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  • What is the the relation between programming and mathematics?

    - by Math Grad
    Programmers seem to think that their work is quite mathematical. I understand this when you try to optimize something in performance, find the most efficient alogithm, etc.. But it patently seems false when you look at a billing application for a shop, or a systems software riddled with I/O calls. So what is it exactly? Is computation and associated programming really mathematical? Here I have in mind particularly the words of the philosopher Schopenhauer in mind: That arithmetic is the basest of all mental activities is proved by the fact that it is the only one that can be accomplished by means of a machine. Take, for instance, the reckoning machines that are so commonly used in England at the present time, and solely for the sake of convenience. But all analysis finitorum et infinitorum is fundamentally based on calculation. Therefore we may gauge the “profound sense of the mathematician,” of whom Lichtenberg has made fun, in that he says: “These so-called professors of mathematics have taken advantage of the ingenuousness of other people, have attained the credit of possessing profound sense, which strongly resembles the theologians’ profound sense of their own holiness.” I lifted the above quote from here. It seems that programmers are doing precisely the sort of mechanized base mental activity the grand old man is contemptuous about. So what exactly is the deal? Is programming really the "good" kind of mathematics, or just the baser type, or altogether something else just meant for business not to be confused with a pure discipline?

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  • MVC pattern implementation. What is the n-relation between its components

    - by Srodriguez
    Dear all, I'm working in a C# project and we are , in order to get some unity across the different parts of our UI, trying to use the MVC pattern. The client is windows form based and I'm trying to create a simple MVC pattern implementation. It's been more challenging than expected, but I still have some questions regarding the MVC pattern. The problem comes mostly from the n-n relationships between its components: Here is what I've understood, but I'm not sure at all of it. Maybe someone can correct me? Model: can be shared among different Views. 1-n relationship between Model-View View: shows the state of the model. only one controller (can be shared among different views?). 1-1 relationship with the Model, 1-1 relationship with the controller Controller: handles the user actions on the view and updates the model. One controller can be shared among different views, a controller interacts only with one model? I'm not sure about the two last ones: Can a view have several controller? Or can a view share a controller with another view? Or is it only a 1:1 relationship? Can a controller handle several views? can it interact with several models? Also, I take advantage of this question to ask another MVC related question. I've suppressed all the synchronous calls between the different members of the MVC, making use of the events and delegates. One last call is still synchronous and is actually the most important one: The call between the view and the controller is still synchronous, as I need to know rather the controller has been able to handle the user's action or not. This is very bad as it means that I could block the UI thread (hence the client itself) while the controller is processing or doing some work. How can I avoid this? I can make use of the callback but then how do i know to which event the callback comes from? PS: I can't change the pattern at this stage, so please avoid answers of type "use MVP or MVVC, etc ;) Thanks!

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  • MVC pattern implementation. What is the n-relation between its components

    - by Srodriguez
    Dear all, I'm working in a C# project and we are , in order to get some unity across the different parts of our UI, trying to use the MVC pattern. The client is windows form based and I'm trying to create a simple MVC pattern implementation. It's been more challenging than expected, but I still have some questions regarding the MVC pattern. The problem comes mostly from the n-n relationships between its components: Here is what I've understood, but I'm not sure at all of it. Maybe someone can correct me? Model: can be shared among different Views. 1-n relationship between Model-View View: shows the state of the model. only one controller (can be shared among different views?). 1-1 relationship with the Model, 1-1 relationship with the controller Controller: handles the user actions on the view and updates the model. One controller can be shared among different views, a controller interacts only with one model? I'm not sure about the two last ones: Can a view have several controller? Or can a view share a controller with another view? Or is it only a 1:1 relationship? Can a controller handle several views? can it interact with several models? Also, I take advantage of this question to ask another MVC related question. I've suppressed all the synchronous calls between the different members of the MVC, making use of the events and delegates. One last call is still synchronous and is actually the most important one: The call between the view and the controller is still synchronous, as I need to know rather the controller has been able to handle the user's action or not. This is very bad as it means that I could block the UI thread (hence the client itself) while the controller is processing or doing some work. How can I avoid this? I can make use of the callback but then how do i know to which event the callback comes from? PS: I can't change the pattern at this stage, so please avoid answers of type "use MVP or MVVC, etc ;) Thanks!

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  • [Database] How to model this one-to-one relation?

    - by pbean
    I have several entities which respresent different types of users who need to be able to log in to a particular system. Additionally, they have different types of information associated with them. For example: a "general user", which has an e-mail address and "admin user", which has a workstation number (note that this a hypothetical case). Both entities also share common properties like first name, surname, address and telephone number. Finally, they naturally need to have a (unique) user name and a password to log in. In the application, the user just has to fill in his user name and password, and the functionality of the application changes slightly according to the type of the user. You can imagine that the username needs to be unique for this work. How should I model this effectively? I can't just create two tables, because then I can't force a unique constaint on the user name. I also can't put them all in just one table, because they have different types of specific information associated to them. I think I might need 3 seperate tables, one for "users" (with user name and password), one for the "general users" and another one for the "admin users", but how would the relations between these work? Or is there another solution? (By the way, the target DBMS is MySQL, so I don't think generalization is supported in the database system itself).

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  • Django: way to test what class a generic relation content_object is?

    - by bitbutter
    In my project I have a class, NewsItem. Instances of NewsItem act like a wrapper. They can be associated with either an ArtWork instance, or an Announcement instance. Here's how the NewsItem model looks: class NewsItem(models.Model): content_type = models.ForeignKey(ContentType) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey('content_type', 'object_id') date = models.DateTimeField(default=datetime.datetime.now,) class Meta: ordering = ('-date',) def __unicode__(self): return (self.title()) In a template I'm dealing with a NewsItem instance, and would like to output a certain bunch of html it it's 'wrapping' an Artwork instance, and a different bunch of html if it's wrapping an Announcement instance. Could someone explain how I can write a conditional to test for this? My first naive try looked like this: {% if news_item.content_object.type=='Artwork' %}do this{% else %}do that{% endif %}

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  • How to retrieve row count of one-to-many relation while also include original entity?

    - by kaa
    Say I have two entities Foo and Bar where Foo has-many Bar's, class Foo { int ImportantNumber { get; set; } IEnumerable<Bar> Bars { get; set; } } class FooDTO { Foo Foo { get; set; } int BarCount { get; set; } } How can I efficiently sum up the number of Bars per Foo in a DTO using a single query, preferrably only with the Criteria interface. I have tried any number of ways to get the original entity out of a query with ´SetProjection´ but no luck. The current theory is to do something like SELECT Foo.*, BarCounts.counts FROM Foo LEFT JOIN ( SELECT fooId, COUNT(*) as counts FROM Bar GROUP BY fooId ) AS BarCounts ON Foo.id=BarCounts.fooId but with Criterias, and I just can't seem to figure out how.

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  • How to show raw_id value of a ManyToMany relation in the Django admin?

    - by luc
    Hello, I have an app using raw_id on both ForeignKeyField and ManyToManyField. The admin displays the value of the foreign key on the right of the edit box. Unfortunatey, it doesn't work with ManyToMany. I've checked the code and I think that it is the normal behavior. However I would like to know if someone has an easy tip to change this behavior? Thanks in advance Update: I've tried to subclass the ManyToManyRawIdWidget but I don't know how to say that the raw_id_fields should use my custom widget. formfield_overrides doesn't seem to work with raw_id fields

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  • Relation to multiple tables of different types for rating?

    - by Tronic
    i have a table structure like this Products Team Images and want to implement a rating/commenting-feature, where users can rate each entry of all tables. what's the best way to make a single rating table? e.g. a user votes a a product and a team entry, and it should be possible to get alle these entries from a single table. what kind of table-structure is best for this purpose? i hope, my questions is clear enough :/ thanks in advance!

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  • How to represent a 3-way relation with JPA?

    - by simpatico
    A user may have several labels, and links. Then, a user associates a label (or more) to a link. How does one represent the later relationship? A solution could be a many-to-many relationship btw user and link with the optional attribute label. http://en.wikibooks.org/wiki/Java_Persistence/ManyToMany#Mapping_a_Join_Table_with_Additional_Columns In this case the relationship btw user and label may better be 'virtual'. Any alternative I'm not seeing? PS: I've used google bookmarks terminology, as it matches my case quite well.

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  • How does timezone really work in relation to PHP and MYSQL?

    - by Rick
    I am getting very strange results in terms of timezones. I am currently using Wordpress and everytime I register a new user, I see the wrong datetime in the database. Ok so I am suspecting it is picking up the server time. So then I then set in php.ini to have date.timezone = "America/Los_Angeles" but again the time is still not correct in the database...And yes I have also set the timezone in Wordpress correctly. So how can this be done?

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  • How can I traverse a reverse generic relation in a Django template?

    - by user569139
    I have the following class that I am using to bookmark items: class BookmarkedItem(models.Model): is_bookmarked = models.BooleanField(default=False) user = models.ForeignKey(User) content_type = models.ForeignKey(ContentType) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey() And I am defining a reverse generic relationship as follows: class Link(models.Model): url = models.URLField() bookmarks = generic.GenericRelation(BookmarkedItem) In one of my views I generate a queryset of all links and add this to a context: links = Link.objects.all() context = { 'links': links } return render_to_response('links.html', context) The problem I am having is how to traverse the generic relationship in my template. For each link I want to be able to check the is_bookmarked attribute and change the add/remove bookmark button according to whether the user already has it bookmarked or not. Is this possible to do in the template? Or do I have to do some additional filtering in the view and pass another queryset?

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  • Entity diagram with tables that have foreign keys that point to a non-PK column do not show relation

    - by Jason Coyne
    I have two tables parent and child. If I make a foreign key on child that points to the primary key of parent, and then make an entity diagram, the relationship is shown correctly. If I make the foreign key point to a different column, the relationship is not shown. I have tried adding indexes to the column, but it does not have an effect. The database is sqlite, but I am not sure if that has an effect since its all hidden behind ADO.net. How do I get the relationship to work correctly?

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  • Any easy way to delete a user (having many to many relation with role) in acegi, grails?

    - by john
    Hi, In default acegi setting, person and authority have many to many relations. Thus, in addtion to people and authorities, there is a table authotiries-people. To delete a person (a user) I have to delete the related record in authotiries-people first....then come back to delete the record... the problem is: other people are still using this authority (ROLE) could some one enlighten me how to delete the user without deleting the authority? thanks.

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  • C# RegEx - find html tags (div and anchor)

    - by czesio
    Hi I have to retrieve several div section (of specific class name "row ") with it's content, and additionally find all anchor tags (link urls) (with class "underline red bold"). Shortly speaing : get section of: ... (divs, tags ...) and collections of urls string[] urls = {"/searchClickThru? pid=prod56534895&q=&rpos=109181&rpp=10&_dyncharset=UTF-8&sort=&url=/culture-and-gender-intimate-relation-ksiazka,prod56534895,p"} the entire page looks like that: <html> ... a lot of stuff <div class="row "> <div class="photo"> <a rel="nofollow" href="/searchClickThru?pid=prod56534895&amp;q=&amp;rpos=109181&amp;rpp=10&amp;_dyncharset=UTF-8&amp;sort=&amp;url=/culture-and-gender-intimate-relation-ksiazka,prod56534895,p"> <img alt="alt msg" src="/b/s/b9/03/b9038292d147a582add07ee1f0607827.jpg"> </a> </div> <div class="desc"> <div class="l1"> <div class="icons"> </div> <table cellspacing="0" cellpadding="0" border="0"> <tbody> <tr> <td> <div class="fleft"> <a class="underline red bold" href="/searchClickThru?pid=prod56534895&amp;q=&amp;rpos=109181&amp;rpp=10&amp;_dyncharset=UTF-8&amp;sort=&amp;url=/culture-and-gender-intimate-relation-ksiazka,prod56534895,p"> Culture And Gender <br>Intimate Relation</a> </div> <div class="fleft"> </div> </td> </tr> </tbody> </table> </div> <div class="l2"> <div> </div> <div> <div class="but"> </div> </div> </div> <div class="l3"> Long description <a class="underlinepix_red no_wrap" rel="nofollow" href="/searchClickThru?pid=prod56534895&amp;q=&amp;rpos=109181&amp;rpp=10&amp;_dyncharset=UTF-8&amp;sort=&amp;url=/culture-and-gender-intimate-relation-ksiazka,prod56534895,p"> more<img alt="" src="/b/img/arr_red_sm.gif"> </a> </div> </div> </div> <div class="omit"></div> <div class="row "> <div class="photo"> <a rel="nofollow" href="/searchClickThru?pid=prod56534895&amp;q=&amp;rpos=109181&amp;rpp=10&amp;_dyncharset=UTF-8&amp;sort=&amp;url=/culture-and-gender-intimate-relation-ksiazka,prod56534899,p"> <img alt="alt msg" src="/b/s/b9/03/b9038292d147a582add07ee1f06078222.jpg"> </a> </div> <div class="desc"> <div class="l1"> <div class="icons"> </div> <table cellspacing="0" cellpadding="0" border="0"> <tbody> <tr> <td> <div class="fleft"> <a class="underline red bold" href="/searchClickThru?pid=prod56534895&amp;q=&amp;rpos=109181&amp;rpp=10&amp;_dyncharset=UTF-8&amp;sort=&amp;url=/culture-and-gender-intimate-relation-ksiazka,prod5653489225,p"> Culture And Gender <br>Intimate Relation</a> </div> <div class="fleft"> </div> </td> </tr> </tbody> </table> </div> <div class="l2"> <div> </div> <div> <div class="but"> </div> </div> </div> <div class="l3"> Long description <a class="underlinepix_red no_wrap" rel="nofollow" href="/searchClickThru?pid=prod56534895&amp;q=&amp;rpos=109181&amp;rpp=10&amp;_dyncharset=UTF-8&amp;sort=&amp;url=/culture-and-gender-intimate-relation-ksiazka,prod56534895,p"> more<img alt="" src="/b/img/arr_red_sm.gif"> </a> </div> </div> </div> Can anybody help me to create suitable reg ex?

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  • SQL Alchemy related Objects Error

    - by alex
    from sqlalchemy.orm import relation, backref from sqlalchemy import Table, Column, Integer, String, MetaData, ForeignKey, Date, Sequence from sqlalchemy.ext.declarative import declarative_base Base = declarative_base() class GUI_SCENARIO(Base): __tablename__ = 'GUI_SCENARIO' Scenario_ID = Column(Integer, primary_key=True) Definition_Date = Column(Date) guiScenarioDefinition = relation('GUI_SCENARIO_DEFINITION', order_by='GUI_SCENARIO_DEFINITION.Scenario_Definition_ID', backref='guiScenario') def __init__(self, Scenario_ID=None, Definition_Date=None): self.Scenario_ID = Scenario_ID self.Definition_Date = Definition_Date class GUI_SCENARIO_DEFINITION(Base): __tablename__='GUI_SCENARIO_DEFINITION' Scenario_Definition_ID = Column(Integer, Sequence('Scenario_Definition_ID_SEQ'), primary_key=True) Scenario_FK = Column(Integer, ForeignKey('GUI_SCENARIO.Scenario_ID')) Definition_Date=Column(Date) guiScenario = relation(GUI_SCENARIO, backref=backref('guiScenarioDefinition', order_by=Scenario_Definition_ID)) def __init__(self, Scenario_FK, Definition_Date): self.Scenario_FK = Scenario_FK self.Definition_Date = Definition_Date guiScenario = relation(GUI_SCENARIO, backref=backref('guiScenarioDefinition', order_by=Scenario_Definition_ID)) tableNameScenario = "GUI_SCENARIO" scenarioClass = getattr(MappingTablesScenario, tableNameScenario) tableScenario = Table(tableNameScenario, meta, autoload=True) mapper(scenarioClass, tableScenario) scenarioName = scenarioDefinition.name scenarioDefinitionDate = datetime.today() newScenario = MappingTablesScenario.GUI_SCENARIO(scenarioName, scenarioDefinitionDate) print newScenario.guiScenarioDefinition If I try to get the objects related to a scenarioObject, I always get this error: AttributeError: 'GUI_SCENARIO' object has no attribute 'guiScenarioDefinition' Does anyone know, why I get this error?

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  • Django filter bool not iterable

    - by dana
    I want to filter all Relation Objects where (relation= following relation in a virtual community) the date one has initiated the following is in the past, related to the moment now. The following declaration seems to be wrong, as a bool object is not iterable. Is there another way to do that? d = Relations.objects.filter(date_follow < datetime.now())

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  • How to test if a doctrine records has any relations that are used

    - by murze
    Hi, I'm using a doctrine table that has several optional relations (of types Doctrine_Relation_Association and Doctrine_Relation_ForeignKey) with other tables. How can I test if a record from that table has connections with records from the related table. Here is an example to make my question more clear. Assume that you have a User and a user has a many to many relation with Usergroups and a User can have one Userrole How can I test if a give user is part of any Usergroups or has a role. The solution starts I believe with $relations = Doctrine_Core::getTable('User')->getRelations(); $user = Doctrine_Core::getTable('User')->findOne(1); foreach($relations as $relation) { //here should go a test if the user has a related record for this relation if ($relation instanceof Doctrine_Relation_Association) { //here the related table probably has more then one foreign key (ex. user_id and group_id) } if ($relation instanceof Doctrine_Relation_ForeignKey) { //here the related table probably has the primary key of this table (id) as a foreign key (user_id) } } //true or false echo $result I'm looking for a general solution that will work no matter how many relations there are between user and other tables. Thanks!

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  • Copy a Doctrine object with all relations

    - by elManolo
    I want to copy a record with all his relations. I'm trying with: $o = Doctrine::getTable('Table')->Find(x); $copy = $object->copy(); $relations = $o->getRelations(); foreach ($relations as $name => $relation) { $copy->$relation = $object->$relation->copy(); } $copy->save(); This code doesn't works, but I think it's on the way.

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  • Selecting rows with references across tables in SQLite 3

    - by ChristianK
    Hey there, I have a problem with a SQLite photo/album database. The database contains 3 tables: Albums id name hide -------------------------- 1 Holiday 2010 1 2 Day Trip 0 Photos id file ----------------- 1 photo1.jpg 2 photo2.jpg 3 photo3.jpg 4 photo4.jpg Relation (connects photos with albums) album photo ----------------- 1 1 1 2 2 3 2 1 A photo can be assigned to zero, one or several albums. Each album has a column 'hide' that indicates, whether the photos of this album should be ignored. I'm trying to find a SELECT query that returns all photos that are not assigned to an album + all the photos that are in albums which are not hidden (i.e. that have their 'hide' value set to 0). I came up with a query that selects photos in visible albums, but I don't know how to include the photos that are not assigned to an album. SELECT file FROM photos, albums, relation WHERE photos.id = relation.photo AND albums.id = relation.album AND albums.hide = 0 This query returns photo3.jpg and the required result would be photo3.jpg photo4.jpg because photo4.jpg is not assigned to album in the Relation table. Do you know how to solve this? Thank you very much for your help!

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  • Core Data not-reverse relationship subquery

    - by user561485
    Hi, I have the following entities in CoreData: Village - villageID Bookmark - (relation) village There are multiple villages with each an unique villageID. I have a entity Bookmark which only has a relation to a Village entity; it isn't possible to make a reverse relation. Now I would like to get the village entities where there exists a Bookmark relation. I've red something about subqueries, but I can't get it right for this situation. It must be something like: Village.villageID IN (Bookmark.village.villageID) It isn't possible to get first all the Bookmarks and then loop to get all the Villages, because of the design of the framework. Can this be done in CoreData (I presume the answer is "Yes, of course!") and how?

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  • Dictionary not deserializing

    - by Shadow
    I'm having a problem where one Dictionary in my project is either not serializing or not deserializing. After deserializing, the data I serialized is simply not in the object. Here's the relevant snip of the class being serialized: class Person : ISerializable { private Dictionary<Relation,List<int>> Relationships = new Dictionary<Relation,List<int>>(); public Person(SerializationInfo info, StreamingContext context) { this.Relationships = (Dictionary<Relation, List<int>>) info.GetValue("Relationships", typeof(Dictionary<Relation, List<int>>)); } public void GetObjectData(SerializationInfo info, StreamingContext context) { info.AddValue("Relationships", this.Relationships); } } Note, this is binary serialization. Everything else in the project serializes and deserialzes correctly.

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