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• Database design - alternatives for Entity Attribute Value (AEV)

  - by Bob

  Hi, see http://stackoverflow.com/questions/695752/product-table-many-kinds-of-product-each-product-has-many-parameters for similar topic. My question: i want to design a database, that will be used for a production facility of different types of products where each product has its own (number of) parameters. because i want the serial numbers to be in one tabel for overview purposes i have a problem with these different paraeters . One solution could be AEV, but it has its downsides, certainly because we have +- 5 products with every product +- 20.000 serial numbers (records). it looks a bit overkill to me... I just don't know how one could design a database so that you have an attribute in a mastertable that says: 'hey, you could find details of this record in THAT detail-table". 'in a way that you qould easely query the results) currenty i am using Visual Basic & Acces 2007. but i'm going to Visual Basic & MySQL. thanks for your help. Bob

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• Implicitly create associated model from string

  - by singpolyma

  I have a model Post that has_many :tags I want to do: Post.create({:tags = ['tag1', 'tag2']}) How can I make that work?

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• Bypassing Windows Copy design

  - by Scott S

  I have been trying to figure out a way to streamline copying files from one drive (network or external in my case) to my main system drives. Short of creating a program that I will have to activate each time then choosing all the info in it, I have no really good design to bypass it. I have been wondering if there was a way to intercept a straight-forward windows copy with a program to do it my way. The basic design would be that upon grabbing the copy (actually for this to be efficient, a group of different copies), the program would organize all the separate copies into a single stream of copies. I've been wanting to do this as recently I have been needing to make backups of a lot of data and move it a lot as all my drives seem to be failing the past few months.

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• How to perform add/update of a model object that contains EntitySet

  - by David Liddle

  I have a similar concept to the SO questions/tags scenario however am trying to decide the best way of implementation. Tables Questions, QuestionTags and Tags Questions QuestionTags Tags --------- ------------ ---- QID QID TID QName TID TName When adding/updating a question I have 2 textboxes. The important part is a single textbox that allows users to enter in multiple Tags separated by spaces. I am using Linq2Sql so the Questions model has an EntitySet of QuestionTags with then link to Tags. My question is regarding the adding/updating of Questions (part 1), and also how to best show QuestionTags for a Question (part 2). Part 1 Before performing an add/update, my service layer needs to deal with 3 scenarios before passing to their respective repositories. Insert Tags that do not already exist Insert/Update Question Insert QuestionTags - when updating need to remove existing QuestionTags Here is my code below however started to get into a bit of a muddle. I've created extension methods on my repositories to get Tags WithNames etc. public void Add(Question q, string tags) { var tagList = tags.Split(new string[] { " " }, StringSplitOptions.RemoveEmptyEntries).ToList(); using (DB.TransactionScope ts = new DB.TransactionScope()) { var existingTags = TagsRepository.Get() .WithName(tagList) .ToList(); var newTags = (from t in tagList select new Tag { TName = t }).Except(existingTags, new TagsComparer()).ToList(); TagsRepository.Add(newTags); //need to insert QuestionTags QuestionsRepository.Add(q); ts.Complete(); } } Part 2 My second question is, when displaying a list of Questions how is it best to show their QuestionTags? For example, I have an Index view that shows a list of Questions in a table. One of the columns shows an image and when the user hovers over it shows the list of Tags. My current implementation is to create a custom ViewModel and show a List of QuestionIndexViewModel in the View. QuestionIndexViewModel { Question Question { get; set; } string Tags { get; set; } } However, this seems a bit clumsy and quite a few DB calls. public ViewResult Index() { var model= new List<QuestionIndexViewModel>(); //make a call to get a list of questions //foreach question make a call to get their QuestionTags, //to be able to get their Tag names and then join them //to form a single string. return View(model); } Also, just for test purposes using SQL Profiler, I decided to iterate through the QuestionTags entity set of a Question in my ViewModel however nothing was picked up in Profiler? What would be the reason for this?

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• Query for model by key

  - by Jason Hall

  What I'm trying to do is query the datastore for a model where the key is not the key of an object I already have. Here's some code: class User(db.Model): partner = db.SelfReferenceProperty() def text_message(self, msg): user = User.get_or_insert(msg.sender) if not user.partner: # user doesn't have a partner, find them one # BUG: this line returns 'user' himself... :( other = db.Query(User).filter('partner =', None).get() if other: # connect users else: # no one to connect to! The idea is to find another User who doesn't have a partner, that isn't the User we already know. I've tried filter('key !=, user.key()), filter('__key__ !=, user.key()) and a couple others, and nothing returns another User who doesn't have a partner. filter('foo !=, user.key()) also returns nothing, for the record.

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• verbose_name for a model's method

  - by mawimawi

  How can I set a verbose_name for a model's method, so that it might be displayed in the admin's change_view form? example: class Article(models.Model): title = models.CharField(max_length=64) created_date = models.DateTimeField(....) def created_weekday(self): return self.created_date.strftime("%A") in admin.py: class ArticleAdmin(admin.ModelAdmin): readonly_fields = ('created_weekday',) fields = ('title', 'created_weekday') Now the label for created_weekday is "Created Weekday", but I'd like it to have a different label which should be i18nable using ugettext_lazy as well. I've tried created_weekday.verbose_name=... after the method, but that did not show any result. Is there a decorator or something I can use, so I could make my own "verbose_name" / "label" / whateverthename is?

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• ActionLink sending a model of a complex type

  - by Xenph Yan

  I'm trying to paginate the results of a "advanced search", I have a complex model that represents the search options; int ZipCode int MinAge int MaxAge Availability bool Monday bool Tuesday ... bool Friday Requirements bool FirstAid bool DriversLicense I'm using; <%: Html.ActionLink("Next »", "Save", "Notification", Model.options)%> Which correctly sends all the data at the first level, but anything that is a sub-object (Availability or requirements) isn't expanded in the URL, all I get is the class name and so I lose most of the search options when I click the link to change to a different page. Any thoughts?

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• Using Property Builtin with GAE Datastore's Model

  - by ejel

  I want to make attributes of GAE Model properties. The reason is for cases like to turn the value into uppercase before storing it. For a plain Python class, I would do something like: Foo(db.Model): def get_attr(self): return self.something def set_attr(self, value): self.something = value.upper() if value != None else None attr = property(get_attr, set_attr) However, GAE Datastore have their own concept of Property class, I looked into the documentation and it seems that I could override get_value_for_datastore(model_instance) to achieve my goal. Nevertheless, I don't know what model_instance is and how to extract the corresponding field from it. Is overriding GAE Property classes the right way to provides getter/setter-like functionality? If so, how to do it? Added: One potential issue of overriding get_value_for_datastore that I think of is it might not get called before the object was put into datastore. Hence getting the attribute before storing the object would yield an incorrect value.

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• Cannot save model due to bad transaction? Django

  - by Kenneth Love

  Trying to save a model in Django admin and I keep getting the error: Transaction managed block ended with pending COMMIT/ROLLBACK I tried restarting both the Django (1.2) and PostgreSQL (8.4) processes but nothing changed. I added "autocommit": True to my database settings but that didn't change anything either. Everything that Google has turned up has either not been answered or the answer involved not having records in the users table, which I definitely have. The model does not have a custom save method and there are no pre/post save signals tied to it. Any ideas or anything else I can provide to make answering this easier?

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• R: including model specifications in xtable(anova(...))

  - by HamiltonUlmer

  Hello R comrades: I have a bunch of loglinear models, which, for our purposes will just be glm() objects called mx, my, mz. I want to get a nicely-formatted xtable of the analysis of deviance, so naturally I would want to perform xtable(anova(mx, my, mz, test = "Chisq")). The vanilla output of xtable, however, doesn't include the model specifications. I'd like to include those for all the ANOVA tests I'm running, so if there is not a param I'm missing that does this I'll probably just have to hack up my own solution. But looking over the help page, there doesn't seem to be an easy way to include the model specifications. Any thoughts? Alternatives? If it helps this was done in 2.9.1 with xtable 1.5-5.

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• SQL - Updating records based on most recent date

  - by Remnant

  I am having difficulty updating records within a database based on the most recent date and am looking for some guidance. By the way, I am new to SQL. As background, I have a windows forms application with SQL Express and am using ADO.NET to interact with the database. The application is designed to enable the user to track employee attendance on various courses that must be attended on a periodic basis (e.g. every 6 months, every year etc.). For example, they can pull back data to see the last time employees attended a given course and also update attendance dates if an employee has recently completed a course. I have three data tables: EmployeeDetailsTable - simple list of employees names, email address etc., each with unique ID CourseDetailsTable - simple list of courses, each with unique ID (e.g. 1, 2, 3 etc.) AttendanceRecordsTable - has 3 columns { EmployeeID, CourseID, AttendanceDate, Comments } For any given course, an employee will have an attendance history i.e. if the course needs to be attended each year then they will have one record for as many years as they have been at the company. What I want to be able to do is to update the 'Comments' field for a given employee and given course based on the most recent attendance date. What is the 'correct' SQL syntax for this? I have tried many things (like below) but cannot get it to work: UPDATE AttendanceRecordsTable SET Comments = @Comments WHERE AttendanceRecordsTable.EmployeeID = (SELECT EmployeeDetailsTable.EmployeeID FROM EmployeeDetailsTable WHERE (EmployeeDetailsTable.LastName =@ParameterLastName AND EmployeeDetailsTable.FirstName =@ParameterFirstName) AND AttendanceRecordsTable.CourseID = (SELECT CourseDetailsTable.CourseID FROM CourseDetailsTable WHERE CourseDetailsTable.CourseName =@CourseName)) GROUP BY MAX(AttendanceRecordsTable.LastDate) After much googling, I discovered that MAX is an aggregate function and so I need to use GROUP BY. I have also tried using the HAVING keyword but without success. Can anybody point me in the right direction? What is the 'conventional' syntax to update a database record based on the most recent date?

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• CURL alternative - Design ideas

  - by Vincent

  All, I am looking for some web application design ideas here. I have a server X that hosts an SDK, which has the capacity to talk a piece of hardware. When I make an HTTPS request from an external PHP web application (hosted on Server Y) to Server X through curl, Server X gives JSON data as a response. I use this data to render my UI for the web app on Server Y. The above method seems to be slow and has a tendency to fail in production if there are too many concurrent requests. Can anybody let me know if there is an alternative to CURL or any other design people are using to pull data like this from servers? Thanks

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• Passing values from action class to model class in symfony

  - by THOmas

  I have a action class for saving some data to a database.In action class iam getting a id through url.I have to save the id in table. I am getting the id by $request-getParameter('id') I used this code for saving $this-form-bind($request-getParameter('question_answers')); if ($this-form-isValid()) { $this-form-save(); $this-redirect('@homepage'); } in model class i used a override save method to save extra field public function save(Doctrine_Connection $conn = null) { if ($this-isNew()) { $now=date('Y-m-d H:i:s', time()); $this->setPostedAt($now); } return parent::save($conn); so i want to get the id value here . So how can i pass id value from action class to model class is any-other way to save the id in action class itself Thanks in advance

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• Get a queryset of objects through an intermediary model

  - by skyl

  I want get all of the Geom objects that are related to a certain content_object (see the function I'm trying to build at the bottom, get_geoms_for_obj() class Geom(models.Model): ... class GeomRelation(models.Model): ''' For tagging many objects to a Geom object and vice-versa''' geom = models.ForeignKey(Geom) content_type = models.ForeignKey(ContentType) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey() def get_geoms_for_object(obj): ''' takes an object and gets the geoms that are related ''' ct = ContentType.objects.get_for_model(obj) id = obj.id grs = GeomRelation.objects.filter( content_type=ct, object_id=id ) # how with django orm magic can I build the queryset instead of list # like below to get all of the Geom objects for a given content_object geoms = [] for gr in grs: geoms.append(gr.geom) return set(geoms) # A set makes it so that I have no redundant entries but I want the # queryset ordering too .. need to make it a queryset for so many reasons...

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• Basic Client-Server Design for persistent connections?

  - by cam

  Here's as far as I understand it: Client & Server make connection Client sends server data Server interprets data, sends client data So on, and so forth, until client sends disconnect signal. I'm just wondering about implementation. Step 2 and 3 are confusing to me, maybe I'm over-complicating it. Is there anymore to interpreting the data than a giant switch statement? Any good books on client/server design? Specifically talking about multithreaded servers, scalability, and message design (byte 1 = header info, byte 2 = blah blah, etc)? Specifically geared towards C++.

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• How can I cluster short messages [Tweets] based on topic ? [Topic Based Clustering]

  - by Jagira

  Hello, I am planning an application which will make clusters of short messages/tweets based on topics. The number of topics will be limited like Sports [ NBA, NFL, Cricket, Soccer ], Entertainment [ movies, music ] and so on... I can think of two approaches to this Ask for users to tag questions like Stackoverflow does. Users can select tags from a predefined list of tags. Then on server side I will cluster them on based of tags. Pros:- Simple design. Less complexity in code. Cons:- Choices for users will be restricted. Clusters will not be dynamic. If a new event occurs, the predefined tags will miss it. Take the message, delete the stopwords [ predefined in a dictionary ] and apply some clustering algorithm to make a cluster and depending on its popularity, display the cluster. The cluster will be maintained according to its sustained popularity. New messages will be skimmed and assigned to corresponding clusters. Pros:- Dynamic clustering based on the popularity of the event/accident. Cons:- Increased complexity. More server resources required. I would like to know whether there are any other approaches to this problem. Or are there any ways of improving the above mentioned methods? Also suggest some good clustering algorithms.I think "K-Nearest Clustering" algorithm is apt for this situation.

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• how to load a 3d model in processing?

  - by ulrich

  i want to load a 3d model from blender ...

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• How to model dependency injection in UML ?

  - by hjo1620

  I have a Contract class. The contract is valid 1 Jan 2010 - 31 Dec 2010. It can be in state Active or Passive, depending on which date I ask the instance for it's state. ex. if I ask 4 July 2010, it's in state Active, but if I ask 1 Jan 2011, it's in state Passive. Instances are created using constructor dependency injection, i.e. they are either Active or Passive already when created, null is not allowed as a parameter for the internal state member. One initial/created vertex is drawn in UML. I have two arrows, leading out from the initial vertex, one leading to state Active and the other to state Passive. Is this a correct representation of dependency injection in UML ? This is related to http://stackoverflow.com/questions/2779922/how-model-statemachine-when-state-is-dependent-on-a-function which initiated the question on how to model DI in general, in UML.

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• Convert executed SQL result to a list of Model object

  - by huynq9

  I'm wondering that is it possible to convert the executed query result to a list of models. I'm using Ruby with ActiveRecord and need to execute custom SQL query to join two or many tables. The code looks like below: connection = ActiveRecord::Base.connection sql = "select T1.f1, T2.f2 from T1 left join T2 on T1.id = T2.id" @result = connection.execute(sql) In Ruby code, I defined a models to manage the executed SQL result: class Model property :f1, :f2 end Is there any way to convert @result to list of Model object? so I can deal with each item in the list as following @result.each do |item| puts item.f1 puts item.f2 end

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• asp.net mvc default model binding problem

  - by csetzkorn

  I have some problems with ASP.NET MVC’s default model binder. The View contains HTML like this: <input name="SubDTO[0].Id" value="1" type="checkbox"> <input name="SubDTO[1].Id" value="2" type="checkbox"> This is my simplified ‘model’: public class SubDTO { public virtual string Id { get; set; } } public class DTO { public List<SubDTO> SubDTOs { get; set; } public DTO() { SubDTOs = new List< SubDTO>(); } } All this works fine if the user selects at least the first checkbox (SubDTO[0].Id). The controller ‘receives’ a nicely initialised/bound DTO. However, if the first check box is not selected but only, for example, SubDTO[1].Id the object SubDTOs is null. Can someone please explain this ‘strange’ behaviour and how to overcome it? Thanks. Best wishes, Christian

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• Model state inferno - how can Model.A be two different things at the same time?

  - by Martin

  I have this <%=Model.StartDate%> <%=Html.Hidden("StartDate", Model.StartDate)%> it outputs: 2010-05-11 11:00:00 +01:00 <input type="hidden" value="2010-03-17 11:00:00 +01:00" name="StartDate" id="StartDate"> What the... It's a paging mechanism so the hidden value was valid on the first page and I've been able to move forward to the next page. But since the values won't update properly it ends there. What do I need to do? Using firefox.

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• Model Django Poll

  - by MacPython

  I followed the django tutorial here: http://docs.djangoproject.com/en/dev/intro/tutorial01/ and now I am at creating a poll. The code below works fine until I want to create choices, where for some reason I always get this error message: line 22, in unicode return self.question AttributeError: 'Choice' object has no attribute 'question' Unfortunatley, I dont understand where I made an error. Any help would be greatly appreciated. Thanks for the time! CODE: import datetime from django.db import models class Poll(models.Model): question = models.CharField(max_length=200) pub_date = models.DateTimeField('date published') def __unicode__(self): return self.question def was_published_today(self): return self.pub_date.date() == datetime.date.today() class Choice(models.Model): poll = models.ForeignKey(Poll) choice = models.CharField(max_length=200) votes = models.IntegerField() def __unicode__(self): return self.question

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• ASP.NET MVC: View does not get rendered with updated model value

  - by Newton

  I'm experiencing the a challenge in populating the child records. My previous code was like - <%= Html.TextBox("DyeOrder.Summary[" + i + "].Ratio", Model.DyeOrder.Summary[i].Ratio.ToString("#0.00"), ratioProperties) %> This code does not render the updated values after post back. To resolve this issue my work around was like - <%= "<input id='DyeOrder_Summary_" + i + "__Ratio' name='DyeOrder.Summary[" + i + "].Ratio' value='" + Model.DyeOrder.Summary[i].Ratio.ToString("#0.00") + "' " + ratioCss + " type='text' />"%> This is very clumsy to me. Is there any better ideas...

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• How to handle this type of model validation in Ruby on Rails

  - by randombits

  I have a controller/model hypothetically named Pets. Pets has the following declarations: :belongs_to owner :has_many dogs :has_many cats Not the best example, but again, it demonstrates what I'm trying to solve. Now when a request comes in as an HTTP POST to http://127.0.0.1/pets, I want to create an instance of Pets. The restriction here is, if the user doesn't submit at least one dog or one cat, it should fail validation. It can have both, but it can't be missing both. How does one handle this in Ruby on Rails? Dogs don't care if cats exists and the inverse is also true. Can anyone show some example code of what the Pets model would look like to ensure that one or the other exists, or fail otherwise? errors.add also takes an attribute, in this case, there is no particular attribute that's failing. It's almost a 'virtual' combination that's missing.

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• Model Binding with Parent/Child Relationship

  - by user296297

  I'm sure this has been answered before, but I've spent the last three hours looking for an acceptable solution and have been unable to find anything, so I apologize for what I'm sure is a repeat. I have two domain objects, Player and Position. Player's have a Position. My domain objects are POCOs tied to my database with NHibernate. I have an Add action that takes a Player, so I'm using the built in model binding. On my view I have a drop down list that lets a user select the Position for the Player. The value of the drop down list is the Id of the position. Everything gets populated correctly except that my Position object fails validation (ModelState.IsValid) because at the point of model binding it only has an Id and none of it's other required attributes. What is the preferred solution for solving this with ASP.NET MVC 2? Solutions I've tried... Fetch the Position from the database based on the Id before ModelState.IsValid is called in the Add action of my controller. I can't get the model to run the validation again, so ModelState.IsValid always returns false. Create a custom ModelBinder that inherits from the default binder and fetch the Position from the database after the base binder is called. The ModelBinder seems to be doing the validation so if I use anything from the default binder I'm hosed. Which means I have to completely roll my own binder and grab every value from the form...this seems really wrong and inefficient for such a common use-case. Solutions I think might work, I just can't figure out how to do... Turn off the validation for the Position class when used in Player. Write a custom ModelBinder leverages the default binder for most of the property binding, but lets me get the Position from the database BEFORE the default binder runs validation. So, how do the rest of you solve this? Thanks, Dan P.S. In my opinion having a PositionId on Player just for this case is not a good solution. There has to be solvable in a more elegant fashion.

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