/// <summary>
/// When item in database is removed, we need to adjust cache model
/// 1. Get all affected tokens and their documentIds where it appeared
/// 2. Remove {document} cache data
/// 3. Recalculate TfIdf vector for affected documentIds
/// </summary>
public async Task RemoveAsync(Document document)
{
var documentsAffected = GetRelatedDocuments(document);
Documents.Remove(document.Id);
foreach (var token in document.Tokens)
{
var key = _tokenContextCacheKey(token);
var tokenContext = await _keyValueStorage.GetAsync <TokenContext>(key);
tokenContext.DocumentIds.Remove(document.Id);
await _keyValueStorage.SetAsync(key, tokenContext);
await _keyValueStorage.RemoveAsync(_tfIdfCacheKey(document, token));
}
await Task.WhenAll(documentsAffected.Select(SaveTfIdfVectorAsync));
}
/// <summary>
/// Here is algorithm for cache adjusting when article is removed
/// 1. Get similarityResults for {article} from cache
/// 2. Remove similarityResults from cache for removed {article}
/// 3. Remove similarityScore in other articles
///
/// Here is better AND faster to use graph data structure,
/// where each node is connected to all others,
/// and connection weight is SimilarityScore (from 0 to 1),
/// but I used simple List of Lists, because didn't have time...
/// </summary>
public async Task Handle(ArticleRemovedEvent notification, CancellationToken cancellationToken)
{
await _similarityScoring.RemoveAsync(notification.Article.ToDocument());
var results = await _cache.GetAsync <List <SimilarityResult> >(_articleSimilarityCacheKey(notification.Article))
?? new List <SimilarityResult>();
await _cache.RemoveAsync(_articleSimilarityCacheKey(notification.Article));
foreach (var similarityResult in results.Where(r => r.Id != notification.Article.Id))
{
var cacheKey = _articleSimilarityCacheKey(new Article {
Id = similarityResult.Id
});
var articleSimilarities = await _cache.GetAsync <List <SimilarityResult> >(cacheKey);
articleSimilarities = articleSimilarities.Where(x => x.Id != notification.Article.Id)
.ToList();
await _cache.SetAsync(cacheKey, articleSimilarities);
}
}