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• WCF: Exposed Object Model - stuck in a loop

  - by Mark

  Hi I'm working on a pretty big WSSF project. I have a normal object model in the business layer. Eg a customer has an orders collection property, when this is accessed then it loads from the data layer (lazy loading). An order has a productCollection property etc etc.. Now the bit I'm finding tricky is exposing this via WCF. I want to export a collection of orders. The client app will also need information about the customers. Using the WSSF data contract designer I have set it up so that customers have a property called "order collection". This is fine if you have a customer object and would like to look at the orders but if you have an order object there is no customer property so it doesn't work going up the hierarchy. I've tried adding a customer property to the orders object but then the code gets stuck in a loop when it loads the data contracts up. This is because it doesn't load on demand like in the business layer. I need to load all properties up before the objects can be sent out via WCF. It ends up loading an order, then the customer for that order, then the orders for that customer, then the customer for that order etc etc... I'm sure I've got all this wrong. Help!!

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• Is there any way to provide custom factory for .Net Framework creation Entities from EF4 ?

  - by ILICH

  There are a lot of posts about how cool POCO objects are and how Entity Framework 4 supports them. I decided to try it out with domain driven development oriented architecture and finished with domain entities that has dependencies from services. So far so good. Imagine my Products are POCO objects. When i query for objects like this: NorthwindContext db = new NorthwindContext(); var products = db.Products.ToList(); EF creates instances of products for me. Now I want to inject dependencies in my POCO objects (products) The only way I see is make some method within NorthwindContext that makes something like pseudo-code below: public List<Product> GetProducts(){ var products = database.Products.ToList(); container.BuildUp(products); //inject dependencies return products; } But what if i want to make my repository to be more flexible like this: public ObjectSet<Product> GetProducts() { ... } So, I really need a factory to make it more lazy and linq friendly. Please help !

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• Implementing a c/c++ style union as a column in MySQL

  - by user81338

  Friends, I have a strange need and cannot think my way through the problem. The great and mighty Google is of little help due to keyword recycling (as you'll see). Can you help? What I want to do is store data of multiple types in a single column in MySQL. This is the database equivalent to a C union (and if you search for MySQL and Union, you obviously get a whole bunch of stuff on the UNION keyword in SQL). [Contrived and simplified case follows] So, let us say that we have people - who have names - and STORMTROOPERS - who have TK numbers. You cannot have BOTH a NAME and a TK number. You're either BOB SMITH -or- TK409. In C I could express this as a union, like so: union { char * name; int tkNo; } EmperialPersonnelRecord; This makes it so that I am either storing a pointer to a char array or an ID in the type EmperialPersonnelRecord, but not both. I am looking for a MySQL equivalent on a column. My column would store either an int, double, or varchar(255) (or whatever combination). But would only take up the space of the largest element. Is this possible? (of course anything is possible given enough time, money and will - I mean is it possible if I am poor, lazy and on a deadline... aka "out of the box")

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• why when I delete a parent on a one to many relationship on grails the beforeInsert event is called

  - by nico

  hello, I have a one to many relationship and when I try to delete a parent that haves more than one child the berforeInsert event gets called on the frst child. I have some code in this event that I mean to call before inserting a child, not when i'm deleting the parent! any ideas on what might be wrong? the entities: class MenuItem { static constraints = { name(blank:false,maxSize:200) category() subCategory(nullable:true, validator:{ val, obj -> if(val == null){ return true }else{ return obj.category.subCategories.contains(val)? true : ['invalid.category.no.subcategory'] } }) price(nullable:true) servedAtSantaMonica() servedAtWestHollywood() highLight() servedAllDay() dateCreated(display:false) lastUpdated(display:false) } static mapping = { extras lazy:false } static belongsTo = [category:MenuCategory,subCategory:MenuSubCategory] static hasMany = [extras:MenuItemExtra] static searchable = { extras component: true } String name BigDecimal price Boolean highLight = false Boolean servedAtSantaMonica = false Boolean servedAtWestHollywood = false Boolean servedAllDay = false Date dateCreated Date lastUpdated int displayPosition void moveUpDisplayPos(){ def oldDisplayPos = MenuItem.get(id).displayPosition if(oldDisplayPos == 0){ return }else{ def previousItem = MenuItem.findByCategoryAndDisplayPosition(category,oldDisplayPos - 1) previousItem.displayPosition += 1 this.displayPosition = oldDisplayPos - 1 this.save(flush:true) previousItem.save(flush:true) } } void moveDownDisplayPos(){ def oldDisplayPos = MenuItem.get(id).displayPosition if(oldDisplayPos == MenuItem.countByCategory(category) - 1){ return }else{ def nextItem = MenuItem.findByCategoryAndDisplayPosition(category,oldDisplayPos + 1) nextItem.displayPosition -= 1 this.displayPosition = oldDisplayPos + 1 this.save(flush:true) nextItem.save(flush:true) } } String toString(){ name } def beforeInsert = { displayPosition = MenuItem.countByCategory(category) } def afterDelete = { def otherItems = MenuItem.findAllByCategoryAndDisplayPositionGreaterThan(category,displayPosition) otherItems.each{ it.displayPosition -= 1 it.save() } } } class MenuItemExtra { static constraints = { extraOption(blank:false, maxSize:200) extraOptionPrice(nullable:true) } static searchable = true static belongsTo = [menuItem:MenuItem] BigDecimal extraOptionPrice String extraOption int displayPosition void moveUpDisplayPos(){ def oldDisplayPos = MenuItemExtra.get(id).displayPosition if(oldDisplayPos == 0){ return }else{ def previousExtra = MenuItemExtra.findByMenuItemAndDisplayPosition(menuItem,oldDisplayPos - 1) previousExtra.displayPosition += 1 this.displayPosition = oldDisplayPos - 1 this.save(flush:true) previousExtra.save(flush:true) } } void moveDownDisplayPos(){ def oldDisplayPos = MenuItemExtra.get(id).displayPosition if(oldDisplayPos == MenuItemExtra.countByMenuItem(menuItem) - 1){ return }else{ def nextExtra = MenuItemExtra.findByMenuItemAndDisplayPosition(menuItem,oldDisplayPos + 1) nextExtra.displayPosition -= 1 this.displayPosition = oldDisplayPos + 1 this.save(flush:true) nextExtra.save(flush:true) } } String toString(){ extraOption } def beforeInsert = { if(menuItem){ displayPosition = MenuItemExtra.countByMenuItem(menuItem) } } def afterDelete = { def otherExtras = MenuItemExtra.findAllByMenuItemAndDisplayPositionGreaterThan(menuItem,displayPosition) otherExtras.each{ it.displayPosition -= 1 it.save() } } }

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• How to create view model without sorting collections in memory.

  - by Chevex

  I have a view model (below). public class TopicsViewModel { public Topic Topic { get; set; } public Reply LastReply { get; set; } } I want to populate an IQueryable<TopicsViewModel> with values from my IQueryable<Topic> collection and IQueryable<Reply> collection. I do not want to use the attached entity collection (i.e. Topic.Replies) because I only want the last reply for that topic and doing Topic.Replies.Last() loads the entire entity collection in memory and then grabs the last one in the list. I am trying to stay in IQueryable so that the query is executed in the database. I also don't want to foreach through topics and query replyRepository.Replies because looping through IQueryable<Topic> will start the lazy loading. I'd prefer to build one expression and have all the leg work done in the lower layers. I have the following: IQueryable<TopicsViewModel> topicsViewModel = from x in topicRepository.Topics from y in replyRepository.Replies where y.TopicID == x.TopicID orderby y.PostedDate ascending select new TopicsViewModel { Topic = x, LastReply = y }; But this isn't working. Any ideas how I can populate an IQueryable or IEnumerable of TopicsViewModel so that it queries the database and grabs topics and that topic's last reply? I am trying really hard to avoid grabbing all replies related to that topic. I only want to grab the last reply. Thank you for any insight you have to offer.

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• Web API Getting Http 500 error : Issue Solved See Below

  - by Joe Grasso

  Here is my MVC Controller and everything is fine: private UnitOfWork UOW; public InventoryController() { UOW = new UnitOfWork(); } // GET: /Inventory/ public ActionResult Index() { var products = UOW.ProductRepository.GetAll().ToList(); return View(products); } Same method call in API Controller gives me an Http 500 Error: private UnitOfWork _unitOfWork; public TestController() { _unitOfWork = new UnitOfWork(); } public IEnumerable<Product> Get() { var products = _unitOfWork.ProductRepository.GetAll().ToList(); return products; } Debugging shows that indeed there is data being returned in both controllers' UOW calls. I then added a customer configuration in Global: public static void CustomizeConfig(HttpConfiguration config) { config.Formatters.Remove(config.Formatters.XmlFormatter); var json = config.Formatters.JsonFormatter; json.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver(); } I am still receiving an Http 500 in API Controller ONLY and at a loss as to why. Any ideas? UPDATE: It appears using lazy loading caused the problem. When I set the associated properties to NON-VIRTUAL the Test API provided the necessary JSON string. However, whereas before I had the Vendor class included, I only have VendorId. I really wanted to included the associated classes. Any ideas? I know there are alot of smart people out there. Anyone?

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• Exception when retrieving record using Nhibernate

  - by Muhammad Akhtar

  I am new to NHibernate and have just started right now. I have very simple table contain Id(Int primary key and auto incremented), Name(varchar(100)), Description(varchar(100)) Here is my XML <class name="DevelopmentStep" table="DevelopmentSteps" lazy="true"> <id name="Id" type="Int32" column="Id"> </id> <property name="Name" column="Name" type="String" length="100" not-null="false"/> <property name="Description" column="Description" type="String" length="100" not-null="false"/> here is how I want to get all the record public List<DevelopmentStep> getDevelopmentSteps() { List<DevelopmentStep> developmentStep; developmentStep = Repository.FindAll<DevelopmentStep>(new OrderBy("Name", Order.Asc)); return developmentStep; } But I am getting exception The element 'id' in namespace 'urn:nhibernate-mapping-2.2' has incomplete content. List of possible elements expected: 'urn:nhibernate-mapping-2.2:meta urn:nhibernate-mapping- 2.2:column urn:nhibernate-mapping-2.2:generator'. Please Advise me --- Thanks

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• Should I invest in GraniteDS for Flex + Java development?

  - by Boden

  I'm new to Flex development, and RIAs in general. I've got a CRUD-style Java + Spring + Hibernate service on top of which I'm writing a Flex UI. Currently I'm using BlazeDS. This is an internal application running on a local network. It's become apparent to me that the way RIAs work is more similar to a desktop application than a web application in that we load up the entire model and work with it directly on the client (or at least the portion that we're interested in). This doesn't really jive well with BlazeDS because really it only supports remoting and not data management, thus it can become a lot of extra work to make sure that clients are in sync and to avoid reloading the model which can be large (especially since lazy loading is not possible). So it feels like what I'm left with is a situation where I have to treat my Flex application more like a regular old web application where I do a lot of fine grained loading of data. LiveCycle is too expensive. The free version of WebOrb for Java really only does remoting. Enter GraniteDS. As far as I can determine, it's the only free solution out there that has many of the data management features of LiveCycle. I've started to go through its documentation a bit and suddenly feel like it's yet another quagmire of framework that I'll have to learn just to get an application running. So my question(s) to the StackOverflow audience is: 1) do you recommend GraniteDS, especially if my current Java stack is Spring + Hibernate? 2) at what point do you feel like it starts to pay off? That is, at what level of application complexity do you feel that using GraniteDS really starts to make development that much better? In what ways?

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• JSP/Struts2/Hibernate: loop through a self-referencing table.

  - by TBW

  Hello everyone, Let's say we have a self-referencing table called PERSON, with the following columns: ID, PARENT, where PARENT is a foreign key to the ID column of another element in the PERSON table. Of course, many persons can have the same parent. I use Hibernate 3 in lazy fetching mode to deal with the database. Hibernate fetches a person element from the database, which is then put in the ValueStack by the Struts2 action, to be used on the result JSP page. Now the question is : In JSP, how can I do to display all the child (and the child's child, and so on, like a family tree) of this person element? Of course, for the n+1 children I can use the < s:iterator tag over the person.person. I can also nest another < s:iterator tag over person.person.person to get the n+2 children. But what if I want to do this in an automated manner, up to the last n+p child, displaying in the process all the children of all the n+1..n+p elements? I hope I have been clear enough. Thank you all for your time. -- TBW.

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• Java Executor: Small tasks or big ones?

  - by Arash Shahkar

  Consider one big task which could be broken into hundreds of small, independently-runnable tasks. To be more specific, each small task is to send a light network request and decide upon the answer received from the server. These small tasks are not expected to take longer than a second, and involve a few servers in total. I have in mind two approaches to implement this using the Executor framework, and I want to know which one's better and why. Create a few, say 5 to 10 tasks each involving doing a bunch of send and receives. Create a single task (Callable or Runnable) for each send & receive and schedule all of them (hundreds) to be run by the executor. I'm sorry if my question shows that I'm lazy to test these and see for myself what's better (at least performance-wise). My question, while looking after an answer to this specific case, has a more general aspect. In situations like these when you want to use an executor to do all the scheduling and other stuff, is it better to create lots of small tasks or to group those into a less number of bigger tasks?

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• Java 8 Stream, getting head and tail

  - by lyomi

  Java 8 introduced a Stream class that resembles Scala's Stream, a powerful lazy construct using which it is possible to do something like this very concisely: def from(n: Int): Stream[Int] = n #:: from(n+1) def sieve(s: Stream[Int]): Stream[Int] = { s.head #:: sieve(s.tail filter (_ % s.head != 0)) } val primes = sieve(from(2)) primes takeWhile(_ < 1000) print // prints all primes less than 1000 I wondered if it is possible to do this in Java 8, so I wrote something like this: IntStream from(int n) { return IntStream.iterate(n, m -> m + 1); } IntStream sieve(IntStream s) { int head = s.findFirst().getAsInt(); return IntStream.concat(IntStream.of(head), sieve(s.skip(1).filter(n -> n % head != 0))); } IntStream primes = sieve(from(2)); PrimitiveIterator.OfInt it = primes.iterator(); for (int prime = it.nextInt(); prime < 1000; prime = it.nextInt()) { System.out.println(prime); } Fairly simple, but it produces java.lang.IllegalStateException: stream has already been operated upon or closed because both findFirst() and skip() is a terminal operation on Stream which can be done only once. I don't really have to use up the stream twice since all I need is the first number in the stream and the rest as another stream, i.e. equivalent of Scala's Stream.head and Stream.tail. Is there a method in Java 8 Stream that I can achieve this? Thanks.

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• Problem with 2 levels of inheritance in hibernate mapping

  - by Seth

  Here's my class structure: class A class B extends A class C extends A class D extends C class E extends C And here are my mappings (class bodies omitted for brevity): Class A: @Entity @Inheritance(strategy=InheritanceType.SINGLE_TABLE) @MappedSuperclass @DiscriminatorColumn( name="className", discriminatorType=DiscriminatorType.STRING ) @ForceDiscriminator public abstract class A Class B: @Entity @DiscriminatorValue("B") public class B extends A Class C: @Entity @DiscriminatorValue("C") @MappedSuperclass @DiscriminatorColumn( name="cType", discriminatorType=DiscriminatorType.STRING ) @ForceDiscriminator public abstract class C extends A Class D: @Entity @DiscriminatorValue("D") public class D extends C Class E: @Entity @DiscriminatorValue("E") public class E extends C I've got a class F that contains a set of A: @Entity public class F { ... @OneToMany(fetch=FetchType.LAZY, cascade=CascadeType.ALL) @JoinTable( name="F_A", joinColumns = @JoinColumn(name="A_ID"), inverseJoinColumns = @JoinColumn(name="F_ID") ) private Set<A> aSet = new HashSet<A>(); ... The problem is that whenever I add a new E instance to aSet and then call session.saveOrUpdate(fInstance), hibernate saves with "A" as the discrimiator string. When I try to access the aSet in the F instance, I get the following exception (full stacktrace ommitted for brevity): org.hibernate.InstantiationException: Cannot instantiate abstract class or interface: path.to.class.A Am I mapping the classes incorrectly? How am I supposed to map multiple levels of inheritance? Thanks for the help!

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• Sync two SqlExpress using NHibernate

  - by Christian

  Hello, I am creating a simple project management system which uses NHibernate for object storage. The underlying database is SQL express (at least currently for development). The client runs on either the desktop or laptop. I know I could use web-services and store the DB only on the desktop, but this would force the desktop to be available all the time. I am currently thinking about duplicating the DB, having two instances with "different data". To clarify, we are not talking about a productive app here, its a prototype. One way to achieve this very simple would be the following process: Client: Check if desktop DB is available (through web service) Client: If yes, use desktop storage, no problem here Client: If not, use own DB as storage Client: Poll desktop regulary, as soon as it comes on, sync Client: Switch to desktop storage ... Desktop: Do not attempt any DB operation before checking for required sync Desktop: If sync needed, do it... My question is now, how would you sync? Assume 4 or 5 types of objects, all have GUID as identifiers. Would you always manually "lazy load" all objects of a certain type and feed them to the DB. Would you always drop the whole desktop DB in case the client DB may be newer and out of sync? Again, I want to stress out, I am not assuming any conflicts or stale data, I basically just want to "copy the whole DB from the client". Would you use NHibernate for this? Or would you separate the copy process? When I think about it, my questions comes down to this: Is there any function from NHibernate: SyncDBs_SourceWins_(SourceDB, TargetDB) Thanks for help, Chris

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• What Getters and Setters should and shouldn't do.

  - by cyclotis04

  I've run into a lot of differing opinions on Getters and Setters lately, so I figured I should make it into it's own question. A previous question of mine received an immediate comment (later deleted) that stated setters shouldn't have any side effects, and a SetProperty method would be a better choice. Indeed, this seems to be Microsoft's opinion as well. However, their properties often raise events, such as Resized when a form's Width or Height property is set. OwenP also states "you shouldn't let a property throw exceptions, properties shouldn't have side effects, order shouldn't matter, and properties should return relatively quickly." Yet Michael Stum states that exceptions should be thrown while validating data within a setter. If your setter doesn't throw an exception, how could you effectively validate data, as so many of the answers to this question suggest? What about when you need to raise an event, like nearly all of Microsoft's Control's do? Aren't you then at the mercy of whomever subscribed to your event? If their handler performs a massive amount of information, or throws an error itself, what happens to your setter? Finally, what about lazy loading within the getter? This too could violate the previous guidelines. What is acceptable to place in a getter or setter, and what should be kept in only accessor methods?

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• Can ScalaCheck/Specs warnings safely be ignored when using SBT with ScalaTest?

  - by pdbartlett

  I have a simple FunSuite-based ScalaTest: package pdbartlett.hello_sbt import org.scalatest.FunSuite class SanityTest extends FunSuite { test("a simple test") { assert(true) } test("a very slightly more complicated test - purposely fails") { assert(42 === (6 * 9)) } } Which I'm running with the following SBT project config: import sbt._ class HelloSbtProject(info: ProjectInfo) extends DefaultProject(info) { // Dummy action, just to show config working OK. lazy val solveQ = task { println("42"); None } // Managed dependencies val scalatest = "org.scalatest" % "scalatest" % "1.0" % "test" } However, when I runsbt test I get the following warnings: ... [info] == test-compile == [info] Source analysis: 0 new/modified, 0 indirectly invalidated, 0 removed. [info] Compiling test sources... [info] Nothing to compile. [warn] Could not load superclass 'org.scalacheck.Properties' : java.lang.ClassNotFoundException: org.scalacheck.Properties [warn] Could not load superclass 'org.specs.Specification' : java.lang.ClassNotFoundException: org.specs.Specification [warn] Could not load superclass 'org.specs.Specification' : java.lang.ClassNotFoundException: org.specs.Specification [info] Post-analysis: 3 classes. [info] == test-compile == For the moment I'm assuming these are just "noise" (caused by the unified test interface?) and that I can safely ignore them. But it is slightly annoying to some inner OCD part of me (though not so annoying that I'm prepared to add dependencies for the other frameworks). Is this a correct assumption, or are there subtle errors in my test/config code? If it is safe to ignore, is there any other way to suppress these errors, or do people routinely include all three frameworks so they can pick and choose the best approach for different tests? TIA, Paul. (ADDED: scala v2.7.7 and sbt v0.7.4)

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• Ruby core documentation quality

  - by karatedog

  I'm relatively new to Ruby and have limited time therefore I try out simple things. Recently I needed to create a file and because I'm lazy as hell, I run to Google. The result: File.open(local_filename, 'w') {|f| f.write(doc) } Shame on me, it is very straightforward, should have done it myself. Then I wanted to check what ruby magic the File class' methods offer or if there's any 'simplification' when invoking those methods, so I headed for the documentation here, and checked for the File class. 1.8.6 documentation presents me with "ftools.rb: Extra tools for the File class" under 'File' class, which is not what I'm looking for. 1.8.7 documentation seems OK for 'File' class, there are a plethora of methods. Except 'open'. 1.9 documentation finally shows me the 'open' method. And I had an almost same tour with Net::HTTP. Do I exaggerate when I think good old Turbo Pascal's 7.0 documentation was better organized than Ruby documentation is right now? Is there any other source for the uninitiated to collect knowledge? Or is it possible that I just tumbled into a documentation hole and the rest are super-brilliant-five-star organized? Thanks

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• nHibernate storage of an object with self referencing many children and many parents

  - by AdamC

  I have an object called MyItem that references children in the same item. How do I set up an nhibernate mapping file to store this item. public class MyItem { public virtual string Id {get;set;} public virtual string Name {get;set;} public virtual string Version {get;set;} public virtual IList<MyItem> Children {get;set;} } So roughly the hbm.xml would be: <class name="MyItem" table="tb_myitem"> <id name="Id" column="id" type="String" length="32"> <generator class="uuid.hex" /> </id> <property name="Name" column="name" /> <property name="Version" column="version" /> <bag name="Children" cascade="all-delete-orphan" lazy="false"> <key column="children_id" /> <one-to-many class="MyItem" not-found="ignore"/> </bag> </class> This wouldn't work I don't think. Perhaps I need to create another class, say MyItemChildren and use that as the Children member and then do the mapping in that class? This would mean having two tables. One table holds the MyItem and the other table holds references from my item. NOTE: A child item could have many parents.

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• Are there good reasons not to use an ORM?

  - by hangy

  During my apprenticeship, I have used NHibernate for some smaller projects which I mostly coded and designed on my own. Now, before starting some bigger project, the discussion arose how to design data access and whether or not to use an ORM layer. As I am still in my apprenticeship and still consider myself a beginner in enterprise programming, I did not really try to push in my opinion, which is that using an object relational mapper to the database can ease development quite a lot. The other coders in the development team are much more experienced than me, so I think I will just do what they say. :-) However, I do not completely understand two of the main reasons for not using NHibernate or a similar project: One can just build one’s own data access objects with SQL queries and copy those queries out of Microsoft SQL Server Management Studio. Debugging an ORM can be hard. So, of course I could just build my data access layer with a lot of SELECTs etc, but here I miss the advantage of automatic joins, lazy-loading proxy classes and a lower maintenance effort if a table gets a new column or a column gets renamed. (Updating numerous SELECT, INSERT and UPDATE queries vs. updating the mapping config and possibly refactoring the business classes and DTOs.) Also, using NHibernate you can run into unforeseen problems if you do not know the framework very well. That could be, for example, trusting the Table.hbm.xml where you set a string’s length to be automatically validated. However, I can also imagine similar bugs in a “simple” SqlConnection query based data access layer. Finally, are those arguments mentioned above really a good reason not to utilise an ORM for a non-trivial database based enterprise application? Are there probably other arguments they/I might have missed? (I should probably add that I think this is like the first “big” .NET/C# based application which will require teamwork. Good practices, which are seen as pretty normal on Stack Overflow, such as unit testing or continuous integration, are non-existing here up to now.)

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• nhibernate mapping: delete collection, insert new collection with old IDs

  - by npeBeg

  my issue lokks similar to this one: (link) but i have one-to-many association: <set name="Fields" cascade="all-delete-orphan" lazy="false" inverse="true"> <key column="[TEMPLATE_ID]"></key> <one-to-many class="MyNamespace.Field, MyLibrary"/> </set> (i also tried to use ) this mapping is for Template object. this one and the Field object has their ID generators set to identity. so when i call session.Update for the Template object it works fine, well, almost: if the Field object has an Id number, UPDATE sql request is called, if the Id is 0, the INSERT is performed. But if i delete a Field object from the collection it has no effect for the Database. I found that if i also call session.Delete for this Field object, everything will be ok, but due to client-server architecture i don't know what to delete. so i decided to delete all the collection elements from the DB and call session.Update with a new collection. and i've got an issue: nhibernate performs the UPDATE operation for the Field objects that has non-zero Id, but they are removed from DB! maybe i should use some other Id generator or smth.. what is the best way to make nhibernate perform "delete all"/"insert all" routine for the collection?

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• Large ListView containing images in Android

  - by Marco W.

  For various Android applications, I need large ListViews, i.e. such views with 100-300 entries. All entries must be loaded in bulk when the application is started, as some sorting and processing is necessary and the application cannot know which items to display first, otherwise. So far, I've been loading the images for all items in bulk as well, which are then saved in an ArrayList<CustomType> together with the rest of the data for each entry. But of course, this is not a good practice, as you're very likely to have an OutOfMemoryException then: The references to all images in the ArrayList prevent the garbage collector from working. So the best solution is, obviously, to load only the text data in bulk whereas the images are then loaded as needed, right? The Google Play application does this, for example: You can see that images are loaded as you scroll to them, i.e. they are probably loaded in the adapter's getView() method. But with Google Play, this is a different problem, anyway, as the images must be loaded from the Internet, which is not the case for me. My problem is not that loading the images takes too long, but storing them requires too much memory. So what should I do with the images? Load in getView(), when they are really needed? Would make scrolling sluggish. So calling an AsyncTask then? Or just a normal Thread? Parametrize it? I could save the images that are already loaded into a HashMap<String,Bitmap>, so that they don't need to be loaded again in getView(). But if this is done, you have the memory problem again: The HashMap stores references to all images, so in the end, you could have the OutOfMemoryException again. I know that there are already lots of questions here that discuss "Lazy loading" of images. But they mainly cover the problem of slow loading, not too much memory consumption.

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• Loading child entities with JPA on Google App Engine

  - by Phil H

  I am not able to get child entities to load once they are persisted on Google App Engine. I am certain that they are saving because I can see them in the datastore. For example if I have the following two entities. public class Parent implements Serializable{ @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String key; @OneToMany(cascade=CascadeType.ALL) private List<Child> children = new ArrayList<Child>(); //getters and setters } public class Child implements Serializable{ @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String key; private String name; @ManyToOne private Parent parent; //getters and setters } I can save the parent and a child just fine using the following: Parent parent = new Parent(); Child child = new Child(); child.setName("Child Object"); parent.getChildren().add(child); em.persist(parent); However when I try to load the parent and then try to access the children (I know GAE lazy loads) I do not get the child records. //parent already successfully loaded parent.getChildren.size(); // this returns 0 I've looked at tutorial after tutorial and nothing has worked so far. I'm using version 1.3.3.1 of the SDK. I've seen the problem mentioned on various blogs and even the App Engine forums but the answer is always JDO related. Am I doing something wrong or has anyone else had this problem and solved it for JPA?

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• jquery autosuggest: what is wrong with this code?

  - by Abu Hamzah

  i have been struggling to make it work my autosugest/autocomplete and its acting strange unless i am doing completely silly here. please have a look 1) does not do anything, does not work or nor fire the event. <script src="Scripts/jquery-1.4.2.js" type="text/javascript"></script> <script src="Scripts/jquery.autocomplete.js" type="text/javascript"></script> <form id="form1" runat="server"> <script type="text/javascript"> $(document).ready(function() { $("#<%=txtHost.UniqueID %>").autocomplete("HostService.asmx/GetHosts", { dataType: 'json' , contentType: "application/json; charset=utf-8" , parse: function(data) { var rows = Array(); debugger for (var i = 0; i < data.length; i++) { rows[i] = { data: data[i], value: data[i].LName, result: data[i].LName }; } return rows; } , formatItem: function(row, i, max) { return data.LName + ", " + data.FName; } }); }); </script> 2) this works if i remove the above code and replace with this code: <script type="text/javascript"> $(document).ready(function() { $("#txtHost").autocomplete("lazy blazy crazy daisy maisy ugh".split(" ")); }); </script> any help ?

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• Entity Framework not populating context

  - by stimms

  I'm just starting out with some entity framework exploration, I figured it was time to see what everybody was complaining about. I am running into an issue where the entities don't seem to be returning any of the object context. I generated the model from a database with three tables which link to one another. Courses Instructors CanTeach Relationships are as you would expect: a course can relate to multiple CanTeach entities and an instructor can also relate to multiple CanTeach entities. I also added an OData service to my project which also makes use of the same model. So I can run queries like from a in CanTeach where a.Instructor.FirstName == "Barry" select new { Name = a.Instructor.FirstName + " " + a.Instructor.LastName, Course = a.Course.Name} without issue against the OData endpoint using LINQPad. However when I do a simple query like public Instructor GetInstructorFromID(int ID) { return context.Instructors.Where(i => i.ID == ID).FirstOrDefault(); } The CanTeach list is empty. I know everything in EF is lazy loaded and it is possible that my context is out of scope by the time I look at the object context, however even trying to get the object context as soon as the query is run results in and empty object context. What am I doing wrong?

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• Parsing: How to make error recovery in grammars like " a* b*"?

  - by Lavir the Whiolet

  Let we have a grammar like this: Program ::= a* b* where "*" is considered to be greedy. I usually implement "*" operator naively: Try to apply the expression under "*" to input one more time. If it has been applied successfully then we are still under current "*"-expression; try to apply the expression under "*" one more time. Otherwise we have reached next grammar expression; put characters parsed by expression under "*" back into input and proceed with next expression. But if there are errors in input in any of "a*" or "b*" part such a parser will "think" that in position of error both "a*" and "b*" have finished ("let's try "a"... Fail! OK, it looks like we have to proceed to "b*". Let's try "b"... Fail! OK, it looks like the string should have been finished...). For example, for string "daaaabbbbbbc" it will "say": "The string must end at position 1, delete superflous characters: daaaabbbbbbc". In short, greedy "*" operator becomes lazy if there are errors in input. How to make "*" operator to recover from errors nicely?

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• What's the best Linux backup solution?

  - by Jon Bright

  We have a four Linux boxes (all running Debian or Ubuntu) on our office network. None of these boxes are especially critical and they're all using RAID. To date, I've therefore been doing backups of the boxes by having a cron job upload tarballs containing the contents of /etc, MySQL dumps and other such changing, non-packaged data to a box at our geographically separate hosting centre. I've realised, however that the tarballs are sufficient to rebuild from, but it's certainly not a painless process to do so (I recently tried this out as part of a hardware upgrade of one of the boxes) long-term, the process isn't sustainable. Each of the boxes is currently producing a tarball of a couple of hundred MB each day, 99% of which is the same as the previous day partly due to the size issue, the backup process requires more manual intervention than I want (to find whatever 5GB file is inflating the size of the tarball and kill it) again due to the size issue, I'm leaving stuff out which it would be nice to include - the contents of users' home directories, for example. There's almost nothing of value there that isn't in source control (and these aren't our main dev boxes), but it would be nice to keep them anyway. there must be a better way So, my question is, how should I be doing this properly? The requirements are: needs to be an offsite backup (one of the main things I'm doing here is protecting against fire/whatever) should require as little manual intervention as possible (I'm lazy, and box-herding isn't my main job) should continue to scale with a couple more boxes, slightly more data, etc. preferably free/open source (cost isn't the issue, but especially for backups, openness seems like a good thing) an option to produce some kind of DVD/Blu-Ray/whatever backup from time to time wouldn't be bad My first thought was that this kind of incremental backup was what tar was created for - create a tar file once each month, add incrementally to it. rsync results to remote box. But others probably have better suggestions.

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