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  • What is the most elegant way to validate the presence of ONLY one out of two attributes using Rails?

    - by marcgg
    class Followup < ActiveRecord::Base belongs_to :post belongs_to :comment end This model needs to only have either a post or a comment, but only one of the two. Here's the rspec for what I'm trying to do: it "should be impossible to have both a comment and a post" do followup = Followup.make followup.comment = Comment.make followup.should be_valid followup.post = Post.make followup.should_not be_valid end I can see a bunch of ways of doing this, but what would be the most elegant way of doing this?

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  • When is a good time to start thinking about scaling?

    - by Slokun
    I've been designing a site over the past couple days, and been doing some research into different aspects of scaling a site horizontally. If things go as planned, in a few months (years?) I know I'd need to worry about scaling the site up and out, since the resources it would end up consuming would be huge. So, this got me to thinking, when is the best time to start thinking about, and designing for, scalability? If you start too early on, you could easily over complicate your design, and make it impossible to actually build. You could also get too caught up in the details, the architecture, whatever, and wind up getting nothing done. Also, if you do get it working, but the site never takes off, you may have wasted a good chunk of extra effort. On the other hand, you could be saving yourself a ton of effort down the road. Designing it from the ground up to be big would make it much easier later on to let it grow big, with very little rewriting going on. I know for what I'm working on, I've decided to make at least a few choices now on the side of scaling, but I'm not going to do a complete change of thinking to get it to scale completely. Notably, I've redesigned my database from a conventional relational design to one similar to what was suggested on the Reddit site linked below, and I'm going to give memcache a try. So, the basic question, when is a good time to start thinking or worrying about scaling, and what are some good designs, tips, etc. for when doing so? A couple of things I've been reading, for those who are interested: http://www.codinghorror.com/blog/2009/06/scaling-up-vs-scaling-out-hidden-costs.html http://highscalability.com/blog/2010/5/17/7-lessons-learned-while-building-reddit-to-270-million-page.html http://developer.yahoo.com/performance/rules.html

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  • How to make emacs stay in the current directory

    - by Mad Wombat
    When I start working on a project in emacs, I use M-x cd to get into the project root directory. But every time I use C-x C-f to open a file in one of the subdirectories (like app/model/Store.rb) emacs changes current directory to that of the file. Is there a way to make emacs stay at the root?

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  • Many-To-Many Query with Linq-To-NHibernate

    - by rjygraham
    Ok guys (and gals), this one has been driving me nuts all night and I'm turning to your collective wisdom for help. I'm using Fluent Nhibernate and Linq-To-NHibernate as my data access story and I have the following simplified DB structure: CREATE TABLE [dbo].[Classes]( [Id] [bigint] IDENTITY(1,1) NOT NULL, [Name] [nvarchar](100) NOT NULL, [StartDate] [datetime2](7) NOT NULL, [EndDate] [datetime2](7) NOT NULL, CONSTRAINT [PK_Classes] PRIMARY KEY CLUSTERED ( [Id] ASC ) CREATE TABLE [dbo].[Sections]( [Id] [bigint] IDENTITY(1,1) NOT NULL, [ClassId] [bigint] NOT NULL, [InternalCode] [varchar](10) NOT NULL, CONSTRAINT [PK_Sections] PRIMARY KEY CLUSTERED ( [Id] ASC ) CREATE TABLE [dbo].[SectionStudents]( [SectionId] [bigint] NOT NULL, [UserId] [uniqueidentifier] NOT NULL, CONSTRAINT [PK_SectionStudents] PRIMARY KEY CLUSTERED ( [SectionId] ASC, [UserId] ASC ) CREATE TABLE [dbo].[aspnet_Users]( [ApplicationId] [uniqueidentifier] NOT NULL, [UserId] [uniqueidentifier] NOT NULL, [UserName] [nvarchar](256) NOT NULL, [LoweredUserName] [nvarchar](256) NOT NULL, [MobileAlias] [nvarchar](16) NULL, [IsAnonymous] [bit] NOT NULL, [LastActivityDate] [datetime] NOT NULL, PRIMARY KEY NONCLUSTERED ( [UserId] ASC ) I omitted the foreign keys for brevity, but essentially this boils down to: A Class can have many Sections. A Section can belong to only 1 Class but can have many Students. A Student (aspnet_Users) can belong to many Sections. I've setup the corresponding Model classes and Fluent NHibernate Mapping classes, all that is working fine. Here's where I'm getting stuck. I need to write a query which will return the sections a student is enrolled in based on the student's UserId and the dates of the class. Here's what I've tried so far: 1. var sections = (from s in this.Session.Linq<Sections>() where s.Class.StartDate <= DateTime.UtcNow && s.Class.EndDate > DateTime.UtcNow && s.Students.First(f => f.UserId == userId) != null select s); 2. var sections = (from s in this.Session.Linq<Sections>() where s.Class.StartDate <= DateTime.UtcNow && s.Class.EndDate > DateTime.UtcNow && s.Students.Where(w => w.UserId == userId).FirstOrDefault().Id == userId select s); Obviously, 2 above will fail miserably if there are no students matching userId for classes the current date between it's start and end dates...but I just wanted to try. The filters for the Class StartDate and EndDate work fine, but the many-to-many relation with Students is proving to be difficult. Everytime I try running the query I get an ArgumentNullException with the message: Value cannot be null. Parameter name: session I've considered going down the path of making the SectionStudents relation a Model class with a reference to Section and a reference to Student instead of a many-to-many. I'd like to avoid that if I can, and I'm not even sure it would work that way. Thanks in advance to anyone who can help. Ryan

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  • How can I await the first completed async task of a list in .Net?

    - by Eyal
    My input is a long list of files located on an Amazon S3 server. I'd like to download the metadata of the files, compute the hashes of the local files, and compare the metadata hash with the local files' hash. Currently, I use a loop to start all the metadata downloads asynchronously, then as each completes, compute MD5 on the local file if needed and compare. Here's the code (just the relevant lines): Dim s3client As New AmazonS3Client(KeyId.Text, keySecret.Text) Dim responseTasks As New List(Of System.Tuple(Of ListViewItem, Task(Of GetObjectMetadataResponse))) For Each lvi As ListViewItem In lvStatus.Items Dim gomr As New Amazon.S3.Model.GetObjectMetadataRequest gomr.BucketName = S3FileDialog.GetBucketName(lvi.SubItems(2).Text) gomr.Key = S3FileDialog.GetPrefix(lvi.SubItems(2).Text) responseTasks.Add(New System.Tuple(Of ListViewItem, Task(Of GetObjectMetadataResponse))(lvi, s3client.GetObjectMetadataAsync(gomr))) Next For Each t As System.Tuple(Of ListViewItem, Task(Of GetObjectMetadataResponse)) In responseTasks Dim response As GetObjectMetadataResponse = Await t.Item2 If response.ETag.Trim(""""c) = MD5CalcFile(lvi.SubItems(1).Text) Then lvi.SubItems(3).Text = "Match" UpdateLvi(lvi) End If Next I've got two problems: I'm awaiting the reponses in the order that I made them. I'd rather process them in the order that they complete so that I get them faster. The MD5 calculation is long and synchronous. I tried making it async but the process locked up. I think that the MD5 task was added to the end of .Net's task list and it didn't get to run until all the downloads completed. Ideally, I process the response as they arrive, not in order, and the MD5 is asynchronous but gets a chance to run. Edit: Incorporating WhenAll, it looks like this now: Dim s3client As New Amazon.S3.AmazonS3Client(KeyId.Text, keySecret.Text) Dim responseTasks As New Dictionary(Of Task(Of GetObjectMetadataResponse), ListViewItem) For Each lvi As ListViewItem In lvStatus.Items Dim gomr As New Amazon.S3.Model.GetObjectMetadataRequest gomr.BucketName = S3FileDialog.GetBucketName(lvi.SubItems(2).Text) gomr.Key = S3FileDialog.GetPrefix(lvi.SubItems(2).Text) responseTasks.Add(s3client.GetObjectMetadataAsync(gomr), lvi) Next Dim startTime As DateTimeOffset = DateTimeOffset.Now Do While responseTasks.Count > 0 Dim currentTask As Task(Of GetObjectMetadataResponse) = Await Task.WhenAny(responseTasks.Keys) Dim response As GetObjectMetadataResponse = Await currentTask If response.ETag.Trim(""""c) = MD5CalcFile(lvi.SubItems(1).Text) Then lvi.SubItems(3).Text = "Match" UpdateLvi(lvi) End If Loop MsgBox((DateTimeOffset.Now - startTime).ToString) The UI locks up momentarily whenever MDSCalcFile is done. The whole loop takes about 45s and the first file's MD5 result happens within 1s of starting. If I change the line to: If response.ETag.Trim(""""c) = Await Task.Run(Function () MD5CalcFile(lvi.SubItems(1).Text)) Then The UI doesn't lock up when MD5CalcFile is done. The whole loop takes about 75s, up from 45s, and the first file's MD5 result happens after 40s of waiting.

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  • Convert integer enum to string

    - by user216205
    Hi Guys, considering the following enum: public enum LeadStatus { Cold = 1, Warm = 2, Hot = 3, Quote = 5, Convert = 6 } How can I convert the integer value back to string when I pull the value from a database. I've tried: DomainModel.LeadStatus status = (DomainModel.LeadStatus)Model.Status; but all I seem to get is "status = 0"

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  • Wicket and Spring Intergation

    - by Vinothbabu
    I have a wicket contact form, and i receive the form object. Now i need to pass this object to Spring Service. package com.mysticcoders.mysticpaste.web.pages; import org.apache.wicket.markup.html.WebPage; import org.apache.wicket.markup.html.form.Form; import org.apache.wicket.markup.html.form.TextField; import org.apache.wicket.markup.html.panel.FeedbackPanel; import com.mysticcoders.mysticpaste.model.Contact; import org.apache.wicket.model.CompoundPropertyModel; import com.mysticcoders.mysticpaste.services.IContact; public class FormPage extends WebPage { private Contact contact; private IContact icontact; public FormPage() { // Add a FeedbackPanel for displaying our messages FeedbackPanel feedbackPanel = new FeedbackPanel("feedback"); add(feedbackPanel); Form<Object> form = new Form<Object>("contactForm", new CompoundPropertyModel<Object>(contact)) { private static final long serialVersionUID = 1L; protected void onSubmit(Contact contact) { icontact.saveContact(contact); } }; form.add(new TextField<Object>("name")); form.add(new TextField<Object>("email")); form.add(new TextField<Object>("country")); form.add(new TextField<Object>("age")); add(form); // add a simple text field that uses Input's 'text' property. Nothing // can go wrong here } } I am pretty much sure that we need to do something with application-context xml where i may need to wire out. My Application-context.xml <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd"> <bean id="WicketApplication" class="com.mysticcoders.mysticpaste.web.pages.WicketApplication" /> </beans> My Question is simple. What should i do which can make my onSubmit method call the Spring Service? Could someone let me know what needs to modified in my Application-context.xml so that once the form gets submitted, it contacts the Spring Service class.

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  • Recalculate Counter Cache of 120k Records [Rails / ActiveRecord]

    - by Sebastian
    The following situation: I have a poi model, which has many pictures (1:n). I want to recalculate the counter_cache column, because the values are inconsistent. I've tried to iterate within ruby over each record, but this takes much too long and quits sometimes with some "segmentation fault" bugs. So i wonder, if its possible to do this with a raw sql query?

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  • finding ALL cycles in a huge sparse matrix

    - by Andy
    Hi there, First of all I'm quite a Java beginner, so I'm not sure if this is even possible! Basically I have a huge (3+million) data source of relational data (i.e. A is friends with B+C+D, B is friends with D+G+Z (but not A - i.e. unmutual) etc.) and I want to find every cycle within this (not necessarily connected) directed graph. I've found this thread (http://stackoverflow.com/questions/546655/finding-all-cycles-in-graph/549402#549402) which has pointed me to Donald Johnson's (elementary) cycle-finding algorithm which, superficially at least, looks like it'll do what I'm after (I'm going to try when I'm back at work on Tuesday - thought it wouldn't hurt to ask in the meanwhile!). I had a quick scan through the code of the Java implementation of Johnson's algorithm (in that thread) and it looks like a matrix of relations is the first step, so I guess my questions are: a) Is Java capable of handling a 3+million*3+million matrix? (was planning on representing A-friends-with-B by a binary sparse matrix) b) Do I need to find every connected subgraph as my first problem, or will cycle-finding algorithms handle disjoint data? c) Is this actually an appropriate solution for the problem? My understanding of "elementary" cycles is that in the graph below, rather than picking out A-B-C-D-E-F it'll pick out A-B-F, B-C-D etc. but that's not the end of the world given the task. E / \ D---F / \ / \ C---B---A d) If necessary, I can simplify the problem by enforcing mutuality in relations - i.e. A-friends-with-B <== B-friends-with-A, and if really necessary I can maybe cut down the data size, but realistically it is always going to be around the 1mil mark. z) Is this a P or NP task?! Am I biting off more than I can chew? Thanks all, any help appreciated! Andy

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  • Recommend me an architecture for this Facebook application

    - by andybaird
    Firstly, this question is subjective. There is not a right answer for this question and it really depends on what works for you. I'm hoping to use this thread as a breeding ground for ideas. I hope this is acceptable in this medium. I'm working on building a Facebook app that will be replacing an already popular app that gets ~50k hits a day. The original app is using a very typical LAMP setup with help from some Zend libraries for database layer extraction. For the most part the app worked well, except to solve a lot of issues I ended up fragmenting tables to speed things up. As a result, I couldn't do a lot of things with the app that I wanted to (namely any processing using aggregate data that needed to be returned quickly) So I'm starting to design plans for the next version of this application, and I have a whole bunch of new and cool features that I know would choke my current setup. I'm looking for technological recommendations of data storage methods that scale well. The database does not necessarily need to be relational, simple key/value storage would suffice (although at present time I know little to nothing about KV stores) What's your recommendation? How would you tackle this? I'd like to take a completely free approach to this -- although I am most familiar and comfortable using PHP, I want to leave all technical options open.

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  • Django: Setting up database code tables (aka reference tables, domain tables)?

    - by User
    Often times applications will need some database code tables (aka reference tables or domain tables or lookup tables). Suppose I have a model class called Status with a field called name that could hold values like: Canceled Pending InProgress Complete Where and at what point would I setup these values in Django? Its like a one time operation to setup these values in the database. Infrequently, these values could be added to.

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  • What RESTful API would you use for a turn-based game server?

    - by Ross
    How would you model a turn-based game server as a RESTful API? For example, a chess server, where you could play a game of chess against another client of the same API. You would need some way of requesting and negotiating a game with the other client, and some way of playing the individual moves of the game. Is this a good candidate for a REST (RESTful) API? Or should this be modelled a different way?

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  • retrieving object information with Doctrine

    - by ajsie
    i want to fetch information from the database using objects. i really like this approach cause this is more OOP: $user = Doctrine_Core::getTable('User')->find(1); echo $user->Email['address']; echo $user->Phonenumbers[0]->phonenumber; rather than: $q = Doctrine_Query::create() ->from('User u') ->leftJoin('u.Email e') ->leftJoin('u.Phonenumbers p') ->where('u.id = ?', 1); $user = $q->fetchOne(); echo $user->Email['address']; echo $user->Phonenumbers[0]['phonenumber']; the problem is that the first one uses 3 queries (3 different tables), while the second one uses only 1 (and is therefore recommended technique). but i feel that it destroys the object oriented design. cause ORM is meant to give us an OOP approach so that we could focus on objects and not the relational database. but now they want us to go back to use SQL like pattern. there isn't a way to get information form multiple tables not using DQL? the above examples are taken from the documentation: doctrine

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  • XML Schema for a .NET type that inherits and implements

    - by John Ruiz
    Hi, Please consider the following three .NET types: I have an interface, an abstract class, and a concrete class. My question is how to write the XML Schema to include the properties from the interface and from the abstract class. public interface IStartable { bool RequiresKey { get; set; } void Start(object key); } public abstract class Vehicle { uint WheelCount { get; set; } } public class Car : Vehicle, IStartable { public bool RequiresKey { get; set; } public string Make { get; set; } publilc string Model { get; set; } public Car() {} public void Start(object key) { // start car with key } } I don't know how to complete this schema: <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="cars" xmlns="cars" xmlns:c="cars"> <!-- How do I get car to have vehicle's wheelcount AND IStartable's RequiresKey? --> <xs:element name="Car" type="c:Car" /> <xs:complexType name="Car"> <xs:complexContent> <xs:extension base="c:Vehicle"> <xs:group ref=c:CarGroup" /> </xs:extension> </xs:complexContent> </xs:complexType> <xs:group name="CarGroup"> <xs:sequence> <xs:element name="Make" type="xs:token" /> <xs:element name="Model" type="xs:token" /> </xs:sequence> </xs:group> <xs:complexType name="Vehicle"> <xs:sequence> <xs:element name="WheelCount" type="xs:unsignedInt" /> </xs:sequence> </xs:complexType> <xs:complexType name="IStartable"> <xs:sequence> <xs:element name="RequiresKey" type="xs:boolean" /> </xs:sequence> </xs:complexType> </xs:schema>

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  • Pylons error handling

    - by TJ Huffington
    Hello, I am just getting started with Pylons and am confused as to how to account for exceptions. What is the proper way to error check user input (ensure a correct email address, check that it doesn't yet exist in the database, etc ...)? Should these checks go inside the model classes or somewhere else? Sample code would be great.

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  • Sparse (Pseudo) Infinite Grid Data Structure for Web Game

    - by Ming
    I'm considering trying to make a game that takes place on an essentially infinite grid. The grid is very sparse. Certain small regions of relatively high density. Relatively few isolated nonempty cells. The amount of the grid in use is too large to implement naively but probably smallish by "big data" standards (I'm not trying to map the Internet or anything like that) This needs to be easy to persist. Here are the operations I may want to perform (reasonably efficiently) on this grid: Ask for some small rectangular region of cells and all their contents (a player's current neighborhood) Set individual cells or blit small regions (the player is making a move) Ask for the rough shape or outline/silhouette of some larger rectangular regions (a world map or region preview) Find some regions with approximately a given density (player spawning location) Approximate shortest path through gaps of at most some small constant empty spaces per hop (it's OK to be a bad approximation often, but not OK to keep heading the wrong direction searching) Approximate convex hull for a region Here's the catch: I want to do this in a web app. That is, I would prefer to use existing data storage (perhaps in the form of a relational database) and relatively little external dependency (preferably avoiding the need for a persistent process). Guys, what advice can you give me on actually implementing this? How would you do this if the web-app restrictions weren't in place? How would you modify that if they were? Thanks a lot, everyone!

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  • Struts2 data tranfer from Jsp to Action using Complex Objects

    - by indra
    Hi, how to use Model-driven or Object-backed approaches to map Complex Object with depth more than one. for example, I have action class with property User object and USer has a address object as its property. Address has street name as property. like .. User.address.streetName In JSP, using s:textfield or other tags how can I represent street name.? Thanks

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  • javascript conflict on accesing DOM

    - by justjoe
    i read this statement from a book i read The Document Object Model or DOM is really not a part of JavaScript but a separate entity existing outside it. Although you can use JavaScript to manipulate DOM objects, other scripting languages may equally well access them too. what is the best way to avoid conflict between javascript and other client-siede scripting language when we have to deal with XMLHTTPRequest object

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  • not unique ids in a route in Rails

    - by Victor P
    In a blog in Rails I want to have paths like http://mydomain.com/posts/28383/comments#21 This is the 21st comment of the 28383th post. The 21 is not an unique id, but the pair 28383, #21 is unique. How can I do this in Rails? Do I have to change the routes? the model? I will be very thankful if you can point me in the right direction Thanks

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  • [Django] How to post to a facebook page

    - by patrick
    Hi! I need to post a status update of one of my facebook page when I create a model into my django project, but I don't know how to do it using the new facebook graph api: http://github.com/facebook/python-sdk/blob/master/src/facebook.py can you explain to me how to do it? Thanks in advance :)

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  • add properties to users google app engine

    - by juanefren
    What is the best way to save a user profile with Google App Engine (Python) ? What I did to solve this problem is create another Model, with a UserProperty, but requesting the profile from the user I have to do something like this: if user: profile = Profile.all().filter('user =', user).fetch(1) if profile: property = s.get().property Any ideas?

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  • Classes to Entities; Like-class inheritence problems

    - by Stacey
    Beyond work, some friends and I are trying to build a game of sorts; The way we structure some of it works pretty well for a normal object oriented approach, but as most developers will attest this does not always translate itself well into a database persistent approach. This is not the absolute layout of what we have, it is just a sample model given for sake of representation. The whole project is being done in C# 4.0, and we have every intention of using Entity Framework 4.0 (unless Fluent nHibernate can really offer us something we outright cannot do in EF). One of the problems we keep running across is inheriting things in database models. Using the Entity Framework designer, I can draw the same code I have below; but I'm sure it is pretty obvious that it doesn't work like it is expected to. To clarify a little bit; 'Items' have bonuses, which can be of anything. Therefore, every part of the game must derive from something similar so that no matter what is 'changed' it is all at a basic enough level to be hooked into. Sounds fairly simple and straightforward, right? So then, we inherit everything that pertains to the game from 'Unit'. Weights, Measures, Random (think like dice, maybe?), and there will be other such entities. Some of them are similar, but in code they will each react differently. We're having a really big problem with abstracting this kind of thing into a database model. Without 'Enum' support, it is proving difficult to translate into multiple tables that still share a common listing. One solution we've depicted is to use a 'key ring' type approach, where everything that attaches to a character is stored on a 'Ring' with a 'Key', where each Key has a Value that represents a type. This works functionally but we've discovered it becomes very sluggish and performs poorly. We also dislike this approach because it begins to feel as if everything is 'dumped' into one class; which makes management and logical structure difficult to adhere to. I was hoping someone else might have some ideas on what I could do with this problem. It's really driving me up the wall; To summarize; the goal is to build a type (Unit) that can be used as a base type (Table per Type) for generic reference across a relatively global scope, without having to dump everything into a single collection. I can use an Interface to determine actual behavior so that isn't too big of an issue. This is 'roughly' the same idea expressed in the Entity Framework.

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