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• What Can A 'TreeDict' (Or Treemap) Be Used For In Practice?

  - by Seun Osewa

  I'm developing a 'TreeDict' class in Python. This is a basically a dict that allows you to retrieve its key-value pairs in sorted order, just like the Treemap collection class in Java. I've implemented some functionality based on the way unique indexes in relational databases can be used, e.g. functions to let you retrieve values corresponding to a range of keys, keys greater than, less than or equal to a particular value in sorted order, strings or tuples that have a specific prefix in sorted order, etc. Unfortunately, I can't think of any real life problem that will require a class like this. I suspect that the reason we don't have sorted dicts in Python is that in practice they aren't required often enough to be worth it, but I want to be proved wrong. Can you think of any specific applications of a 'TreeDict'? Any real life problem that would be best solved by this data structure? I just want to know for sure whether this is worth it.

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• What happens to a class in PHP once its been instantiated?

  - by Caylem

  Hi I'm just playing around with some PHP and was wondering what happens when an object from a class is created within another PHP script? I assume once its created and been processed their is no way of then going back and 'playing' around with it from another script? The idea is i'm trying to create a kind of deck of cards using a card class, each card has specific data that is added to each individual object to make it unique, suit, value etc. Once its created i need to be able to go back to specific cards to use them. In java i'd have an arraylist of card objects, i'm not sure how to approach the same area in PHP. Thanks.

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• Can I grant explicit Javascript methods to a different-host iframe?

  - by Matchu

  I'm thinking about a system in which I allow users to create Javascript-empowered widgets for other users to embed in their dashboard on my website. I'd like to limit these widgets fairly strictly, so each would exist as an iframe kept on its own unique hostname: the widget with ID #47 would be accessible at w47.widgets.example.com, for example. It would be helpful, for permission-granting dialogs and the like, to allow the widget to call very specific methods explicitly granted by the parent window, without authorizing the iframe to do whatever it likes with the parent frame on the user's behalf. Is it possible for a parent document to explicitly allow certain method calls to a child document on a different host?

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• How do I trigger a single event defined for a class of objects

  - by mrbinky3000

  I have a question. I have 8 buttons that have unique incrementing id's and a shared class. <button class="btnChapter" id="btnChapter_1" value="1">1</button> <button class="btnChapter" id="btnChapter_2" value="2">2</button> <button class="btnChapter" id="btnChapter_3" value="3">3</button> ... In order to prevent me from duplicating code, I bound a click event to the btnChapter class instead of binding an event individually to each button's ID. $('.btnChapter').click(function(){ .. do stuff .. }); How do I trigger() the click() event only for #btnChapter_2? The following doesn't seem to work. $('#btnChapter_2').click()

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• a completely decoupled OO system ?

  - by shrini1000

  To make an OO system as decoupled as possible, I'm thinking of the following approach: 1) we run an RMI/directory like service where objects can register and discover each other. They talk to this service through an interface 2) we run a messaging service to which objects can publish messages, and register subscription callbacks. Again, this happens through interfaces 3) when object A wants to invoke a method on object B, it discovers the target object's unique identity through #1 above, and publishes a message on the message service for object B 4) message services invokes B's callback to give it the message 5) B processes the request and sends the response for A on message service 6) A's callback is called and it gets the response. I feel this system is as decoupled as practically possible, but it has the following problems: 1) communication is typically asynchronous 2) hence it's non real time 3) the system as a whole is less efficient. Are there any other practical problems where this design obviously won't be applicable ? What are your thoughts on this design in general ?

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• Insert or Update using Oracle and PL/SQL

  - by Shane

  I have a PL/SQL function that performs an update/insert on an Oracle database that maintains a target total and returns the difference between the existing value and the new value. Here is the code I have so far: FUNCTION calcTargetTotal(accountId varchar2, newTotal numeric ) RETURN number is oldTotal numeric(20,6); difference numeric(20,6); begin difference := 0; begin select value into oldTotal from target_total WHERE account_id = accountId for update of value; if (oldTotal != newTotal) then update target_total set value = newTotal WHERE account_id = accountId difference := newTotal - oldTotal; end if; exception when NO_DATA_FOUND then begin difference := newTotal; insert into target_total ( account_id, value ) values ( accountId, newTotal ); -- sometimes a race condition occurs and this stmt fails -- in those cases try to update again exception when DUP_VAL_ON_INDEX then begin difference := 0; select value into oldTotal from target_total WHERE account_id = accountId for update of value; if (oldTotal != newTotal) then update target_total set value = newTotal WHERE account_id = accountId difference := newTotal - oldTotal; end if; end; end; end; return difference end calcTargetTotal; This works as expected in unit tests with multiple threads never failing. However when loaded on a live system we have seen this fail with a stack trace looking like this: ORA-01403: no data found ORA-00001: unique constraint () violated ORA-01403: no data found The line numbers (which I have removed since they are meaningless out of context) verify that the first update fails due to no data, the insert fail due to uniqueness, and the 2nd update is failing with no data, which should be impossible. From what I have read on other thread a MERGE statement is also not atomic and could suffer similar problems. Does anyone have any ideas how to prevent this from occurring?

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• Setting id to a panel control in gridview

  - by mariki

  I have a panel control in gridview's template. I need to hide/unhide panel in javascript function, for that i need to pass panel's id to the javascript. The problem is that all panels have the same id in gridview, so I need to set unique id to each panel. I tried to do: <asp:Panel id= "Panel_<%# Eval("ID")%>" and some other variations but always get an error. The panel contains some other controls, I need it to be server side because I need to set at code-behind (after checking if user is authenticated) What can I do? p.s. It doesn't have to be Panel, any other control that I can find with Findcontrol and can hold other controls.

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• How can I generate a random human-readable colour from a seed? C#

  - by SLC

  Got a logfile, and it has all kinds of text in it. Currently it is just displayed as one colour, and each entry says something like: Log from section 1: Some text here Log from section 125: Some text here Log from section 17: Some text here Log from section 1: Some text here Log from section 125: Some text here Log from section 1: Some text here Log from section 17: Some text here Now the logfile is displayed in real time, and it would be nice to make the rows with the same section number the same colour. However there could be potentially quite a large range of numbers. What I want to do is create a method that will take a number, and randomly generate a unique colour. The colour must be readable against a black background though, so #000000 is no good, nor is #101010 or anything too dark to read. Ideally two similar numbers will not produce the same colour because in the above examples, the numbers 1 and 17 might be too similar, and some numbers might be in the 10,000 range. Any ideas on this?

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• Need a Count, but Multiple other fields

  - by user3727752

  I have a table that looks like this: person trip_id date home destination joe 1 3/10 chicago new york joe 2 4/10 chicago l.a. joe 3 5/10 chicago boston luther 4 3/12 new york chicago luther 5 3/18 new york boston I want to get a result like person trips firstDate home joe 3 3/10 chicago luther 2 3/12 new york Currently I've got Select person, count(trip_id) as trips, min(date) as firstDate from [table] group by person order by firstDate I can't figure out how to get home in there as well. Home is always unique to the person. But my DBMS doesn't know that. Is there an easy way around this problem? Appreciate it.

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• How to add a sequence column to an existing table with records

  - by user1888543

  I had created a new table named USERLOG with two fields from a previous VIEW. The table already consist of about 9000 records. The two fields taken from the VIEW, i.e. weblog_views consist of IP (consists of IP address), and WEB_LINK (consists of URL). This is the code I used, CREATE TABLE USERLOG AS SELECT C_IP, WEB_LINK FROM weblog_views; I want to add another column to this table called the USER_ID, which would consists of a sequence starting with 1 to 9000 records to create a unique id for each existing rows. I need help with this part. I'm using Oracle SQL Developer: ODMiner version 3.0.04. I tried using the AUTO-INCREMENT option, ALTER TABLE USERLOG ADD USER_ID INT UNSIGNED NOT NULL AUTO_INCREMENT; But I get an error with this, Error report: SQL Error: ORA-01735: invalid ALTER TABLE option 01735. 00000 - "invalid ALTER TABLE option" So, I would really appreciate any help that I can get!

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• AWS Load Balancer with a static IP address

  - by user965904

  I have a set-up running on Amazon cloud with a couple of EC2 Instances running through a load balancer. It is important that the site has a unique(static) IP or set of IPs as I'm plugging in 3rd party APIs which only accept requests made from IPs which have been added to their whitelist. So basically unless we can give these 3rd parties a static IP or range of IPs that the requests from the site will always come from then we would be unable to make any calls to them. Anyone knows how to achieve this as I know that Elastic IPs are not compatible with load balancers? If I were to look up the IP of the load balancer DNS name (e.g. dualstack.awseb-BAMobile-ENV-xxxxxxxxx.eu-west-1.elb.amazonaws.com resolves to 200.200.200.200) would that IP be Static? Any help/advise is greatly appreciated guys.

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• Fix DB duplicate entries (MySQL bug)

  - by Silence

  I'm using MySQL 4.1. Some tables have duplicates entries that go against the constraints. When I try to group rows, MySQL doesn't recognise the rows as being similar. Example: Table A has a column "Name" with the Unique proprety. The table contains one row with the name 'Hach?' and one row with the same name but a square at the end instead of the '?' (which I can't reproduce in this textfield) A "Group by" on these 2 rows return 2 separate rows This cause several problems including the fact that I can't export and reimport the database. On reimporting an error mentions that a Insert has failed because it violates a constraint. In theory I could try to import, wait for the first error, fix the import script and the original DB, and repeat. In pratice, that would take forever. Is there a way to list all the anomalies or force the database to recheck constraints (and list all the values/rows that go against them) ? I can supply the .MYD file if it can be helpful.

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• How to Retrieve Values of A Dynamically Created Control's Child Controls on PostBack?

  - by Jordan

  Given: I have a custom server control in the markup of an aspx page. This control creates child controls in its CreateChildControls() method (e.g. it retrieves content from a database and based on that content dynamically creates either a CheckBoxList or a RadioButtonList) Now I understand that I cannot access the dynamically created controls on postback unless I add them again on Page_Init or Page_PreInit (as per here). My question is, how do I add them again explicitly in Page_Init or Page_PreInit if they are just going to be added yet again when we get around to calling Render() on each of the custom server controls? I'm very certain this is not a unique problem, so there must be a best practice way of doing it...I just don't know what it is :/

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• ASP.NET: How to assign ID to a field in DetailsView?

  - by jawonlee

  I have a master-detail page, in which I use GridView to display multiple rows of data, and DetailsView + jQuery dialog to display the details of a single records. only one DetailsView is open at a time. I need to be able to pull out a single field of the open DetailsView, for manipulation using JavaScript. Is there a way to give a unique ID to a given field in DetailsView, so I can use getElementByID? Or is there another way to accomplish what I'm trying to do? Thank you in advance.

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• How to handle set based consistency validation in CQRS?

  - by JD Courtoy

  I have a fairly simple domain model involving a list of Facility aggregate roots. Given that I'm using CQRS and an event-bus to handle events raised from the domain, how could you handle validation on sets? For example, say I have the following requirement: Facility's must have a unique name. Since I'm using an eventually consistent database on the query side, the data in it is not guaranteed to be accurate at the time the event processesor processes the event. For example, a FacilityCreatedEvent is in the query database event processing queue waiting to be processed and written into the database. A new CreateFacilityCommand is sent to the domain to be processed. The domain services query the read database to see if there are any other Facility's registered already with that name, but returns false because the CreateNewFacilityEvent has not yet been processed and written to the store. The new CreateFacilityCommand will now succeed and throw up another FacilityCreatedEvent which would blow up when the event processor tries to write it into the database and finds that another Facility already exists with that name.

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• Best way to get a reasonably random key for MYSQL records

  - by Steve N

  Hi there, I need to generate a reasonably random unique key for a table. It should be something like a GUID for MYSQL. I've tried UUID, but it looks like only the first few characters are actually random- the rest are the same every time I insert them. Essentially, it is desirable for this key field to be very difficult to guess, even if you already have one known value in the column. What is the best way to do this, and how should I set up the field data type to store the value efficiently? Thank you, Steve

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• How to perform a join with CodeIgniter's Active Record class on a multicolumn key?

  - by Scott Southworth

  I've been able to make this code work using CodeIgniter's db->query as follows: $sql = 'SELECT mapping_code,zone_name,installation_name FROM installations,appearances,zones WHERE installations.installation_id = zones.installation_fk_id AND appearances.installation_fk_id = installations.installation_id AND appearances.zone_fk_id = zones.zone_id AND appearances.barcode = ? '; return $this->db->query($sql,array($barcode)); The 'appearances' table throws a 'not unique table' error if I try this using the Active Record class. I need to join appearances on both the zone and installations tables. How can I do this?

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• Network message serialization for game

  - by George R

  Exit-games make a network library product called photon, and they have and actively develop a limited mmo demo. Rather than shooting off json or XML, etc. saying "MovePlayer" (with associated params), they nut that message down to a 2 digit int, via an enum - something like Operations.MovePlayer. There's no denying that a 2 digit int is smaller than a longer string, however I really hate the idea of statically burning each and every message into an enum. Would there be an alternative way to have a MessageID property assign itself a unique 2 digit int based on a lookup table or something? Has anyone dealt with this kind of thing before?

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• Linq-to-XML explicit casting in a generic method

  - by vlad

  I've looked for a similar question, but the only one that was close didn't help me in the end. I have an XML file that looks like this: <Fields> <Field name="abc" value="2011-01-01" /> <Field name="xyz" value="" /> <Field name="tuv" value="123.456" /> </Fields> I'm trying to use Linq-to-XML to get the values from these fields. The values can be of type Decimal, DateTime, String and Int32. I was able to get the fields one by one using a relatively simple query. For example, I'm getting the 'value' from the field with the name 'abc' using the following: private DateTime GetValueFromAttribute(IEnumerable<XElement> fields, String attName) { return (from field in fields where field.Attribute("name").Value == "abc" select (DateTime)field.Attribute("value")).FirstOrDefault() } this is placed in a separate function that simply returns this value, and everything works fine (since I know that there is only one element with the name attribute set to 'abc'). however, since I have to do this for decimals and integers and dates, I was wondering if I can make a generic function that works in all cases. this is where I got stuck. here's what I have so far: private T GetValueFromAttribute<T>(IEnumerable<XElement> fields, String attName) { return (from field in fields where field.Attribute("name").Value == attName select (T)field.Attribute("value").Value).FirstOrDefault(); } this doesn't compile because it doesn't know how to convert from String to T. I tried boxing and unboxing (i.e. select (T) (Object) field.Attribute("value").Value but that throws a runtime Specified cast is not valid exception as it's trying to convert the String to a DateTime, for instance. Is this possible in a generic function? can I put a constraint on the generic function to make it work? or do I have to have separate functions to take advantage of Linq-to-XML's explicit cast operators?

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• Filtering and then counting distinct values

  - by Deon

  This is for Excel: I've been tasked with counting distinct records after I have filtered the data. I have 330 rows with column A containing the 'name' and in Column B I have the name of a test that was done for each 'name', which each 'name' could have taken several iterations of the same test. The test results are in Column C. Col A -Student Col B -Exam Col C - Grade Student 1 Exam 1 .80 Student 2 Exam 1 .50 Student 3 Exam 1 .90 Student 2 Exam 1 .75 Student 4 Exam 1 .90 Student 5 Exam 1 .55 Student 2 Exam 2 .90 Student 1 Exam 2 .90 .... .... ... If I filter col B for Exam 1, I want to count the unique number of students that have taken Exam 1.

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• Which video format(s) should a webapp serve?

  - by NoozNooz42

  I need to put up a few videos on a Webapp and I'm a bit lost. My requirements are: DRM is not a concern at all it should work on the iPhone (and iPad) and on the main browsers (Safari, Internet Explorer, Firefox, Opera). it is not a problem at all if the video doesn't play on Linux (because it's a video/screencast of a Windows/OS X software targetted at, well, Windows and OS X users) it is not a problem at all if it also works on Linux (I'm a Linux user myself) Can a unique format be served (like H.264) and play without any additional work on my part or do I need to convert the videos to different formats and have the webapp serve different video formats depending on the browser used? Should I use the "video" tag of HTML5 when I detect an HTML5 capable browser? What's the "safest" bet here? I take it that Flash is out of the equation seen that iPhone/iPad is a requirement.

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• How to access a website's url programmatically from within the page

  - by Jeff

  For work, I am working on a site that has a feature that lets users make custom instances of the site depending on who they want to show it to. So if they want to show their potential employer a little bit about themselves, they can send them a custom url, that has a uid on the end of it that tells the database what to show and what not to when the site is loaded up. Now, I need to be able to take the value that is on the end of the url, this unique uid that corresponds with their preferences in the db, accessable on run time. Meaning that when someone types in this custom url, I need to be able to show the name of the person whose portfolio is being viewed BEFORE password authentication takes place... If I could get the URL, I suppose I could parse through it to find the necessary UID...but how do I get the url? Maybe I am just missing something here, but if anyone has any thoughts or ideas, it would be appreciated!! Thanks

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• Questions about my program and Polymorphism

  - by Strobe_

  Ok, so basically I'm creating a program which allows the user to select a shape (triangle, square, circle) and then it takes in a int and calculates the boundary length and area. I have no problem doing this and have a program that's working perfectly. (https://gist.github.com/anonymous/c63a03c129560a7b7434 4 classes) But now I have to implement this with polymorphism concepts and I'm honestly struggling as to how to do it. I have a basic idea of what I want to do when it comes to inheritance Main | Shapes / | \ triangle circle square But I don't understand how I'm supposed to override when all the methods within the triangle/square/circle classes are unique, there are no "abstract" methods as such that I could inherit from the "Shapes" class. If somebody could make look quickly at the code I linked and suggest a way to do this it would be much appreciated. Sorry if I was bad at explaining this. Thanks.

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• MYSQL Inserting rows that reference main rows.

  - by Andrew M

  I'm transferring my access logs into a database. I've got two tables: urlRequests id : int(10) host : varchar(100) path: varchar(300) unique index (host, path) urlAccesses id : int(10) request : int(10) <-- reference to urlRequests row ip : int(4) query : varchar(300) time : timestamp I need to insert a row into urlAccesses for every page load, but first a row in urlRequests has to exist with the requested host and path so that urlAccesses's row can reference it. I know I can do it this way: A. check if a row exists in urlRequests B. insert a row in urlRequests if it needs it C. insert a row into urlAccesses with the urlRequests's row id referenced That's three queries for every page load if the urlRequests row doesn't exist. I'm very new to MySQL, so I'm guessing that there's a way to go about this that would be faster and use less queries.

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• Which isolation level should I use for the following insert-if-not-present transaction?

  - by Steve Guidi

  I've written a linq-to-sql program that essentially performs an ETL task, and I've noticed many places where parallelization will improve its performance. However, I'm concerned about preventing uniquness constraint violations when two threads perform the following task (psuedo code). Record CreateRecord(string recordText) { using (MyDataContext database = GetDatabase()) { Record existingRecord = database.MyTable.FirstOrDefault(record.KeyPredicate()); if(existingRecord == null) { existingRecord = CreateRecord(recordText); database.MyTable.InsertOnSubmit(existingRecord); } database.SubmitChanges(); return existingRecord; } } In general, this code executes a SELECT statement to test for record existance, followed by an INSERT statement if the record doesn't exist. It is encapsulated by an implicit transaction. When two threads run this code for the same instance of recordText, I want to prevent them from simultaneously determining that the record doesn't exist, thereby both attempting to create the same record. An isolation level and explicit transaction will work well, except I'm not certain which isolation level I should use -- Serializable should work, but seems too strict. Is there a better choice?

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