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  • How can CopyOnWriteArrayList be thread-safe?

    - by Shooshpanchick
    I've taken a look into OpenJDK's sources of CopyOnWriteArrayList and it seems that all write operations are protected by the same lock and read operations are not protected at all. As I understand, under JMM all accesses to a variable (both read and write) should be protected by lock or reordering effects may occur. For example, set(int, E) method contains these lines (under lock): /* 1 */ int len = elements.length; /* 2 */ Object[] newElements = Arrays.copyOf(elements, len); /* 3 */ newElements[index] = element; /* 4 */ setArray(newElements); The get(int) method, on the other hand, only does return get(getArray(), index);. In my understanding of JMM, this means that get may observe the array in an inconsistent state if statements 1-4 are reordered like 1-2(new)-4-2(copyOf)-3. Do I understand JMM incorrectly or is there any other explanations on why CopyOnWriteArrayList is thread-safe?

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  • How the swing's BoxModel works ?

    - by sasquatch90
    Let's say I would like to create a simple calculator. It consists of 3 fields. Text field to show result, field with checkboxes to select system and field with numbers. What kind of component should I use for each element ? How can I position elements in my window ? How can I position elements inside component (ie checkboxes) ? This is what I'm trying to achieve. http://img28.imageshack.us/img28/7691/lab8c.jpg

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  • C# Interface Method calls from a controller

    - by ArjaaAine
    I was just working on some application architecture and this may sound like a stupid question but please explain to me how the following works: Interface: public interface IMatterDAL { IEnumerable<Matter> GetMattersByCode(string input); IEnumerable<Matter> GetMattersBySearch(string input); } Class: public class MatterDAL : IMatterDAL { private readonly Database _db; public MatterDAL(Database db) { _db = db; LoadAll(); //Private Method } public virtual IEnumerable<Matter> GetMattersBySearch(string input) { //CODE return result; } public virtual IEnumerable<Matter> GetMattersByCode(string input) { //CODE return results; } Controller: public class MatterController : ApiController { private readonly IMatterDAL _publishedData; public MatterController(IMatterDAL publishedData) { _publishedData = publishedData; } [ValidateInput(false)] public JsonResult SearchByCode(string id) { var searchText = id; //better name for this var results = _publishedData.GetMattersBySearch(searchText).Select( matter => new { MatterCode = matter.Code, MatterName = matter.Name, matter.ClientCode, matter.ClientName }); return Json(results); } This works, when I call my controller method from jquery and step into it, the call to the _publishedData method, goes into the class MatterDAL. I want to know how does my controller know to go to the MatterDAL implementation of the Interface IMatterDAL. What if I have another class called MatterDAL2 which is based on the interface. How will my controller know then to call the right method? I am sorry if this is a stupid question, this is baffling me.

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  • ado.net data entity problem

    - by ognjenb
    I have this error Cannot implicitly convert type 'System.Linq.IQueryable' to 'Mvc.Models.engineer'. An explicit conversion exists (are you missing a cast?) after write this code engineer Ing = new engineer(); Ing = from j in testPersons.ibekoengineer select j.Name; What is wrong?

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  • How best to implement support for multiple devices in a web application.

    - by Kabeer
    Hello. My client would like a business application to support 'every possible device'. The application in question is essentially a web application and 'every possible device', I believe encompasses mobile phones, netbooks, ipad, other browser supporting devices, etc. The application is somewhat complex w.r.t. the data it captures and other functions it performs (reporting). If I continue to honor increasing complexity in the application, I guess there are more chances of it not working on other devices. I'd like to know how web applications support multiple devices conventionally? Are there multiple versions of presentation layer (like many times I find m.website.com dedicated for mobile devices)? Further, if my application is to take advantage of Java Script, RIA (Flash, SilverLight) then what are the consequences and workarounds? Mine is a .Net based application and the stack also contains Ext JS Java Script library. While I would like to use it for sure, considering that I would be doing a lot of work in Java Script rather than HTML, this could be a problem. The answer to the above could be descriptive. If there is something already prescribed out there, please share the link(s). Thanks.

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  • Improve SQL strategy - denormalize in object-children-images case

    - by fesja
    Hi, I have a Tour object which has many Place objects. For the list of tours, I want to show some info of the tour, the number of places of the tour, and three Place's images. Right one my SQL queries are (i'm using Doctrine with Symfony on MySQL) get Tour get Tour 1 places get Tour 2 places get Tour 3 places ... get Tour n places If I have a three Tour list, it's not so bad; but I'm sure it can get bad if I do a 10-20 tour-list. So, thinking on how to improve the queries I've thought of several measures: Having a place count cache Storing the urls of three images on a new tour field. The problem with 2. is that if I change the image, I have to check all the tours to update that image for another one. What solution do you think is best to scale the system in a near future? Any other suggestion. thanks!

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  • How do I insert data into a object relational table with multiple ref in the schema.

    - by Yiling
    I have a table with a schema of Table(number, ref, ref, varchar2, varchar2,...). How would I insert a row of data into this table? When I do: "insert into table values (1, select ref(p), ref(d), '239 F.3d 1343', '35 USC § 283', ... from plaintiff p, defendant d where p.name='name1' and d.name='name2');" I get a "missing expression" error. If I do: "insert into table 1, select ref(p), ref(d), ... from plaintiff p, defendant where p.name=...;" I get a "missing keyword VALUES" error.

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  • Is there an ORM with APIs to be used programatically?

    - by Kabeer
    Hello. Neither did not get any response for my previous question, nor enough views :) So here I am now framing my query afresh. Is there any ORM that offers APIs to be used programatically? In my situation, a user will be helped through a wizard to define some entities. Thereafter those entites will be created in a database in form of tables (there will of course be some improvization). I need an ORM that offers APIs for modeling and creating entities during application runtime and not just during design time. Mine is a .Net application, therefore I was looking at Entity Framework. However, to me it looked tied to Visual Studio (I may be wrong also as I am new to it). Any recommendations? Or alternative point of view?

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  • MVC Design Pattern to Combine Multiple Models for use

    - by roverred
    In my design, I have multiple models and each model has a controller. I need to use all the models to process some operation. Most examples I see are pretty simple with 1 view, 1 controller, and 1 model. How would you get all these models together? Only ways I can think of are 1) Have a top-level controller which has a reference to every controller. Those controllers will have a getter/setter function for their model. Does this violate MVC because every controller should have a model? 2) Have an Intermediate class to combine every model into a one model. Then you create a controller for that new super model. Do you know of any better ideas? Thanks.

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  • Dojo treemodel- adding large number of items

    - by Ashley
    I am trying to add a large number of items (100+) to my tree via ForestStoreModel by calling newItem in a loop. This seems to be quite slow and locks up the browser. Is there any way I can do something similar to grid's beginUpdate & endUpdate? I want to basically 'turn off' my tree, add 100 items in a batch, then 'turn on' my tree. Any ideas? Thanks!

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  • Magento, 1 db field not saved

    - by david parloir
    Hi there, I have a problem with 1 field of the db. With this code: $expireMonth = Mage::getStoreConfig('points_options/config_points/expiration_period', Mage::app()->getStore()->getId()); if (!is_null($expireMonth) && ($expireMonth > 0)) { $expireDate = date("Y-m-d H:i:s", strtotime("+" . $expireMonth . " month")); } else { $expireDate = NULL; } //die($expireDate); //store in points history table $this->_pointsModel->setCustomerId($this->_customer->getId()) ->setOrdersId('welcome') ->setPointsPending($pointsForNewCustomer) ->setPointsComment(Mage::helper('points')->__('welcome points')) ->setDateAdded(date('Y-m-d H:i:s')) ->setPointsStatus(2)//confirmed ->setPointsType('WE') ->setStoreId(Mage::app()->getStore()->getId()) ->setExpireDate($expireDate) ->save(); every field is saved in the table, except for expire_date. If I uncoment the die($expireData), I see the correct value, something like 2012-01-13 13:21:12. The filed is defined as: `expire_date` datetime NULL Any thaughts? edit: the solution is: $expireDate = date("Y-m-d H:i:s", strtotime("+" . $expireMonth . " months")); check out the "s" in my strtotime expression

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  • Creating objects and referencing before saving object to db

    - by Flexo
    Sorry about the vague title, but i didnt know how to ask the question in one line :) I have an order with nested itemgroups that again have nested items. the user specify the amount of item that he would like to have in each itemgroup. I would like to create these items in the create method of the orders controller when the order itself is being created. I kinda have 2 problems here. First, how do i set the reference of the items, or better yet, put the items into the @order object so they are saved when the @order is saved? the items are being stored in the db as the code is now, but the reference is not set because the order is not stored in the db yet so it doesnt have an id yet. Second, im not sure im using the correct way to get the id from my itemgroup. @order = Order.new(params[:order]) @order.itemgroups.each do |f| f.amount.times do @item = Item.new() @item.itemgroup_id = f.id @item.save end end

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  • MVC4 not binding a list of basic types

    - by admanb
    I cannot, for the life of me, get this data to bind. Here's my JavaScript: var params = { 'InvItemIDs': ["188475", "188490"]}; $.post("api/Orders/OrderFromInventory?" + $.param(params)) and the Controller action: public HttpResponseMessage OrderFromInventory(IList<int> InvItemIDs) { return new HttpResponseMessage(); } I've built the query string so that it's sending: ?InvItemIDs=188475&InvItemIDs=188490 as well as ?InvItemIDs[]=188475&InvItemIDs[]=188490 and even ?InvItemIDs[0]=188475&InvItemIDs[1]=188490 and none of them are binding. InvItemIDs is always null. What am I doing wrong? EDIT: So it turns out all this is a bug (or something) in the new Web API controller code in MVC4. As soon as I moved the exact same code over to a standard controller it started working. I'm still interested if anyone has any insight as to why the Web API would break this binding.

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  • Entities used to serialize data have changed. How can the serialized data be upgraded for the new entities?

    - by i8abug
    Hi, I have a bunch of simple entity instances that I have serialized to a file. In the future, I know that the structure of these entities (ie, maybe I will rename Name to Header or something). The thing is, I don't want to lose the data that I have saved in all these old files. What is the proper way to either load the data from the old entities into new entities upgrade the old files so that they can be used with new entities Note: I think I am stuck with binary serialization, not xml serialization. Thanks in advance! Edit: So I have an answer for the case I have described. I can use a dataContractSerializer and do something like [DataMember("bar")] private string foo; and change the name in the code and keep the same name that was used for serialization. But what about the following additional cases: The original entity has new members which can be serialized Some serialized members that were in the original entity are removed Some members have actually changed in function (suppose that the original class had a FirstName and LastName member and it has been refactored to have only a FullName member which combines the two) To handle these, I need some sort of interpreter/translator deserialization class but I have no idea what I should use

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  • Rails: Serializing objects in a database?

    - by keruilin
    I'm looking for some general guidance on serializing objects in a database. What are serialized objects? What are some best-practice scenarios for serializing objects in a DB? What attributes do you use when creating the column in the DB so you can use a serialized object? How to save a serialized object? And how to access the serialized object and its attributes? (Using hashes?)

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  • mvc - how to avoid log out when refresh a page

    - by user235973457
    I have built the MVC application with WCF service. The major problem I have experienced with refreshing page. I have created a login page with session (username and password). But when you refresh the home page by pressing F5, it would automatically log out. That is my problem. I need to stay the home page after refresh. I have been googling around to find a solution but it seems not helpful. Any idea? Your advise or code example much appreciated.

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  • How to do comments in Activity Stream? (like Facebook)

    - by fesja
    Hi, I'm starting to develop an activity stream. I've read both How to implement the activity stream in a social network and What’s the best manner of implementing a social activity stream?. What I haven't found is the best way to add comments to the activities. As in facebook, each comment can be commented by another person. If each activity comment is saved as another activity, then I would not be able to get the activity of that comment without doing a query. So the solution I'm thinking is to save the comments inside the serialize data field of each activity. If the user wants to delete his comment, I would have to update that activity. Is this the correct solution? Is there a better approach? Thanks!

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  • How to handle notifications to several partial views of the same model?

    - by Seki
    I am working on refactoring an old simulation of a Turing machine. The application uses a class that contains the state and the logic of program execution, and several panels to display the tape representation and show the state, messages, and the GUI controls (start, stop, program listing, ...). I would like to refactor it using the MVC architecture that was not used originaly: the Frame is the only way to get access to the different panels and there is also a strong coupling between the "engine" class and the GUI updates in the way of frame.displayPanel.state.setText("halted"); or frame.outputPanel.messages.append("some thing"); It looks to me that I should put the state related code into an observable model class and make the different panels observers. My problem is that the java Observable class only provides a global notification to the Observers, while I would prefer not to refresh every Observers everytime, but only when the part that specificaly observe has changed. I am thinking of implementing myself several vectors of listeners (for the state / position, for the output messages, ...) but I feel like reinventing the wheel. I though also about adding some flags that the observers could check like isNewMessageAvailable(), hasTapeMoved(), etc but it sounds also approximative design. BTW, is it ok to keep the fetch / execute loop into the model or should I move it in another place? We can think in a theorical ideal way as I am completely revamping this small application.

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  • How can I keep my MVC Views, models, and model binders as clean as possible?

    - by MBonig
    I'm rather new to MVC and as I'm getting into the whole framework more and more I'm finding the modelbinders are becoming tough to maintain. Let me explain... I am writing a basic CRUD-over-database app. My domain models are going to be very rich. In an attempt to keep my controllers as thin as possible I've set it up so that on Create/Edit commands the parameter for the action is a richly populated instance of my domain model. To do this I've implemented a custom model binder. As a result, though, this custom model binder is very specific to the view and the model. I've decided to just override the DefaultModelBinder that ships with MVC 2. In the case where the field being bound to my model is just a textbox (or something as simple), I just delegate to the base method. However, when I'm working with a dropdown or something more complex (the UI dictates that date and time are separate data entry fields but for the model it is one Property), I have to perform some checks and some manual data munging. The end result of this is that I have some pretty tight ties between the View and Binder. I'm architecturally fine with this but from a code maintenance standpoint, it's a nightmare. For example, my model I'm binding here is of type Log (this is the object I will get as a parameter on my Action). The "ServiceStateTime" is a property on Log. The form values of "log.ServiceStartDate" and "log.ServiceStartTime" are totally arbitrary and come from two textboxes on the form (Html.TextBox("log.ServiceStartTime",...)) protected override object GetPropertyValue(ControllerContext controllerContext, ModelBindingContext bindingContext, PropertyDescriptor propertyDescriptor, IModelBinder propertyBinder) { if (propertyDescriptor.Name == "ServiceStartTime") { string date = bindingContext.ValueProvider.GetValue("log.ServiceStartDate").ConvertTo(typeof (string)) as string; string time = bindingContext.ValueProvider.GetValue("log.ServiceStartTime").ConvertTo(typeof (string)) as string; DateTime dateTime = DateTime.Parse(date + " " + time); return dateTime; } if (propertyDescriptor.Name == "ServiceEndTime") { string date = bindingContext.ValueProvider.GetValue("log.ServiceEndDate").ConvertTo(typeof(string)) as string; string time = bindingContext.ValueProvider.GetValue("log.ServiceEndTime").ConvertTo(typeof(string)) as string; DateTime dateTime = DateTime.Parse(date + " " + time); return dateTime; } The Log.ServiceEndTime is a similar field. This doesn't feel very DRY to me. First, if I refactor the ServiceStartTime or ServiceEndTime into different field names, the text strings may get missed (although my refactoring tool of choice, R#, is pretty good at this sort of thing, it wouldn't cause a build-time failure and would only get caught by manual testing). Second, if I decided to arbitrarily change the descriptors "log.ServiceStartDate" and "log.ServiceStartTime", I would run into the same problem. To me, runtime silent errors are the worst kind of error out there. So, I see a couple of options to help here and would love to get some input from people who have come across some of these issues: Refactor any text strings in common between the view and model binders out into const strings attached to the ViewModel object I pass from controller to the aspx/ascx view. This pollutes the ViewModel object, though. Provide unit tests around all of the interactions. I'm a big proponent of unit tests and haven't started fleshing this option out but I've got a gut feeling that it won't save me from foot-shootings. If it matters, the Log and other entities in the system are persisted to the database using Fluent NHibernate. I really want to keep my controllers as thin as possible. So, any suggestions here are greatly welcomed! Thanks

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  • Breaking 1NF to model subset constraints. Does this sound sane?

    - by Chris Travers
    My first question here. Appologize if it is in the wrong forum but this seems pretty conceptual. I am looking at doing something that goes against conventional wisdom and want to get some feedback as to whether this is totally insane or will result in problems, so critique away! I am on PostgreSQL 9.1 but may be moving to 9.2 for this part of this project. To re-iterate: Does it seem sane to break 1NF in this way? I am not looking for debugging code so much as where people see problems that this might lead. The Problem In double entry accounting, financial transactions are journal entries with an arbitrary number of lines. Each line has either a left value (debit) or a right value (credit) which can be modelled as a single value with negatives as debits and positives as credits or vice versa. The sum of all debits and credits must equal zero (so if we go with a single amount field, sum(amount) must equal zero for each financial journal entry). SQL-based databases, pretty much required for this sort of work, have no way to express this sort of constraint natively and so any approach to enforcing it in the database seems rather complex. The Write Model The journal entries are append only. There is a possibility we will add a delete model but it will be subject to a different set of restrictions and so is not applicable here. If and when we allow deletes, we will probably do them using a simple ON DELETE CASCADE designation on the foreign key, and require that deletes go through a dedicated stored procedure which can enforce the other constraints. So inserts and selects have to be accommodated but updates and deletes do not for this task. My Proposed Solution My proposed solution is to break first normal form and model constraints on arrays of tuples, with a trigger that breaks the rows out into another table. CREATE TABLE journal_line ( entry_id bigserial primary key, account_id int not null references account(id), journal_entry_id bigint not null, -- adding references later amount numeric not null ); I would then add "table methods" to extract debits and credits for reporting purposes: CREATE OR REPLACE FUNCTION debits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount < 0 THEN $1.amount * -1 ELSE NULL END; $$; CREATE OR REPLACE FUNCTION credits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount > 0 THEN $1.amount ELSE NULL END; $$; Then the journal entry table (simplified for this example): CREATE TABLE journal_entry ( entry_id bigserial primary key, -- no natural keys :-( journal_id int not null references journal(id), date_posted date not null, reference text not null, description text not null, journal_lines journal_line[] not null ); Then a table method and and check constraints: CREATE OR REPLACE FUNCTION running_total(journal_entry) returns numeric language sql immutable as $$ SELECT sum(amount) FROM unnest($1.journal_lines); $$; ALTER TABLE journal_entry ADD CONSTRAINT CHECK (((journal_entry.running_total) = 0)); ALTER TABLE journal_line ADD FOREIGN KEY journal_entry_id REFERENCES journal_entry(entry_id); And finally we'd have a breakout trigger: CREATE OR REPLACE FUNCTION je_breakout() RETURNS TRIGGER LANGUAGE PLPGSQL AS $$ BEGIN IF TG_OP = 'INSERT' THEN INSERT INTO journal_line (journal_entry_id, account_id, amount) SELECT NEW.id, account_id, amount FROM unnest(NEW.journal_lines); RETURN NEW; ELSE RAISE EXCEPTION 'Operation Not Allowed'; END IF; END; $$; And finally CREATE TRIGGER AFTER INSERT OR UPDATE OR DELETE ON journal_entry FOR EACH ROW EXECUTE_PROCEDURE je_breaout(); Of course the example above is simplified. There will be a status table that will track approval status allowing for separation of duties, etc. However the goal here is to prevent unbalanced transactions. Any feedback? Does this sound entirely insane? Standard Solutions? In getting to this point I have to say I have looked at four different current ERP solutions to this problems: Represent every line item as a debit and a credit against different accounts. Use of foreign keys against the line item table to enforce an eventual running total of 0 Use of constraint triggers in PostgreSQL Forcing all validation here solely through the app logic. My concerns are that #1 is pretty limiting and very hard to audit internally. It's not programmer transparent and so it strikes me as being difficult to work with in the future. The second strikes me as being very complex and required a series of contraints and foreign keys against self to make work, and therefore it strikes me as complex, hard to sort out at least in my mind, and thus hard to work with. The fourth could be done as we force all access through stored procedures anyway and this is the most common solution (have the app total things up and throw an error otherwise). However, I think proof that a constraint is followed is superior to test cases, and so the question becomes whether this in fact generates insert anomilies rather than solving them. If this is a solved problem it isn't the case that everyone agrees on the solution....

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