Observable.Interval(new TimeSpan.FromSeconds(seconds)).Subscribe( x => { var results = this.checker.Refresh(this.knownEntities); // Update this.knownEntities with results. // Inform produce a value on the observable ???? // I could call .OnNext If I had a subject exposed for my Observable. } } public Stop() { this.timerCancel.Dispose(); // Complete on all subscriptions? // If I were using subjects I could just call .OnComplete here. } } </code></pre> <p>How do I create the Observable without using subjects and how to I pass results through it? I want to do this all with only one timer and not a timer per subscription to my observables.</p>

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