Realm Queries on Background Queue

ChatDetailsRepoRealm.swift

    public func storeChatDetailsAsync(
        _ item: ChatDetailsInfoType,
        callback: @escaping GroupChatDetailsFetchCompletion)
    {
        self._queue.async
        {
            [weak weakSelf = self] in
            
            guard let strongSelf = weakSelf
            else
            {
                callback(.error(WeakifyError()))
                return
            }
            
            if let saveError = strongSelf.implStoreChatDetails(item)
            {
                callback(.error(saveError))
            }
            else
            {
                callback(.success(item))
            }
        }
    }
    
    private func implStoreChatDetails(_ item: ChatDetailsInfoType) -> Error?
    {
        precondition(!Thread.isMainThread)
        let realm: Realm = self._realmBuilder()
        
        do
        {
            try realm.write
            {
                let newItem = ChatDetailsInfoRealm(withChatDetails: item)
                realm.add(newItem, update: true)                
            }
            
            return nil
        }
        catch
        {
            return error
        }
    }

Factory.swift

func buildChatDetailsController()
{
    // The repo class might be created on main thread
  
    let chatDetailsRepo: ChatDetailsRepoType =
        ChatDetailsRepoRealm(
            withRealmBuilder: appSession.getRealmStorageBuilderBlock(),
            queue: chatDetailsDbQueue)
}        

Session.swift

public typealias RealmBuilderBlock = () -> RealmSwift.Realm


public func getRealmStorageBuilderBlock() -> RealmBuilderBlock
{
    let result: RealmBuilderBlock =
    {
        // creates a default realm
        //
        return Realm()
    }
        
    return result
}