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  • Is it possible to define a generic lambda?

    - by Mike OBrien
    I have some logic in a method that operates on a specified type and I'd like to create a generic lambda that encapsulates the logic. This is the spirit of what I'm trying to do: public void DoSomething() { // ... Func<T> GetTypeName = () => T.GetType().Name; GetTypeName<string>(); GetTypeName<DateTime>(); GetTypeName<int>(); // ... } I know I can pass the type as a parameter or create a generic method but I'm interested if it can just be a generic lambda (So I'm not looking for alternatives). From what I can tell C# 3.0 doesn't support this. TIA, m

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  • Depth First Search Basics

    - by cam
    I'm trying to improve my current algorithm for the 8 Queens problem, and this is the first time I'm really dealing with algorithm design/algorithms. I want to implement a depth-first search combined with a permutation of the different Y values described here: http://en.wikipedia.org/wiki/Eight_queens_puzzle#The_eight_queens_puzzle_as_an_exercise_in_algorithm_design I've implemented the permutation part to solve the problem, but I'm having a little trouble wrapping my mind around the depth-first search. It is described as a way of traversing a tree/graph, but does it generate the tree graph? It seems the only way that this method would be more efficient only if the depth-first search generates the tree structure to be traversed, by implementing some logic to only generate certain parts of the tree. So essentially, I would have to create an algorithm that generated a pruned tree of lexigraphic permutations. I know how to implement the pruning logic, but I'm just not sure how to tie it in with the permutation generator since I've been using next_permutation. Is there any resources that could help me with the basics of depth first searches or creating lexigraphic permutations in tree form?

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  • To Wrap or Not to Wrap: Wrapping Data Access in a Service Facade

    - by PureCognition
    For a while now, my team and I have been wrapping our data access layer in a web service facade (using WCF) and calling it from the business logic layer. Meanwhile, we could simply use the repository pattern where the business logic layer consumes the data access layer locally through an interface, and at any point in time, we can switch things out for it to hit a service instead (if necessary). The question is: When is it a good time to wrap the data access layer in a service facade and when isn't it? Right now, it seems like the main advantage is that other applications can consume the service, but if they are internal applications written in .NET then they can just consume the .NET assembly instead. Are there other advantages of having the DAL be wrapped in a service that I am unaware of?

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  • Dynamic scoping in Clojure?

    - by j-g-faustus
    Hi, I'm looking for an idiomatic way to get dynamically scoped variables in Clojure (or a similar effect) for use in templates and such. Here is an example problem using a lookup table to translate tag attributes from some non-HTML format to HTML, where the table needs access to a set of variables supplied from elsewhere: (def *attr-table* ; Key: [attr-key tag-name] or [boolean-function] ; Value: [attr-key attr-value] (empty array to ignore) ; Context: Variables "tagname", "akey", "aval" '( ; translate :LINK attribute in <a> to :href [:LINK "a"] [:href aval] ; translate :LINK attribute in <img> to :src [:LINK "img"] [:src aval] ; throw exception if :LINK attribute in any other tag [:LINK] (throw (RuntimeException. (str "No match for " tagname))) ; ... more rules ; ignore string keys, used for internal bookkeeping [(string? akey)] [] )) ; ignore I want to be able to evaluate the rules (left hand side) as well as the result (right hand side), and need some way to put the variables in scope at the location where the table is evaluated. I also want to keep the lookup and evaluation logic independent of any particular table or set of variables. I suppose there are similar issues involved in templates (for example for dynamic HTML), where you don't want to rewrite the template processing logic every time someone puts a new variable in a template. Here is one approach using global variables and bindings. I have included some logic for the table lookup: ;; Generic code, works with any table on the same format. (defn rule-match? [rule-val test-val] "true if a single rule matches a single argument value" (cond (not (coll? rule-val)) (= rule-val test-val) ; plain value (list? rule-val) (eval rule-val) ; function call :else false )) (defn rule-lookup [test-val rule-table] "looks up rule match for test-val. Returns result or nil." (loop [rules (partition 2 rule-table)] (when-not (empty? rules) (let [[select result] (first rules)] (if (every? #(boolean %) (map rule-match? select test-val)) (eval result) ; evaluate and return result (recur (rest rules)) ))))) ;; Code specific to *attr-table* (def tagname) ; need these globals for the binding in html-attr (def akey) (def aval) (defn html-attr [tagname h-attr] "converts to html attributes" (apply hash-map (flatten (map (fn [[k v :as kv]] (binding [tagname tagname akey k aval v] (or (rule-lookup [k tagname] *attr-table*) kv))) h-attr )))) (defn test-attr [] "test conversion" (prn "a" (html-attr "a" {:LINK "www.google.com" "internal" 42 :title "A link" })) (prn "img" (html-attr "img" {:LINK "logo.png" }))) user=> (test-attr) "a" {:href "www.google.com", :title "A link"} "img" {:src "logo.png"} This is nice in that the lookup logic is independent of the table, so it can be reused with other tables and different variables. (Plus of course that the general table approach is about a quarter of the size of the code I had when I did the translations "by hand" in a giant cond.) It is not so nice in that I need to declare every variable as a global for the binding to work. Here is another approach using a "semi-macro", a function with a syntax-quoted return value, that doesn't need globals: (defn attr-table [tagname akey aval] `( [:LINK "a"] [:href ~aval] [:LINK "img"] [:src ~aval] [:LINK] (throw (RuntimeException. (str "No match for " tagname))) ; ... more rules [(string? ~akey)] [] ))) Only a couple of changes are needed to the rest of the code: In rule-match?, when syntax-quoted the function call is no longer a list: - (list? rule-val) (eval rule-val) + (seq? rule-val) (eval rule-val) In html-attr: - (binding [tagname tagname akey k aval v] - (or (rule-lookup [k tagname] *attr-table*) kv))) + (or (rule-lookup [k tagname] (attr-table tagname k v)) kv))) And we get the same result without globals. (And without dynamic scoping.) Are there other alternatives to pass along sets of variable bindings declared elsewhere, without the globals required by Clojure's binding? Is there an idiomatic way of doing it, like Ruby's binding or Javascript's function.apply(context)?

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  • Polling versus socket servers for online Flash games

    - by justin
    Hi, I want to make an online flash game, it will have social features but the gameplay will be primarily single-player. For example, no two players will appear on the screen at once, the social interaction will be through asynchronous messages, there won't be real-time chat or anything. Much of the logic would happen in the client, the server would validate the client logic, but it wouldn't need to be totally synchronous, which is why I'm thinking polling might be satisfactory. I have read in many places that socket servers can be more efficient than using polling for online games, but is that mainly a consideration for games that are more multi-player with more mult-player interactions than the game I have descriebed? If many users are playing online at the same time, but each playing a relatively isolated game, and not interacting to in real-time with each players, could polling be okay, or would using sockets be advisable no matter what if you have an online game that you envision many people playing at the same time? Thanks!

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  • Custom spring interceptor

    - by Hari
    Hi, I want to convert some of our internal API into a spring bean spring interceptor that we can use in other projects. This API needs some instantiation and other logic which I want to encapsulate in this bean so that we can just put the bean into our app context with necessary propoerties alone, and this will then apply the logic. I remember having read an article on this somewhere in the past - but cant find it now. Any pointers to something similar will be helpful EDIT: Sorry, I meant a spring interceptor, not a bean - my bad - please see my edit. I want to apply this interceptor to another bean dealing in XML messages.

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  • ASP.Net MVC elegant UI and ModelBinder authorization

    - by SDReyes
    We know authorization stuff is a cross cutting concern, and we do anything we could to avoid merge business logic in our views. But I still not found an elegant way to filter UI components (e.g. widgets, form elements, tables, etc) using the current user roles without contaminate the view with business logic. same applies for model binding. Example Form: Product Creation Fields: Name Price Discount Roles: Role Administrator Is allowed to see and modify the Name field Is allowed to see and modify the Price field Is allowed to see and modify the Discount Role Administrator assistant Is allowed to see and modify the Name Is allowed to see and modify the Price Fields shown in each role are different, and model binding needs to ignore the discount field for 'Administrator assistant' role. How would you do it?

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  • How sophisticated should be DAL?

    - by Andrew Florko
    Basically, DAL (Data Access Layer) should provide simple CRUD (Create/Read/Update/Delete) methods but I always have a temptation to create more sophisticated methods in order to minimize database access roundtrips from Business Logic Layer. What do you think about following extensions to CRUD (most of them are OK I suppose): Read: GetById, GetByName, GetPaged, GetByFilter... e.t.c. methods Create: GetOrCreate methods (model entity is returned from DB or created if not found and returned), Create(lots-of-relations) instead of Create and multiple AssignTo methods calls Update: Merge methods (entities list are updated, created and deleted in one call) Delete: Delete(bool children) - optional children delete, Cleanup methods Where do you usually implement Entity Cache capabilities? DAL or BLL? (My choice is BLL, but I have seen DAL implementations also) Where is the boundary when you decide: this operation is too specific so I should implement it in Business Logic Layer as DAL multiple calls? I often found insufficient BLL operations that were implemented in dozen database roundtrips because developer was afraid to create a bit more sophisticated DAL. Thank you in advance!

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  • Good programming style when handling multiple objects

    - by Glitch
    I've been programming a software version of a board game. Thus far I have written the classes which will correspond to physical objects on the game board. I'm well into writing the program logic, however I've found that many of the logic classes require access to the same objects. At first I was passing the appropriate objects to methods as they were called, but this was getting very tedious, particularly when the methods required many objects to perform their tasks. To solve this, I created a class which initialises and stores all the objects I need. This allows me to access an object from any class by calling Assets.dice(), for example. But now that I've thought about it, this doesn't seem right. This is why I'm here, I fear that I've created some sort of god class. Is this fear unfounded, or have I created a recipe for disaster?

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  • Identity column SQL Server 2005 inserting same value twice

    - by DannykPowell
    I have a stored procedure that inserts into a table (where there is an identity column that is not the primary key- the PK is inserted initially using the date/time to generate a unique value). We then use SCOPEIDENTITY() to get the value inserted, then there is some logic to generate the primary key field value based on this value, which is then updated back to the table. In some situations the stored procedure is called simultaneously by more than one process, resulting in "Violation of PRIMARY KEY constraint..." errors. This would seem to indicate that the identity column is allowing the same number to be inserted for more than one record. First question- how is this possible? Second question- how to stop it...there's no error handling currently so I'm going to add some try/ catch logic- but would like to understand the problem fully to deal with properly

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  • JSP taglib with tags-appender

    - by tabdulin
    Using tiles, spring web mvc and a lot of jsp files. I need some tags with following logic: <tl:append tag="script"> ... javascript code ... </tl:append> This jsp tag would append javascript code to bottom of in the . Just wanna have javascript in one place. Also, I wanna use such taglib for css styles and so on. Are there any appropriate taglibs with such logic?

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  • Combine query results from one table with the defaults from another

    - by pulegium
    This is a dumbed down version of the real table data, so may look bit silly. Table 1 (users): id INT username TEXT favourite_food TEXT food_pref_id INT Table 2 (food_preferences): id INT food_type TEXT The logic is as follows: Let's say I have this in my food preference table: 1, 'VEGETARIAN' and this in the users table: 1, 'John', NULL, 1 2, 'Pete', 'Curry', 1 In which case John defaults to be a vegetarian, but Pete should show up as a person who enjoys curry. Question, is there any way to combine the query into one select statement, so that it would get the default from the preferences table if the favourite_food column is NULL? I can obviously do this in application logic, but would be nice just to offload this to SQL, if possible. DB is SQLite3...

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  • Can't see or add Website Data Sources in RDLC report in ASP.NET MVC

    - by RobertC
    In the RDLC report, in Design view in Visual Studio 2008, we don't see anything in the Website Data Sources tab and the button to Add New Data Source is grayed out. Only the Refresh button is enabled, and clicking it doesn't do anything. Our business logic layer returns Lists of business objects and the business logic and business object projects are both referenced by the MVC project. This is an MVC app, so there is no App_Code folder. How do we get our business objects to appear in the Website Data Sources list so we can drag and drop fields from the object onto our RDLC report?

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  • i want to search my database for example i want to search the word "google yahoo"

    - by user2926370
    i want to search my database for example i want to search the word "google yahoo" and when i enter that i should able to look the rows which has google and yahoo. It is not required to be in the same order and google besides yahoo. No matter wherever it is in the line and give me a simple logic to it. i can able to query that thing.something like select * from table where column like("%google%yahoo%"). I want to develop this thing in php but how can i insert %. Do i need to use if statement so that i can insert % in between the words whenever i find spaces orelse is there any other logic to do it simpler?

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  • mockito mock a constructor with parameter

    - by Shengjie
    I have a class as below: public class A { public A(String test) { bla bla bla } public String check() { bla bla bla } } The logic in the constructor A(String test) and check() are the things I am trying to mock. I want any calls like: new A($$$any string$$$).check() returns a dummy string "test". I tried: A a = mock(A.class); when(a.check()).thenReturn("test"); String test = a.check(); // to this point, everything works. test shows as "tests" whenNew(A.class).withArguments(Matchers.anyString()).thenReturn(rk); // also tried: //whenNew(A.class).withParameterTypes(String.class).withArguments(Matchers.anyString()).thenReturn(rk); new A("random string").check(); // this doesn't work But it doesn't seem to be working. new A($$$any string$$$).check() is still going through the constructor logic instead of fetch the mocked object of A.

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  • Reverse a singly linked list

    - by Madhan
    I would be wondered if there exists some logic to reverse the linked list using only two pointers. The following is used to reverse the single linked list using three pointers namely p, q, r: struct node { int data; struct node *link; }; void reverse() { struct node *p = first, *q = NULL, *r; while (p != NULL) { r = q; q = p; p = p->link; q->link = r; } q = first; } Is there any other alternate to reverse the linked list? what would be the best logic to reverse a singly linked list, in terms of time complexity?

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  • Best approach to design a service oriented system

    - by Gustavo Paulillo
    Thinking about service orientation, our team are involved on new application designs. We consist in a group of 4 developers and a manager (that knows something about programming and distributed systems). Each one, having own opinion on service design. It consists in a distributed system: a user interface (web app) accessing the services in a dedicated server (inside the firewall), to obtain the business logic operations. So we got 2 main approachs that I list above : Modular services Having many modules, each one consisting of a service (WCF). Example: namespaces SystemX.DebtService, SystemX.CreditService, SystemX.SimulatorService Unique service All the business logic is centralized in a unique service. Example: SystemX.OperationService. The web app calls the same service for all operations. In your opinion, whats the best? Or having another approach is better for this scenario?

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  • Send a "304 Not Modified" for images stored in the datastore

    - by Emilien
    I store user-uploaded images in the Google App Engine datastore as db.Blob, as proposed in the docs. I then serve those images on /images/<id>.jpg. The server always sends a 200 OK response, which means that the browser has to download the same image multiple time (== slower) and that the server has to send the same image multiple times (== more expensive). As most of those images will likely never change, I'd like to be able to send a 304 Not Modified response. I am thinking about calculating some kind of hash of the picture when the user uploads it, and then use this to know if the user already has this image (maybe send the hash as an Etag?) I have found this answer and this answer that explain the logic pretty well, but I have 2 questions: Is it possible to send an Etag in Google App Engine? Has anyone implemented such logic, and/or is there any code snippet available?

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  • Where to open sessions in a Spring/Hibernate stack?

    - by CaptainAwesomePants
    I'm trying to figure out a good design for a Spring/Hibernate app. When creating such an app, it appears like there are a handful of major decisions. The first major decision seems to be where to put the session/transaction boundary. It seems like I have 3 major choices: as a filter before controllers are even invoked, immediately below the controllers at the service call level, and stuffed way below the business level in repository calls. It seems to me like the right call is the middle path, but I'm not sure. I don't want my transactions open too long, but at the same time, I don't want to constantly worry about detached objects and lazy loading in the business logic. Still, there are some downsides. For instance, it makes it hard for the business logic to make a remote call without holding up a transaction for a few seconds. I wonder if there's a better way?

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  • Rails best practice on conditional parameters in a controller action

    - by randombits
    I have a controller create action looks for one or more parameters in the following ruleset. Let's say we have two parameters, foo and bar. The rules are the following: 1) if foo doesn't exist in the parameter list, bar must. 2) if bar doesn't exist in the parameter list, foo must. 3) they can both co-exist. they can't both be omitted (that's redundant with my rules above :) ) Can anyone show an example in Rails on how this is handled in the controller? Should I use a before_filter? Would appreciate some guidance as this isn't something that ActiveRecord validates.. so I'd need to build an error message to the user directly from controller logic, not model logic. For bonus points, I output the error in XML, so if you can show how that's done, that'd be great. Hypothetically let's call the resource "Lorem", so it is created via http://foo/lorem.xml and we have lorem_controller.rb.

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  • Save jQuery callback functions in a separate file

    - by Danny Herran
    Probably I missed something, but lets say I have this: $('a.delete').click(function(){ resp=window.confirm("Are you sure you want to delete this?"); if(resp) return true; else return false; } Now, I want to save that callback function into a separate js file, because I will use it in several pages. My logic told me to do this: $('a.del').click(delete_element()); Having my js file like this: function delete_element(){ resp=window.confirm("Are you sure you want to delete this?"); if(resp) return true; else return false; } This doesn't work. Everytime my page loads, it displays the confirm window, even if I haven't clicked the link. It is clear that my logic failed this time. What am I missing?

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  • How to secure authiorization of methods

    - by Kurresmack
    I am building a web site in C# using MVC.Net How can I secure that no unauthorized persons can access my methods? What I mean is that I want to make sure that only admins can create articles on my page. If I put this logic in the method actually adding this to the database, wouldn't I have business logic in my data layer? Is it a good practise to have a seperate security layer that is always in between of the data layer and the business layer to make? The problem is that if I protect at a higher level I will have to have checks on many places and it is more likely that I miss one place and users can bypass security. Thanks!

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  • Does the <script> tag position in HTML affects performance of the webpage?

    - by Rahul Joshi
    If the script tag is above or below the body in a HTML page, does it matter for the performance of a website? And what if used in between like this: <body> ..blah..blah.. <script language="JavaScript" src="JS_File_100_KiloBytes"> function f1() { .. some logic reqd. for manipulating contents in a webpage } </script> ... some text here too ... </body> Or is this better?: <script language="JavaScript" src="JS_File_100_KiloBytes"> function f1() { .. some logic reqd. for manipulating contents in a webpage } </script> <body> ..blah..blah.. ..call above functions on some events like onclick,onfocus,etc.. </body> Or this one?: <body> ..blah..blah.. ..call above functions on some events like onclick,onfocus,etc.. <script language="JavaScript" src="JS_File_100_KiloBytes"> function f1() { .. some logic reqd. for manipulating contents in a webpage } </script> </body> Need not tell everything is again in the <html> tag!! How does it affect performance of webpage while loading? Does it really? Which one is the best, either out of these 3 or some other which you know? And one more thing, I googled a bit on this, from which I went here: Best Practices for Speeding Up Your Web Site and it suggests put scripts at the bottom, but traditionally many people put it in <head> tag which is above the <body> tag. I know it's NOT a rule but many prefer it that way. If you don't believe it, just view source of this page! And tell me what's the better style for best performance.

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  • Reference the oncomplete event by an external java script function

    - by user339637
    Hi , I want to do some logic at the oncomplete attribute of the a4j:commandButton ,but my logic is too complicated , can I reference the code using a java script functions located in a external java-script file to have a better maintenance ? I found it has error because the JavaScript file cannot understand the EL expression . For example , originally I have , <a4j:commandButton id="btn1" action="#{MBena1.action1}" oncomplete="if( {MBena1.variable1}){Richfaces.showModalPanel('modelPanel1');};if (......) then "> I want to do something like this: <a4j:commandButton action="#{MBena1.action1}" oncomplete="Btn1OnComplete();"> the code is put inside the java script function Btn1OnComplete() which is located in a external java-script file. Thanks

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