Crash: Realm.SyncSession is only valid for synchronized Realms about realm-dotnet

[sync-by-unito]

➤ PM Bot commented:

Jira ticket: RNET-1128

[papafe]

Hi @softlion, thanks for your report.
The exception that you're seeing should be raised when trying to get a SyncSession on a local realm. From the code snippets that you posted it seems you're indeed creating a local realm, but I don't see you accessing SyncSession anywhere, so I'm not sure how it could happen. I also took a look at our source code and we access SyncSession only with a synchronized realm (when opening the realm with FlexibleSyncConfiguration or PartitionSyncConfiguration), so it shouldn't be possible.

Is that the whole stack trace you're getting? From that I can't see where the SyncSession is accessed.
Would it be possible to for you to create a repro case and send it to us? This would be really helpful

[softlion]

That triggers the issue.

The key that triggers it is the json serializer (using System.Text.Json;)

    [Fact]
    public async Task TriggerRealmBug()
    {
        using var db = Realm.GetInstance(new InMemoryConfiguration("unittests"));

        var walletId = "someId";
        var wallet = new DbWallet { WalletId = walletId };
        await db.WriteAsync(() => { db.Add(wallet); });
        
        wallet = db.Find<DbWallet>(walletId);
        await db.WriteAsync(() =>  { wallet.Alias = "some new value"; });
        
        var dbWallets = db.All<DbWallet>().ToList();
        Assert.Single(dbWallets);

        //Crash here
        var jsonWallets = JsonSerializer.Serialize(db.All<DbWallet>().ToList());
    }

 public partial class DbWallet : IRealmObject
{
    [PrimaryKey]
    public string WalletId { get; set; }
    public string? Alias { get; set; }
}

I worked around using a new domain object and mapperly.
But that used to work, as I am only republishing an existing app with the latest nugets.

[papafe]

Ok, this makes sense. It seems that System.Text.Json is ignoring the IgnoreDataMember attribute we put on the source generated class properties so that they're ignored by the serialization. During the serialization System.Text.Json is trying to access DbWallet.Realm.SyncSession and so the exception is raised.

It seems we need to add the JsonIgnore attribute to be compatible with System.Text.Json. In the meanwhile, you can add special support for IgnoreDataMember as explained here:

//NOTE: This is copied from the link above
var options = new JsonSerializerOptions
{
    TypeInfoResolver = new DefaultJsonTypeInfoResolver
    {
        Modifiers = { DetectIgnoreDataMemberAttribute }
    }
};

JsonSerializer.Serialize(new MyPoco(), options); // {"Value":3}

static void DetectIgnoreDataMemberAttribute(JsonTypeInfo typeInfo)
{
    if (typeInfo.Kind != JsonTypeInfoKind.Object)
        return;

    foreach (JsonPropertyInfo propertyInfo in typeInfo.Properties)
    {
        if (propertyInfo.AttributeProvider is ICustomAttributeProvider provider &&
            provider.IsDefined(typeof(IgnoreDataMemberAttribute), inherit: true))
        {
            // Disable both serialization and deserialization 
            // by unsetting getter and setter delegates
            propertyInfo.Get = null;
            propertyInfo.Set = null;
        }
    }
}

To be honest I am surprised this was working before. You said you updated your nuget packages and this stopped working. What nuget packages did you exactly update?

[nirinchev]

Edit: Looks like @papafe beat me to this 😅 This is just repeating what Ferdinando is saying, but with less detail.

Looks like the json serializer is trying to serialize the Realm property on DBWallet, even though it's annotated with IgnoreDataMember. I don't think we can polyfill JsonIgnoreAttribute, so we'll probably need to apply it if possible based on the compilation target.

[softlion]

Ok, this makes sense. It seems that System.Text.Json is ignoring the IgnoreDataMember attribute we put on the source generated class properties so that they're ignored by the serialization. During the serialization System.Text.Json is trying to access DbWallet.Realm.SyncSession and so the exception is raised.

It seems we need to add the JsonIgnore attribute to be compatible with System.Text.Json. In the meanwhile, you can add special support for IgnoreDataMember as explained here:

//NOTE: This is copied from the link above
var options = new JsonSerializerOptions
{
    TypeInfoResolver = new DefaultJsonTypeInfoResolver
    {
        Modifiers = { DetectIgnoreDataMemberAttribute }
    }
};

JsonSerializer.Serialize(new MyPoco(), options); // {"Value":3}

static void DetectIgnoreDataMemberAttribute(JsonTypeInfo typeInfo)
{
    if (typeInfo.Kind != JsonTypeInfoKind.Object)
        return;

    foreach (JsonPropertyInfo propertyInfo in typeInfo.Properties)
    {
        if (propertyInfo.AttributeProvider is ICustomAttributeProvider provider &&
            provider.IsDefined(typeof(IgnoreDataMemberAttribute), inherit: true))
        {
            // Disable both serialization and deserialization 
            // by unsetting getter and setter delegates
            propertyInfo.Get = null;
            propertyInfo.Set = null;
        }
    }
}

To be honest I am surprised this was working before. You said you updated your nuget packages and this stopped working. What nuget packages did you exactly update?

maui, realm, json, and some others.
It may not have worked previously though, it may only not have reported the crash.
The tools have improved and now report the crash.

Anyway now we found the issue.