C#•12mo ago

✅ How to find objects that changed?

I have following records:

public record NotificationSettingsDto
{
    public string? NotificationSettingsId { get; set; }
    public HashSet<string> EventCategories { get; set; }
    public HashSet<string> EventNames { get; set; }
    public HashSet<ChannelSettingsDto> ChannelSettings { get; set; }
    public bool IsEnabled { get; set; }
    public string TemplateMessage { get; set; }
}

public record ChannelSettingsDto
{
    public string ChannelName { get; set; }
    public BehaviorType Behavior { get; set; }
    public TimeSpan Ttl { get; set; }
}

public enum BehaviorType
{
    Simple,
    RequiresConfirmation,
    RequiresPersonalConfirmation
}

public record NotificationSettingsDto
{
    public string? NotificationSettingsId { get; set; }
    public HashSet<string> EventCategories { get; set; }
    public HashSet<string> EventNames { get; set; }
    public HashSet<ChannelSettingsDto> ChannelSettings { get; set; }
    public bool IsEnabled { get; set; }
    public string TemplateMessage { get; set; }
}

public record ChannelSettingsDto
{
    public string ChannelName { get; set; }
    public BehaviorType Behavior { get; set; }
    public TimeSpan Ttl { get; set; }
}

public enum BehaviorType
{
    Simple,
    RequiresConfirmation,
    RequiresPersonalConfirmation
}

Than I create lists with objects and trying to find objects that was changed. I don't know why but changedItems.Count is 1

var firstLst = new List<NotificationSettingsDto>()
{ 
    new NotificationSettingsDto
    {
        NotificationSettingsId = "2",
        IsEnabled = false,
        EventCategories = new HashSet<string>(){"ac", "bc"},
        EventNames = new HashSet<string>(){"cc", "dd"},
        ChannelSettings = new HashSet<ChannelSettingsDto>()
        {
            new ChannelSettingsDto(){ ChannelName = "operator_notifications" }
        }
    }
};

var secondLst = new List<NotificationSettingsDto>()
{
    new NotificationSettingsDto
    {
        NotificationSettingsId = "2",
        IsEnabled = false,
        EventCategories = new HashSet<string>(){"ac", "bc"},
        EventNames = new HashSet<string>(){"cc", "dd"},
        ChannelSettings = new HashSet<ChannelSettingsDto>()
        {
            new ChannelSettingsDto(){ChannelName = "operator_notifications"}
        }
    }
};

var changedItems = firstLst
    .Join(secondLst,
        f => f.NotificationSettingsId,
        s => s.NotificationSettingsId,
        (f, s) => new {First = f, Second = s})
    .Where(pair => !pair.First.Equals(pair.Second))
    .ToList();

var firstLst = new List<NotificationSettingsDto>()
{ 
    new NotificationSettingsDto
    {
        NotificationSettingsId = "2",
        IsEnabled = false,
        EventCategories = new HashSet<string>(){"ac", "bc"},
        EventNames = new HashSet<string>(){"cc", "dd"},
        ChannelSettings = new HashSet<ChannelSettingsDto>()
        {
            new ChannelSettingsDto(){ ChannelName = "operator_notifications" }
        }
    }
};

var secondLst = new List<NotificationSettingsDto>()
{
    new NotificationSettingsDto
    {
        NotificationSettingsId = "2",
        IsEnabled = false,
        EventCategories = new HashSet<string>(){"ac", "bc"},
        EventNames = new HashSet<string>(){"cc", "dd"},
        ChannelSettings = new HashSet<ChannelSettingsDto>()
        {
            new ChannelSettingsDto(){ChannelName = "operator_notifications"}
        }
    }
};

var changedItems = firstLst
    .Join(secondLst,
        f => f.NotificationSettingsId,
        s => s.NotificationSettingsId,
        (f, s) => new {First = f, Second = s})
    .Where(pair => !pair.First.Equals(pair.Second))
    .ToList();

20 Replies

SWEETPONYOP•12mo ago

but actually objects are the same

exokem•12mo ago

What do you mean by objects that changed The Join call produces a list with one element, I think because it's doing the equivalent of an inner join What is your goal with these two lists? Their contents seem to be identical except the objects will not point to the same reference

cap5lut•12mo ago

the HashSet<T>s use the default Equals() check, which is a reference equality check

MODiX•12mo ago

cap5lut

REPL Result: Success

record R(HashSet<string> Names);
Console.WriteLine(new R(new()).Equals(new R(new())));

record R(HashSet<string> Names);
Console.WriteLine(new R(new()).Equals(new R(new())));

Console Output

False

False

Compile: 580.747ms | Execution: 107.539ms | React with ❌ to remove this embed.

cap5lut•12mo ago

long story short, u would have to provide ur own implementation of bool Equals(object? other) for NotificationSettingsDto. which means u have to rewrite it as normal class as u can not override that method (note that u have to override int GetHashCode() as well then) oh, and this is also the case for most other reference types (especially collections)

SWEETPONYOP•12mo ago

oh no

Ok, I will try to write my own implementation of GetHashCode and Equals

cap5lut•12mo ago

dotnet provides a helper struct for the hash code: https://learn.microsoft.com/en-us/dotnet/api/system.hashcode?view=net-8.0 but it will still be tricky because of the hash set. even with the same contents, they could have a different order which u will have to account for

SWEETPONYOP•12mo ago

public virtual bool Equals( NotificationSettingsDto? other )             
{                                                                        
    return other != null                                                 
           && NotificationSettingsId.Equals(other.NotificationSettingsId)
           && EventCategories.SequenceEqual(other.EventCategories)       
           && EventNames.SequenceEqual(other.EventNames)                 
           && ChannelSettings.SequenceEqual(other.ChannelSettings)       
           && IsEnabled.Equals(other.IsEnabled)                          
           && TemplateMessage.Equals(other.TemplateMessage);             
}

public virtual bool Equals( NotificationSettingsDto? other )             
{                                                                        
    return other != null                                                 
           && NotificationSettingsId.Equals(other.NotificationSettingsId)
           && EventCategories.SequenceEqual(other.EventCategories)       
           && EventNames.SequenceEqual(other.EventNames)                 
           && ChannelSettings.SequenceEqual(other.ChannelSettings)       
           && IsEnabled.Equals(other.IsEnabled)                          
           && TemplateMessage.Equals(other.TemplateMessage);             
}

is it correct? hmm doesn't work as expected for me haha

cap5lut•12mo ago

if the underlying arrays of the hash sets have a different size, it can affect the buckets and thus the order in which the items are stored. so eg if u have an hashset A and B and they both contain only "hello" and "world", it could be that on iteration one would yield "hello" first, while the other yields "world" first thus SequenceEqual wont be enough either

SWEETPONYOP•12mo ago

ok I will use List instead harold

cap5lut•12mo ago

u would have to do something like

HashSet<string> temp = new(EventNames);
temp.UnionWith(other.EventNames);
temp.Count == EventNames.Count

HashSet<string> temp = new(EventNames);
temp.UnionWith(other.EventNames);
temp.Count == EventNames.Count

to test if they contain the same elements for the hash code u would have to sort the elements somehow and use that to compute the hash code

SWEETPONYOP•12mo ago

I don't think it is optimal solution catshy

Imagine doing this in each Equals

cap5lut•12mo ago

or u use a SortedSet<T>, then u can use at least SequenceEqual and alike

SWEETPONYOP•12mo ago

now it works:

public bool Equals( NotificationSettingsDto? other )                     
{                                                                        
    return other != null                                                 
           && NotificationSettingsId.Equals(other.NotificationSettingsId)
           && EventCategories.SequenceEqual(other.EventCategories)       
           && EventNames.SequenceEqual(other.EventNames)                 
           && ChannelSettings.SequenceEqual(other.ChannelSettings)       
           && IsEnabled.Equals(other.IsEnabled)                          
           && TemplateMessage.Equals(other.TemplateMessage);             
}                                                                        
                                                                         
public override int GetHashCode()                                        
{                                                                        
    return HashCode.Combine(                                             
        NotificationSettingsId,                                          
        EventCategories,                                                 
        EventNames,                                                      
        ChannelSettings,                                                 
        IsEnabled,                                                       
        TemplateMessage);                                                
}

public bool Equals( NotificationSettingsDto? other )                     
{                                                                        
    return other != null                                                 
           && NotificationSettingsId.Equals(other.NotificationSettingsId)
           && EventCategories.SequenceEqual(other.EventCategories)       
           && EventNames.SequenceEqual(other.EventNames)                 
           && ChannelSettings.SequenceEqual(other.ChannelSettings)       
           && IsEnabled.Equals(other.IsEnabled)                          
           && TemplateMessage.Equals(other.TemplateMessage);             
}                                                                        
                                                                         
public override int GetHashCode()                                        
{                                                                        
    return HashCode.Combine(                                             
        NotificationSettingsId,                                          
        EventCategories,                                                 
        EventNames,                                                      
        ChannelSettings,                                                 
        IsEnabled,                                                       
        TemplateMessage);                                                
}

thanks for helping

cap5lut•12mo ago

im pretty sure the hashcode is still wrong

MODiX•12mo ago

cap5lut

REPL Result: Success

Console.WriteLine(new SortedSet<string>().GetHashCode());
Console.WriteLine(new SortedSet<string>().GetHashCode());

Console.WriteLine(new SortedSet<string>().GetHashCode());
Console.WriteLine(new SortedSet<string>().GetHashCode());

Console Output

37582766
45729591

37582766
45729591

Compile: 458.462ms | Execution: 31.802ms | React with ❌ to remove this embed.

cap5lut•12mo ago

u would have to do something like

HashCode hashCode = new();
hashCode.Add(NotificationSettingsId);
foreach (var category in EventCategories) hashCode.Add(category);
// ...
return hashCode.ToHashCode();

HashCode hashCode = new();
hashCode.Add(NotificationSettingsId);
foreach (var category in EventCategories) hashCode.Add(category);
// ...
return hashCode.ToHashCode();

SWEETPONYOP•12mo ago

public override int GetHashCode()                    
{                                                    
    var hash = new HashCode();                       
                                                     
    hash.Add(NotificationSettingsId);                
    hash.Add(IsEnabled);                             
    hash.Add(TemplateMessage);                       
                                                     
    foreach (var eventCategory in EventCategories)   
        hash.Add(eventCategory);                     
                                                     
    foreach (var eventName in EventNames)            
        hash.Add(eventName);                         
                                                     
    foreach (var channelSettings in ChannelSettings) 
        hash.Add(channelSettings);                   
                                                     
    return hash.ToHashCode();                        
}

public override int GetHashCode()                    
{                                                    
    var hash = new HashCode();                       
                                                     
    hash.Add(NotificationSettingsId);                
    hash.Add(IsEnabled);                             
    hash.Add(TemplateMessage);                       
                                                     
    foreach (var eventCategory in EventCategories)   
        hash.Add(eventCategory);                     
                                                     
    foreach (var eventName in EventNames)            
        hash.Add(eventName);                         
                                                     
    foreach (var channelSettings in ChannelSettings) 
        hash.Add(channelSettings);                   
                                                     
    return hash.ToHashCode();                        
}

done! I hope it's optimal way to get hashcode

cap5lut•12mo ago

its definitifely the recommended way ;p but now that i think about it, it might also be okay to just use the NotificationSettingsId for the hash code the contract is basically, if 2 objects of the same type yield true for Equals(), they have to have the same hash code, but not vice versa, meaning two objects producing the same hash code, do not have to return true for Equals()

SWEETPONYOP•12mo ago

thanks for helping bro

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✅ How to find objects that changed?