I am developing a dictionary app which has many interconnected tables, so when a user makes a query the app searches through almost all of those tables and across many their fields, which results in heavy queries to the database and UI freezes.
So, how can I make these queries in a separate task asynchronously each time updating the UI with the results?
I've seen findAllAsync and the like for android version of the realm but for .net I couldn't find any alternatives, I tried to reinitialize as suggested elsewhere the database each time I run the async, but somehow it doesn't work and give me the same error.
System.Exception: 'Realm accessed from incorrect thread.'
The error gets thrown on ToList() when I try to convert the realm results to normal list to handle on UI, please help to fix this behavior
Here is my code
using Data.Models;
using Microsoft.EntityFrameworkCore.Internal;
using Realms;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Data
{
public class RealmAsync
{
IQueryable<Entry> Entries { get; set; }
public async void Run()
{
Realm RealmDatabase = Realm.GetInstance();
Entries = RealmDatabase.All<Entry>();
var entries = await FindAsync("а", Entries);
Console.WriteLine($"async result async {entries.Count()}");
}
public async Task<IEnumerable<Entry>> FindAsync(string needle, IQueryable<Entry> haystack)
{
var foregroundRealm = Realm.GetInstance();
var haystackRef = ThreadSafeReference.Create<Entry>(haystack);
var filteredEntriesRef = await Task.Run(() =>
{
using (var realm = Realm.GetInstance())
{
var bgHaystack = realm.ResolveReference(haystackRef);
return ThreadSafeReference.Create(bgHaystack.Where(entry => entry.Content.ToLower().StartsWith(needle)));
}
});
var result = foregroundRealm.ResolveReference(filteredEntriesRef).ToArray();
return result;
}
}
Entry model class:
using System.ComponentModel.DataAnnotations.Schema;
using Realms;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System;
namespace Data.Models
{
[Table("entry")]
public class Entry : RealmObject
{
public class EntryType
{
public const byte Word = 1;
public const byte Phrase = 2;
public const byte Text = 3;
};
[Key]
[PrimaryKey]
[Column("entry_id")]
public int Id { get; set; }
[Column("user_id")]
public int UserId { get; set; }
[Column("source_id")]
public int SourceId { get; set; }
[Indexed]
[Column("type")]
public byte Type { get; set; }
[Column("rate")]
public int Rate { get; set; }
[Column("created_at")]
public string CreatedAt { get; set; }
[Column("updated_at")]
public string UpdatedAt { get; set; }
[NotMapped]
public Phrase Phrase { get; set; }
[NotMapped]
public Word Word { get; set; }
[NotMapped]
public Text Text { get; set; }
[NotMapped]
public IList<Translation> Translations { get; }
[NotMapped]
public string Content
{
get {
switch (Type)
{
case EntryType.Phrase:
return Phrase?.Content;
case EntryType.Word:
return Word?.Content;
case EntryType.Text:
return Text?.Content;
}
return "";
}
}
}
}
So, in case somebody needs this, here is how I ended up with my real implementation which works nicely (it's not the example code in the question, but I thought this can be more useful and practical) - let me know if you'll need more info about it:
public async override Task<List<Entry>> FindAsync(string inputText)
{
// Checks for previous results to speed up the search while typing
// For realm to be able to work cross-thread, when having previous results this has to be passed to the search task
ThreadSafeReference.Query<Entry> previousResultsRef = null;
if (PreviousInputText != null)
{
if ((PreviousInputText.Length == inputText.Length - 1) && (inputText == PreviousInputText + inputText.Last()))
{
// Characters are being inserted
if (PreviousResults.ContainsKey(PreviousInputText.Length - 1))
{
previousResultsRef = ThreadSafeReference.Create(PreviousResults[PreviousInputText.Length - 1]);
}
} else if ((PreviousInputText.Length == inputText.Length + 1) && (inputText == PreviousInputText.Substring(0, PreviousInputText.Length - 1)))
{
// Characters are being removed
PreviousResults[PreviousInputText.Length] = null;
PreviousInputText = inputText;
return PreviousResults[PreviousInputText.Length - 1].ToList();
}
}
// Receives reference to the search results from the dedicated task
var resultingEntries = await Task.Run(() =>
{
// Preserves current input text for the further uses
PreviousInputText = inputText;
// Gets the source entries - either previous or all
var sourceEntries = (previousResultsRef == null) ? Realm.GetInstance(DbPath).All<Entry>() : Realm.GetInstance(DbPath).ResolveReference(previousResultsRef);
// Because realm doesn't support some of the LINQ operations on not stored fields (Content)
// the set of entries @sourceEntries is assigned to a IEnumerable through conversion when passing to Search method as a parameter
IEnumerable<Entry> foundEntries = Search(inputText, sourceEntries);
// Extracts ids
var foundEntryIds = ExtractIdsFromEntries(foundEntries);
if (foundEntryIds.Count() == 0)
{
return null;
}
// Select entries
var filteredEntries = FilterEntriesByIds(sourceEntries, foundEntryIds.ToArray());
if (filteredEntries == null)
{
// Something went wrong
return null;
}
// Creates reference for the main thread
ThreadSafeReference.Query<Entry> filteredEntriesRef = ThreadSafeReference.Create(filteredEntries);
return filteredEntriesRef;
});
if (resultingEntries == null)
{
// Next search will be a new search
PreviousResults[inputText.Length - 1] = null;
return new List<Entry>();
}
var results = RealmDatabase.ResolveReference(resultingEntries);
// Preserve the current results and the input text for the further uses
PreviousInputText = inputText;
if (PreviousResults.ContainsKey(inputText.Length - 1))
{
PreviousResults[inputText.Length - 1] = results;
} else
{
PreviousResults.Add(inputText.Length - 1, results);
}
return Sort(results, inputText).ToList();
}
This is a method to make async search while typing, that's why there is this PreviousInputText and PreviousResults - to spare from superfluous queries