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• A Combinations of Items in Given List

  - by mecablaze

  Hello stackoverflow, I'm currently in Python land. This is what I need to do. I have already looked into the itertools library but it seems to only do permutations. I want to take an input list, like ['yahoo', 'wikipedia', 'freebase'] and generate every unique combination of one item with zero or more other items... ['yahoo', 'wikipedia', 'freebase'] ['yahoo', 'wikipedia'] ['yahoo', 'freebase'] ['wikipedia', 'freebase'] ['yahoo'] ['freebase'] ['wikipedia'] A few notes. Order does not matter and I am trying to design the method to take a list of any size. Also, is there a name for this kind of combination? Thanks for your help!

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• Database Design Question: GUID + Natural Numbers

  - by Alan

  For a database I'm building, I've decided to use natural numbers as the primary key. I'm aware of the advantages that GUID's allow, but looking at the data, the bulk of row's data were GUID keys. I want to generate XML records from the database data, and one problem with natural numbers is that I don't want to expose my database key's to the outside world, and allow users to guess "keys." I believe GUID's solve this problem. So, I think the solution is to generate a sparse, unique iD derived from the natural ID (hopefully it would be 2-way), or just add an extra column in the database and store a guid (or some other multibyte id) The derived value is nicer because there is no storage penalty, but it would be easier to reverse and guess compared to a GUID. I'm (buy) curious as to what others on SO have done, and what insights they have.

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• Two entities with @ManyToOne joins the same table

  - by Ivan Yatskevich

  I have the following entities Student @Entity public class Student implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; //getter and setter for id } Teacher @Entity public class Teacher implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; //getter and setter for id } Task @Entity public class Task implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; @ManyToOne(optional = false) @JoinTable(name = "student_task", inverseJoinColumns = { @JoinColumn(name = "student_id") }) private Student author; @ManyToOne(optional = false) @JoinTable(name = "student_task", inverseJoinColumns = { @JoinColumn(name = "teacher_id") }) private Teacher curator; //getters and setters } Consider that author and curator are already stored in DB and both are in the attached state. I'm trying to persist my Task: Task task = new Task(); task.setAuthor(author); task.setCurator(curator); entityManager.persist(task); Hibernate executes the following SQL: insert into student_task (teacher_id, id) values (?, ?) which, of course, leads to null value in column "student_id" violates not-null constraint Can anyone explain this issue and possible ways to resolve it?

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• ModelName(django.contrib.auth.models.User) vs ModelName(models.Model)

  - by amr.negm

  I am developing a django project. I created some apps, some of those are related to User model, for instance, I have a feeds app that handles user feeds, and another app that deals with extra user data like age, contacts, and friends. for each of these, I created a table that should be connected to the User model, which I using for storing and authenticating users. I found two ways to deal with this issue. One, is through extending User model to be like this: ModelName(User): friends = models.ManyToMany('self') ..... Two, is through adding a foreign key to the new table like this: ModelName(models.Model): user = models.ForeignKey(User, unique=True) friends = friends = models.ManyToMany('self') ...... I can't decide which to use in which case. in other words, what are the core differences between both?

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• Check if DateTime in specific range

  - by katit

  Need to check if DateTime is in specific range. I think I need to calculate knowing YEAR first and last date of DST time in this year. How would I figure "Sunday of week 2 of March" date? From 1/1/2007 12:00:00 AM to 12/31/9999 12:00:00 AM Begins at 2:00 AM on Sunday of week 2 of March Ends at 2:00 AM on Sunday of week 1 of November For example, I need to check if 11/21/2011 is between Sunday of week 2 in March and Sunday of week 1 of November - answer should be NO If I pass 8/8/2011 - answer should be yes. Basically, I need to write function to check if my date belongs to daylight savings time. My only idea so far is to write loops to find 2nd week for example. So, I would loop from Day 1 in March until I hit Sunday second time. Same thing I would loop (increment days by 1) from day 1 of November until I hit Sunday first time. In another words, I need function to check if input data is in Daylight Savings time period. Time period defined by constraint above. P.S. I can't use TimeZoneInfo since it's in Silverlight P.P.S I can't use DateTime.IsDaylightSavingsTime as I don't have times with kind "local"

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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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• Initializing new instances of a class in a loop, how can I persist an assignment to an event handler

  - by Pydroid

  This is a follow on question from http://stackoverflow.com/questions/3020960/why-is-my-prototype-function-not-returning-the-property-of-the-instance $.getJSON(myjson, function(data) { var json = data; for (i in json) { juuvies[i] = new Juuvy(i,json[i], font, keyfontsize, valfontsize, orbcol, orbkeycol, orbvalcol, paper); juuvies[i].juuv_it(); var mykey = juuvies[i].init_nodes(); juuvies[i].orb.node.onmouseover = function() { console.log(mykey);}; } }); And my init_nodes function, Juuvy.prototype.init_nodes = function() { return this.key; } At this point of time, I get only the last key in the loop, instead of a unique pass each time. Is there a way I can persist the assignment for the event handler?

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• ASP.MVC 2 Model Data Persistance

  - by toccig

  I'm and MVC1 programmer, new to the MVC2. The data will not persist to the database in an edit scenario. Create works fine. Controller: // // POST: /Attendee/Edit/5 [Authorize(Roles = "Admin")] [AcceptVerbs(HttpVerbs.Post)] public ActionResult Edit(Attendee attendee) { if (ModelState.IsValid) { UpdateModel(attendee, "Attendee"); repository.Save(); return RedirectToAction("Details", attendee); } else { return View(attendee); } } Model: [MetadataType(typeof(Attendee_Validation))] public partial class Attendee { } public class Attendee_Validation { [HiddenInput(DisplayValue = false)] public int attendee_id { get; set; } [HiddenInput(DisplayValue = false)] public int attendee_pin { get; set; } [Required(ErrorMessage = "* required")] [StringLength(50, ErrorMessage = "* Must be under 50 characters")] public string attendee_fname { get; set; } [StringLength(50, ErrorMessage = "* Must be under 50 characters")] public string attendee_mname { get; set; } } I tried to add [Bind(Exclude="attendee_id")] above the Class declaration, but then the value of the attendee_id attribute is set to '0'. View (Strongly-Typed): <% using (Html.BeginForm()) {%> ... <%=Html.Hidden("attendee_id", Model.attendee_id) %> ... <%=Html.SubmitButton("btnSubmit", "Save") %> <% } %> Basically, the repository.Save(); function seems to do nothing. I imagine it has something to do with a primary key constraint violation. But I'm not getting any errors from SQL Server. The application appears to runs fine, but the data is never persisted to the Database.

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• Django and a referrer system question

  - by Hellnar

  Hello, I am trying develop a basic referrer system to my Django website, system will be generating a unique url for each users to share with their friends. Once these friends enter this website, system somehow keep the data that "this user is browsing by the reference of X user" and once this invited person decided to register for an account, system will save this information (maybe as an extra Foreign Key of the inviting user in the UserProfile model) Now how can I keep track of the inviting user from the moment entering using the referred link to the point where he/she registers to the site. Would session framework work on this? If not how could this be done ?

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• Determining the order of a list of numbers (possibly without sorting)

  - by Victor Liu

  I have an array of unique integers (e.g. val[i]), in arbitrary order, and I would like to populate another array (ord[i]) with the the sorted indexes of the integers. In other words, val[ord[i]] is in sorted order for increasing i. Right now, I just fill in ord with 0, ..., N, then sort it based on the value array, but I am wondering if we can be more efficient about it since ord is not populated to begin with. This is more of a question out of curiousity; I don't really care about the extra overhead from having to prepopulate a list and then sort it (it's small, I use insertion sort). This may be a silly question with an obvious answer, but I couldn't find anything online.

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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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• 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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• Setting a preferred item of a many-to-one in Django

  - by Mike DeSimone

  I'm trying to create a Django model that handles the following: An Item can have several Names. One of the Names for an Item is its primary Name, i.e. the Name displayed given an Item. (The model names were changed to protect the innocent.) The models.py I've got looks like: class Item(models.Model): primaryName = models.OneToOneField("Name", verbose_name="Primary Name", related_name="_unused") def __unicode__(self): return self.primaryName.name class Name(models.Model): item = models.ForeignKey(Item) name = models.CharField(max_length=32, unique=True) def __unicode__(self): return self.name class Meta: ordering = [ 'name' ] The admin.py looks like: class NameInline(admin.TabularInline): model = Name class ItemAdmin(admin.ModelAdmin): inlines = [ NameInline ] admin.site.register(Item, ItemAdmin) It looks like the database schema is working fine, but I'm having trouble with the admin, so I'm not sure of anything at this point. My main questions are: How do I explain to the admin that primaryName needs to be one of the Names of the item being edited? Is there a way to automatically set primaryName to the first Name found, if primaryName is not set, since I'm using inline admin for the names?

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• [jquery] Appending to Second Last element

  - by Shishant

  Hello, This is the final output My HTML <li id='$id'>TEXT <ul class='indent'> <li id='$id'>TEXT</li> <li id='$id'>TEXT</li> <li class='formContainer'> FORM </li> </ul> </li> I want to append a li between form after all other li So in this example new li will be appended between Test141 APPEND Input Box The $id are db ids of li which are unique

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• Appropriate data structure for a buffer of the packets

  - by psihodelia

  How to implement a buffer of the packets where each packet is of the form: typedef struct{ int32 IP; //4-byte IP-address int16 ID; //unique sequence id }t_Packet; What should be the most appropriate data structure which: (1) allows to collect at least 8000 such packets (fast Insert and Delete operations) (2) allows very fast filtering using IP address, so that only packets with given IP will be selected (3) allows very fast find operation using ID as a key (4) allows very fast (2), then (3) within filtered results ? RAM size does matter, e.g. no huge lookup table is possible to use.

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• Reuse C++ Header files

  - by Amrish

  Guys, I have a Visual C++ solution with 2 projects AlgorithmA & AlgorithmB and both share a common header file RunAlgo.h with the class declaration. Each project in the solution has its own unique implementation for the header file. I am trying to compile a DLL out of the common header file RunAlgo.h and add reference to this DLL in the projects AlgorithmA & AlgorithmB. I have then included separate RunAlgo.cpp definition file in both my projects. The problem is that I am getting linker errors while compiling the new DLL project which has only the header file. So, the question is Can a header file with only class declaration be compiled into a DLL (Similar to class library containing an Interface in C#)? For the above scenario, is there a better approach to reuse the common Header file among projects? Should the above method work (re-check my code?)

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• How can I get my div id to reload via ajax and jquery

  - by Matt Nathanson

  I'm creating a CMS using jQuery and AJAX. When I click, my "Add Campaign" buttom, it creates a unique client ID in the DB and on a hard reload, the new client shows up in its container. I am trying to use ajax to reload the container on the fly and I'm not having the exact luck i am hoping for. I can get it to reload, but it's like it's pulling in descriptions of each of the clients as well! function AddNewClient() { dataToLoad = 'clientID=' + clientID + '&addClient=yes'; $.ajax({ type: 'post', url: '/clients/controller.php', datatype: 'html', data: dataToLoad, target: ('#clientssidebar'), async: false, success: function(html){ $('#clientssidebar').html(html); }, error: function() { alert('An error occured!'); } }); };

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• How to remove duplicate records in a table?

  - by Mason Wheeler

  I've got a table in a testing DB that someone apparently got a little too trigger-happy on when running INSERT scripts to set it up. The schema looks like this: ID UNIQUEIDENTIFIER TYPE_INT SMALLINT SYSTEM_VALUE SMALLINT NAME VARCHAR MAPPED_VALUE VARCHAR It's supposed to have a few dozen rows. It has about 200,000, most of which are duplicates in which TYPE_INT, SYSTEM_VALUE, NAME and MAPPED_VALUE are all identical and ID is not. Now, I could probably make a script to clean this up that creates a temporary table in memory, uses INSERT .. SELECT DISTINCT to grab all the unique values, TRUNCATE the original table and then copy everything back. But is there a simpler way to do it, like a DELETE query with something special in the WHERE clause?

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• CakePHP: How can I disable auto-increment on Model.id?

  - by tomws

  CakePHP 1.3.0, mysqli I have a model, Manifest, whose ID should be the unique number from a printed form. However, with Manifest.id set as the primary key, CakePHP is helping me by setting up auto-increment on the field. Is there a way to flag the field via schema.php and/or elsewhere to disable auto-increment? I need just a plain, old primary key without it. The only other solution I can imagine is adding on a separate manifest number field and changing foreign keys in a half dozen other tables. A bit wasteful and not as intuitive.

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• Hibernate Auto-Increment not working

  - by dharga

  I have a column in my DB that is set with Identity(1,1) and I can't get hibernate annotations to work for it. I get errors when I try to create a new record. In my entity I have the following. @GeneratedValue(strategy=GenerationType.IDENTITY, generator="native") @Column(name="SeqNo", unique=true, nullable=false) BigDecimal seqNo; But when I try to add a new record I get the following error. Cannot insert explicit value for identity column in table 'MemberSelectedOptions' when IDENTITY_INSERT is set to OFF. I don't want to set IDENTIY_INSERT to ON because I want the identity column in the db to manage the values. The SQL that is run is the following; where you can clearly see the insert. insert into dbo.MemberSelectedOptions (OptionStatusCd, EffectiveDate, TermDate, SelectionStatusDate, SysLstUpdtUserId, SysLstTrxDtm, SourceApplication, GroupId, MemberId, OptionId, SeqNo) values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?) What am I missing?

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• Command Query Separation validating for retries

  - by Neil Barnwell

  So I'm comfortable with the basic concept of CQS, where you might have a command that writes to one database, and that updates the query database that you read from. However, consider the scenario where you are entering data, and want to prevent duplicates. Using new employee data entry an employee register as an example, working through a pile of application forms to key in the new employees' details: Take top sheet. Key in employee name and unique payroll number to UI. Submit. Put paper in "completed pile". Repeat. How would you now prevent the user from keying in the same payroll number again, say for instance if they get distracted and can't remember whether they've keyed one in already and the "message" hasn't got all the way back to the query db for the user to search?

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• How can this code be made more Pythonic?

  - by usethedeathstar

  This next part of code does exactly what I want it to do. dem_rows and dem_cols contain float values for a number of things i can identify in an image, but i need to get the nearest pixel for each of them, and than to make sure I only get the unique points, and no duplicates. The problem is that this code is ugly and as far as I get it, as unpythonic as it gets. If there would be a pure-numpy-solution (without for-loops) that would be even better. # next part is to make sure that we get the rounding done correctly, and than to get the integer part out of it # without the annoying floatingpoint-error, and without duplicates fielddic={} for i in range(len(dem_rows)): # here comes the ugly part: abusing the fact that i overwrite dictionary keys if I get duplicates fielddic[int(round(dem_rows[i]) + 0.1), int(round(dem_cols[i]) + 0.1)] = None # also very ugly: to make two arrays of integers out of the first and second part of the keys field_rows = numpy.zeros((len(fielddic.keys())), int) field_cols = numpy.zeros((len(fielddic.keys())), int) for i, (r, c) in enumerate(fielddic.keys()): field_rows[i] = r field_cols[i] = c

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• MySQL query problem

  - by Luke

  Ok, I have the following problem. I have two InnoDB tables: 'places' and 'events'. One place can have many events, but event can be created without entering place. In this case event's foreign key is NULL. Simplified structure of the tables looks as follows: CREATE TABLE IF NOT EXISTS `events` ( `id` int(11) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(255) COLLATE utf8_bin NOT NULL, `places_id` int(9) unsigned DEFAULT NULL, PRIMARY KEY (`id`), KEY `fk_events_places` (`places_id`), ) ENGINE=InnoDB; ALTER TABLE `events` ADD CONSTRAINT `events_ibfk_1` FOREIGN KEY (`places_id`) REFERENCES `places` (`id`) ON DELETE CASCADE ON UPDATE NO ACTION; CREATE TABLE IF NOT EXISTS `places` ( `id` int(9) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(255) COLLATE utf8_bin NOT NULL, PRIMARY KEY (`id`), ) ENGINE=InnoDB; Question is, how to construct query which contains name of the event and name of the corresponding place (or no value, in case there is no place assigned?). I am able to do it with two queries, but then I am visibly separating events which have place assigned from the ones that are without place. Help really appreciated.

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• Can tomcat perform ssl redirection by filtering host alias?

  - by Stephen

  Hi, We have a tomcat server (6.0.20) running one web application behind two urls, e.g. www.foo and secure.foo This is configured in the server.xml as one host with a single alias: <Host name="www.foo" appBase="webapps"> <Context docBase="foo" path=""></Context> <Alias>secure.foo</Alias> </Host> Ideally we'd like any requests to secure.foo on port 80 to be automatically redirected to use ssl. However, I can only find instructions for redirecting based on the path after the hostname, so I could add a /* security constraint but then this would apply to both urls. Does anyone know if it's possible to apply the redirection by filtering on hostname requested? (We've already got the ssl connector, certificate, etc. working ok). I know we could do it by sticking an apache server in front of tomcat and handling the redirection there, but I'm curious to know if tomcat can do this on its own. Thanks

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• django: Selecting questions that was not asked

  - by Oleg Tarasenko

  Hi, I am creating small django application which holds some few questions (and answers for them) What I want to do is to show user random question, but only from those which was not solved by him yet. I wonder how to do this. For now, I defined user profile model this way: class UserProfile(models.Model): rank = models.IntegerField(default = 1) solvedQ = models.ManyToManyField(Question) user = models.ForeignKey(User, unique=True) So solved problems are added this way: if user.is_authenticated(): profile = user.get_profile() profile.rank += 1 profile.solvedQ.add(Question.objects.get(id=id)) Now if the view must show random question, but not from already solved list... Is there a good way to intersect Questions and solvedQuestions.... so question is chosen from the unsolved list?

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