Realm search in async function and use the result in main thread - multithreading

Question

I need to perform a search to one of my Realm table based on a keyword. The search function is done in an async function but it is quite slow: 3-5 seconds to search and show the results for 9000 data.
The search is done in three steps:
Search based on the query and return the list of Guid
Return the list of objects based on list of Guid
Use the result value to update the UI
When I try to return List<IssueTable> directly from SearchIssueInProject, I can't access its property later because "this realm instance has been closed" (something like that).
This is my search functions:
public async Task<List<IssueTable>> GetFilteredIssuesInProject(string query)
{
if (!string.IsNullOrEmpty(query))
{
var searchResults = await Task.Run(() => SearchIssueInProject(query));
return searchResults.Select(i => RealmConnection.Find<IssueTable>(i)).ToList();
}
return this.AllIssuesInProject;
}
List<string> SearchIssueInProject(string query)
{
using (var realm = Realm.GetInstance(RealmConfiguration))
{
Func<IssueTable, bool> searchIssue = d =>
string.IsNullOrEmpty(query) ? true :
Contains(d.Id.ToString(), query) ||
Contains(d.Status.DisplayName, query) ||
Contains(d.Status.Value, query) ||
Contains(d.Team.Name, query) ||
Contains(d.Team.Initial, query) ||
Contains(d.StandardIssueCategory.Title, query) ||
Contains(d.StandardIssueType.Title, query) ||
Contains(d.Drawing.Title, query) ||
Contains(d.Location.Title, query) ||
Contains(d.CreatedBy.DisplayName, query) ||
Contains(d.UpdatedBy.DisplayName, query);
var result = realm.All<IssueTable>().Where(searchIssue)
.OrderByDescending(i => i.UpdatedDate)
.Select(i => i.Guid)
.ToList();
return result;
}
}
public List<IssueTable> GetAllIssues()
{
return RealmConnection.All<IssueTable>()
.OrderByDescending(i => i.UpdatedDate)
.ToList();
}
Contains function:
public static bool Contains(string source, string filter)
{
return source.IndexOf(filter, StringComparison.OrdinalIgnoreCase) >= 0;
}
And this is how I use the search function:
this.WhenAnyValue(x => x.ViewModel.IssueSearchQuery)
.Throttle(TimeSpan.FromMilliseconds(1000), RxApp.MainThreadScheduler)
.DistinctUntilChanged()
.Do(_ =>
{
this.IssueAdapter.Issues.Clear();
})
.Select(searchTerm =>
{
if (SearchingProgressDialog == null && Activity != null)
{
ShowLoadingProgress();
}
var result = this.ViewModel.GetFilteredIssuesInProject(searchTerm);
return result
.ToObservable()
.ObserveOn(RxApp.MainThreadScheduler);
})
.Switch()
.Subscribe(searchResult =>
{
this.IssueAdapter.Issues.AddRange(searchResult);
this.IssueAdapter.NotifyDataSetChanged();
if (SearchingProgressDialog != null)
{
SearchingProgressDialog.Dismiss();
SearchingProgressDialog = null;
}
});
How to improve the search function?

Answer 1

Because you're creating a function and not an expression, the query isn't evaluated by Realm, but rather by LINQ to objects which means every object needs to be fetched by Realm, then the accessed properties will be fetched one by one to be used by the comparison. Unfortunately, all the fields you search by need traversing a related object which is not yet supported by Realm .NET.
One approach to resolve this would be to denormalize your data and copy these properties on the IssueTable object. Then you can execute a query like:
var result = realm.All<IssueTable>()
// Note that the .Where overload we select uses Expression<Func<>>
// Also, StatusDisplayName is a copy of Status.DisplayName
.Where(i => i.StatusDisplayName || ...)
.OrderByDescending(i => i.UpdatedDate)
.ToArray()
.Select(i => i.Guid)
.ToList();