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Autoscaling in a modern world…. Part 1

- by Steve Loethen

It has been a while since I have had time to sit down and blog. I need to make sure I take the time. It helps me to focus on technology and not let the administrivia keep me from doing the things I love. I have been focusing on the cloud for the last couple of years. Specifically the PaaS platform from Microsoft called Azure. Time to dig in.. I wanted to explore Autoscaling. Autoscaling is not native part of Azure. The platform has the needed connection points. You can write code that looks at the health and performance of your application components and react to needed scaling changes. But that means you have to write all the code. Luckily, an add on to the Enterprise Library provides a lot of code that gets you a long way to being able to autoscale without having to start from scratch. The tool set is primarily composed of a Autoscaler object that you need to host. This object, when hosted and configured, looks at the performance criteria you specify and adjusts your application based on your needs. Sounds perfect. I started with the a set of HOL’s that gave me a good basis to understand the mechanics. I worked through labs 1 and 2 just to get the feel, but let’s start our saga at the end of lab3. Lab3 end results in a web application, hosted in Azure and a console app running on premise. The web app has a few buttons on it. One set adds messages to a queue, another removes them. A second set of buttons drives processor utilization to 100%. If you want to guess, a safe bet is that the Autoscaler is configured to react to a queue that has filled up or high cpu usage. We will continue our saga in the next post…

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Edit in desktop application with DataGridView

- by SAMIR BHOGAYTA

private void DataGridView_CellContentClick(object sender, DataGridViewCellEventArgs e) { if (e.ColumnIndex == 0) { string s = DataGridView.Rows[e.RowIndex].Cells[1].FormattedValue.ToString(); srno = Convert.ToInt16(s); FormName objFrm = new FormName(s); objFrm.MdiParent = this.MdiParent; objFrm.Show(); } } //Into the New Form public FormName(string id) { uid = id; i = Convert.ToInt16(id); InitializeComponent(); } //Get Detail As per id public void GetDetail() { string detail = "SELECT fieldname1,fieldname2 FROM TableName where PrimaryKeyField = "+id+""; DataSet ds = new DataSet(); ds = (DataSet)prm.RetriveData(detail); } //RetriveData Function public object RetriveData(string query) { // If you have sql connection use SqlConnection OleDbConnection con = new OleDbConnection(constr); OleDbDataAdapter drap = new OleDbDataAdapter(query, con); con.Open(); DataSet ds = new DataSet(); drap.Fill(ds); con.Close(); return ds; }

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indirect rendering issue on 12.04, using ati driver

- by lurscher

I have ubuntu 12.04 64-bit system, when i run glxinfo i see some strange error about indirect rendering and failed to load some lib32/dri/swrast_dri libraries. Any idea what is going on? please let me know if i can enhance the relevant information provided in this question $ LIBGL_DEBUG=verbose glxinfo name of display: :0 libGL: screen 0 does not appear to be DRI2 capable libGL: OpenDriver: trying /usr/lib32/dri/tls/swrast_dri.so libGL: OpenDriver: trying /usr/lib32/dri/swrast_dri.so libGL error: dlopen /usr/lib32/dri/swrast_dri.so failed (/usr/lib32/dri/swrast_dri.so: cannot open shared object file: No such file or directory) libGL: OpenDriver: trying /usr/lib/dri/tls/swrast_dri.so libGL: OpenDriver: trying /usr/lib/dri/swrast_dri.so libGL error: dlopen /usr/lib/dri/swrast_dri.so failed (/usr/lib/dri/swrast_dri.so: cannot open shared object file: No such file or directory) libGL error: unable to load driver: swrast_dri.so libGL error: reverting to indirect rendering display: :0 screen: 0 direct rendering: No (If you want to find out why, try setting LIBGL_DEBUG=verbose) server glx vendor string: ATI server glx version string: 1.4 server glx extensions: GLX_ARB_multisample, GLX_EXT_import_context, GLX_EXT_texture_from_pixmap, GLX_EXT_visual_info, GLX_EXT_visual_rating, GLX_OML_swap_method, GLX_SGI_make_current_read, GLX_SGI_swap_control, GLX_SGIS_multisample, GLX_SGIX_fbconfig, GLX_SGIX_pbuffer, GLX_SGIX_visual_select_group client glx vendor string: Mesa Project and SGI client glx version string: 1.4 client glx extensions: GLX_ARB_create_context, GLX_ARB_create_context_profile, GLX_ARB_get_proc_address, GLX_ARB_multisample, GLX_EXT_import_context, GLX_EXT_visual_info, GLX_EXT_visual_rating, GLX_EXT_framebuffer_sRGB, GLX_EXT_create_context_es2_profile, GLX_MESA_copy_sub_buffer, GLX_MESA_multithread_makecurrent, GLX_MESA_swap_control, GLX_OML_swap_method, GLX_OML_sync_control, GLX_SGI_make_current_read, GLX_SGI_swap_control, GLX_SGI_video_sync, GLX_SGIS_multisample, GLX_SGIX_fbconfig, GLX_SGIX_pbuffer, GLX_SGIX_visual_select_group, GLX_EXT_texture_from_pixmap, GLX_INTEL_swap_event GLX version: 1.4 GLX extensions: GLX_ARB_get_proc_address, GLX_ARB_multisample, GLX_EXT_import_context, GLX_EXT_visual_info, GLX_EXT_visual_rating, GLX_MESA_multithread_makecurrent, GLX_OML_swap_method, GLX_SGI_make_current_read, GLX_SGI_swap_control, GLX_SGIS_multisample, GLX_SGIX_fbconfig, GLX_SGIX_pbuffer, GLX_SGIX_visual_select_group, GLX_EXT_texture_from_pixmap OpenGL vendor string: ATI Technologies Inc. OpenGL renderer string: AMD Radeon HD 6800 Series OpenGL version string: 1.4 (2.1 (4.2.11762 Compatibility Profile Context)) OpenGL extensions: GL_ARB_depth_texture, GL_ARB_draw_buffers, GL_ARB_fragment_program, GL_ARB_fragment_program_shadow, GL_ARB_framebuffer_object, GL_ARB_imaging, GL_ARB_multisample, GL_ARB_multitexture, GL_ARB_occlusion_query, GL_ARB_point_parameters, GL_ARB_point_sprite, GL_ARB_shadow, GL_ARB_shadow_ambient, GL_ARB_texture_border_clamp, GL_ARB_texture_compression, GL_ARB_texture_cube_map, GL_ARB_texture_env_add, GL_ARB_texture_env_combine, GL_ARB_texture_env_crossbar, GL_ARB_texture_env_dot3, GL_ARB_texture_mirrored_repeat, GL_ARB_texture_non_power_of_two, GL_ARB_texture_rectangle, GL_ARB_transpose_matrix, GL_ARB_vertex_program, GL_ARB_window_pos, GL_EXT_abgr, GL_EXT_bgra, GL_EXT_blend_color, GL_EXT_blend_equation_separate, GL_EXT_blend_func_separate, GL_EXT_blend_minmax, GL_EXT_blend_subtract, GL_EXT_copy_texture, GL_EXT_draw_range_elements, GL_EXT_fog_coord, GL_EXT_framebuffer_blit, GL_EXT_framebuffer_multisample, GL_EXT_framebuffer_object, GL_EXT_multi_draw_arrays, GL_EXT_packed_pixels, GL_EXT_point_parameters, GL_EXT_rescale_normal, GL_EXT_secondary_color, GL_EXT_separate_specular_color, GL_EXT_shadow_funcs, GL_EXT_stencil_wrap, GL_EXT_subtexture, GL_EXT_texture3D, GL_EXT_texture_compression_s3tc, GL_EXT_texture_edge_clamp, GL_EXT_texture_env_add, GL_EXT_texture_env_combine, GL_EXT_texture_env_dot3, GL_EXT_texture_lod, GL_EXT_texture_lod_bias, GL_EXT_texture_mirror_clamp, GL_EXT_texture_object, GL_EXT_texture_rectangle, GL_EXT_vertex_array, GL_ATI_draw_buffers, GL_ATI_texture_env_combine3, GL_ATI_texture_mirror_once, GL_ATIX_texture_env_combine3, GL_IBM_texture_mirrored_repeat, GL_INGR_blend_func_separate, GL_NV_texture_rectangle, GL_SGIS_generate_mipmap, GL_SGIS_texture_border_clamp, GL_SGIS_texture_edge_clamp, GL_SGIS_texture_lod, GL_SGIX_shadow_ambient, GL_SUN_multi_draw_arrays

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Java - System design with distributed Queues and Locks

- by sunny

Looking for inputs to evaluate a design for a system (java) which would have a distributed queue serving several (but not too many) nodes. These nodes would process objects present in the distributed queue and on occasion require a distributed lock across the cluster on an arbitrary (distributed) data structures. These (distributed) data structures could potentially lie in a distributed cache. Eliminating Terracotta (DSO),Hazelcast and Akka what could be alternative choices. Currently considering zookeeper as a distributed locking mechanism. Since the recommendation of a znode is not to exceed the 1M size , the understanding is that zookeeper should not be used a distributed queue. And also from Netflix curator tech note 4. So should a distributed cache, say like memcached, or redis be used to emulate a distributed queue ? i.e. The distributed queue will be stored in the caches and will be locked cluster-wide via zookeeper. Are there potential pitfalls with this high-level approach. The objects don't need to be taken off the queue. The object will pass through a lifecycle which will determine its removal from the queue. There would be about 10k+ objects in a queue at a given time changing states and any node could service one stage of the object's lifecycle. (Although not strictly necessary .. i.e. one node could serve the entire lifecycle if that is more efficient.) Any suggestions/alternatives ? sidenote: new to zookeeper ; redis etc.

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Code Trivia #4

- by João Angelo

Got the inspiration for this one in a recent stackoverflow question. What should the following code output and why? class Program { class Author { public string FirstName { get; set; } public string LastName { get; set; } public override string ToString() { return LastName + ", " + FirstName; } } static void Main() { Author[] authors = new[] { new Author { FirstName = "John", LastName = "Doe" }, new Author { FirstName = "Jane", LastName="Doe" } }; var line1 = String.Format("Authors: {0} and {1}", authors); Console.WriteLine(line1); string[] serial = new string[] { "AG27H", "6GHW9" }; var line2 = String.Format("Serial: {0}-{1}", serial); Console.WriteLine(line2); int[] version = new int[] { 1, 0 }; var line3 = String.Format("Version: {0}.{1}", version); Console.WriteLine(line3); } } Update: The code will print the first two lines // Authors: Doe, John and Doe, Jane // Serial: AG27H-6GHW9 and then throw an exception on the third call to String.Format because array covariance is not supported in value types. Given this the third call of String.Format will not resolve to String.Format(string, params object[]), like the previous two, but to String.Format(string, object) which fails to provide the second argument for the specified format and will then cause the exception.

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Libraries for eclipse with CCSv5 from Texas Instruments

- by Alex

My system is Ubuntu 11.10 64bit and i have to run a 32bit version of eclipse to use the TI plugins for CCSv5 but it doesn't work. I tried to run eclipse in a 62bit java environment but it doesn't even start. Now I got "java version "1.6.0_30"" from Sun in 32bit and now eclipse starts but can't use the TI plug ins and I get the following errors in bash: /usr/lib/gtk-2.0/2.10.0/menuproxies/libappmenu.so: falsche ELF-Klasse: ELFCLASS64 /usr/lib/gio/modules/libgvfsdbus.so: falsche ELF-Klasse: ELFCLASS64 Failed to load module: /usr/lib/gio/modules/libgvfsdbus.so and this in a popup-window when Itry to use the plugin: The selected wizard could not be started. Plug-in com.ti.ccstudio.project.ui was unable to load class com.ti.ccstudio.project.ui.internal.wizards.importexport.temp.ExternalProjectImportWizard. An error occurred while automatically activating bundle com.ti.ccstudio.project.ui (352). T tested the libraries with file: /usr/lib/gio/modules/libgvfsdbus.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, stripped /usr/lib/gtk-2.0/2.10.0/menuproxies/libappmenu.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, stripped The ia32-libs are installed.

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HTML5 point and click adventure game code structure with CreateJS

- by user1612686

I'm a programming beginner. I made a tiny one scene point and click adventure game to try to understand simple game logic and came up with this: CreateJS features prototypes for creating bitmap images, sprites and sounds objects. I create them and define their properties in a corresponding function (for example images(); spritesheets(), sounds()...). I then create functions for each animation sequence and "game level" functions, which handle user interactions and play the according animations and sounds for a certain event (when the level is complete, the current level function calls the next level function). And I end up with quite the mess. What would be the "standard (if something like that exists)" OOP approach to structure simple game data and interactions like that? I thought about making game.images, game.sprites, game.sounds objects, which contain all the game data with its properties using CreateJS constructors. game.spriteAnimations and game.tweenAnimations objects for sprite animations and tweens and a game.levelN object, which communicates with a game.interaction object, processing user interaction. Does this make any sense? How do you structure your simple game code? Thanks in advance!

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How can a single script attached to multiple enemies provide separate behavior for each enemy?

- by Syed

I am making a TD game and now stucked at multiple enemies using same script. All is well with scripts attached with one enemy only. Problem is in running multiple enemies. Here is the overview. I have a Enemy object with which I have attached a 'RunEnemy' script. Flow of this script is: RunEnemy.cs: PathF p; p = gameObject.GetComponent<PathF>(); //PathF is a pathfinding algo which has 'search; function which returns a array of path from starting position PathList = p.search(starting position); //------------------------------- if(PathList != null) { //if a way found! if(moving forward) transform.Translate(someXvalue,0,0); //translates on every frame until next grid point else if(moving back) transform.Translate(0,someXvalue,0); ...and so on.. if(reached on next point) PathList = p.search(from this point) //call again from next grid point so that if user placed a tower enemy will run again on the returned path } Now I have attached this script and "PathF.cs" to a single enemy which works perfect. I have then made one more enemy object and attached both of these script to it as well, which is not working they both are overlapping movements. I can't understand why, I have attached these scripts on two different gameobjects but still their values change when either enemy changes its value. I don't want to go with a separate script for each enemy because there would be 30 enemies in a scene. How can I fix this problem?

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SQL Developer: Describe versus Ctrl+Click to Open Database Objects

- by thatjeffsmith

In yesterday’s post I talked about you could use SQL Developer’s Describe (SHIFT+F4) to open a PL/SQL Package at your cursor. You might get an error if you try to describe this… If you actually try to describe the package as you see it in the above screenshot, you’ll get an error: Doh! I neglected to say in yesterday’s post that I was highlighting the package name before I hit SHIFT+F4. This works just fine, but it will work even better in our next release as we’ve fixed this issue. Until then, you can also try the Ctrl+Hover with your mouse. For PL/SQL calls you can open the source immediately based on what you’re hovering over with your mouse cursor. You could try this with “dbms_output.put_line(” too Ctrl+Click, It’s not just for PL/SQL If you don’t like the floating describe windows you get when you do a SHIFT+F4 on a database object, the ctrl+click will work too. Instead of opening a normal ‘hover’ panel, you’ll be taken directly to the object editor for that table, view, etc. Go ahead and try it right now. Paste this into your worksheet, then ctrl+click with your mouse over the table name: select * from scott.emp And now you know, the rest of the story.

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Silverlight Cream for May 29, 2010 -- #872

- by Dave Campbell

In this Issue: Michael Washington, Chris Koenig, Kunal Chowdhury, SilverLaw, Shayne Burgess, Ian T. Lackey, Alan Beasley, Marlon Grech. Shoutouts: Ozymandias has a post up that's not Silverlight necessarily, but it's pretty cool: Typeface Selection Flowchart Damian Schenkelman posted about the latest: Prism 2.2 Release available. Get it at Codeplex. From SilverlightCream.com: Silverlight 4 OData Paging with RX Extensions Michael Washington continues with this OData and Rx post using the View Model Style. Michael has some good external links, good info, and all the code. WP7 Part 4: Morphing and Mapping Chris Koenig has the 4th in his WP7 series he's doing, and this one is on MVVMLight and BingMaps ... code included. Silverlight 4: Interoperability with Excel using the COM Object Kunal Chowdhury has a post up about Excel Interoperability using the COM object including opening an Excel Workbook and writing data out, then modifying the data in the spreadsheet and seeing it updated in the app. Creating A Flexible Surface Effect – Silverlight 4 (Part 1) SilverLaw put up a demo of an awesome 'water ripple' SL4 demo a couple days ago, and now he's got part 1 of a great tutorial explaining it all. Service Operations and the WCF Data Services Client Shayne Burgess has a post up about Service Operations and how they can be used by the WCF Data Services client. Role Based Silverlight Behaviors Also from the Open Light Group, Ian T. Lackey has a post up about Behaviors that takes a list of roles and updates the UI appropriatetly. How to Toggle (Show/Hide) using Behaviours (Behaviors) between Visual States or Storyboards in Expression Blend for Windows Phone Alan Beasley has a quick post up talking about the solution he found to a problem he was having with state switching in a WP7 app. MEFedMVVM: Testability Marlon Grech has another MEFedMVVM post up and he's discussing Testability all rolled in there with everything else :) Stay in the 'Light! Twitter SilverlightNews | Twitter WynApse | WynApse.com | Tagged Posts | SilverlightCream Join me @ SilverlightCream | Phoenix Silverlight User Group Technorati Tags: Silverlight Silverlight 3 Silverlight 4 Windows Phone MIX10

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A WPF Image Button

- by psheriff

Instead of a normal button with words, sometimes you want a button that is just graphical. Yes, you can put an Image control in the Content of a normal Button control, but you still have the button outline, and trying to change the style can be rather difficult. Instead I like creating a user control that simulates a button, but just accepts an image. Figure 1 shows an example of three of these custom user controls to represent minimize, maximize and close buttons for a borderless window. Notice the highlighted image button has a gray rectangle around it. You will learn how to highlight using the VisualStateManager in this blog post.Figure 1: Creating a custom user control for things like image buttons gives you complete control over the look and feel.I would suggest you read my previous blog post on creating a custom Button user control as that is a good primer for what I am going to expand upon in this blog post. You can find this blog post at http://weblogs.asp.net/psheriff/archive/2012/08/10/create-your-own-wpf-button-user-controls.aspx.The User ControlThe XAML for this image button user control contains just a few controls, plus a Visual State Manager. The basic outline of the user control is shown below:<Border Grid.Row="0" Name="borMain" Style="{StaticResource pdsaButtonImageBorderStyle}" MouseEnter="borMain_MouseEnter" MouseLeave="borMain_MouseLeave" MouseLeftButtonDown="borMain_MouseLeftButtonDown"> <VisualStateManager.VisualStateGroups> ... MORE XAML HERE ... </VisualStateManager.VisualStateGroups> <Image Style="{StaticResource pdsaButtonImageImageStyle}" Visibility="{Binding Path=Visibility}" Source="{Binding Path=ImageUri}" ToolTip="{Binding Path=ToolTip}" /></Border>There is a Border control named borMain and a single Image control in this user control. That is all that is needed to display the buttons shown in Figure 1. The definition for this user control is in a DLL named PDSA.WPF. The Style definitions for both the Border and the Image controls are contained in a resource dictionary names PDSAButtonStyles.xaml. Using a resource dictionary allows you to create a few different resource dictionaries, each with a different theme for the buttons.The Visual State ManagerTo display the highlight around the button as your mouse moves over the control, you will need to add a Visual State Manager group. Two different states are needed; MouseEnter and MouseLeave. In the MouseEnter you create a ColorAnimation to modify the BorderBrush color of the Border control. You specify the color to animate as “DarkGray”. You set the duration to less than a second. The TargetName of this storyboard is the name of the Border control “borMain” and since we are specifying a single color, you need to set the TargetProperty to “BorderBrush.Color”. You do not need any storyboard for the MouseLeave state. Leaving this VisualState empty tells the Visual State Manager to put everything back the way it was before the MouseEnter event.<VisualStateManager.VisualStateGroups> <VisualStateGroup Name="MouseStates"> <VisualState Name="MouseEnter"> <Storyboard> <ColorAnimation To="DarkGray" Duration="0:0:00.1" Storyboard.TargetName="borMain" Storyboard.TargetProperty="BorderBrush.Color" /> </Storyboard> </VisualState> <VisualState Name="MouseLeave" /> </VisualStateGroup></VisualStateManager.VisualStateGroups>Writing the Mouse EventsTo trigger the Visual State Manager to run its storyboard in response to the specified event, you need to respond to the MouseEnter event on the Border control. In the code behind for this event call the GoToElementState() method of the VisualStateManager class exposed by the user control. To this method you will pass in the target element (“borMain”) and the state (“MouseEnter”). The VisualStateManager will then run the storyboard contained within the defined state in the XAML.private void borMain_MouseEnter(object sender, MouseEventArgs e){ VisualStateManager.GoToElementState(borMain, "MouseEnter", true);}You also need to respond to the MouseLeave event. In this event you call the VisualStateManager as well, but specify “MouseLeave” as the state to go to.private void borMain_MouseLeave(object sender, MouseEventArgs e){ VisualStateManager.GoToElementState(borMain, "MouseLeave", true);}The Resource DictionaryBelow is the definition of the PDSAButtonStyles.xaml resource dictionary file contained in the PDSA.WPF DLL. This dictionary can be used as the default look and feel for any image button control you add to a window. <ResourceDictionary ... >     <Style TargetType="Border" x:Key="pdsaButtonImageBorderStyle"> <Setter Property="Margin" Value="4" /> <Setter Property="Padding" Value="2" /> <Setter Property="BorderBrush" Value="Transparent" /> <Setter Property="BorderThickness" Value="1" /> <Setter Property="VerticalAlignment" Value="Top" /> <Setter Property="HorizontalAlignment" Value="Left" /> <Setter Property="Background" Value="Transparent" /> </Style>  <Style TargetType="Image" x:Key="pdsaButtonImageImageStyle"> <Setter Property="Width" Value="40" /> <Setter Property="Margin" Value="6" /> <Setter Property="VerticalAlignment" Value="Top" /> <Setter Property="HorizontalAlignment" Value="Left" /> </Style></ResourceDictionary>Using the Button ControlOnce you make a reference to the PDSA.WPF DLL from your WPF application you will see the “PDSAucButtonImage” control appear in your Toolbox. Drag and drop the button onto a Window or User Control in your application. I have not referenced the PDSAButtonStyles.xaml file within the control itself so you do need to add a reference to this resource dictionary somewhere in your application such as in the App.xaml.<Application.Resources> <ResourceDictionary> <ResourceDictionary.MergedDictionaries> <ResourceDictionary Source="/PDSA.WPF;component/PDSAButtonStyles.xaml" /> </ResourceDictionary.MergedDictionaries> </ResourceDictionary></Application.Resources>This will give your buttons a default look and feel unless you override that dictionary on a specific Window or User Control or on an individual button. After you have given a global style to your application and you drag your image button onto a window, the following will appear in your XAML window.<my:PDSAucButtonImage ... />There will be some other attributes set on the above XAML, but you simply need to set the x:Name, the ToolTip and ImageUri properties. You will also want to respond to the Click event procedure in order to associate an action with clicking on this button. In the sample code you download for this blog post you will find the declaration of the Minimize button to be the following:<my:PDSAucButtonImage x:Name="btnMinimize" Click="btnMinimize_Click" ToolTip="Minimize Application" ImageUri="/PDSA.WPF;component/Images/Minus.png" />The ImageUri property is a dependency property in the PDSAucButtonImage user control. The x:Name and the ToolTip we get for free. You have to create the Click event procedure yourself. This is also created in the PDSAucButtonImage user control as follows:private void borMain_MouseLeftButtonDown(object sender, MouseButtonEventArgs e){ RaiseClick(e);}public delegate void ClickEventHandler(object sender, RoutedEventArgs e);public event ClickEventHandler Click;protected void RaiseClick(RoutedEventArgs e){ if (null != Click) Click(this, e);}Since a Border control does not have a Click event you will create one by using the MouseLeftButtonDown on the border to fire an event you create called “Click”.SummaryCreating your own image button control can be done in a variety of ways. In this blog post I showed you how to create a custom user control and simulate a button using a Border and Image control. With just a little bit of code to respond to the MouseLeftButtonDown event on the border you can raise your own Click event. Dependency properties, such as ImageUri, allow you to set attributes on your custom user control. Feel free to expand on this button by adding additional dependency properties, change the resource dictionary, and even the animation to make this button look and act like you want.NOTE: You can download the sample code for this article by visiting my website at http://www.pdsa.com/downloads. Select “Tips & Tricks”, then select “A WPF Image Button” from the drop down list.

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Do I need path finding to make AI avoid obstacles?

- by yannicuLar

How do you know when a path-finding algorithm is really needed? There are contexts, where you just want to improve AI navigation to avoid an object, like a space -ship that won't crash on a planet or a car that already knows where to steer, but needs small corrections to avoid a road bump. As I've seen on similar posts, the obvious solution is to implement some path-finding algorithm, most likely like A*, and let your AI-controlled object to navigate through the path. Now, I have the necessary skills to implement a path-finding algorithm, and I'm not being lazy here, but I'm still a bit skeptical on if this is really needed. I have the impression that path-finding is appropriate to navigate through a maze, or picking a path when there are many alternatives. But in obstacle avoidance, when you do know the path, but need to make slight corrections, is path finding really necessary? Even when the obstacles are too sparse or small ? I mean, in real life, when you're driving and notice a bump on the road, you will just have to pick between steering a bit on the left (and have the bump on your right side) or the other way around. You will not consider stopping, or going backwards. A path finding would be appropriate when you need to pick a route through the city, right ? So, are there any other methods to help AI navigation, except path-finding? And if there are, how do you know when path-fining is the appropriate algorithm ? Thanks for any thoughts

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Converting world space coordinate to screen space coordinate and getting incorrect range of values

- by user1423893

I'm attempting to convert from world space coordinates to screen space coordinates. I have the following code to transform my object position Vector3 screenSpacePoint = Vector3.Transform(object.WorldPosition, camera.ViewProjectionMatrix); The value does not appear to be in screen space coordinates and is not limited to a [-1, 1] range. What step have I missed out in the conversion process? EDIT: Projection Matrix Perspective(game.GraphicsDevice.Viewport.AspectRatio, nearClipPlaneZ, farClipPlaneZ); private void Perspective(float aspect_Ratio, float z_NearClipPlane, float z_FarClipPlane) { nearClipPlaneZ = z_NearClipPlane; farClipPlaneZ = z_FarClipPlane; float yZoom = 1f / (float)Math.Tan(fov * 0.5f); float xZoom = yZoom / aspect_Ratio; matrix_Projection.M11 = xZoom; matrix_Projection.M12 = 0f; matrix_Projection.M13 = 0f; matrix_Projection.M14 = 0f; matrix_Projection.M21 = 0f; matrix_Projection.M22 = yZoom; matrix_Projection.M23 = 0f; matrix_Projection.M24 = 0f; matrix_Projection.M31 = 0f; matrix_Projection.M32 = 0f; matrix_Projection.M33 = z_FarClipPlane / (nearClipPlaneZ - farClipPlaneZ); matrix_Projection.M34 = -1f; matrix_Projection.M41 = 0f; matrix_Projection.M42 = 0f; matrix_Projection.M43 = (nearClipPlaneZ * farClipPlaneZ) / (nearClipPlaneZ - farClipPlaneZ); matrix_Projection.M44 = 0f; } View Matrix // Make our view matrix Matrix.CreateFromQuaternion(ref orientation, out matrix_View); matrix_View.M41 = -Vector3.Dot(Right, position); matrix_View.M42 = -Vector3.Dot(Up, position); matrix_View.M43 = Vector3.Dot(Forward, position); matrix_View.M44 = 1f; // Create the combined view-projection matrix Matrix.Multiply(ref matrix_View, ref matrix_Projection, out matrix_ViewProj); // Update the bounding frustum boundingFrustum.SetMatrix(matrix_ViewProj);

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Strange Misleading Error[XML -2018/ AC-10006] when doing the R12 Cloning

- by [email protected]

During the recent Multi Node to Single Node R12 Clone, Encountered an strange error. When doing the database portion of the clone. Below command 'adclonectx.pl' creates the Context file perl adclonectx.pl contextfile=$ORACLE_HOME/appsutil/SOURCE_CONTEXT_FILE.xml template=$ORACLE_HOME/appsutil/template/adxdbctx.tmp pairsfile=$ORACLE_HOME/appsutil/clone/pairsfile.txt initialnode When running the same command, It dumped the below error, file:/tmp/tmpCtxClone.xml<Line 1, Column 1>: XML-20108: (Fatal Error) Start of root element expected. AC-10006: Exception - org.xml.sax.SAXParseException: file:/tmp/tmpCtxClone.xml<Line 1, Column 1>: XML-20108: (Fatal Error) Start of root element expected. thrown while creating OAVars object for file: /tmp/tmpCtxClone.xml The new database context file has been created : /opt/oracle/product/11.1.0_IOFT/appsutil/IOFT_frws35ta.xml At first site, I suspected that the issue is with format of the source xml file. Hence compared with the working XML file. Result is clean. Below portion of the error struck me Thrown while creating OAVars object for file: /tmp//dummy.xml Cause : The /tmp is 100% full. Fix: Either remove the old files in /tmp directory OR export TEMP=/new/location where there is plenty of free space.

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Converting to and from local and world 3D coordinate spaces?

- by James Bedford

Hey guys, I've been following a guide I found here (http://knol.google.com/k/matrices-for-3d-applications-view-transformation) on constructing a matrix that will allow me to 3D coordinates to an object's local coordinate space, and back again. I've tried to implement these two matrices using my object's look, side, up and location vectors and it seems to be working for the first three coordinates. I'm a little confused as to what I should expect for the w coordinate. Here are couple of examples from the print outs I've made of the matricies that are constructed. I'm passing a test vector of [9, 8, 14, 1] each time to see if I can convert both ways: Basic example: localize matrix: Matrix: 0.000000 -0.000000 1.000000 0.000000 0.000000 1.000000 0.000000 0.000000 1.000000 0.000000 0.000000 0.000000 5.237297 -45.530716 11.021271 1.000000 globalize matrix: Matrix: 0.000000 0.000000 1.000000 0.000000 -0.000000 1.000000 0.000000 0.000000 1.000000 0.000000 0.000000 0.000000 -11.021271 -45.530716 -5.237297 1.000000 test: Vector4f(9.000000, 8.000000, 14.000000, 1.000000) localTest: Vector4f(14.000000, 8.000000, 9.000000, -161.812256) worldTest: Vector4f(9.000000, 8.000000, 14.000000, -727.491455) More complicated example: localize matrix: Matrix: 0.052504 -0.000689 -0.998258 0.000000 0.052431 0.998260 0.002068 0.000000 0.997241 -0.052486 0.052486 0.000000 58.806095 2.979346 -39.396252 1.000000 globalize matrix: Matrix: 0.052504 0.052431 0.997241 0.000000 -0.000689 0.998260 -0.052486 0.000000 -0.998258 0.002068 0.052486 0.000000 -42.413120 5.975957 -56.419727 1.000000 test: Vector4f(9.000000, 8.000000, 14.000000, 1.000000) localTest: Vector4f(-13.508600, 8.486917, 9.290090, 2.542114) worldTest: Vector4f(9.000190, 7.993863, 13.990230, 102.057129) As you can see in the more complicated example, the coordinates after converting both ways loose some precision, but this isn't a problem. I'm just wondering how I should deal with the last (w) coordinate? Should I just set it to 1 after performing the matrix multiplication, or does it look like I've done something wrong? Thanks in advance for your help!

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Why is there never any controversy regarding the switch statement? [closed]

- by Nick Rosencrantz

We all know that the gotostatement should only be used on very rare occasions if at all. It has been discouraged to use the goto statement countless places countless times. But why it there never anything like that about the switch statement? I can understand the position that the switch statement should always be avoided since anything with switch can always be expressed by if...else... which is also more readable and the syntax of the switch statement if difficult to remember. Do you agree? What are the arguments in favor of keeping the 'switch` statement? It can also be difficult to use if what you're testing changes from say an integer to an object, then C++ or Java won't be able to perform the switch and neither C can perform switch on something like a struct or a union. And the technique of fall-through is so very rarely used that I wonder why it was never presented any regret of having switch at all? The only place I know where it is best practice is GUI code and even that switch is probably better coded in a more object-oriented way.

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Screen becomes black after pressing dash or alt-tab

- by cegerxwin

I did an upgrade from 11.04 to 11.10. Unity 3d becomes a black screen after pressing the dash-button or after pressing alt-tab to switch between open windows. I can see the panel on the top(lock,sound,..) and the panel on the left (launcher) but the rest is black. It looks like a maximised black window. The open Windows are active but I cant see them. I logout by pressing logout in the right top corner and pressing enter (because logout is default focused on the dialogue screen) and leave unity3d. Unity3d worked with 11.04 very good. If I press the dash button the dash looks like an 16-Bit or 8-Bit window and buttons for maximise, minimise and close are displayed and looks inverted. I have rebooted my notebook just now and log in to Unity 3D and tested some features of Unity and everything works well. The black thing is only a layer. I can use my desktop but cant see anything because of the layer, but everything works. It seems so, that a layer appear when pressing dash or alt-tab and does not disappear when close dash or choose a running app with alt-tab. you will see the necessary info related video problems: Unity support: /usr/lib/nux/unity_support_test -p OpenGL vendor string: X.Org R300 Project OpenGL renderer string: Gallium 0.4 on ATI RC410 OpenGL version string: 2.1 Mesa 7.11-devel Not software rendered: yes Not blacklisted: yes GLX fbconfig: yes GLX texture from pixmap: yes GL npot or rect textures: yes GL vertex program: yes GL fragment program: yes GL vertex buffer object: yes GL framebuffer object: yes GL version is 1.4+: yes Unity 3D supported: yes xorg glxinfo lspci -nn | grep VGA 01:05.0 VGA compatible controller [0300]: ATI Technologies Inc RC410 [Radeon Xpress 200M] [1002:5a62]

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New Big Data Appliance Security Features

- by mgubar

The Oracle Big Data Appliance (BDA) is an engineered system for big data processing. It greatly simplifies the deployment of an optimized Hadoop Cluster – whether that cluster is used for batch or real-time processing. The vast majority of BDA customers are integrating the appliance with their Oracle Databases and they have certain expectations – especially around security. Oracle Database customers have benefited from a rich set of security features: encryption, redaction, data masking, database firewall, label based access control – and much, much more. They want similar capabilities with their Hadoop cluster. Unfortunately, Hadoop wasn’t developed with security in mind. By default, a Hadoop cluster is insecure – the antithesis of an Oracle Database. Some critical security features have been implemented – but even those capabilities are arduous to setup and configure. Oracle believes that a key element of an optimized appliance is that its data should be secure. Therefore, by default the BDA delivers the “AAA of security”: authentication, authorization and auditing. Security Starts at Authentication A successful security strategy is predicated on strong authentication – for both users and software services. Consider the default configuration for a newly installed Oracle Database; it’s been a long time since you had a legitimate chance at accessing the database using the credentials “system/manager” or “scott/tiger”. The default Oracle Database policy is to lock accounts thereby restricting access; administrators must consciously grant access to users. Default Authentication in Hadoop By default, a Hadoop cluster fails the authentication test. For example, it is easy for a malicious user to masquerade as any other user on the system. Consider the following scenario that illustrates how a user can access any data on a Hadoop cluster by masquerading as a more privileged user. In our scenario, the Hadoop cluster contains sensitive salary information in the file /user/hrdata/salaries.txt. When logged in as the hr user, you can see the following files. Notice, we’re using the Hadoop command line utilities for accessing the data: $ hadoop fs -ls /user/hrdataFound 1 items-rw-r--r-- 1 oracle supergroup 70 2013-10-31 10:38 /user/hrdata/salaries.txt$ hadoop fs -cat /user/hrdata/salaries.txtTom Brady,11000000Tom Hanks,5000000Bob Smith,250000Oprah,300000000 User DrEvil has access to the cluster – and can see that there is an interesting folder called “hrdata”. $ hadoop fs -ls /user Found 1 items drwx------ - hr supergroup 0 2013-10-31 10:38 /user/hrdata However, DrEvil cannot view the contents of the folder due to lack of access privileges: $ hadoop fs -ls /user/hrdata ls: Permission denied: user=drevil, access=READ_EXECUTE, inode="/user/hrdata":oracle:supergroup:drwx------ Accessing this data will not be a problem for DrEvil. He knows that the hr user owns the data by looking at the folder’s ACLs. To overcome this challenge, he will simply masquerade as the hr user. On his local machine, he adds the hr user, assigns that user a password, and then accesses the data on the Hadoop cluster: $ sudo useradd hr $ sudo passwd $ su hr $ hadoop fs -cat /user/hrdata/salaries.txt Tom Brady,11000000 Tom Hanks,5000000 Bob Smith,250000 Oprah,300000000 Hadoop has not authenticated the user; it trusts that the identity that has been presented is indeed the hr user. Therefore, sensitive data has been easily compromised. Clearly, the default security policy is inappropriate and dangerous to many organizations storing critical data in HDFS. Big Data Appliance Provides Secure Authentication The BDA provides secure authentication to the Hadoop cluster by default – preventing the type of masquerading described above. It accomplishes this thru Kerberos integration. Figure 1: Kerberos Integration The Key Distribution Center (KDC) is a server that has two components: an authentication server and a ticket granting service. The authentication server validates the identity of the user and service. Once authenticated, a client must request a ticket from the ticket granting service – allowing it to access the BDA’s NameNode, JobTracker, etc. At installation, you simply point the BDA to an external KDC or automatically install a highly available KDC on the BDA itself. Kerberos will then provide strong authentication for not just the end user – but also for important Hadoop services running on the appliance. You can now guarantee that users are who they claim to be – and rogue services (like fake data nodes) are not added to the system. It is common for organizations to want to leverage existing LDAP servers for common user and group management. Kerberos integrates with LDAP servers – allowing the principals and encryption keys to be stored in the common repository. This simplifies the deployment and administration of the secure environment. Authorize Access to Sensitive Data Kerberos-based authentication ensures secure access to the system and the establishment of a trusted identity – a prerequisite for any authorization scheme. Once this identity is established, you need to authorize access to the data. HDFS will authorize access to files using ACLs with the authorization specification applied using classic Linux-style commands like chmod and chown (e.g. hadoop fs -chown oracle:oracle /user/hrdata changes the ownership of the /user/hrdata folder to oracle). Authorization is applied at the user or group level – utilizing group membership found in the Linux environment (i.e. /etc/group) or in the LDAP server. For SQL-based data stores – like Hive and Impala – finer grained access control is required. Access to databases, tables, columns, etc. must be controlled. And, you want to leverage roles to facilitate administration. Apache Sentry is a new project that delivers fine grained access control; both Cloudera and Oracle are the project’s founding members. Sentry satisfies the following three authorization requirements: Secure Authorization: the ability to control access to data and/or privileges on data for authenticated users. Fine-Grained Authorization: the ability to give users access to a subset of the data (e.g. column) in a database Role-Based Authorization: the ability to create/apply template-based privileges based on functional roles. With Sentry, “all”, “select” or “insert” privileges are granted to an object. The descendants of that object automatically inherit that privilege. A collection of privileges across many objects may be aggregated into a role – and users/groups are then assigned that role. This leads to simplified administration of security across the system. Figure 2: Object Hierarchy – granting a privilege on the database object will be inherited by its tables and views. Sentry is currently used by both Hive and Impala – but it is a framework that other data sources can leverage when offering fine-grained authorization. For example, one can expect Sentry to deliver authorization capabilities to Cloudera Search in the near future. Audit Hadoop Cluster Activity Auditing is a critical component to a secure system and is oftentimes required for SOX, PCI and other regulations. The BDA integrates with Oracle Audit Vault and Database Firewall – tracking different types of activity taking place on the cluster: Figure 3: Monitored Hadoop services. At the lowest level, every operation that accesses data in HDFS is captured. The HDFS audit log identifies the user who accessed the file, the time that file was accessed, the type of access (read, write, delete, list, etc.) and whether or not that file access was successful. The other auditing features include: MapReduce: correlate the MapReduce job that accessed the file Oozie: describes who ran what as part of a workflow Hive: captures changes were made to the Hive metadata The audit data is captured in the Audit Vault Server – which integrates audit activity from a variety of sources, adding databases (Oracle, DB2, SQL Server) and operating systems to activity from the BDA. Figure 4: Consolidated audit data across the enterprise. Once the data is in the Audit Vault server, you can leverage a rich set of prebuilt and custom reports to monitor all the activity in the enterprise. In addition, alerts may be defined to trigger violations of audit policies. Conclusion Security cannot be considered an afterthought in big data deployments. Across most organizations, Hadoop is managing sensitive data that must be protected; it is not simply crunching publicly available information used for search applications. The BDA provides a strong security foundation – ensuring users are only allowed to view authorized data and that data access is audited in a consolidated framework.

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ASP.NET: Using conditionals in data binding expressions

- by DigiMortal

ASP.NET 2.0 has no support for using conditionals in data binding expressions but it will change in ASP.NET 4.0. In this posting I will show you how to implement Iif() function for ASP.NET 2.0 and how ASP.NET 4.0 solves this problem smoothly without any code. Problem Let’s say we have simple repeater. <asp:Repeater runat="server" ID="itemsList"> <HeaderTemplate> <table border="1" cellspacing="0" cellpadding="5"> </HeaderTemplate> <ItemTemplate> <tr> <td align="right"><%# Container.ItemIndex + 1 %>.</td> <td><%# Eval("Title") %></td> </tr> </ItemTemplate> <FooterTemplate> </table> </FooterTemplate> </asp:Repeater> Repeater is bound to data when form loads. protected void Page_Load(object sender, EventArgs e) { var items = new[] { new { Id = 1, Title = "Headline 1" }, new { Id = 2, Title = "Headline 2" }, new { Id = 2, Title = "Headline 3" }, new { Id = 2, Title = "Headline 4" }, new { Id = 2, Title = "Headline 5" } }; itemsList.DataSource = items; itemsList.DataBind(); } We need to format even and odd rows differently. Let’s say we want even rows to be with whitesmoke background and odd rows with white background. Just like shown on screenshot on right. Our first thought is to use some simple expression to avoid writing custom methods. We cannot use construct like this <%# Container.ItemIndex % 2==0 ? "white" : "whitesmoke" %> because all we get are template compilation errors. ASP.NET 2.0: Iif() method For ASP.NET 2.0 pages and controls we can create Iif() method and call it from our templates. This is out Iif() method. protected object Iif(bool condition, object trueResult, object falseResult) { return condition ? trueResult : falseResult; } And here you can see how to use it. <asp:Repeater runat="server" ID="itemsList"> <HeaderTemplate> <table border="1" cellspacing="0" cellpadding="5"> </HeaderTemplate> <ItemTemplate> <tr style='background-color:' <%# Iif(Container.ItemIndex % 2==0 ? "white" : "whitesmoke") %>'> <td align="right"> <%# Container.ItemIndex + 1 %>.</td> <td> <%# Eval("Title") %></td> </tr> </ItemTemplate> <FooterTemplate> </table> </FooterTemplate> </asp:Repeater> This method does not care about types because it works with all objects (and value-types). I had to define this method in code-behind file of my user control because using this method as extension method made it undetectable for ASP.NET template engine. ASP.NET 4.0: Conditionals are supported In ASP.NET 4.0 we will write … hmm … we will write nothing special. Here is solution. <asp:Repeater runat="server" ID="itemsList"> <HeaderTemplate> <table border="1" cellspacing="0" cellpadding="5"> </HeaderTemplate> <ItemTemplate> <tr style='background-color:' <%# Container.ItemIndex % 2==0 ? "white" : "whitesmoke" %>'> <td align="right"> <%# Container.ItemIndex + 1 %>.</td> <td> <%# Eval("Title") %></td> </tr> </ItemTemplate> <FooterTemplate> </table> </FooterTemplate> </asp:Repeater> Yes, it works well. :)

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How to enable Unity 3D support in 12.04 using open-source drivers for RadeonHD cards?

- by martin

As the title says I can't enable the Unity 3D support when I'm using open-source drivers (xorg-edgers). I have an xfx Radeon HD 6950 by the way. If I install the proprietary 12.3 drivers from AMD it works, but I get poorer 2D performance than the open-source drivers and also I get some freezes and lock ups at random. So because of this I'm trying the open-source drivers and so far no issues at all, except this one. Running this command $ /usr/lib/nux/unity_support_test -p shows this: OpenGL vendor string: VMware, Inc. OpenGL renderer string: Gallium 0.4 on llvmpipe (LLVM 0x300) OpenGL version string: 2.1 Mesa 8.0.2 Not software rendered: no Not blacklisted: yes GLX fbconfig: yes GLX texture from pixmap: yes GL npot or rect textures: yes GL vertex program: yes GL fragment program: yes GL vertex buffer object: yes GL framebuffer object: yes GL version is 1.4+: yes Unity 3D supported: no And this command $ lspci -nn | grep VGA shows: 01:00.0 VGA compatible controller [0300]: Advanced Micro Devices [AMD] nee ATI Cayman PRO [Radeon HD 6950] [1002:6719] So, is this normal? Do I need to go back to proprietary drivers to enable Unity 3D? If anyone can give me help, I'll much appreciate it.

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Level editor event system, how to translate event to game action

- by Martino Wullems

Hello, I've been busy trying to create a level editor for a tile based game i'm working on. It's all going pretty fine, the only thing i'm having trouble with is creating a simple event system. Let's say the player steps on a particulair tile that had the action "teleport" assigned to it in the editor. The teleport string is saved in the tile object as a variable. When creating the tilegrid an actionmanager class scans the action variable and assigns actions to the variable. public static class ActionManager { public static function ParseTileAction(tile:Tile) { switch(tile.action) { case "TELEPORT": //assign action here break; } } } Now this is an collision event, so I guess I should also provide an object to colide with the tile. But what if it would have to count for collision with all objects in the world? Also, checking for collisions in the actionmanager class doesn't seem very efficient. Am I even on the right track here? I'm new to game design so I could be completly off track. Any tips on how handeling and creating events using an editor is usually done would be great. The main problem i'm having is the Thanks in advance.

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How to improve batching performance

- by user4241

Hello, I am developing a sprite based 2D game for mobile platform(s) and I'm using OpenGL (well, actually Irrlicht) to render graphics. First I implemented sprite rendering in a simple way: every game object is rendered as a quad with its own GPU draw call, meaning that if I had 200 game objects, I made 200 draw calls per frame. Of course this was a bad choice and my game was completely CPU bound because there is a little CPU overhead assosiacted in every GPU draw call. GPU stayed idle most of the time. Now, I thought I could improve performance by collecting objects into large batches and rendering these batches with only a few draw calls. I implemented batching (so that every game object sharing the same texture is rendered in same batch) and thought that my problems are gone... only to find out that my frame rate was even lower than before. Why? Well, I have 200 (or more) game objects, and they are updated 60 times per second. Every frame I have to recalculate new position (translation and rotation) for vertices in CPU (GPU on mobile platforms does not support instancing so I can't do it there), and doing this calculation 48000 per second (200*60*4 since every sprite has 4 vertices) simply seems to be too slow. What I could do to improve performance? All game objects are moving/rotating (almost) every frame so I really have to recalculate vertex positions. Only optimization that I could think of is a look-up table for rotations so that I wouldn't have to calculate them. Would point sprites help? Any nasty hacks? Anything else? Thanks.

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Finding the normals of an oriented bounding box?

- by Milo

Here is my problem. I'm working on the physics for my 2D game. All objects are oriented bounding boxes (OBB) based on the separate axis theorem. In order to do collision resolution, I need to be able to get an object out out of the object it is penetrating. To do this I need to find the normal of the face(s) that the other OBB is touching. Example: The small red OBB is a car lets say, and the big OBB is a static building. I need to determine the unit vector that is the normal of the building edge(s) the car is penetrating to get the car out of there. Here are my questions: How do I determine which edges the car is penetrating. I know how to determine the normal of an edge, but how do I know if I need (-dy, dx) or (dy, -dx)? In the case I'm demonstrating the car is penetrating 2 edges, which edge(s) do I use to get it out? Answers or help with any or all of these is greatly appreciated. Thank you

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Please recommend a patterns book for iOS development

- by Brett Ryan

I've read several books on iOS development and Objective-C, however what a lot of them teach is how to work with interfaces and all contain the model inside the view controller, i.e. a UITableViewController based view will simply have an NSArray as it's model. I'm interested in what the best practices are for designing the structure of an application. Specifically I'm interested in best practices for the following: How to separate a model from the view controller. I think I know how to do this by simply replacing the NSArray style example with a specific model object, however what I do not know how to do is alert the view when the model changes. For example in .NET I would solve this by conforming to INotifyPropertyChanged and databinding, and similarly with Java I would use PropertyChangeListener. How to create a service model for my domain objects. For example I want to learn the best way to create a service for a hypothetical Widget object to manage an internal DB and also services for communicating with remote endpoints. I need to learn the best ways to do this in a way that interface components can subscribe to events such as widgetUpdated. These services should be singleton classes and some how dependency injected into model/controller objects. Books I've read so far are: Programming in Objective-C (4th Edition) Beginning iOS 5 Development: Exploring the iOS SDK The iOS 5 Developer's Cookbook: Expanded Electronic Edition: Essentials and Advanced Recipes for iOS Programmers Learn Objective-C on the Mac: For OS X and iOS I've also purchased the following updated books but not yet read them. The Core iOS 6 Developer's Cookbook (4th edition Programming in Objective-C (5th Edition) I come from a Java and C# background with 15 years experience, I understand that many of the ways I would do things in these languages may not fit to the ObjC way of developing applications. Any guidance on the topic is very much appreciated.

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DDD Model Design and Repository Persistence Performance Considerations

- by agarhy

So I have been reading about DDD for some time and trying to figure out the best approach on several issues. I tend to agree that I should design my model in a persistent agnostic manner. And that repositories should load and persist my models in valid states. But are these approaches realistic practically? I mean its normal for a model to hold a reference to a collection of another type. Persisting that model should mean persist the entire collection. Fine. But do I really need to load the entire collection every time I load the model? Probably not. So I can have specialized repositories. Some that load maybe a subset of the object graph via DTOs and others that load the entire object graph. But when do I use which? If I have DTOs, what's stopping client code from directly calling them and completely bypassing the model? I can have mappers and factories to create my models from DTOs maybe? But depending on the design of my models that might not always work. Or it might not allow my models to be created in a valid state. What's the correct approach here?

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