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• Physical Cores vs Virtual Cores in Parallelism

  - by Code Curiosity

  When it comes to virtualization, I have been deliberating on the relationship between the physical cores and the virtual cores, especially in how it effects applications employing parallelism. For example, in a VM scenario, if there are less physical cores than there are virtual cores, if that's possible, what's the effect or limits placed on the application's parallel processing? I'm asking, because in my environment, it's not disclosed as to what the physical architecture is. Is there still much advantage to parallelizing if the application lives on a dual core VM hosted on a single core physical machine?

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• Simplest one-to-many Map case in Hibernate doesn't work in MySQL

  - by Malvolio

  I think this is pretty much the simplest case for mapping a Map (that is, an associative array) of entities. @Entity @AccessType("field") class Member { @Id protected long id; @OneToMany(cascade = CascadeType.ALL, fetch=FetchType.LAZY) @MapKey(name = "name") private Map<String, Preferences> preferences = new HashMap<String, Preferences>(); } @Entity @AccessType("field") class Preferences { @ManyToOne Member member; @Column String name; @Column String value; } This looks like it should work, and it does, in HSQL. In MySQL, there are two problems: First, it insists that there be a table called Members_Preferences, as if this were a many-to-many relationship. Second, it just doesn't work: since it never populates Members_Preferences, it never retrieves the Preferences. [My theory is, since I only use HSQL in memory-mode, it automatically creates Members_Preferences and never really has to retrieve the preferences map. In any case, either Hibernate has a huge bug in it or I'm doing something wrong.]

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• MySQL count problem

  - by Skuja

  I have 3 tables users(id,name),groups(id,name) and users_groups(user_id,group_id). users and groups have many to many relationship, so the third one is for storing users and groups relations. I would like to select all the data from groups with user count in each group. So far I came up with this: SELECT groups.*, COUNT(users_groups.user_id) AS user_count FROM groups LEFT JOIN users_groups ON users_groups.group_id = groups.id The problem is that query result is not returning any of groups which has no users (users_groups doesnt have any records with group_id of those groups). How should I create my query to select all the groups and they user count, or user count as 0 if there are no users for that group?

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• CakePHP hasAndBelongsToMany (HABTM) Delete Joining Record

  - by Jason McCreary

  I have a HABTM relationship between Users and Locations. Both Models have the appropriate $hasAndBelongsToMany variable set. When I managing User Locations, I want to delete the association between the User and Location, but not the Location. Clearly this Location could belong to other users. I would expect the following code to delete just the join table record provided the HABTM associations, but it deleted both records. $this->Weather->deleteAll(array('Weather.id' => $this->data['weather_ids'], false); However, I am new to CakePHP, so I am sure I am missing something. I have tried setting cascade to false and changing the Model order with User, User-Weather, Weather-User. No luck. Thanks in advance for any help.

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• Entity Framework This property descriptor does not support the SetValue

  - by Gayan

  Hello guys, below are my entities which i have created using entity frame work. retailer id name childs(navigation) generated database schema [Id] [int] IDENTITY(1,1) NOT NULL, [Name] nvarchar NOT NULL childern id name RETAILER(navigation) generated database schema [Id] [int] IDENTITY(1,1) NOT NULL, [name] nvarchar NOT NULL [Retailer_Id] [int] NOT NULL, As you can see in the above model the relationship is 1 retailer can have 0 or 1 child. my problem is when i create a new child and set the retailer navigation property of it to a retailer entity it throws the following exception.how do i solve it Error while setting property 'retailer': 'This property descriptor does not support the SetValue method.'.

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• I get "stack level too deep" error when using a named scope

  - by Brian Roisentul

  I'm using ruby on rails 2.3.8 and when I write the syntax shown below I get the "stack level too deep" error message. The model is called Announcement and the line of the error looks like this: Tag.find(category_id).announcements.published Where published is named_scope :published, :conditions => "announcements.state = 'published'" I use this named scope in many other places and it works fine. What am I doing wrong? (the relationship between Tag and Announcement model is ok because if I remove the ".published" method from that line it works just fine).

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• Hibernate and Child Objects (add versus clear)

  - by tyndall

  Lets say I have domain model with Automobile and Wheels. Wheels is a List of Wheels Wheels has a many-to-one relationship to Automobile. If I get an object back from Hibernate and it has 4 wheels. I take that object remove the 4 wheels and add 4. And then Save. If I ask Hibernate for the object again and it returns an auto with 8 wheels... what are we doing wrong? I don't have access to the source for a few days but want to give our Java devs a push in the right direction. Thanks.

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• How to: Display multiple related classes in an ASP.NET GridView ?

  - by kversch

  I would like to display students and their grades with a GridView and LinqToSQL like this: assignment1 assignment2 Student 1 55 89 Student 2 87 56 Student 3 92 34 I found this topic but it doesn't answer my question: http://forums.asp.net/t/1557987.aspx I have a many-to-many relationship between students and assignments called "grades". The grade for the assignment is stored in that table in a "gradeNumber" column. I would also like to specify which assignments should be displayed in the grid. Btw, my LINQ entities are extended to allow me to write/get studentx.Assignments or assignmentx.Students.

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• d3 tree - parents having same children

  - by Larry Anderson

  I've been transitioning my code from JIT to D3, and working with the tree layout. I've replicated http://mbostock.github.com/d3/talk/20111018/tree.html with my tree data, but I wanted to do a little more. In my case I will need to create child nodes that merge back to form a parent at a lower level, which I realize is more of a directed graph structure, but would like the tree to accomodate (i.e. notice that common id's between child nodes should merge). So basically a tree that divides like normal on the way from parents to children, but then also has the ability to bring those children nodes together to be parents (sort of an incestual relationship or something :)). Asks something similar - How to layout a non-tree hierarchy with D3 It sounds like I might be able to use hierarchical edge bundling in conjunction with the tree hierarchy layout, but I haven't seen that done. I might be a little off with that though.

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• How would you create a notification system like on SO or Facebook in RoR?

  - by Justin Meltzer

  I'm thinking that notifications would be it's own resource and have a has_many, through relationship with the user model with a join table representing the associations. A user having many notifications is obvious, and then a notification would have many users because there would be a number of standardized notifications (a commenting notification, a following notification etc.) that would be associated with many users. Beyond this setup, I'm unsure how to trigger the creation of notifications based on certain events in your application. I'm also a little unsure of how I'd need to set up routing - would it be it's own separate resource or nested in the user resource? I'd find it very helpful if someone could expand on this. Lastly, ajax polling would likely improve such a feature. There's probably some things I'm missing, so please fill this out so that it is a good general resource.

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• Rails 2.3.5: How does one add an error when it doesn't make sense to put it in a validation?

  - by randombits

  I recently was trying to add errors.add_to_base code in the middle of some model logic and was wondering why it wasn't showing up in my view that was iterating over all errors. I then ran across this e-mail which explains why: http://groups.google.com/group/rubyonrails-talk/browse_thread/thread/e045ec1dead1ff06?pli=1 The question is then, how does one add errors with add_to_base if it doesn't make sense to put them into a validate method? I have some complex logic. The model needs to talk to a has_many relationship which has its own relationships that go through a myriad of conditionals to figure out if a request makes sense. It's nothing that can be tied to a validate method easily. How does one add errors then accordingly?

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• JPA and aggregate functions. How do I use the result of the query?

  - by Bogdan

  Hey guys, I'm new to ORM stuff and I need some help understanding something. Let's assume I have the following standard SQL query: SELECT *, COUNT(test.testId) AS noTests FROM inspection LEFT JOIN test ON inspection.inspId = test.inspId GROUP BY inspection.inspId which I want to use in JPA. I have an Inspection entity with a one-to-many relationship to a Test entity. (an inspection has many tests) I tried writing this in JPQL: Query query = em.createQuery("SELECT insp, COUNT(???what???) FROM Inspection insp LEFT JOIN insp.testList " + "GROUP BY insp.inspId"); 1) How do I write the COUNT clause? I'd have to apply count to elements from the test table but testList is a collection, so I can't do smth like COUNT(insp.testList.testId) 2) Assuming 1 is resolved, what type of object will be returned. It will definitely not be an Inspection object... How do I use the result?

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• Mapping enum to a table with hibernate annotation

  - by Thierry-Dimitri Roy

  I have a table DEAL and a table DEAL_TYPE. I would like to map this code: public class Deal { DealType type; } public enum DealType { BASE("Base"), EXTRA("Extra"); } The problem is that the data already exist in the database. And I'm having a hard time mapping the classes to the database. The database looks something like that: TABLE DEAL { Long id; Long typeId; } TABLE DEAL_TYPE { Long id; String text; } I know I could use a simple @OneToMany relationship from deal to deal type, but I would prefer to use an enum. Is this possible? I almost got it working by using a EnumType.ORDINAL type. But unfortunately, my IDs in my deal type table are not sequential, and do not start at 1. Any suggestions?

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• Accessing properties through Generic type parameter

  - by Veer

  I'm trying to create a generic repository for my models. Currently i've 3 different models which have no relationship between them. (Contacts, Notes, Reminders). class Repository<T> where T:class { public IQueryable<T> SearchExact(string keyword) { //Is there a way i can make the below line generic //return db.ContactModels.Where(i => i.Name == keyword) //I also tried db.GetTable<T>().Where(i => i.Name == keyword) //But the variable i doesn't have the Name property since it would know it only in the runtime //db also has a method ITable GetTable(Type modelType) but don't think if that would help me } } In MainViewModel, I call the Search method like this: Repository<ContactModel> _contactRepository = new Repository<ContactModel>(); public void Search(string keyword) { var filteredList = _contactRepository.SearchExact(keyword).ToList(); } I use Linq-To-Sql.

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• Doctrine 1.2 Column Naming Conventions for Many To Many Relationships

  - by Alan Storm

  I'm working with an existing database schema, and trying to setup two Doctrine models with a Many to Many relationship, as described in this document When creating tables from scratch, I have no trouble getting this working. However, the existing join tables use a different naming convention that what's described in the Doctrine document. Specifically Table 1 -------------------------------------------------- table_1_id ....other columns.... Table 2 -------------------------------------------------- table_2_id ....other columns.... Join Table -------------------------------------------------- fktable1_id fktable_2_id Basically, the previous developers prefaced all forign keys with an fk. From the examples I've seen and some brief experimenting with code, it appears that Doctrine 1.2 requires that the join table use the same column names as the tables it's joining in Is my assumption correct? If so, has the situation changed in Doctrine 2? If the answers to either of the above are true, how do you configure the models so that all the columns "line up"

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• How to find the entity with the greatest primary key?

  - by simpatico

  I've an entity LearningUnit that has an int primary key. Actually, it has nothing more. Entity Concept has the following relationship with it: @ManyToOne @Size(min=1,max=7) private LearningUnit learningUnit; In a constructor of Concept I need to retrieve the LearningUnit with the greatest primary key. If no LearningUnit exists yet I instantiate one. I then set this.learningUnit to the retrieved/instantied. Finally, I call the empty constructor of Concept in a try-catch block, to have the entitymanager do the cardinality check. If an exception is thrown (I expect one in the case that already another 7 Concepts are referring to the same LearningUnit. In that case, I case instantiate a new LearningUnit with a new greater primary key. Please, also point out, if any, clear pitfalls in my outlined algorithm above.

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• iPhone , core data, whether NSManagedObject use lazy load mechanism when it was create ?

  - by Robin

  Hi, all, I have use core data in app, I have definite a class that most like as follows: @interface Master : NSManagedObject { } @property (nonatomic, retain) NSSet* Details; .... the entity Master contains a property 'Details' that is relate to another table, this is typical Master-Details relationship, I trace the app , but I find a issue that the property 'Details' value was construct even it never be invoked ..... but I consider that the core data 'should' use some lazy mechanism to improve performance, or maybe I miss some configure step ? because the Master entity contains at least five 'Child' table properties , I have to consider this problem before use the core data .... any help ? thanks for your time!

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• Drupal Views limiting content posted by group membership

  - by digital

  Hi, I have various different content types and I want to filter by using views. So say a block only displays content posted in groups that you are a member of. I've created my generic view which so far displays all content of that type, but I'm struggling with linking this to content only posted in groups your a member of. I've looked at the Organic Groups filters but no luck there. I suspect I might need to use some sort of relationship but I'm stuck there. Any help would be greatly appreciated.

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• 'Recursive' LINQ calls

  - by Sir Psycho

  Hi, I'm trying to build an XML tree of some data with a parent child relationship, but in the same table. The two fields of importance are CompetitionID ParentCompetitionID Some data might be CompetitionID=1, ParentCompetitionID=null CompetitionID=2, ParentCompetitionID=1 CompetitionID=3, ParentCompetitionID=1 The broken query I have simply displays results in a flat format. Seeing that I'm working with XML, some sort of recursive functionality is required. I can do this using recursion, but would like to see the linq version. Any help appreciated. var results = from c1 in comps select new { c.CompetitionID, SubComps= from sc in comps.Where (c2 => c2.CompetitionID == c1.CompetitionID) select sc };

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• how to made one-to-one bidirectional relationships in grails?

  - by user369759

  I have two domain classes and want to have one-to-one BIDIRECTIONAL relation between them. I write: class Person { Book book; String name Integer age Date lastVisit static constraints = { book unique: true // "one-to-one". Without that = "Many-to-one". } } class Book { String title Date releaseDate String ISBN static belongsTo = [person:Person] // it makes relationship bi-directional regarding the grails-docs } So, i want to have bi-directional, i could NOT find link from Book to Person in generated SQL: CREATE TABLE `book` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `version` bigint(20) NOT NULL, `isbn` varchar(255) NOT NULL, `release_date` datetime NOT NULL, `title` varchar(255) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM AUTO_INCREMENT=2 DEFAULT CHARSET=latin1 So then it means it is not bidirectional then? How to make bidirectional?

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• Select an entity according to a list of associated entities

  - by Maverickch

  I have the following database schema : Two tables, books and tags, with n-m relationship. Books - Tags We can have for example the book 1, with tags {A,B,C}, and book 2, with tags {A}. I would like to select the books according to a list of tags. For example : selected tags list : {A,B} - book 1 My idea was to use the MINUS SQL function, to subtract book tags list to the selected tags list, and return the book if the list was empty. Unfortunately, this SQL function is not supported by HQL. Any idea about that ?

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• Symfony 1.4: Deleting a sfGuardUser

  - by Tom

  Hi, I'm having some trouble with the following... I have a sfGuardUser table set up normally, and it has a one-to-one relationship with a Profile table, which contains some additional user info. When a user wants to delete themselves from the site, I'd like to retain their info in the Profile table for various purposes BUT delete the sfGuardUser in order to keep that table cleaner/shorter (not just set it to inactive). I was under the impression that I could set the FK in the Profile table to NULL and then delete the sfGuardUser, but it seems the FK-constraint fails. Indeed, it seems I can't delete either and the queries fail: If I try to delete the sfGuardUser, the Profile table will have an invalid FK If I try to delete a Profile, the sfGuardUser will have an invalid FK Other than leaving outdated sfGuardUsers and Profiles in these tables, or having to use a cascaded delete to get rid of both, can anyone tell me if there's any other way around this? Thank you.

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• Storing object into cache using Linq classes and velocity

  - by Arun

  I careated couple of linq classes & marked the datacontext as unidirectional. Out of four classes; one is main class while other three are having the one to many relationship with first one; When I load the object of main class & put into the memory OR serialize it into an XML file; I never get the child class data while it is maked as DataContractAttribute. How can I force object to put the child class data into XML file or into cache ?

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• Implementing a 'many-to-many' database

  - by Raven Dreamer

  Greetings, stack*overflow* In my database, I already have one table, 'contacts' that contains records of individual people. I also have several other tables in my database which represent "skill sets" that contain records denoting a particular skill. 1) Am I correct in plotting this as a "many-to-many" relationship? (each contact can have multiple skill sets, and each skill set can belong to multiple contacts) 2) I'm new to databases -- do I want to link the tables? 3) Is there a way to implement this in my program (C# + windows forms) such that for any given record in the 'contacts' table, either the names of all associated 'skill set' tables or all the 'skill' records associated with the 'contact' record could be retrieved? (Database is located on SQL Server Express 2008)

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• Reduce the number of queries in EF

  - by Gio2k

  I have the following Model: Entities: Product (Contains basic data for products: price, etc) Attribute (Contains data for all possible optional attributes) ProductAttribute (Contains data for optional attributes of a product, eg. Color, Model, Size). ProductAttribute is essentially a many to many relationship with payload (ProductId, AttributeID, Value) And this piece of code: private static void ListAttributes(Product p) { p.ProductAttributes.Load(); foreach (var att in p.ProductAttributes) { att.Attribute.load(); Console.WriteLine("\tAttribute Name:{0} - Value {1}", att.Attribute.Name, att.AttributeValue); } } This piece of code will fire a query for each time the att.Attribute.Load() method is called in the foreach loop, only so i can get display the name of the attribute. I would like to fetch the Attribute.Name together with the query that fetches all attribute values, i.e. join ProductAttribute and Attribute. Is there any way to achieve this within my method?

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