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• How can I lookup data about a book from its barcode number?

  - by Joel Spolsky

  I'm building the world's simplest library application. All I want to be able to do is scan in a book's UPC (barcode) using a typical scanner (which just types the numbers of the barcode into a field) and then use it to look up data about the book... at a minimum, title, author, year published, and either the Dewey Decimal or Library of Congress catalog number. The goal is to print out a tiny sticker ("spine label") with the card catalog number that I can stick on the spine of the book, and then I can sort the books by card catalog number on the shelves in our company library. That way books on similar subjects will tend to be near each other, for example, if you know you're looking for a book about accounting, all you have to do is find SOME book about accounting and you'll see the other half dozen that we have right next to it which makes it convenient to browse the library. There seem to be lots of web APIs to do this, including Amazon and the Library of Congress. But those are all extremely confusing to me. What I really just want is a single higher level function that takes a UPC barcode number and returns some basic data about the book.

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• JQuery Tabbed Nav Menu and PHP Forms Question?

  - by SlAcKeR

  I'm using a JQuery Tabbed Menu which holds different types of forms and when I select a different form located under a different tab and submit the form the tab will jump to the default tab instead of the current tab the form is located in. I was wondering how would I go about fixing this so that when the form is submitted the current tab is still selected, is it the JQuery or PHP problem? Here is the JQuery. $(document).ready(function() { //When page loads... $(".form-content").hide(); //Hide all content var firstMenu = $("#home-menu ul li:first"); firstMenu.show(); firstMenu.find("a").addClass("selected-link"); //Activate first tab $(".form-content:first").show(); //Show first tab content //On Click Event $("#home-menu ul li").click(function() { $("#home-menu ul li a").removeClass("selected-link"); //Remove any "selected-link" class $(this).find("a").addClass("selected-link"); //Add "selected-link" class to selected tab $(".form-content").hide(); //Hide all tab content var activeTab = $(this).find("a").attr("href"); //Find the href attribute value to identify the selected-link tab + content $(activeTab).fadeIn(); //Fade in the selected-link ID content return false; }); });

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• Will my LinqToSql execution be deffered if i filter with IEnumerable<T> instead of IQueryable<T>?

  - by cottsak

  I have been using these common EntityObjectFilters as a "pipes and filters" way to query from a collection a particular item with an ID: public static class EntityObjectFilters { public static T WithID<T>(this IQueryable<T> qry, int ID) where T : IEntityObject { return qry.SingleOrDefault<T>(item => item.ID == ID); } public static T WithID<T>(this IList<T> list, int ID) where T : IEntityObject { return list.SingleOrDefault<T>(item => item.ID == ID); } } ..but i wondered to myself: "can i make this simpler by just creating an extension for all IEnumerable<T> types"? So i came up with this: public static class EntityObjectFilters { public static T WithID<T>(this IEnumerable<T> qry, int ID) where T : IEntityObject { return qry.SingleOrDefault<T>(item => item.ID == ID); } } Now while this appears to yield the same result, i want to know that when applied to IQueryable<T>s will the expression tree be passed to LinqToSql for evaluating as SQL code or will my qry be evaluated in it's entirety first, then iterated with Funcs? I'm suspecting that (as per Richard's answer) the latter will be true which is obviously what i don't want. I want the same result, but the added benefit of the delayed SQL execution for IQueryable<T>s. Can someone confirm for me what will actually happen and provide simple explanation as to how it would work?

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• passing an "unknown enumeration" to a method

  - by firoso

  I'm currently trying to make a class that can register strings as identifiers and accociate them with different types of Enumerations, these enumerations are being evaluated only in so much that I am ensuring that when it's used, that the parameter passed to broadcast (messageType) is an instance of the associated Enum Type. This would work something like this: Diagnostics.RegisterIdentifier("logger", typeof(TestEnum)); Diagnostics.Broadcast("logger", TestEnum.Info, null, "Hello World", null); here's the code I currently have, I need to be able to verify that messageTypesEnum is contained in messageTypesFromIdentifier. private static Dictionary<string, Type> identifierMessageTypeMapping = new Dictionary<string, Type>(); private static List<IListener> listeners = new List<IListener>(); public static void RegisterIdentifier(string identifier, Type messageTypesEnum) { if (messageTypesEnum.BaseType.FullName == "System.Enum") { identifierMessageTypeMapping.Add(identifier, messageTypesEnum); } else { throw new ArgumentException("Expected type of messageTypesEnum to derive from System.Enum", "messageTypesEnum"); } } public static void Broadcast(string identifier, object messageType, string metaIdentifier, string message, Exception exception) { if (identifierMessageTypeMapping.ContainsKey(identifier)) { Type messageTypesFromIdentifier = identifierMessageTypeMapping[identifier]; foreach (var listener in listeners) { DiagnosticsEvent writableEvent = new DiagnosticsEvent(identifier, messageType, metaIdentifier, message, exception); listener.Write(writableEvent); } } }

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• Scala: Correcting type inference of representation type over if statement

  - by drhagen

  This is a follow-up to two questions on representation types, which are type parameters of a trait designed to represent the type underlying a bounded type member (or something like that). I've had success creating instances of classes, e.g ConcreteGarage, that have instances cars of bounded type members CarType. trait Garage { type CarType <: Car[CarType] def cars: Seq[CarType] def copy(cars: Seq[CarType]): Garage def refuel(car: CarType, fuel: CarType#FuelType): Garage = copy( cars.map { case `car` => car.refuel(fuel) case other => other }) } class ConcreteGarage[C <: Car[C]](val cars: Seq[C]) extends Garage { type CarType = C def copy(cars: Seq[C]) = new ConcreteGarage(cars) } trait Car[C <: Car[C]] { type FuelType <: Fuel def fuel: FuelType def copy(fuel: C#FuelType): C def refuel(fuel: C#FuelType): C = copy(fuel) } class Ferrari(val fuel: Benzin) extends Car[Ferrari] { type FuelType = Benzin def copy(fuel: Benzin) = new Ferrari(fuel) } class Mustang(val fuel: Benzin) extends Car[Mustang] { type FuelType = Benzin def copy(fuel: Benzin) = new Mustang(fuel) } trait Fuel case class Benzin() extends Fuel I can easily create instances of Cars like Ferraris and Mustangs and put them into a ConcreteGarage, as long as it's simple: val newFerrari = new Ferrari(Benzin()) val newMustang = new Mustang(Benzin()) val ferrariGarage = new ConcreteGarage(Seq(newFerrari)) val mustangGarage = new ConcreteGarage(Seq(newMustang)) However, if I merely return one or the other, based on a flag, and try to put the result into a garage, it fails: val likesFord = true val new_car = if (likesFord) newFerrari else newMustang val switchedGarage = new ConcreteGarage(Seq(new_car)) // Fails here The switch alone works fine, it is the call to ConcreteGarage constructor that fails with the rather mystical error: error: inferred type arguments [this.Car[_ >: this.Ferrari with this.Mustang <: this.Car[_ >: this.Ferrari with this.Mustang <: ScalaObject]{def fuel: this.Benzin; type FuelType<: this.Benzin}]{def fuel: this.Benzin; type FuelType<: this.Benzin}] do not conform to class ConcreteGarage's type parameter bounds [C <: this.Car[C]] val switchedGarage = new ConcreteGarage(Seq(new_car)) // Fails here ^ I have tried putting those magic [C <: Car[C]] representation type parameters everywhere, but without success in finding the magic spot.

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• Java/JAXB: Accessing property of object in a list

  - by Mark Lewis

  Hello Using JAXB I've created a series of classes which represent my XML schema. Validating against the schema an XML file has thus become a 'tree' of java objects representing the XML. Now I'd like to access, delete and add an object of one the created types in my tree. If I've got classes' methods arranged like this: RootType class has: public List<FQType> getFq() { // and setter return fq; } FQType class has: public RemapType getRemap() { // and setter return remap; } RemapType class has: public String getSource() { // and setter return source; } What's the most concise way to code reading and writing of the 'source' member of a RemapType instance in an FQType instance with, say, fqtypeID=1, in an array of type RootType (in which RootType instances also each have rootID)? Currently I'm using a for loop Iterator in which is an if rootID = mySelectedRootID. In the if I nest a second for loop Iterator over the contained FQType instances and in that a second if fqTypeID = mySelectedFQTypeID. IE for loop iterator/if statement pairs to recognise the object of desire. With all the bells and whistles this way is nearly 15 lines of code to access a data type - can I do this in one line? Thanks

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• Generic validate input data via regex. Input error when match.count == 0

  - by Valamas

  Hi, I have a number of types of data fields on an input form, for example, a web page. Some fields are like, must be an email address, must be a number, must be a number between, must have certain characters. Basically, the list is undefinable. I wish to come up with a generic way of validating the data inputed. I thought I would use regex to validate the data. The fields which need validation would be related to a "regex expression" and a "regex error message" stating what the field should contain. My current mock up has that when the match count is zero, that would signify an error and to display the message. While still a white belt regex designer I have come to understand that in certain situations that it is difficult to write a regex which results in a match count of zero for every case. A complex regex case I looked for help on was Link Here. The forum post was a disaster because I confused people helping me. But one of the statements said that it was difficult to make a regex with a match count of zero meaning the input data was invalid; that the regex was very difficult to write that for. Does anyone have comments or suggestions on this generic validation system I am trying to create? thanks

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• check properties of two objects for changes

  - by k-hoffmann

  Hi, i have to develop a mechanism to check two object properties for changes. All properties which are needed to check are marked with an attribute. Atm i - read all properties from acutal object via linq - read the corresponding property from old object - fill an own object with the two properties (old and new value) In Code the call to the workerclass looks like this public void CreateHistoryMap(BaseEntity actual, BaseEntity old) { CreateHistoryMap(actualEntity, oldEntity) .ForEach(mapEntry => CreateHistoryEntry(mapEntry), mapEntry => IfChangesDetected(mapEntry)); } CreateHistoryMap builds up the HistoryMapEntry which contains the two properties. CreateHistoryEntry build up the object which is saved to database, the IfChangesDetected check the object for changes. I have to handle own special application types to generate history values to database (like concatinating list values and so on). My problem is now, that i have to read the values of the properties twice - for change detection - and for the concreate CreateHistoryEntry How can i eliminate this problem or how can i implement the change tracking scenario with the nice c# 3.5 features? Thanks a lot.

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• Setting Nullable Integer to String Containing Nothing yields 0

  - by Brian MacKay

  I've been pulling my hair out over some unexpected behavior from nullable integers. If I set an Integer to Nothing, it becomes Nothing as expected. If I set an Integer? to a String that is Nothing, it becomes 0! Of course I get this whether I explicitly cast the String to Integer? or not. I realize I could work around this pretty easily but I want to know what I'm missing. Dim NullString As String = Nothing Dim NullableInt As Integer? = CType(NullString, Integer?) 'Expected NullableInt to be Nothing, but it's 0! NullableInt = Nothing 'This works -- NullableInt now contains Nothing. How is this EDIT: Previously I had my code up here so without the explicit conversion to 'Integer?' and everyone seemed to be fixated on that. I want to be clear that this is not an issue that would have been caught by Option Strict On -- check out the accepted answer. This is a quirk of the string-to-integer conversion rules which predate nullable types, but still impact them.

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• Google Maps: Simple app not working on IE

  - by Peter Bridger

  We have a simple Google Maps traffic application up at: http://www.avonandsomerset.police.uk/newsroom/traffic/ For some reason it's recently stopped working in IE correctly. At this point in time it was using V2 of the API, so I've just upgraded it to use V3 - but it still won't work in IE. It works fine in Chrome & Firefox. But in all versions of IE I've tired (6,7,8) the Google Map doesn't load fully. The problem The Google Map DIV will generally load all the controls (Zoom, Powered by Google, map types) but the actual map tiles do not appear in IE. I can just see the grey background of the DIV What I've tried I've commented down the JavaScript code to just the following on the page, but it still has the same problem: <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script> <script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=false"></script> <script type="text/javascript" > var map; $(document).ready(function () { initialize(); // Set-up Google map }); function initialize() { var options = { zoom: 9, center: new google.maps.LatLng(51.335759, -2.870178), mapTypeId: google.maps.MapTypeId.ROADMAP }; map = new google.maps.Map(document.getElementById("googleMap"), options); } </script>

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• Looking for a RESTful or SOAP pipeline between WordPress and InterWoven TeamSite

  - by deanpeters

  I've been Googling my brains out trying see if there's a simple way to bridge content to and from WordPress to and from TeamSite. I'm coming at this from the perspective of a WordPress developer. I see in the book "The Definitive Guide to Interwoven TeamSite" (http://bit.ly/d3z4wI) mention of objects for the Interwoven LiveSite product: com.interwoven.livesite.external.impl.RSS com.interwoven.livesite.external.impl.SOAP If I understand the above objects correctly, these allow me to instantiate objects of these data types, which after populating them via various method calls, allow me to render content using com.interwoven.livesite.external.ExternalCall ... but I'm not sure. Nor do I think this approach provides me the 2-way street I seek. As it stands now, from my limited understanding, it appears that the least path of resistance is deploying Interwoven's LiveSite with the existing TeamSite implementation so content can be both consumed and rendered via RSS ... an channel which WordPress can produce and consume; the latter with plugins such as wp-o-matic and/or feedpress. So the question is, does anyone out there have experience with a SOAP or RESTful API approach to InterWoven's TeamSite? If so, can I get some direction on documentation? Or is the addition of LiveSite + RSS the most feasible 2-way channel?

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• How to use boost::fusion::transform on heterogeneous containers?

  - by Kyle

  Boost.org's example given for fusion::transform is as follows: struct triple { typedef int result_type; int operator()(int t) const { return t * 3; }; }; // ... assert(transform(make_vector(1,2,3), triple()) == make_vector(3,6,9)); Yet I'm not "getting it." The vector in their example contains elements all of the same type, but a major point of using fusion is containers of heterogeneous types. What if they had used make_vector(1, 'a', "howdy") instead? int operator()(int t) would need to become template<typename T> T& operator()(T& const t) But how would I write the result_type? template<typename T> typedef T& result_type certainly isn't valid syntax, and it wouldn't make sense even if it was, because it's not tied to the function.

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• page.insert_html not rendering partial correctly

  - by mathee

  The following is in the text_field. = f.text_field :title, :size => 50, :onchange => remote_function(:update => :suggestions, :url => {:action => :display_question_search_results}) The following is in display_questions_search_results.rjs. page.insert_html :bottom, 'suggestions', :partial => 'suggestions' Whenever the user types, I'd like to search the database for any tuples that match the keywords in the text field. Then, display those results. But, at the moment, _suggestions.haml only contains the word "suggestions!!". But, instead of seeing "suggestions!!" in the suggestions div tag, I get: try { Element.insert("suggestions", { bottom: "suggestions!!" }); } catch (e) { alert('RJS error:\n\n' + e.toString()); alert('Element.insert(\"suggestions\", { bottom: \"suggestions!!\" });'); throw e } I've been trying to find out why this is being done, but the previously asked questions I found seem more complicated than what I'm doing...

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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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• deleting object with template for int and object

  - by Yokhen

  Alright so Say I have a class with all its definition, bla bla bla... template <class DT> class Foo{ private: DT* _data; //other stuff; public: Foo(DT* data){ _data = data } virtual ~Foo(){ delete _data } //other methods }; And then I have in the main method: int main(){ int number = 12; Foo<anyRandomClass>* noPrimitiveDataObject = new Foo<anyRandomClass>(new anyRandomClass()); Foo<int>* intObject = new Foo<int>(number); delete noPrimitiveDataObject; //Everything goes just fine. delete intObject; //It messes up here, I think because primitive data types such as int are allocated in a different way. return 0; } My question is: What could I do to have both delete statements in the main method work just fine? P.S.: Although I have not actually compiled/tested this specific code, I have reviewed it extensively (as well as indented. You're welcome.), so if you find a mistake, please be nice. Thank you.

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• What characters are NOT escaped with a mysqli prepared statement?

  - by barfoon

  Hey everyone, I'm trying to harden some of my PHP code and use mysqli prepared statements to better validate user input and prevent injection attacks. I switched away from mysqli_real_escape_string as it does not escape % and _. However, when I create my query as a mysqli prepared statement, the same flaw is still present. The query pulls a users salt value based on their username. I'd do something similar for passwords and other lookups. Code: $db = new sitedatalayer(); if ($stmt = $db->_conn->prepare("SELECT `salt` FROM admins WHERE `username` LIKE ? LIMIT 1")) { $stmt->bind_param('s', $username); $stmt->execute(); $stmt->bind_result($salt); while ($stmt->fetch()) { printf("%s\n", $salt); } $stmt->close(); } else return false; Am I composing the statement correctly? If I am what other characters need to be examined? What other flaws are there? What is best practice for doing these types of selects? Thanks,

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• What do I name classes whose only purpose is to act as a structure?

  - by Sergio Tapia

  For example, take my Actor class: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Drawing; namespace FreeIMDB { class Actor { public string Name { get; set; } public Image Portrait { get; set; } public DateTime DateOfBirth { get; set; } public List<string> ActingRoles { get; set; } public List<string> WritingRoles { get; set; } public List<string> ProducingRoles { get; set; } public List<string> DirectingRoles { get; set; } } } This class will only be used to stuff information into it, and allow other developers to get their values. What are these types of classes officially called? What is the correct nomenclature?

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• Grails - Removing an item from a hasMany association List on data bind?

  - by ecrane

  Grails offers the ability to automatically create and bind domain objects to a hasMany List, as described in the grails user guide. So, for example, if my domain object "Author" has a List of many "Book" objects, I could create and bind these using the following markup (from the user guide): <g:textField name="books[0].title" value="the Stand" /> <g:textField name="books[1].title" value="the Shining" /> <g:textField name="books[2].title" value="Red Madder" /> In this case, if any of the books specified don't already exist, Grails will create them and set their titles appropriately. If there are already books in the specified indices, their titles will be updated and they will be saved. My question is: is there some easy way to tell Grails to remove one of those books from the 'books' association on data bind? The most obvious way to do this would be to omit the form element that corresponds to the domain instance you want to delete; unfortunately, this does not work, as per the user guide: Then Grails will automatically create a new instance for you at the defined position. If you "skipped" a few elements in the middle ... Then Grails will automatically create instances in between. I realize that a specific solution could be engineered as part of a command object, or as part of a particular controller- however, the need for this functionality appears repeatedly throughout my application, across multiple domain objects and for associations of many different types of objects. A general solution, therefore, would be ideal. Does anyone know if there is something like this included in Grails?

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• Are UTF16 (as used by for example wide-winapi functions) characters always 2 byte long?

  - by Cray

  Please clarify for me, how does UTF16 work? I am a little confused, considering these points: There is a static type in C++, WCHAR, which is 2 bytes long. (always 2 bytes long obvisouly) Most of msdn and some other documentation seem to have the assumptions that the characters are always 2 bytes long. This can just be my imagination, I can't come up with any particular examples, but it just seems that way. There are no "extra wide" functions or characters types widely used in C++ or windows, so I would assume that UTF16 is all that is ever needed. To my uncertain knowledge, unicode has a lot more characters than 65535, so they obvisouly don't have enough space in 2 bytes. UTF16 seems to be a bigger version of UTF8, and UTF8 characters can be of different lengths. So if a UTF16 character not always 2 bytes long, how long else could it be? 3 bytes? or only multiples of 2? And then for example if there is a winapi function that wants to know the size of a wide string in characters, and the string contains 2 characters which are each 4 bytes long, how is the size of that string in characters calculated? Is it 2 chars long or 4 chars long? (since it is 8 bytes long, and each WCHAR is 2 bytes)

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• WCF data services (OData), query with inheritance limitation?

  - by Mathieu Hétu

  Project: WCF Data service using internally EF4 CTP5 Code-First approach. I configured entities with inheritance (TPH). See previous question on this topic: Previous question about multiple entities- same table The mapping works well, and unit test over EF4 confirms that queries runs smoothly. My entities looks like this: ContactBase (abstract) Customer (inherits from ContactBase), this entity has also several Navigation properties toward other entities Resource (inherits from ContactBase) I have configured a discriminator, so both Customer and Resource map to the same table. Again, everythings works fine on the Ef4 point of view (unit tests all greens!) However, when exposing this DBContext over WCF Data services, I get: - CustomerBases sets exposed (Customers and Resources sets seems hidden, is it by design?) - When I query over Odata on Customers, I get this error: Navigation Properties are not supported on derived entity types. Entity Set 'ContactBases' has a instance of type 'CodeFirstNamespace.Customer', which is an derived entity type and has navigation properties. Please remove all the navigation properties from type 'CodeFirstNamespace.Customer'. Stacktrace: at System.Data.Services.Serializers.SyndicationSerializer.WriteObjectProperties(IExpandedResult expanded, Object customObject, ResourceType resourceType, Uri absoluteUri, String relativeUri, SyndicationItem item, DictionaryContent content, EpmSourcePathSegment currentSourceRoot) at System.Data.Services.Serializers.SyndicationSerializer.WriteEntryElement(IExpandedResult expanded, Object element, ResourceType expectedType, Uri absoluteUri, String relativeUri, SyndicationItem target) at System.Data.Services.Serializers.SyndicationSerializer.<DeferredFeedItems>d__b.MoveNext() at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteItems(XmlWriter writer, IEnumerable`1 items, Uri feedBaseUri) at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteFeedTo(XmlWriter writer, SyndicationFeed feed, Boolean isSourceFeed) at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteFeed(XmlWriter writer) at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteTo(XmlWriter writer) at System.Data.Services.Serializers.SyndicationSerializer.WriteTopLevelElements(IExpandedResult expanded, IEnumerator elements, Boolean hasMoved) at System.Data.Services.Serializers.Serializer.WriteRequest(IEnumerator queryResults, Boolean hasMoved) at System.Data.Services.ResponseBodyWriter.Write(Stream stream) Seems like a limitation of WCF Data services... is it? Not much documentation can be found on the web about WCF Data services (OData) and inheritance specifications. How can I overpass this exception? I need these navigation properties on derived entities, and inheritance seems the only way to provide mapping of 2 entites on the same table with Ef4 CTP5... Any thoughts?

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• C++: defining maximum/minimum limits for a class

  - by Luis

  Basically what the title says... I have created a class that models time slots in a variable-granularity daily schedule (where for example the first time slot is 30 minutes, but the second time slot can be 40 minutes); the first available slot starts at (a value comparable to) 1. What I want to do now is to define somehow the maximum and minimum allowable values that this class takes and I have two practical questions in order to do so: 1.- does it make sense to define absolute minimum and maximum in such a way for a custom class? Or better, does it suffice that a value always compares as lower-than any other possible value of the type, given the class's defined relational operators, to be defined the min? (and analogusly for the max) 2.- assuming the previous question has an answer modeled after "yes" (or "yes but ..."), how do I define such max/min? I know that there is std::numeric_limits<> but from what I read it is intended for "numeric types". Do I interpret that as meaning "represented as a number" or can I make a broader assumption like "represented with numbers" or "having a correspondence to integers"? After all, it would make sense to define the minimum and maximum for a date class, and maybe for a dictionary class, but numeric_limits may not be intended for those uses (I don't have much experience with it). Plus, numeric_limits has a lot of extra members and information that I don't know what to make with. If I don't use numeric_limits, what other well-known / widely-used mechanism does C++ offer to indicate the available range of values for a class?

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• Tokenizing numbers for a parser

  - by René Nyffenegger

  I am writing my first parser and have a few questions conerning the tokenizer. Basically, my tokenizer exposes a nextToken() function that is supposed to return the next token. These tokens are distinguished by a token-type. I think it would make sense to have the following token-types: SYMBOL (such as <, :=, ( and the like REMARK (or a comment) NUMBER IDENT (such as the name of a function or a variable) STRING (Something enclosed between "....") Now, do you think this makes sense? Also, I am struggling with the NUMBER token-type. Do you think it makes more sense to further split it up into a NUMBER and a FLOAT token-type? Without a FLOAT token-type, I'd receive NUMBER (eg 402), a SYMBOL (.) followed by another NUMBER (eg 203) if I were about to parse a float. Finally, what do you think makes more sense for the tokenizer to return when it encounters a -909? Should it return the SYMBOL - first, followed by the NUMBER 909 or should it return a NUMBER -909 right away?

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• What's the best way of accessing a DRb object (e.g. Ruby Queue) from Scala (and Java)?

  - by Tom Morris

  I have built a variety of little scripts using Ruby's very simple Queue class, and share the Queue between Ruby and JRuby processes using DRb. It would be nice to be able to access these from Scala (and maybe Java) using JRuby. I've put together something Scala and the JSR-223 interface to access jruby-complete.jar. import javax.script._ class DRbQueue(host: String, port: Int) { private var engine = DRbQueue.factory.getEngineByName("jruby") private var invoker = engine.asInstanceOf[Invocable] engine.eval("require \"drb\" ") private var queue = engine.eval("DRbObject.new(nil, \"druby://" + host + ":" + port.toString + "\")") def isEmpty(): Boolean = invoker.invokeMethod(this.queue, "empty?").asInstanceOf[Boolean] def size(): Long = invoker.invokeMethod(this.queue, "length").asInstanceOf[Long] def threadsWaiting: Long = invoker.invokeMethod(this.queue, "num_waiting").asInstanceOf[Long] def offer(obj: Any) = invoker.invokeMethod(this.queue, "push", obj.asInstanceOf[java.lang.Object]) def poll(): Any = invoker.invokeMethod(this.queue, "pop") def clear(): Unit = { invoker.invokeMethod(this.queue, "clear") } } object DRbQueue { var factory = new ScriptEngineManager() } (It conforms roughly to java.util.Queue interface, but I haven't declared the interface because it doesn't implement the element and peek methods because the Ruby class doesn't offer them.) The problem with this is the type conversion. JRuby is fine with Scala's Strings - because they are Java strings. But if I give it a Scala Int or Long, or one of the other Scala types (List, Set, RichString, Array, Symbol) or some other custom type. This seems unnecessarily hacky: surely there has got to be a better way of doing RMI/DRb interop without having to use JSR-223 API. I could either make it so that the offer method serializes the object to, say, a JSON string and takes a structural type of only objects that have a toJson method. I could then write a Ruby wrapper class (or just monkeypatch Queue) to would parse the JSON. Is there any point in carrying on with trying to access DRb from Java/Scala? Might it just be easier to install a real message queue? (If so, any suggestions for a lightweight JVM-based MQ?)

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• ADO.NET DataTable/DataRow Thread Safety

  - by Allen E. Scharfenberg

  Introduction A user reported to me this morning that he was having an issue with inconsistent results (namely, column values sometimes coming out null when they should not be) of some parallel execution code that we provide as part of an internal framework. This code has worked fine in the past and has not been tampered with lately, but it got me to thinking about the following snippet: Code Sample lock (ResultTable) { newRow = ResultTable.NewRow(); } newRow["Key"] = currentKey; foreach (KeyValuePair<string, object> output in outputs) { object resultValue = output.Value; newRow[output.Name] = resultValue != null ? resultValue : DBNull.Value; } lock (ResultTable) { ResultTable.Rows.Add(newRow); } (No guarantees that that compiles, hand-edited to mask proprietery information.) Explanation We have this cascading type of locking code other places in our system, and it works fine, but this is the first instance of cascading locking code that I have come across that interacts with ADO .NET. As we all know, members of framework objects are usually not thread safe (which is the case in this situation), but the cascading locking should ensure that we are not reading and writing to ResultTable.Rows concurrently. We are safe, right? Hypothesis Well, the cascading lock code does not ensure that we are not reading from or writing to ResultTable.Rows at the same time that we are assigning values to columns in the new row. What if ADO .NET uses some kind of buffer for assigning column values that is not thread safe--even when different object types are involved (DataTable vs. DataRow)? Has anyone run into anything like this before? I thought I would ask here at StackOverflow before beating my head against this for hours on end :) Conclusion Well, the consensus appears to be that changing the cascading lock to a full lock has resolved the issue. That is not the result that I expected, but the full lock version has not produced the issue after many, many, many tests. The lesson: be wary of cascading locks used on APIs that you do not control. Who knows what may be going on under the covers!

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• Database schema for Product Properties

  - by Chemosh

  As so many people I'm looking for a Products /Product Properties database schema. I'm using Ruby on Rails and (Thinking) Sphinx for faceted searches. Requirements: Adding new product types and their options should not require a change to the database schema Support faceted searches using Sphinx. Solutions I've come across: (See Bill Karwin's answer) Option 1: Single Table Inheritance Not an option really. The table would contain way to many columns. Option 2: Class Table Inheritance Ruby on Rails caches the database schema on start-up which means a restart whenever a new type of product is introduced. If you have a size able product catalog this could mean hundreds of tables. Option 3: Serialized LOB Kills being able to do faceted searches without heavy application logic. Option 4: Entity-Attribute-Value For testing purposes, EAV worked fine. However it could quickly become a mess and a maintenance hell as you add more and more options (e.g. when an option increase the prices or delivery time). What option should I go with? What other solutions are out there? Is there a silver bullet (ha) I overlooked?

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