public async Task <QueryResult <BudgetLevel> > ListAsync(BudgetLevelQuery query)
{
IQueryable <BudgetLevel> queryable = _context.BudgetLevels
.Include(p => p.User)
.AsNoTracking();
// AsNoTracking tells EF Core it doesn't need to track changes on listed entities. Disabling entity
// tracking makes the code a little faster
if (query.UserId.HasValue && query.UserId > 0)
{
queryable = queryable.Where(p => p.UserId == query.UserId);
}
// Here I count all items present in the database for the given query, to return as part of the pagination data.
int totalItems = await queryable.CountAsync();
// Here I apply a simple calculation to skip a given number of items, according to the current page and amount of items per page,
// and them I return only the amount of desired items. The methods "Skip" and "Take" do the trick here.
List <BudgetLevel> BudgetLevels = await queryable.Skip((query.Page - 1) *query.ItemsPerPage)
.Take(query.ItemsPerPage)
.ToListAsync();
// Finally I return a query result, containing all items and the amount of items in the database (necessary for client-side calculations ).
return(new QueryResult <BudgetLevel>
{
Items = BudgetLevels,
TotalItems = totalItems,
});
}
private string GetCacheKeyForBudgetLevelQuery(BudgetLevelQuery query)
{
string key = CacheKeys.BudgetLevelsList.ToString();
if (query.UserId.HasValue && query.UserId > 0)
{
key = string.Concat(key, "_", query.UserId.Value);
}
key = string.Concat(key, "_", query.Page, "_", query.ItemsPerPage);
return(key);
}
public async Task <QueryResult <BudgetLevel> > ListAsync(BudgetLevelQuery query)
{
// Here I list the query result from cache if they exist, but now the data can vary according to the category ID, page and amount of
// items per page. I have to compose a cache to avoid returning wrong data.
string cacheKey = GetCacheKeyForBudgetLevelQuery(query);
var products = await _cache.GetOrCreateAsync(cacheKey, (entry) => {
entry.AbsoluteExpirationRelativeToNow = TimeSpan.FromMinutes(1);
return(_budgetLevelRepository.ListAsync(query));
});
return(products);
}
