Querying local cache first before querying server in Breeze JS

Question

I have an app using Breeze to query the data. I want to first check the local cache and then the server cache if no results are returned (I followed John Papa's SPA jumpstart course). However, I have found a flaw in my logic which I am not sure how to fix. Assuming I have 10 items that match my query.

Situation 1 (which works): I go to list page (Page A) displaying all 10. Hits server as cache is empty and adds all 10 to the cache. Then go to page displaying 1 result (Page B) which is found in the cache. So all good.

Situation 2 (the problem): I go to the page displaying 1 record first (Page B). Then I go to my list page (Page A) which checks the cache and finds 1 record and because of this line ( if (recordsInCache.length > 0)) it exits and only shows that 1 record.

I somehow need to know that there are more records on the server (9) that are NOT in the cache, ie. the total records for this query is actually 10, I have 1 therefore I have to hit server for the other 9.

Here is my query for Page A:

function getDaresToUser(daresObservable, criteria, forceServerCall)
{
    var query = EntityQuery.from('Dares')
        .where('statusId', '!=', enums.dareStatus.Deleted)
        .where('toUserId', '==', criteria.userId)
        .expand("fromUser, toUser")
        .orderBy('deadlineDate, changedDate');

    return dataServiceHelper.executeQuery(query, daresObservable, false, forceServerCall);
}

and here is my query for Page B (single item)

function getDare(dareObservable, criteria, forceServerCall)
{
    var query = EntityQuery.from('Dares')
        .expand("fromUser, toUser")
        .where('dareId', '==', criteria.dareId);

    return dataServiceHelper.executeQuery(query, dareObservable, true, forceServerCall);
}



function executeQuery(query, itemsObservable, singleEntity, forceServerCall)
{
    //check local cache first
    if (!manager.metadataStore.isEmpty() && !forceServerCall)
    {
        var recordsInCache = executeLocalQuery(query, itemsObservable, singleEntity);
        if (recordsInCache.length > 0)
        {
            callCompleted();
            return Q.resolve();
        }
    }

return manager.executeQuery(query)
        .then(querySucceeded)
        .fail(queryFailed);

}

function executeLocalQuery(query, itemsObservable, singleEntity)
{
    var recordsInCache = manager.executeQueryLocally(query);
    if (recordsInCache.length > 0)
    {
        processQueryResults(recordsInCache, itemsObservable, singleEntity, true);
    }
    return recordsInCache;
}

Any advice appreciated...

Answer 1

I’ve been thinking about this problem more in the last year (and have since moved from Durandal + Breeze to Angular + Breeze : In Angular you can cache the service call easily using

return $resource(xyz + params}, {'query': { method:'GET', cache: true, isArray:true }}).query(successArrayDataLoad, errorDataLoad);

I guess Angular caches the params of this query and knows when it has it already. So when I switch this method to use Breeze I lose this functionality and all my List calls are hit on every time.

So the real problem here is List data. Single Entities can always check the local cache and if nothing is returned then check the server (because you expect exactly 1).

However, List data varies by params. For example, if I have a GetGames call which takes in a CreatedByUserId, every time I supply a new CreatedByUserId I have to go back to the server.

So I think what I really need to do here to cache my List calls is to cache the Key for each call which is a combination of the QueryName and the Params.

For example, GetGames1 for UserID 1 and then GetGames2 for UserId 2.

The logic would be: Check the Angular cache to see if this call has been made before in this session. If it has, then check the local cache first. If nothing is returned, check the server.

If it has not, check the server as the local cache MIGHT have some data in it for this query but it's not guaranteed to be the full set.

The only other way around it would be to hit the server each time first to get a count for that Query + Params and then hit the local cache and compare the count, but that is more inefficient.

Thoughts?

Answer 2

If you want to just hit the server for comparison purposes then at some point (either when loading up your app or when you hit the list page) call inlineCount to compare total on server vs what you already have like shown in this answer stackoverflow.com/questions/16390897/counts-in-breeze-js/…

A way you can use this creatively while you are querying for the single record would be like this -

Set some variable in your view model or somewhere equal to total count

var totalCount = 0;

When you query the single record get the inline count -

var query = EntityQuery.from('Dares')
    .expand("fromUser, toUser")
    .where('dareId', '==', criteria.dareId)
    .inlineCount(true);

and set totalCount = data.inlineCount; Same thing when you get the total items list, just set the totalCount to inlineCount then too so you always know if you have all of the entities.