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• Accessing Array and Collection using LINQ

  This article will teach you about how you can Access Array elements and Collections using LINQ.

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• Using java classes in Grails

  - by RN

  I have a Java\Spring\Hibernate application - complete with domain classes which are basically Hibernate POJOs There is a piece of functionality that I think can be written well in Grails. I wish to reuse the domain classes that I have created in the main Java app What is the best way to do so ? Should I write new domain classes extending the Java classes ? this sounds tacky Or Can I 'generate' controllers off the Java domain classes ? What are the best practices around reusing Java domain objects in Grails\Groovy I am sure there must be others writing some pieces in grails\groovy If you know about a tutorial which talks about such an integration- that would be awesome !!! PS: I am quite a newbie in grails-groovy so may be missing the obvious. Thanks !!!

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• Is it required to generate java classes to use spring-ws client

  - by vishnu

  Hi, I want to use spring ws to create the webservice client. I have seen some documentation. In all using jaxb marshalling and unmarshalling. But to start of need to create java classes from xsd. I tried to download the elcipse plugin for this. The location in java.net is not showing any thing to download. Sourceforce net showing the link to download. But that plugin is not working. I have tried wsimport, but it is generating only .classes? My question is if i want to use spring ws, is it required to generate .java classes? If so where can i find the elipse plugin or how to generate the classes? Is there any other way we can do without generating these classes?

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• Preventing Netbeans JAXB generation trashing classes

  - by Mac

  I'm developing a SOAP service using JAX-WS and JAXB under Netbeans 6.8, and getting a little frustrated with Netbeans trashing my work every time the XSD schema my JAXB bindings are based upon changes. To elaborate, the IDE automatically generates classes bound to the schema, which can then be (un)marshalled from/to XML using JAXB. To these classes I've added extra methods to (for example) convert to and from separate classes designed to be persisted to database with JPA. The problem is that whenever the schema changes and I rebuild, these classes are regenerated, and all my custom methods are deleted. I can manually replace them by copy-pasting from a backup file, but that is rather time-consuming and tedious. As I'm using an iterative design approach, the schema is changing rather frequently and I'm wasting an awful lot of time whenever it does, simply to reinstate my previous code. While the IDE automatically regenerating the JAXB-bound classes is entirely reasonable and I don't mean to imply otherwise, I was wondering if anyone had any bright ideas as to how to prevent my extra work having to be manually reinstated every time my schema changes?

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• Extending LINQ classes to my own partial classes in different namespaces?

  - by sah302

  I have a .dbml file which of course contains the auto-generated classes based on my tables. I would however, like to extend them to my own classes. Typically I design such that each of my tables get their own namespace in their own folder containing all of their associated dao and service classes. So if I am dealing with a page that only has to do with 'customers' for instance, I can only include the customerNS. But when using LINQ I seem to be unable to do this. I have tried removing a default namespace from the project, I have tried putting the .dbml file into it's own folder with a custom namespace and then adding a 'using' statement, but no nothing works. I also saw the Entity Namespace, Context Namespace, and Custom Tool Namespace properties associated with the .dbml file and tried setting all these to names x and trying 'using x' in my other class to allow me to extend partial classes, but it just doesn't work. Is this possible or do I have to keep all extended partial classes in the same namespace as the .dbml file?

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• Does importing of packages change visibility of classes?

  - by Roman

  I jsut learned that A class may be declared with the modifier public, in which case that class is visible to all classes everywhere. If a class has no modifier (the default, also known as package-private), it is visible only within its own package. This is a clear statement. But this information interfere with my understanding of importing of packages (which easily can be wrong). I thought that importing a package I make classes from the imported package visible to the importing class. So, how does it work? Are public classes visible to all classes everywhere under condition that the package containing the public class is imported? Or there is not such a condition? What about the package-private classes? They are invisible no mater if the containing package was imported or not? ADDED: It seems to me that I got 2 answers which are marked as good (up-voted) and which contradict eachother.

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• Using NetBeans profiler with Guice classes

  - by Karussell

  How can I use the profiler from NetBeans 6.8 or 6.9 (choosing 'entire application') with guice enhanced classes? I am using google guice 2.0 (with warp persist 2.0-20090214) for some classes and wanted to profile those classes. But I cannot see a result for those classes. The only result I can see is for one method 'EnhancedClass.access$000' which is not very helpful. Other classes are working. Does somebody know a workaround? Or know what I am doing wrong?

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• Does importing of packages change visibility of classes?

  - by Roman

  I jsut learned that A class may be declared with the modifier public, in which case that class is visible to all classes everywhere. If a class has no modifier (the default, also known as package-private), it is visible only within its own package. This is a clear statement. But this information interfere with my understanding of importing of packages (which easily can be wrong). I thought that importing a package I make classes from the imported package visible to the importing class. So, how does it work? Are public classes visible to all classes everywhere under condition that the package containing the public class is imported? Or there is not such a condition? What about the package-private classes? They are invisible no mater if the containing package was imported or not? ADDED: It seems to me that I got 2 answers which are marked as good (up-voted) and which contradict eachother.

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• wpf get access to other classes

  - by Calvin

  I am currently working on a wpf application. There are some methods in other classes in which I want to trigger to do some work instead of trying to figure out how to rewrite them in. How is it that I can get to those classes? Would I have to for example instantiate the class? If so, once I instantiate it, how would I be able access them. Keep in mind that these classes have abstract classes on top of abstract classes.

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• C#/.NET Little Wonders: The Useful But Overlooked Sets

  - by James Michael Hare

  Once again we consider some of the lesser known classes and keywords of C#.  Today we will be looking at two set implementations in the System.Collections.Generic namespace: HashSet<T> and SortedSet<T>.  Even though most people think of sets as mathematical constructs, they are actually very useful classes that can be used to help make your application more performant if used appropriately. A Background From Math In mathematical terms, a set is an unordered collection of unique items.  In other words, the set {2,3,5} is identical to the set {3,5,2}.  In addition, the set {2, 2, 4, 1} would be invalid because it would have a duplicate item (2).  In addition, you can perform set arithmetic on sets such as: Intersections: The intersection of two sets is the collection of elements common to both.  Example: The intersection of {1,2,5} and {2,4,9} is the set {2}. Unions: The union of two sets is the collection of unique items present in either or both set.  Example: The union of {1,2,5} and {2,4,9} is {1,2,4,5,9}. Differences: The difference of two sets is the removal of all items from the first set that are common between the sets.  Example: The difference of {1,2,5} and {2,4,9} is {1,5}. Supersets: One set is a superset of a second set if it contains all elements that are in the second set. Example: The set {1,2,5} is a superset of {1,5}. Subsets: One set is a subset of a second set if all the elements of that set are contained in the first set. Example: The set {1,5} is a subset of {1,2,5}. If We’re Not Doing Math, Why Do We Care? Now, you may be thinking: why bother with the set classes in C# if you have no need for mathematical set manipulation?  The answer is simple: they are extremely efficient ways to determine ownership in a collection. For example, let’s say you are designing an order system that tracks the price of a particular equity, and once it reaches a certain point will trigger an order.  Now, since there’s tens of thousands of equities on the markets, you don’t want to track market data for every ticker as that would be a waste of time and processing power for symbols you don’t have orders for.  Thus, we just want to subscribe to the stock symbol for an equity order only if it is a symbol we are not already subscribed to. Every time a new order comes in, we will check the list of subscriptions to see if the new order’s stock symbol is in that list.  If it is, great, we already have that market data feed!  If not, then and only then should we subscribe to the feed for that symbol. So far so good, we have a collection of symbols and we want to see if a symbol is present in that collection and if not, add it.  This really is the essence of set processing, but for the sake of comparison, let’s say you do a list instead: 1: // class that handles are order processing service 2: public sealed class OrderProcessor 3: { 4: // contains list of all symbols we are currently subscribed to 5: private readonly List<string> _subscriptions = new List<string>(); 6:  7: ... 8: } Now whenever you are adding a new order, it would look something like: 1: public PlaceOrderResponse PlaceOrder(Order newOrder) 2: { 3: // do some validation, of course... 4:  5: // check to see if already subscribed, if not add a subscription 6: if (!_subscriptions.Contains(newOrder.Symbol)) 7: { 8: // add the symbol to the list 9: _subscriptions.Add(newOrder.Symbol); 10: 11: // do whatever magic is needed to start a subscription for the symbol 12: } 13:  14: // place the order logic! 15: } What’s wrong with this?  In short: performance!  Finding an item inside a List<T> is a linear - O(n) – operation, which is not a very performant way to find if an item exists in a collection. (I used to teach algorithms and data structures in my spare time at a local university, and when you began talking about big-O notation you could immediately begin to see eyes glossing over as if it was pure, useless theory that would not apply in the real world, but I did and still do believe it is something worth understanding well to make the best choices in computer science). Let’s think about this: a linear operation means that as the number of items increases, the time that it takes to perform the operation tends to increase in a linear fashion.  Put crudely, this means if you double the collection size, you might expect the operation to take something like the order of twice as long.  Linear operations tend to be bad for performance because they mean that to perform some operation on a collection, you must potentially “visit” every item in the collection.  Consider finding an item in a List<T>: if you want to see if the list has an item, you must potentially check every item in the list before you find it or determine it’s not found. Now, we could of course sort our list and then perform a binary search on it, but sorting is typically a linear-logarithmic complexity – O(n * log n) - and could involve temporary storage.  So performing a sort after each add would probably add more time.  As an alternative, we could use a SortedList<TKey, TValue> which sorts the list on every Add(), but this has a similar level of complexity to move the items and also requires a key and value, and in our case the key is the value. This is why sets tend to be the best choice for this type of processing: they don’t rely on separate keys and values for ordering – so they save space – and they typically don’t care about ordering – so they tend to be extremely performant.  The .NET BCL (Base Class Library) has had the HashSet<T> since .NET 3.5, but at that time it did not implement the ISet<T> interface.  As of .NET 4.0, HashSet<T> implements ISet<T> and a new set, the SortedSet<T> was added that gives you a set with ordering. HashSet<T> – For Unordered Storage of Sets When used right, HashSet<T> is a beautiful collection, you can think of it as a simplified Dictionary<T,T>.  That is, a Dictionary where the TKey and TValue refer to the same object.  This is really an oversimplification, but logically it makes sense.  I’ve actually seen people code a Dictionary<T,T> where they store the same thing in the key and the value, and that’s just inefficient because of the extra storage to hold both the key and the value. As it’s name implies, the HashSet<T> uses a hashing algorithm to find the items in the set, which means it does take up some additional space, but it has lightning fast lookups!  Compare the times below between HashSet<T> and List<T>: Operation HashSet<T> List<T> Add() O(1) O(1) at end O(n) in middle Remove() O(1) O(n) Contains() O(1) O(n)   Now, these times are amortized and represent the typical case.  In the very worst case, the operations could be linear if they involve a resizing of the collection – but this is true for both the List and HashSet so that’s a less of an issue when comparing the two. The key thing to note is that in the general case, HashSet is constant time for adds, removes, and contains!  This means that no matter how large the collection is, it takes roughly the exact same amount of time to find an item or determine if it’s not in the collection.  Compare this to the List where almost any add or remove must rearrange potentially all the elements!  And to find an item in the list (if unsorted) you must search every item in the List. So as you can see, if you want to create an unordered collection and have very fast lookup and manipulation, the HashSet is a great collection. And since HashSet<T> implements ICollection<T> and IEnumerable<T>, it supports nearly all the same basic operations as the List<T> and can use the System.Linq extension methods as well. All we have to do to switch from a List<T> to a HashSet<T>  is change our declaration.  Since List and HashSet support many of the same members, chances are we won’t need to change much else. 1: public sealed class OrderProcessor 2: { 3: private readonly HashSet<string> _subscriptions = new HashSet<string>(); 4:  5: // ... 6:  7: public PlaceOrderResponse PlaceOrder(Order newOrder) 8: { 9: // do some validation, of course... 10: 11: // check to see if already subscribed, if not add a subscription 12: if (!_subscriptions.Contains(newOrder.Symbol)) 13: { 14: // add the symbol to the list 15: _subscriptions.Add(newOrder.Symbol); 16: 17: // do whatever magic is needed to start a subscription for the symbol 18: } 19: 20: // place the order logic! 21: } 22:  23: // ... 24: } 25: Notice, we didn’t change any code other than the declaration for _subscriptions to be a HashSet<T>.  Thus, we can pick up the performance improvements in this case with minimal code changes. SortedSet<T> – Ordered Storage of Sets Just like HashSet<T> is logically similar to Dictionary<T,T>, the SortedSet<T> is logically similar to the SortedDictionary<T,T>. The SortedSet can be used when you want to do set operations on a collection, but you want to maintain that collection in sorted order.  Now, this is not necessarily mathematically relevant, but if your collection needs do include order, this is the set to use. So the SortedSet seems to be implemented as a binary tree (possibly a red-black tree) internally.  Since binary trees are dynamic structures and non-contiguous (unlike List and SortedList) this means that inserts and deletes do not involve rearranging elements, or changing the linking of the nodes.  There is some overhead in keeping the nodes in order, but it is much smaller than a contiguous storage collection like a List<T>.  Let’s compare the three: Operation HashSet<T> SortedSet<T> List<T> Add() O(1) O(log n) O(1) at end O(n) in middle Remove() O(1) O(log n) O(n) Contains() O(1) O(log n) O(n)   The MSDN documentation seems to indicate that operations on SortedSet are O(1), but this seems to be inconsistent with its implementation and seems to be a documentation error.  There’s actually a separate MSDN document (here) on SortedSet that indicates that it is, in fact, logarithmic in complexity.  Let’s put it in layman’s terms: logarithmic means you can double the collection size and typically you only add a single extra “visit” to an item in the collection.  Take that in contrast to List<T>’s linear operation where if you double the size of the collection you double the “visits” to items in the collection.  This is very good performance!  It’s still not as performant as HashSet<T> where it always just visits one item (amortized), but for the addition of sorting this is a good thing. Consider the following table, now this is just illustrative data of the relative complexities, but it’s enough to get the point: Collection Size O(1) Visits O(log n) Visits O(n) Visits 1 1 1 1 10 1 4 10 100 1 7 100 1000 1 10 1000   Notice that the logarithmic – O(log n) – visit count goes up very slowly compare to the linear – O(n) – visit count.  This is because since the list is sorted, it can do one check in the middle of the list, determine which half of the collection the data is in, and discard the other half (binary search).  So, if you need your set to be sorted, you can use the SortedSet<T> just like the HashSet<T> and gain sorting for a small performance hit, but it’s still faster than a List<T>. Unique Set Operations Now, if you do want to perform more set-like operations, both implementations of ISet<T> support the following, which play back towards the mathematical set operations described before: IntersectWith() – Performs the set intersection of two sets.  Modifies the current set so that it only contains elements also in the second set. UnionWith() – Performs a set union of two sets.  Modifies the current set so it contains all elements present both in the current set and the second set. ExceptWith() – Performs a set difference of two sets.  Modifies the current set so that it removes all elements present in the second set. IsSupersetOf() – Checks if the current set is a superset of the second set. IsSubsetOf() – Checks if the current set is a subset of the second set. For more information on the set operations themselves, see the MSDN description of ISet<T> (here). What Sets Don’t Do Don’t get me wrong, sets are not silver bullets.  You don’t really want to use a set when you want separate key to value lookups, that’s what the IDictionary implementations are best for. Also sets don’t store temporal add-order.  That is, if you are adding items to the end of a list all the time, your list is ordered in terms of when items were added to it.  This is something the sets don’t do naturally (though you could use a SortedSet with an IComparer with a DateTime but that’s overkill) but List<T> can. Also, List<T> allows indexing which is a blazingly fast way to iterate through items in the collection.  Iterating over all the items in a List<T> is generally much, much faster than iterating over a set. Summary Sets are an excellent tool for maintaining a lookup table where the item is both the key and the value.  In addition, if you have need for the mathematical set operations, the C# sets support those as well.  The HashSet<T> is the set of choice if you want the fastest possible lookups but don’t care about order.  In contrast the SortedSet<T> will give you a sorted collection at a slight reduction in performance.   Technorati Tags: C#,.Net,Little Wonders,BlackRabbitCoder,ISet,HashSet,SortedSet

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• best practice to persist classes model

  - by Yaron Naveh

  My application contains a set of model classes. e.g. Person, Department... The user changes values for instances of these classes in the UI and the classes are persisted to my "project" file. Next time the user can open and edit the project. Next version of my product may change the model classes drastically. It will still need to open existing projects files (I will know how to handle missing data). How is it best to persist my model classes to the project file? The easiest way to persist classes is Data contract serialization. However it will fail on breaking changes (I expect to have such). How to handle this? use some other persistence, e.g. name-value collection or db which is more tolerance ship a "project converter" application to migrate old projects. This requires to either ship with both old and new models or to manipulate xml, which is best?

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• Entity Framework 4 + POCO with custom classes and WCF contracts (serialization problem)

  - by eman

  Yesterday I worked on a project where I upgraded to Entity Framework 4 with the Repository pattern. In one post, I have read that it is necessary to turn off the custom tool generator classes and then write classes (same like entites) by hand. That I can do it, I used the POCO Entity Generator and then deleted the new generated files .tt and all subordinate .cs classes. Then I wrote the "entity classes" by myself. I added the repository pattern and implemented it in the business layer and then implemented a WCF layer, which should call the methods from the business layer. By calling an Insert (Add) method from the presentation layer and everything is OK. But if I call any method that should return some class, then I get an error like (the connection was interrupted by the server). I suppose there is a problem with the serialization or am I wrong? How can by this problem solved? I'm using Visual Studio S2010, Entity Framework 4, C#. UPDATE: I have uploaded the project and hope somebody can help me! link text UPDATE 2: My questions: Why is POCO good (pros/cons)? When should POCO be used? Is POCO + the repository pattern a good choice? Should POCO classes by written by myself or could I use auto generated POCO classes?

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• Roll up project-level tasks to the project collection portal in TFS2010

  - by adam.mokan

  I have a Project Collection setup in my TFS2010RC deployment. I have two Projects setup under this collection with their own task lists, which are populated with data. I fully expected the tasks from these individual projects to "roll up" and appear in the task list at the Project Collection level, but they do not. The Project Collection task list is empty. Basically, I'm looking to provide a view so a supervisor could see all tasks across projects quickly and easily. I'm sure I could write a reporting services report, but it seems like this is something so basic that it would have been included and it just need to be turned on or something. I'm sure I'm probably missing something really simple here. Thanks.

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• Sorting an observable collection with linq

  - by zachary

  I have an observable collection and I sort it using linq. Everything is great, but the problem I have is how do I sort the actual observable collection? Instead I just end up with some IEnumerable thing and I end up clearing the collection and adding the stuff back in. This can't be good for performance. Does anyone know of a better way to do this?

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• Convert Collection to List

  - by Mercer

  Hello, I want to say how to convert a Collection to a List in Java

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• Mapping a child collection without indexing based on database primary key or using bag

  - by Colin Bowern

  I have a existing parent-child relationship I am trying to map in Fluent Nhibernate: [RatingCollection] -- [Rating] Rating Collection has: ID (database generated ID) Code Name Rating has: ID (database generated id) Rating Collection ID Code Name I have been trying to figure out which permutation of HasMany makes sense here. What I have right now: HasMany<Rating>(x => x.Ratings) .WithTableName("Rating") .KeyColumnNames.Add("RatingCollectionId") .Component(c => { c.Map(x => x.Code); c.Map(x => x.Name); ); It works from a CRUD perspective but because it's a bag it ends up deleting the rating contents any time I try to do a simple update / insert to the Ratings property. What I want is an indexed collection but not using the database generated ID (which is in the six digit range right now). Any thoughts on how I could get a zero-based indexed collection (so I can go entity.Ratings[0].Name = "foo") which would allow me to modify the collection without deleting/reinserting it all when persisting?

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• Backbone.Marionette - Collection within CompositeView, which itself is nested in a CollectionView

  - by nicefinly

  *UPDATE: The problem probably involves the tour-template as I've discovered that it thinks the 'name' attribute is undefined. This leads me to think that it's not an array being passed on to the ToursView, but for some reason a string. * After studying similar questions on StackOverflow: How to handle nested CompositeView using Backbone.Marionette? How do you properly display a Backbone marionette collection view based on a model javascript array property? Nested collections with Backbone.Marionette ... and Derick Bailey's excellent blog's on this subject: http://lostechies.com/derickbailey/2012/04/05/composite-views-tree-structures-tables-and-more/ ... including the JSFiddle's: http://jsfiddle.net/derickbailey/AdWjU/ I'm still having trouble with a displaying the last node of a nested CollectionView of CompositeViews. It is the final CollectionView within each CompositeView that is causing the problem. CollectionView { CompositeView{ CollectionView {} //**<-- This is the troublemaker!** } } NOTE: I have already made a point of creating a valid Backbone.Collection given that the collection passed on to the final, child CollectionView is just a simple array. Data returned from the api to ToursList: [ { "id": "1", "name": "Venice", "theTours": "[ {'name': u'test venice'}, {'name': u'test venice 2'} ]" }, { "id": "2", "name": "Rome", "theTours": "[ {'name': u'Test rome'} ]" }, { "id": "3", "name": "Dublin", "theTours": "[ {'name': u'test dublin'}, {'name': u'test dublin 2'} ]" } ] I'm trying to nest these in a dropdown where the nav header is the 'name' (i.e. Dublin), and the subsequent li 's are the individual tour names (i.e. 'test dublin', 'test dublin2', etc.) Tour Models and Collections ToursByLoc = TastypieModel.extend({}); ToursList = TastypieCollection.extend({ model: ToursByLoc, url:'/api/v1/location/', }); Tour Views ToursView = Backbone.Marionette.ItemView.extend({ template: '#tour-template', tagName: 'li', }); ToursByLocView = Backbone.Marionette.CompositeView.extend({ template: '#toursByLoc-template', itemView: ToursView, initialize: function(){ //As per Derick Bailey's comments regarding the need to pass on a //valid Backbone.Collection to the child CollectionView //REFERENCE: http://stackoverflow.com/questions/12163118/nested-collections-with-backbone-marionette var theTours = this.model.get('theTours'); this.collection = new Backbone.Collection(theTours); }, appendHtml: function(collectionView, itemView){ collectionView.$('div').append(itemView.el); } }); ToursListView = Backbone.Marionette.CollectionView.extend({ itemView: ToursByLocView, }); Templates <script id="tour-template" type="text/template"> <%= name %> </script> <script id="toursByLoc-template" type="text/template"> <li class="nav-header"><%= name %></li> <div class="indTours"></div> <li class="divider"></li> </script>

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• Should I use TFS 2010 Project Collection Per Customer

  - by Yoann. B

  Hi, My company is a Software development company. We planned to use TFS 2010 for our future customers development. TFS 2010 introduce Team Project Collection in order to split related Team Projects. So my question is, should i use Project Collection per Customers or should i use a unique Project Collection with a Team Project per Customers which will contains some customer solution projects in it

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• Convert List to Collection

  - by Mercer

  Hello, i want to say how to convert a Collection to a List in Java

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• How to traverse the item in the collection in a List or Observable collection?

  - by Ashish Ashu

  I have a collection that is binded to my Listview. I have provided options to user to "move up" "move down" the selected item in the list view. I have binded the selected item of the listview to my viewmodel, hence I get the item in the collection on which user want to do the operation. I have attached "move up" "move down" commands in my viewmodel. I want what is the best way to move up and down in the collection in the collection which is reflected in the list view. Please suggest.

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• ASP.NET MVC: Accessing ModelMetadata for items in a collection

  - by DanM

  I'm trying to write an auto-scaffolder for Index views. I'd like to be able to pass in a collection of models or view-models (e.g., IEnumerable<MyViewModel>) and get back an HTML table that uses the DisplayName attribute for the headings (th elements) and Html.Display(propertyName) for the cells (td elements). Each row should correspond to one item in the collection. When I'm only displaying a single record, as in a Details view, I use ViewData.ModelMetadata.Properties to obtain the list of properties for a given model. But what happens when the model I pass to the view is a collection of model or view-model objects and not a model or view-model itself? How do I obtain the ModelMetadata for a particular item in a collection?

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• Building resultset using collection object

  - by Bhaskara Krishna Mohan Potam

  Hi, I had an issue in building the resultset using java. Here it goes... I am storing a collection object which is organized as row wise taken from a resultset object and putting the collection object(which is stored as vector/array list) in cache and trying to retrieve the same collection object. Here i need to build back the resultset again using the collection object. Now my doubt is building the resultset in this way possible or not? Please let me know asap. Thanks in advance, Bhaskar

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• NHibernate IQueryable Collection as Property of Root

  - by Khalid Abuhakmeh

  Hello and thank you for taking the time to read this. I have a root object that has a property that is a collection. For example : I have a Shelf object that has Books. // now public class Shelf { public ICollection<Book> Books {get; set;} } // want public class Shelf { public IQueryable<Book> Books {get;set;} } What I want to accomplish is to return a collection that is IQueryable so that I can run paging and filtering off of the collection directly from the the parent. var shelf = shelfRepository.Get(1); var filtered = from book in shelf.Books where book.Name == "The Great Gatsby" select book; I want to have that query executed specifically by NHibernate and not a get all to load a whole collection and then parse it in memory (which is what currently happens when I use ICollection). The reasoning behind this is that my collection could be huge, tens of thousands of records, and a get all query could bash my database. I would like to do this implicitly so that when NHibernate sees and IQueryable on my class it knows what to do. I have looked at NHibernates Linq provider and currently I am making the decision to take large collections and split them into their own repository so that I can make explicit calls for filtering and paging. Linq To SQL offers something similar to what I'm talking about.

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• Retrieve Value Using Key From a Collection in Access 2000

  - by Mikecancook

  I know this is a simple question but it's aggravating me. If I have a key/value pair in a collection but I can't seem to get the value out using the key. I can get the key using the value but not vice versa. Is there some magical way to accomplish this? For example: Dim CycleList As Collection Dim Value as String Set CycleList = New Collection CycleList.Add 1, "Some Value" Value = CycleList(1) I've also tried CycleList.Item(1) and it's the same result, Value = 1.

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• Validating collection elements in WPF

  - by Chris

  I would like to know how people are going about validating collections in WPF. Lets say for example that I have an observable collection of ViewModels that I am binding to the items source of a grid, and the user can add new rows to the grid and needs to fill them. First of all I need to validate on each row to ensure that required fields of each ViewModel are filled in. This is fine and simple to do for each row. However, the second level of validation is on the collection as a whole. For example i want to ensure that no two rows of the collection have the same identifier, or that no two rows have the same name. Im basically checking for duplicate properties within different rows. I also have more complex conditions where I must ensure that there is at least one item within the collection that has some property set. How do I get a validation rule that would allow me to check these rules, validating on the whole collection rather than the individual items. I also want to print any validation error above the datagrid so that the user can fix the problem and the message will update or disappear as the user fixes each different rule. Anyone have any experience of the proper way to do this? Thanks Chris

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