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  • Inverse relationship of two variables

    - by Jam
    this one is maybe pretty stupid.. Or I am just exhausted or something, but I just cant seem to solve it.. Problem : two variables X and Y, value of Y is dependent on value of X. X can have values ranging from some value to some value (lets say from 0 to 250) and y can have different values (lets say from 0.1 to 1.0 or something..) - but it is inverse relatonship (what I mean is: if value of X is e.g. 250, then value of Y would be 0.1 and when X decreases up to 0, value of Y raises up to 1.0.. So how should I do it? lets say I have function: -- double computeValue (double X) { /computation/ return Y; } Also, is there some easy way to somehow make the scaling of the function not so linear? - For example when X raises, Y decreases slower at first but then more rapidly in the end.. (rly dont know how to say it but I hope you guys got it) Thanks in advance for this stupid question :/

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  • The Columns in table <table> do not match an existing primary key or unique constraint

    - by Sven
    I have 2 tables, Stores - storeId (int) and year (int(4)) both Primary Keys. fruit - fruitId - Primary Key and storeId. I need to create 1 to many relationship between the Store and Fruit (Foreign Key held within Fruit) how ever I always get shown the error - The Columns in table <table> do not match an existing primary key or unique constraint. The type's are both int and named the same. Any help would be appreciate in advance, many thanks.

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  • JDO in Google App Engine: order of keys in unowned one-to-many relationship

    - by Kel
    I'm implementing web application with JDO in Google App Engine. According to documentation, in owned one-to-many relationships, order of elements in "owner" object collection is determined either by automatically created index field, or by information given in explicit ordering clause. For example: @PersistenceCapable public class Person { // ... @Order(extensions = @Extension(vendorName="datanucleus", key="list-ordering", value="country asc, city asc")) private List<ContactInfo> contacts = new List<ContactInfo>(); In unowned relationships, "owner" object contains collection of keys of "nested" objects, for example: @PersistenceCapable public class Author { // ... @Persistent private List<Key> books; Is order of keys preserved, if I use List<Key> collection in "owner" object for storing keys of "nested" elements? I could not find answer neither in JDO relationships article, nor in Data Classes article :(

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  • 'Locale' configuration and its relationship with Windows API

    - by The Kaykay
    Can the locale configuration of a system OR the keyboard type configuration of that system in anyway affect which API is called at the Kernel level? To be specific, if a program is invoking 'CreateFile()' API then the windows API documentation says that the call gets delegated to either CreateFileA or CreateFileW. If that program is being run on a system present in China with a Chinese Keyboard then which of the two functions will be called?

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  • Spring-Hibernate: How to submit a for when the object has one-to-many relations?

    - by Czar
    Hi, I have a form changeed the properties of my object CUSTOMER. Each customer has related ORDERS. The ORDER's table has a column customer_id which is used for the mapping. All works so far, I can read customers without any problem. When I now e.g. change the name of the CUSTOMER in the form (which does NOT show the orders), after saving the name is updated, but all relations in the ORDERS table are set to NULL (the customer_id for the items is set to NULL. How can I keep the relationship working? THX

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  • django sort by manytomany relationship

    - by Marconi
    I have the following model: class Service(models.Model): ratings = models.ManyToManyField(User) Now if I wanna get all the service with ratings sorted in descending order I did something: services_list = Service.objects.filter(ratings__gt=0).distinct() services_list = list(services_list) services_list.sort(key=lambda service: service.ratings.all().count(), reverse=True) As you can see its a three step process and I don't feel right about this. Anybody who knows a better way to do this?

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  • Doctrine2 - relationship

    - by Filip Golonka
    I'm developing an application, which is looking for optimal route and timetable in public transport. I have some experience about Doctrine1, but it's my first time with Doctrine2. There is soem new fields to describe relations (mappedBy and inversedBy) and also some new ways of mapping. I have following code: $query = $this->em->createQuery("SELECT partial cls.{stop}, partial t.{arriveTime, departureTime} FROM \Entities\Timetable t JOIN t.ride r JOIN t.carrierLineStop cls WHERE t.departureTime>=:time AND r.idCarrierLine=:carrierLine AND (cls.idStop=:firstStop OR cls.idStop=:lastStop)"); $query->setParameters(array( 'time' => $time, 'carrierLine' => $path->getLine(), 'firstStop' => $path->getFirstStop(), 'lastStop' => $path->getLastStop() )); When I try to execute that script I've got an error: [Semantical Error] line 0, col 24 near '}, partial t.{arriveTime,': Error: There is no mapped field named 'stop' on class Entities\CarrierLineStop. Mapping files: Entities\CarrierLineStop: type: entity table: carrier_line_stop fields: idCarrierLineStop: id: true type: integer unsigned: false nullable: false column: id_carrier_line_stop generator: strategy: IDENTITY nextStop: type: integer unsigned: false nullable: true column: next_stop manyToOne: idCarrierLine: targetEntity: Entities\CarrierLine cascade: { } mappedBy: null inversedBy: null joinColumns: id_carrier_line: referencedColumnName: id_carrier_line orphanRemoval: false stop: column: id_stop targetEntity: Entities\Stop cascade: { } mappedBy: null inversedBy: carrierLineStop joinColumns: id_stop: referencedColumnName: id_stop orphanRemoval: false lifecycleCallbacks: { } - Entities\Stop: type: entity table: stop fields: idStop: id: true type: integer unsigned: false nullable: false column: id_stop generator: strategy: IDENTITY name: type: string length: 45 fixed: false nullable: true miejscowosc: type: string length: 45 fixed: false nullable: true latitude: type: decimal nullable: true longitude: type: decimal nullable: true oneToMany: carrierLineStop: targetEntity: Entities\CarrierLineStop cascade: { } mappedBy: stop inversedBy: null joinColumns: id_stop: referencedColumnName: id_stop orphanRemoval: false lifecycleCallbacks: { } I have no idea about where the problem is...

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  • Enity framework not loading relationship even when using include

    - by dilbert789
    I have this code: Category selectedCategory = (from c in DB.Category.Include("SubCategory") join a in DB.Accessory on c.AccCatUID equals a.Category.AccCatUID where a.AccUID == currentAccessory.AccUID select c).FirstOrDefault(); It works fine, selectedCategory gets populated as expected. BUT selectedCategory has a child table 'SubCategory' which does not get loaded even though there is the include there. It is not loaded until I do this: selectedCategory.SubCategory.Load(); Why do I have to call load explicitly in order to load the child table?

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  • how to model a many to many relationship

    - by Maulin
    Here is the scenario, Articles have many Comments Users can write many Comments for many Articles The comments table contains both user_id article_id as foreign keys My models are set up like so class User < ActiveRecord::Base has_many :comments has_many :articles, :through => :comments class Article < ActiveRecord::Base has_many :comments has_many :users, :through => :comments class Comment < ActiveRecord::Base belongs_to :users belongs_to :articles My routes.rb has the following code map.resources :articles, :has_many => :comments map.resources :users, :has_many => :comments which produces the following routes new_article_comment edit_article_comment new_user_comment edit_user_comment etc... This is not what I want (atleast not what I think I want), since comments must always be related to users and article, how can I get a route like so new_user_article_comment edit_user_article_comment Then I could just do new_user_article_comment_path([@user, @article]) to create a new comment

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  • JPA/Hibernate Parent/Child relationship

    - by NubieJ
    Hi I am quite new to JPA/Hibernate (Java in general) so my question is as follows (note, I have searched far and wide and have not come across an answer to this): I have two entities: Parent and Child (naming changed). Parent contains a list of Children and Children refers back to parent. e.g. @Entity public class Parent { @Id @Basic @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "PARENT_ID", insertable = false, updatable = false) private int id; /* ..... */ @OneToMany(cascade = { CascadeType.ALL }, fetch = FetchType.LAZY) @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID", nullable = true) private Set<child> children; /* ..... */ } @Entity public class Child { @Id @Basic @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "CHILD_ID", insertable = false, updatable = false) private int id; /* ..... */ @ManyToOne(cascade = { CascadeType.REFRESH }, fetch = FetchType.EAGER, optional = false) @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID") private Parent parent; /* ..... */ } I want to be able to do the following: Retrieve a Parent entity which would contain a list of all its children (List), however, when listing Parent (getting List, it of course should omit the children from the results, therefore setting FetchType.LAZY. Retrieve a Child entity which would contain an instance of the Parent entity. Using the code above (or similar) results in two exceptions: Retrieving Parent: A cycle is detected in the object graph. This will cause infinitely deep XML... Retrieving Child: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: xxxxxxxxxxx, no session or session was closed When retrieving the Parent entity, I am using a named query (i.e. calling it specifically) @NamedQuery(name = "Parent.findByParentId", query = "SELECT p FROM Parent AS p LEFT JOIN FETCH p.children where p.id = :id") Code to get Parent (i.e. service layer): public Parent findByParentId(int parentId) { Query query = em.createNamedQuery("Parent.findByParentId"); query.setParameter("id", parentId); return (Parent) query.getSingleResult(); } Why am I getting a LazyInitializationException event though the List property on the Parent entity is set as Lazy (when retrieving the Child entity)?

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  • jpa-Primarykey relationship

    - by megala
    Hi created student entity in gogole app engine datastore using JPA. Student---Coding @Entity @Table(name="StudentPersonalDetails", schema="PUBLIC") public class StudentPersonalDetails { @Id @Column(name = "STUDENTNO") private Long stuno; @Basic @Column(name = "STUDENTNAME") private String stuname; public void setStuname(String stuname) { this.stuname = stuname; } public String getStuname() { return stuname; } public void setStuno(Longstuno) { this.stuno = stuno; } public Long getStuno() { return stuno; } public StudentPersonalDetails(Long stuno,String stuname) { this.stuno = stuno; this.stuname = stuname; } } I stored Property value as follows Stuno Stuname 1 a 2 b If i stored Again Stuno No 1 stuname z means it wont allow to insert the record But. It Overwrite the value Stuno Stuname 1 z 2 b How to solve this?

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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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  • Access Relationship Table in Grails

    - by WaZ
    Hi, I have the following domains classes: class Posts{ String Name String Country static hasMany = [tags:Tags] static constraints = { } } class Tags{ String Name static belongsTo = Posts static hasMany = [posts:Posts] static constraints = { } String toString() { "${TypeName}" } } Grails creates an another table in the database i.e. Posts_Tags. My requirement is: E.g. 1 post has 3 tags. So, in the Posts_Tags table there are 3 rows. How can I access the table Posts_Tags directly in my code so that I can manipulate the data or add some more fields to it.

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  • EFv1 mapping 1 to many Relationship to POCOs

    - by Scott
    I'm trying to work through a problem where I'm mapping EF Entities to POCO which serve as DTO. I have two tables within my database, say Products and Categories. A Product belongs to one category and one category may contain many Products. My EF entities are named efProduct and efCategory. Within each entity there is the proper Navigation Property between efProduct and efCategory. My Poco objects are simple public class Product { public string Name { get; set; } public int ID { get; set; } public double Price { get; set; } public Category ProductType { get; set; } } public class Category { public int ID { get; set; } public string Name { get; set; } public List<Product> products { get; set; } } To get a list of products I am able to do something like public IQueryable<Product> GetProducts() { return from p in ctx.Products select new Product { ID = p.ID, Name = p.Name, Price = p.Price ProductType = p.Category }; } However there is a type mismatch error because p.Category is of type efCategory. How can I resolve this? That is, how can I convert p.Category to type Category? I know in .NET EF has added support for POCO, but I'm forced to use .NET 3.5 SP1.

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  • Django Aggregation Across Reverse Relationship

    - by Tom
    Given these two models: class Profile(models.Model): user = models.ForeignKey(User, unique=True, verbose_name=_('user')) about = models.TextField(_('about'), blank=True) zip = models.CharField(max_length=10, verbose_name='zip code', blank=True) website = models.URLField(_('website'), blank=True, verify_exists=False) class ProfileView(models.Model): profile = models.ForeignKey(Profile) viewer = models.ForeignKey(User, blank=True, null=True) created = models.DateTimeField(auto_now_add=True) I want to get all profiles sorted by total views. I can get a list of profile ids sorted by total views with: ProfileView.objects.values('profile').annotate(Count('profile')).order_by('-profile__count') But that's just a dictionary of profile ids, which means I then have to loop over it and put together a list of profile objects. Which is a number of additional queries and still doesn't result in a QuerySet. At that point, I might as well drop to raw SQL. Before I do, is there a way to do this from the Profile model? ProfileViews are related via a ForeignKey field, but it's not as though the Profile model knows that, so I'm not sure how to tie the two together. As an aside, I realize I could just store views as a property on the Profile model and that may turn out to be what I do here, but I'm still interested in learning how to better use the Aggregation functions.

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  • Creating relationship between two model instances

    - by Lowgain
    This is probably pretty simple, but here: Say I've got two models, Thing and Tag class Thing < ActiveRecord::Base has_and_belongs_to_many :tags end class Tag < ActiveRecord::Base has_and_belongs_to_many :things end And I have an instance of each. I want to link them. Can I do something like: @thing = Thing.find(1) @tag = Tag.find(1) @thing.tags.add(@tag) If not, what is the best way to do this? Thanks!

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  • JOIN in SQL with one-to-many relationship

    - by Kristopher Ives
    I'm making a tool to track calls to house/senate reps, and I have 2 tables of importance here: reps rep_id rep_name # and more info comments rep_id status # enum about result of contact comment I want to query for all reps joining the most recent associated comments and in some cases joining comments of a specific status, but there might not be any comments associated with that rep yet. THANKS!

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  • many to many relationship mysql select

    - by zeina
    Let's consider 2 tables "schools" and "students". Now a student may belong to different schools in his life, and a school have many students. So this is a many to many example. A third table "links" specify the relation between student and school. Now to query this I do the following: Select sc.sid , -- stands for school id st.uid, -- stands for student id sc.sname, -- stands for school name st.uname, -- stands for student name -- select more data about the student joining other tables for that from students s left join links l on l.uid=st.uid -- l.uid stands for the student id on the links table left join schools sc on sc.sid=l.sid -- l.sid is the id of the school in the links table where st.uid=3 -- 3 is an example this query will return duplicate data for the user id if he has more than one school, so to fix this I added group by st.uid, yet I also need the list of school name related to the same user. Is there a way to do it with fixing the query I wrote instead of having 2 queries? So as example I want to have Luci of schools ( X, Y, Z, R, ...) etc

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  • Best datastructure for this relationship...

    - by Travis
    I have a question about database 'style'. I need a method of storing user accounts. Some users "own" other user accounts (sub-accounts). However not all user accounts are owned, just some. Is it best to represent this using a table structure like so... TABLE accounts ( ID ownerID -> ID name ) ...even though there will be some NULL values in the ownerID column for accounts that do not have an owner. Or would it be stylistically preferable to have two tables, like so. TABLE accounts ( ID name ) TABLE ownedAccounts ( accountID -> accounts(ID) ownerID -> accounts(ID) ) Thanks for the advice.

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  • NHibernate - Saving simple parent-child relationship generates unnecessary selects with assigned id

    - by Alice
    Entities: public class Parent { virtual public long Id { get; set; } virtual public string Description { get; set; } virtual public ICollection<Child> Children { get; set; } } public class Child { virtual public long Id { get; set; } virtual public string Description { get; set; } virtual public Parent Parent { get; set; } } Mappings: public class ParentMap : ClassMap<Parent> { public ParentMap() { Id(x => x.Id).GeneratedBy.Assigned(); Map(x => x.Description); HasMany(x => x.Children) .AsSet() .Inverse() .Cascade.AllDeleteOrphan(); } } public class ChildMap : ClassMap<Child> { public ChildMap() { Id(x => x.Id).GeneratedBy.Assigned(); Map(x => x.Description); References(x => x.Parent) .Not.Nullable() .Cascade.All(); } } and using (var session = sessionFactory.OpenSession()) using (var transaction = session.BeginTransaction()) { var parent = new Parent { Id = 1 }; parent.Children = new HashSet<Child>(); var child1 = new Child { Id = 2, Parent = parent }; var child2 = new Child { Id = 3, Parent = parent }; parent.Children.Add(child1); parent.Children.Add(child2); session.Save(parent); transaction.Commit(); } this codes generates following sql NHibernate: SELECT child_.Id, child_.Description as Descript2_0_, child_.Parent_id as Parent3_0_ FROM [Child] child_ WHERE child_.Id=@p0;@p0 = 2 [Type: Int64 (0)] NHibernate: SELECT child_.Id, child_.Description as Descript2_0_, child_.Parent_id as Parent3_0_ FROM [Child] child_ WHERE child_.Id=@p0;@p0 = 3 [Type: Int64 (0)] NHibernate: INSERT INTO [Parent] (Description, Id) VALUES (@p0, @p1);@p0 = NULL[Type: String (4000)], @p1 = 1 [Type: Int64 (0)] NHibernate: INSERT INTO [Child] (Description, Parent_id, Id) VALUES (@p0, @p1, @p2);@p0 = NULL [Type: String (4000)], @p1 = 1 [Type: Int64 (0)], @p2 = 2 [Type:Int64 (0)] NHibernate: INSERT INTO [Child] (Description, Parent_id, Id) VALUES (@p0, @p1, @p2);@p0 = NULL [Type: String (4000)], @p1 = 1 [Type: Int64 (0)], @p2 = 3 [Type:Int64 (0)] Why are these two selects generated and how can I remove it?

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  • why does perl allow mutually "use" relationship between modules

    - by Haiyuan Zhang
    let's say there two modules mutualy use each othe as: package a; use b; sub p {} 1; package b; use a; 1; I think symatically it's wrong to wrote code like the above code, cus the two modules will endlessly copy each other's code to themselves...but I can successfully run the following code, which makes me very surprised. so could any of you explain all of this to me? #! /usr/bin/perl use a; a->p();

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