fk relationship - Page 12

Implementing EAV pattern with Hibernate for User -> Settings relationship

- by Trevor

I'm trying to setup a simple EAV pattern in my web app using Java/Spring MVC and Hibernate. I can't seem to figure out the magic behind the hibernate XML setup for this scenario. My database table "SETUP" has three columns: user_id (FK) setup_item setup_value The database composite key is made up of user_id | setup_item Here's the Setup.java class: public class Setup implements CommonFormElements, Serializable { private Map data = new HashMap(); private String saveAction; private Integer speciesNamingList; private User user; Logger log = LoggerFactory.getLogger(Setup.class); public String getSaveAction() { return saveAction; } public void setSaveAction(String action) { this.saveAction = action; } public User getUser() { return user; } public void setUser(User user) { this.user = user; } public Integer getSpeciesNamingList() { return speciesNamingList; } public void setSpeciesNamingList(Integer speciesNamingList) { this.speciesNamingList = speciesNamingList; } public Map getData() { return data; } public void setData(Map data) { this.data = data; } } My problem with the Hibernate setup, is that I can't seem to figure out how to map out the fact that a foreign key and the key of a map will construct the composite key of the table... this is due to a lack of experience using Hibernate. Here's my initial attempt at getting this to work: <composite-id> <key-many-to-one foreign-key="id" name="user" column="user_id" class="Business.User"> <meta attribute="use-in-equals">true</meta> </key-many-to-one> </composite-id> <map lazy="false" name="data" table="setup"> <key column="user_id" property-ref="user"/> <composite-map-key class="Command.Setup"> <key-property name="data" column="setup_item" type="string"/> </composite-map-key> <element column="setup_value" not-null="true" type="string"/> </map> Any insight into how to properly map this common scenario would be most appreciated!

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Map One-To-One Relationship Doesn't Allow Inserting

- by nfplee

Hi, I'm trying to setup a one-to-one mapping from my Users to the UserDetails table. Say I have the following tables in my database: Users: - UserID (PK, Identity) - UserName - Password UsersDetails: - UserID (PK, FK) - FirstName - LastName I have created the following poco classes: public class User { public virtual int UserID { get; set; } public virtual string UserName { get; set; } public virtual string Password { get; set; } public virtual UserDetails Details { get; set; } } public class UserDetails { public virtual int UserID { get; set; } public virtual User User { get; set; } public virtual string FirstName { get; set; } public virtual string LastName { get; set; } public UserDetails() { } public UserDetails(User user) { User = user; } } Which are fluently mapped (please note the xml mapping is very similar and if all you know is the xml mapping then I would still appreciate you guidance): public class UserMap : ClassMap<User> { public UserMap() { Table("Users"); Id(x => x.UserID); Map(x => x.UserName); Map(x => x.Password); HasOne(x => x.Details) .Constrained() .Cascade.All(); } } public class UserDetailsMap : ClassMap<UserDetails> { public UserDetailsMap() { Table("UsersDetails"); Id(x => x.UserID) .GeneratedBy.Foreign("User"); HasOne(x => x.User) .Constrained(); Map(x => x.FirstName); Map(x => x.LastName); } } Everything displays correctly but if I say: var user = new User() { UserName = "Test", Password = "Test" }; user.Details = new UserDetails(user) { FirstName = "Test", LastName = "Test" }; session.Save(user); I get the error: "NHibernate.Id.IdentifierGenerationException: null id generated for: UserDetails." I'd really appreciate it if someone could show me what I've done wrong. Thanks

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Core Data error when assigning variable with one-to-one relationship

- by Hoang Pham

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How to reset parent child relationship between nested div

- by Shantanu Gupta

I am new to CSS designing and not aware of most of the properties of CSS. I am creating a layout for a web page. I am using div in my layout. My structure is somewhat like this <div id="content1_bg"> <div> <div class="content1_title_img_div"></div> <div class="content1_title_txt_div"></div> <div class="content1_dvider_div"></div> <div class="content1_content_div"></div> </div> <div></div> <div></div> </div> For this my CSS is #content1_bg div{width:250px;height:220px;float:left;border:3px solid blue; margin:20px;} .content1_title_img_div{width:50px;height:100px;} .content1_title_txt_div{width:150px;height:100px;} .content1_dvider_div{width:100%;height:10%;clear:both;} .content1_content_div{width:100%;height:50%;clear:both;} For this layout i was expecting my design to be like ---------------- |BOX1 BOX2 | ---------------- | BOX 3 | ---------------- | BOX 4 | ---------------- But on using my css layout is somewhat like this -------------------- | | | | | |BOX1| | BOX2| | | | | | | -------------------- | | |BOX3| | | -------------------- | | |BOX4| | | Basically i want my inner div's not to inherit the properties of outer div. How can i remove this inheritance relationship between parent div and child div

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Modeling a Generic Relationship in a Database

- by StevenH

This is most likely one for all you sexy DBAs out there: How would I effieciently model a relational database whereby I have a field in an "Event" table which defines a "SportType". This "SportsType" field can hold a link to different sports tables E.g. "FootballEvent", "RubgyEvent", "CricketEvent" and "F1 Event". Each of these Sports tables have different fields specific to that sport. My goal is to be able to genericly add sports types in the future as required, yet hold sport specific event data (fields) as part of my Event Entity. Is it possible to use an ORM such as NHibernate / Entity framework which would reflect such a relationship? I have thrown together a quick C# example to express my intent at a higher level: public class Event<T> where T : new() { public T Fields { get; set; } public Event() { EventType = new T(); } } public class FootballEvent { public Team CompetitorA { get; set; } public Team CompetitorB { get; set; } } public class TennisEvent { public Player CompetitorA { get; set; } public Player CompetitorB { get; set; } } public class F1RacingEvent { public List<Player> Drivers { get; set; } public List<Team> Teams { get; set; } } public class Team { public IEnumerable<Player> Squad { get; set; } } public class Player { public string Name { get; set; } public DateTime DOB { get; set;} }

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Add objects in relationship not work using MagicalRecord saveWithBlock

- by yong ho

The code to perform a save block: [MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) { for (NSDictionary *stockDict in objects) { NSString *name = stockDict[@"name"]; Stock *stock = [Stock MR_createInContext:localContext]; stock.name = name; NSArray *categories = stockDict[@"categories"]; if ([categories count] > 0) { for (NSDictionary *categoryObject in categories) { NSString *categoryId = categoryObject[@"_id"]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"categoryId == %@", categoryId]; NSArray *matches = [StockCategory MR_findAllWithPredicate:predicate inContext:localContext]; NSLog(@"%@", matches); if ([matches count] > 0) { StockCategory *cat = [matches objectAtIndex:0]; [stock addCategoriesObject:cat]; } } } } } completion:^(BOOL success, NSError *error) { }]; The Stock Model: @class StockCategory; @interface Stock : NSManagedObject @property (nonatomic, retain) NSString * name; @property (nonatomic, retain) NSSet *categories; @end @interface Stock (CoreDataGeneratedAccessors) - (void)addCategoriesObject:(StockCategory *)value; - (void)removeCategoriesObject:(StockCategory *)value; - (void)addCategories:(NSSet *)values; - (void)removeCategories:(NSSet *)values; @end The json look like this: [ { "name": "iPad mini ", "categories": [ { "name": "iPad", "_id": "538c655fae9b3e1502fc5c9e", "__v": 0, "createdDate": "2014-06-02T11:51:59.433Z" } ], }, { "name": "iPad Air ", "categories": [ { "name": "iPad", "_id": "538c655fae9b3e1502fc5c9e", "__v": 0, "createdDate": "2014-06-02T11:51:59.433Z" } ], } ] Open the core data pro, You can see only stock with the name of "iPad air" has it's categories saved. I just can't figure out why. You can see in the saveWithBlock part, I first find in the context for the same _id as in json, and then add the category object in the relationship. It's working, but not all of them. Why is that?

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Caching a column in a polymorphic relationship

- by Brendon Muir

I have content management system application that uses a polymorphic tree table as the core of its arrangement. I've come into a problem where once the tree grows quite large, and because we have quite a few different modules (about 25), just doing :include = :instance doesn't cut the mustard. Instance is the name of our polymorphic relationship. The funny part is that in most cases when I want a large list of these items, all I really want is their name from the associated table (for the purposes of an index bar for example), all the rest is in the central table. So I thought that I should probably implement some sort of column cache for the name in the central table. (Like a counter cache that rails already does). I was just wondering if a plugin exists to manage this already? If not, I was just going to add a 'name' column to the central table and because all the polymorphic models inherit off a superclass, just add a callback that pushes the name across to the central table whenever the item is created or updated. I'd then just do a big migration to populate it in the first place? Any flaws to that design? I suppose to be more flexible the column could be some kind of serialised cache where I could store other things later on if need be? Gah! :D

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NSPredicate case-insensitive matching on to-many relationship

- by Brian Webster

I am implementing a search field where the user can type in a string to filter the items displayed in a view. Each object being displayed has a keywords to-many relationship, and I would like to be able to filter the objects based on their keywords. Each keyword object has a name property, so I've set up an NSPredicate to do the filtering that looks like this: NSPredicate* predicate = [NSPredicate predicateWithFormat:@"keywords.name CONTAINS %@", self.searchString]; This works, but the problem is that the search is case-sensitive, so if the keyword has a capital letter but the user types in all lowercase, no matches are found. I've tried the following modification: NSPredicate* predicate = [NSPredicate predicateWithFormat:@"keywords.name CONTAINS[c] %@", self.searchString]; But that doesn't make any difference in the case sensitivity of the matching. Is there a way to do this case-insensitive matching using just a plain predicate? Or will I need to implement some sort of custom accessor on the keyword class, e.g. write a lowercaseName method and match against a lowercased version of the search string instead? Addendum: After further exploration, the workaround of adding a custom accessor works OK for manual use of NSPredicate, but does not work at all when using NSFetchRequest with Core Data, which only works when querying attributes defined in the Core Data model.

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Core Data 1-to-many relationship: List all related objects as section header in UITableView

- by Snej

Hi: I struggle with Core Data on the iPhone about the following: I have a 1-to-many relationship in Core Data. Assume the entities are called recipe and category. A category can have many recipes. I accomplished to get all recipes listed in a UITableView with section headers named after the category. What i want to achieve is to list all categories as section header, even those which have no recipe: category1 <--- this one should be displayed too category2 recipe_x recipe_y category3 recipe_z NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Recipe" inManagedObjectContext:managedObjectContext]; [fetchRequest setEntity:entity]; [fetchRequest setFetchBatchSize:10]; NSSortDescriptor *sortDescriptor1 = [[NSSortDescriptor alloc] initWithKey:@"category.categoryName" ascending:YES]; NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey:@"recipeName" ascending:YES]; NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor1,sortDescriptor2, nil]; [fetchRequest setSortDescriptors:sortDescriptors]; NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:@"category.categoryName" cacheName:@"Recipes"]; What is the most elegant way to achieve this with core data?

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Core Data Relationship problem

- by awattar

I have a very simple model with two objects: Name and Category. One Name can be in many Categories (it's one way relationship). I'm trying to create 8 Categories every with 8 Names. Example code: NSMutableArray *localArray = [NSMutableArray arrayWithObjects: [NSMutableDictionary dictionaryWithObjectsAndKeys: @"g1", @"Name", @"g1", @"Icon", [NSNumber numberWithBool:YES] , @"Male", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"g2", @"Name", @"g2", @"Icon", [NSNumber numberWithBool:YES] , @"Male", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"g3", @"Name", @"g3", @"Icon", [NSNumber numberWithBool:YES] , @"Male", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"g4", @"Name", @"g4", @"Icon", [NSNumber numberWithBool:YES] , @"Male", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"g5", @"Name", @"g5", @"Icon", [NSNumber numberWithBool:YES] , @"Male", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"g6", @"Name", @"g6", @"Icon", [NSNumber numberWithBool:YES] , @"Male", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"g7", @"Name", @"g7", @"Icon", [NSNumber numberWithBool:YES] , @"Male", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"g8", @"Name", @"g8", @"Icon", [NSNumber numberWithBool:YES] , @"Male", nil], nil]; NSMutableArray *localArray2 = [NSMutableArray arrayWithObjects: [NSMutableDictionary dictionaryWithObjectsAndKeys: @"Test1", @"Name", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"Test2", @"Name", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"Test3", @"Name", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"Test4", @"Name", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"Test5", @"Name", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"Test6", @"Name", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"Test7", @"Name", nil], [NSMutableDictionary dictionaryWithObjectsAndKeys: @"Test8", @"Name", nil], nil]; NSError *error; NSManagedObjectContext *moc = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; for(NSMutableDictionary *item in localArray) { NSManagedObject *category = [NSEntityDescription insertNewObjectForEntityForName:@"Category" inManagedObjectContext:managedObjectContext]; [category setValue:[item objectForKey:@"Name"] forKey:@"Name"]; [category setValue:[item objectForKey:@"Icon"] forKey:@"Icon"]; [category setValue:[item objectForKey:@"Male"] forKey:@"Male"]; for(NSMutableDictionary *item2 in localArray2) { NSManagedObject *name = [NSEntityDescription insertNewObjectForEntityForName:@"Name" inManagedObjectContext:managedObjectContext]; [name setValue:[item2 objectForKey:@"Name"] forKey:@"Name"]; [[name mutableSetValueForKey:@"CategoryRelationship"] addObject:category]; } } [moc save:&error]; And here's a problem - i've checked that 8 Categories are saved, 64 Names are saved but only 8 from all Names are connected with any category. So when i query for Names in Categories [NSPredicate predicateWithFormat:@"CategoryRelationship.@count != 0"] there are 8 elements and when [NSPredicate predicateWithFormat:@"CategoryRelationship.@count = 0"] there are 56 elements. What is going one here?

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How to prevent Hibernate from nullifying relationship column during entity removal

- by Grzegorz

I have two entities, A and B. I need to easily retrieve entities A, joined with entities B on the condition of equal values of some column (some column from A equal to some column in B). Those columns are not primary or foreign keys, they contain same business data. I just need to have access from each instance of A to the collection of B's with the same value of this column. So I model it like this: class A { @OneToMany @JoinColumn(name="column_in_B", referencedColumnName="column_in_A") Collection<B> bs; This way, I can run queries like "select A join fetch a.bs b where b...." (Actually, the real relationship here is many-to-many. But when I use @ManyToMany, Hibernate forces me to use join table, which doesnt exist here. So I have to use @OneToMany as workaround). So far so good. The main problem is: whenever I delete an instance of A, hibernate calls "Update B set column_in_B = null", becuase it thinks the column_in_B is foreign key pointing at primary key in A (and because row in A is deleted, it tries to clean the foreign key in B). BUT the column_in_B IS NOT a foreign key, and can't be modified, because it causes data lost (and this column is NOT NULL anyway in my case, causing data integerity exception to be thrown). Plese help me with this. How to model such relationships with Hibernate? (I would call it "virtual relationships", or "secondary relationships" or so: as they are not based on foreign keys, they are just some shortcuts which allows for retrieving related objects and quering for them with HQL)

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When optimizing database queries, what exactly is the relationship between number of queries and siz

- by williamjones

To optimize application speed, everyone always advises to minimize the number of queries an application makes to the database, consolidating them into fewer queries that retrieve more wherever possible. However, this also always comes with the caution that data transferred is still data transferred, and just because you are making fewer queries doesn't make the data transferred free. I'm in a situation where I can over-include on the query in order to cut down the number of queries, and simply remove the unwanted data in the application code. Is there any type of a rule of thumb on how much of a cost there is to each query, to know when to optimize number of queries versus size of queries? I've tried to Google for objective performance analysis data, but surprisingly haven't been able to find anything like that. Clearly this relationship will change for factors such as when the database grows in size, making this somewhat individualized, but surely this is not so individualized that a broad sense of the landscape can't be drawn out? I'm looking for general answers, but for what it's worth, I'm running an application on Heroku.com, which means Ruby on Rails with a Postgres database.

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Efficient way to update SQL 'relationship' table

- by AmbroseChapel

Say I have three properly normalised tables. One of people, one of qualifications and one mapping people to qualifications: People: id | Name ---------- 1 | Alice 2 | Bob Degrees: id | Name --------- 1 | PhD 2 | MA People-to-degrees: person_id | degree_id --------------------- 1 | 2 # Alice has an MA 2 | 1 # Bob has a PhD So then I have to update this mapping via my web interface. (I made a mistake. Bob has a BA, not a PhD, and Alice just got her B Eng.) There are four possible states of these one-to-many relationship mappings: was true before, should now be false was false before, should now be true was true before, should remain true was false before, should remain false what I don't want to do is read the values from four checkboxes, then hit the database four times to say "Did Bob have a BA before? Well he does now." "Did Bob have PhD before? Because he doesn't any more" and so on. How do other people address this issue? I'm curious to see if someone else arrives at the same solution I did.

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Modeling a Generic Relationship (expressed in C#) in a Database

- by StevenH

This is most likely one for all you sexy DBAs out there: How would I effieciently model a relational database whereby I have a field in an "Event" table which defines a "SportType"? This "SportsType" field can hold a link to different sports tables E.g. "FootballEvent", "RubgyEvent", "CricketEvent" and "F1 Event". Each of these Sports tables have different fields specific to that sport. My goal is to be able to genericly add sports types in the future as required, yet hold sport specific event data (fields) as part of my Event Entity. Is it possible to use an ORM such as NHibernate / Entity framework / DataObjects.NET which would reflect such a relationship? I have thrown together a quick C# example to express my intent at a higher level: public class Event<T> where T : new() { public T Fields { get; set; } public Event() { EventType = new T(); } } public class FootballEvent { public Team CompetitorA { get; set; } public Team CompetitorB { get; set; } } public class TennisEvent { public Player CompetitorA { get; set; } public Player CompetitorB { get; set; } } public class F1RacingEvent { public List<Player> Drivers { get; set; } public List<Team> Teams { get; set; } } public class Team { public IEnumerable<Player> Squad { get; set; } } public class Player { public string Name { get; set; } public DateTime DOB { get; set;} }

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Java downcasting and is-A has-A relationship

- by msharma

HI, I have a down casting question, I am a bit rusty in this area. I have 2 clasess like this: class A{ int i; String j ; //Getters and setters} class B extends A{ String k; //getter and setter} I have a method like this, in a Utility helper class: public static A converts(C c){} Where C are objects that are retireved from the database and then converted. The problem is I want to call the above method by passing in a 'C' and getting back B. So I tried this: B bClasss = (B) Utility.converts(c); So even though the above method returns A I tried to downcast it to B, but I get a runtime ClassCastException. Is there really no way around this? DO I have to write a separate converts() method which returns a B class type? If I declare my class B like: class B { String k; A a;} // So instead of extending A it has-a A, getter and setters also then I can call my existing method like this: b.setA(Utility.converts(c) ); This way I can reuse the existing method, even though the extends relationship makes more sense. What should I do? Any help much appreciated. Thanks.

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Domain model for an optional many-many relationship

- by Greg

Let's say I'm modeling phone numbers. I have one entity for PhoneNumber, and one for Person. There's a link table that expresses the link (if any) between the PhoneNumber and Person. The link table also has a field for DisplayOrder. When accessing my domain model, I have several Use Cases for viewing a Person. I can look at them without any PhoneNumber information. I can look at them for a specific PhoneNumber. I can look at them and all of their current (or past) PhoneNumbers. I'm trying to model Person, not only for the standard CRUD operations, but for the (un)assignment of PhoneNumbers to a Person. I'm having trouble expressing the relationship between the two, especially with respects to the DisplayOrder property. I can think of several solutions but I'm not sure of which (if any) would be best. A PhoneNumberPerson class that has a Person and PhoneNumber property (most closely resembles database design) A PhoneCarryingPerson class that inherits from Person and has a PhoneNumber property. A PhoneNumber and/or PhoneNumbers property on Person (and vis-a-versa, a Person property on PhoneNumber) What would be a good way to model this that makes sense from a domain model perspective? How do I avoid misplaced properties (DisplayOrder on Person) or conditionally populated properties?

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EF4 Code First - Many to many relationship issue

- by Yngve B. Nilsen

Hi! I'm having some trouble with my EF Code First model when saving a relation to a many to many relationship. My Models: public class Event { public int Id { get; set; } public string Name { get; set; } public virtual ICollection<Tag> Tags { get; set; } } public class Tag { public int Id { get; set; } public string Name { get; set; } public virtual ICollection<Event> Events { get; set; } } In my controller, I map one or many TagViewModels into type of Tag, and send it down to my servicelayer for persistence. At this time by inspecting the entities the Tag has both Id and Name (The Id is a hidden field, and the name is a textbox in my view) The problem occurs when I now try to add the Tag to the Event. Let's take the following scenario: The Event is already in my database, and let's say it already has the related tags C#, ASP.NET If I now send the following list of tags to the servicelayer: ID Name 1 C# 2 ASP.NET 3 EF4 and add them by first fetching the Event from the DB, so that I have an actual Event from my DbContext, then I simply do myEvent.Tags.Add to add the tags.. Problem is that after SaveChanges() my DB now contains this set of tags: ID Name 1 C# 2 ASP.NET 3 EF4 4 C# 5 ASP.NET This, even though my Tags that I save has it's ID set when I save it (although I didn't fetch it from the DB)

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Database design - table relationship question

- by iama

I am designing schema for a simple quiz application. It has 2 tables - "Question" and "Answer Choices". Question table has 'question ID', 'question text' and 'answer id' columns. "Answer Choices" table has 'question ID', 'answer ID' and 'answer text' columns. With this simple schema it is obvious that a question can have multiple answer choices & hence the need for the answer choices table. However, a question can have only one correct answer and hence the need for the 'answer ID' in the question table. However, this 'answer ID' column in the question table provides a illusion as though there can be multiple questions for a single answer which is not correct. The other alternative to eliminate this illusion is to have another table just for correct answer that will have just 2 columns namely the question ID and the answer ID with a 1-1 relationship between the two tables. However, I think this is redundant. Any recommendation on how best to design this thereby enforcing the rules that a question can have multiple answer choices but only one correct answer? Many Thanks.

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NHibernate many-to-many relationship does not update join-table

- by Davide Vosti

I'm having trouble saving a many-to-many relationship with nhibernate. I searched and looked at almost every same question in SO and google but nothing works. The single classes are update correctly but nothing is inserted in the join-table. I have 2 classes: Event and Category. The mapping is this: Event: <bag name="Categories" access="field.camelcase-underscore" table="EventCategories" inverse="true" cascade="all-delete-orphan" lazy="true"> <key column="Event"/> <many-to-many class="Category" column="Category"/> </bag> Category: <bag name="Events" table="EventCategories" access="field.camelcase-underscore" cascade="all-delete-orphan" lazy="true" > <key column="Category"/> <many-to-many class="Event" column="Event"/> </bag> I tried to swap every parameter in both mappings but nothing works... Do you know what I'm doing wrong or have a right mapping for this case? Thank you very much!

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Entity Framework 1:1 Relationship Identity Colums

- by Hupperware

I cannot for the life of me get two separate tables to save with a relationship and two identity columns. I keep getting errors like A dependent property in a ReferentialConstraint is mapped to a store-generated column. Column: 'OlsTerminalId'. I can't imagine that this setup is abnormal. [DataContract] public class OlsData { private static readonly DateTime theUnixEpoch = new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc); [DatabaseGenerated(DatabaseGeneratedOption.Identity)] public int OlsDataId { get; set; } [DataMember(Name = "id")] public int Id { get; set; } public DateTime Timestamp { get; set; } [DataMember(Name = "created")] [NotMapped] public double Created { get { return (Timestamp - theUnixEpoch).TotalMilliseconds; } set { Timestamp = theUnixEpoch.AddMilliseconds(value); } } [InverseProperty("OlsData")] [DataMember(Name = "terminal")] public virtual OlsTerminal OlsTerminal { get; set; } } [DataContract] public class OlsTerminal { [DatabaseGenerated(DatabaseGeneratedOption.Identity)] public int OlsTerminalId { get; set; } public int OlsDataId { get; set; } [DataMember(Name = "account")] [NotMapped] public virtual OlsAccount OlsAccount { get; set; } [DataMember(Name = "terminalId")] public string TerminalId { get; set; } [DataMember(Name = "merchantId")] public string MerchantId { get; set; } public virtual OlsData OlsData { get; set; } } public class OlsDataContext : DbContext { protected override void OnModelCreating(DbModelBuilder aModelBuilder) { aModelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); } public OlsDataContext(string aConnectionString) : base(aConnectionString) {} public DbSet<OlsData> OlsData { get; set; } public DbSet<OlsTerminal> OlsTerminal { get; set; } public DbSet<OlsAccount> OlsAccount { get; set; } }

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Laravel4: Checking many-to-many relationship attribute even when it does not exist

- by Simo A.

This is my first time with Laravel and also Stackoverflow... I am developing a simple course management system. The main objects are User and Course, with a many-to-many relationship between them. The pivot table has an additional attribute, participant_role, which defines whether the user is a student or an instructor within that particular course. class Course extends Eloquent { public function users() { return $this->belongsToMany('User')->withPivot('participant_role')->withTimestamps(); } } However, there is an additional role, system admin, which can be defined on the User object. And this brings me mucho headache. In my blade view I have the following: @if ($course->pivot->participant_role == 'instructor') { // do something here... } This works fine when the user has been assigned to that particular $course and there is an entry for this user-course combination in the pivot table. However, the problem is the system administrator, who also should be able to access course details. The if-clause above gives Trying to get property of non-object error, apparently because there is no entry in the pivot table for system administrator (as the role is defined within the User object). I could probably solve the problem by using some off-the-shelf bundle for handling role-based permissions. Or I could (but don't want to) do something like this with two internal if-clauses: if (!empty($course->pivot)) { if ($course->pivot->participant_role == 'instructor') { // do something... } } Other options (suggested in partially similar entries in Stackoverflow) would include 1) reading all the pivot table entries to an array, and use in_array to check if a role exists, or even 2) SQL left join to do this on database level. However, ultimately I am looking for a compact one-line solution? Can I do anything similar to this, which unfortunately does not seem to work? if (! empty ($course->pivot->participant_role == 'instructor') ) { // do something... } The shorter the answer, the better :-). Thanks a lot!

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Hibernate 1:M relationship ,row order, constant values table and concurrency

- by EugeneP

table A and B need to have 1:M relationship a and b are added during application runtime, so A created, then say 4 B's created. Each B instance has to come in order, so that I could later extract them in the same order as I added them. The app will be a web-app running on Tomcat, so 10 instances may work simultaneously. So my question are: 1) How to preserve inserting order, so that I could extract B instances that A references in the same order as I persisted them. That's tricky, because we add to a Collection and then it gets saved (am I right?). So, it depends on how Hibernate saves it, what if it changes the order in what we added instances? I've seen something like LIST instead of SET when describing relationships, is that what I need? 2) How to add a 3-rd column to B so that I could differentiate the instances, something like SEX(M,F,U) in B table. Do I need a special table, or there's and easy way to describe constants in Hibernate. What do you recommend? 3) Talking about concurrency, what methods do you recommend to use? There should be no collisions in the db and as you see, there might easily be some if rows are not inserted (PK added) right where it is invoked without delays ?

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NSInvalidArgumentException: Illegal attempt to establish a relationship between objects in different

- by iPhoneDollaraire

I have an app based on the CoreDataBooks example that uses an addingManagedObjectContext to add an Ingredient to a Cocktail in order to undo the entire add. The CocktailsDetailViewController in turn calls a BrandPickerViewController to (optionally) set a brand name for a given ingredient. Cocktail, Ingredient and Brand are all NSManagedObjects. Cocktail requires at least one Ingredient (baseLiquor) to be set, so I create it when the Cocktail is created. If I add the Cocktail in CocktailsAddViewController : CocktailsDetailViewController (merging into the Cocktail managed object context on save) without setting baseLiquor.brand, then it works to set the Brand from a picker (also stored in the Cocktails managed context) later from the CocktailsDetailViewController. However, if I try to set baseLiquor.brand in CocktailsAddViewController, I get: Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Illegal attempt to establish a relationship 'brand' between objects in different contexts' From this question I understand that the issue is that Brand is stored in the app's managedObjectContext and the newly added Ingredient and Cocktail are stored in addingManagedObjectContext, and that passing the ObjectID instead would avoid the crash. What I don't get is how to implement the picker generically so that all of the Ingredients (baseLiquor, mixer, garnish, etc.) can be set during the add, as well as one-by-one from the CocktailsDetailViewController after the Cocktail has been created. In other words, following the CoreDataBooks example, where and when would the ObjectID be turned into the NSManagedObject from the parent MOC in both add and edit cases? -IPD UPDATE - Here's the code: - (IBAction)addCocktail:(id)sender { CocktailsAddViewController *addViewController = [[CocktailsAddViewController alloc] init]; addViewController.title = @"Add Cocktail"; addViewController.delegate = self; // Create a new managed object context for the new book -- set its persistent store coordinator to the same as that from the fetched results controller's context. NSManagedObjectContext *addingContext = [[NSManagedObjectContext alloc] init]; self.addingManagedObjectContext = addingContext; [addingContext release]; [addingManagedObjectContext setPersistentStoreCoordinator:[[fetchedResultsController managedObjectContext] persistentStoreCoordinator]]; Cocktail *newCocktail = (Cocktail *)[NSEntityDescription insertNewObjectForEntityForName:@"Cocktail" inManagedObjectContext:self.addingManagedObjectContext]; newCocktail.baseLiquor = (Ingredient *)[NSEntityDescription insertNewObjectForEntityForName:@"Ingredient" inManagedObjectContext:self.addingManagedObjectContext]; newCocktail.mixer = (Ingredient *)[NSEntityDescription insertNewObjectForEntityForName:@"Ingredient" inManagedObjectContext:self.addingManagedObjectContext]; newCocktail.volume = [NSNumber numberWithInt:0]; addViewController.cocktail = newCocktail; UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:addViewController]; [self.navigationController presentModalViewController:navController animated:YES]; [addViewController release]; [navController release]; }

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One-to-many relationship with JDO in Google App Engine

- by Marvin

I've followed the GAE docs on setting up one-to-many relationship in JDO but I'm still having trouble in retrieving the collection data back. I have no problem getting the other non-collection fields back. Here are my classes: @PersistenceCapable public class User{ @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key key; @Persistent private String uniqueId; @Persistent private String email; @Persistent private List<Address> addresses = new ArrayList<Address>() ; ... } @PersistenceCapable public class Phone{ @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key key; @Persistent private String number; ... } public class UserDaoImpl implements UserDao { public void insertUser(User user) { if(user.getKey() == null) { com.google.appengine.api.datastore.Key key = KeyFactory.createKey(User.class.getSimpleName(), user.getEmail()); user.setKey(key); } PersistenceManager pm = PersistenceManagerWrapper.getPersistenceManager(); notNull(user); try { pm.makePersistent(user); } finally { pm.close(); } } @SuppressWarnings("unchecked") public User getUser(String uniqueId) { PersistenceManager pm = PersistenceManagerWrapper.getPersistenceManager(); Query query = pm.newQuery(User.class); query.setFilter("uniqueId == uniqueIdParam"); query.declareParameters("String uniqueIdParam"); User user = null; try { List<User> users = (List<User>)(query.execute(uniqueId)); //TODO abstract this if(users.size() > 0) user = users.get(0); } finally { pm.close(); } return user; } } public class UserDaoImplTest { @Test public void getUserTest() { User user = createTestUser(); assertNotNull("The user object should not be null", user); userDao.insertUser(user); User returnedUser = userDao.getUser(TEST_USER_ID); assertNotNull("The returnedUser object should not be null", returnedUser); Assert.assertPropertyEqualsExcludeProperties("User Object", user, returnedUser, ""); } } When I run the test, all the properties for User is populated but the list of Phone if I get is empty.

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Complex relationship between tables in NHibernate

- by Ilya Kogan

Hi all, I'm writing a Fluent NHibernate mapping for a legacy Oracle database. The challenge is that the tables have composite primary keys. If I were at total freedom, I would redesign the relationships and auto-generate primary keys, but other applications must write to the same database and read from it, so I cannot do it. These are the two tables I'll focus on: Example data Trips table: 1, 10:00, 11:00 ... 1, 12:00, 15:00 ... 1, 16:00, 19:00 ... 2, 12:00, 13:00 ... 3, 9:00, 18:00 ... Faults table: 1, 13:00 ... 1, 23:00 ... 2, 12:30 ... In this case, vehicle 1 made three trips and has two faults. The first fault happened during the second trip, and the second fault happened while the vehicle was resting. Vehicle 2 had one trip, during which a fault happened. Constraints Trips of the same vehicle never overlap. So the tables have an optional one-to-many relationship, because every fault either happens during a trip or it doesn't. If I wanted to join them in SQL, I would write: select ... from Faults left outer join Trips on Faults.VehicleId = Trips.VehicleId and Faults.FaultTime between Trips.TripStartTime and Trips.TripEndTime and then I'd get a dataset where every fault appears exactly once (one-to-many as I said). Note that there is no Vehicles table, and I don't need one. But I did create a view that contains all VehicleIds from both tables, so I can use it as a junction table. What am I actually looking for? The tables are huge because they cover years of data, and every time I only need to fetch a range of a few hours. So I need a mapping and a criteria that will run something like the following SQL underneath: select ... from Faults left outer join Trips on Faults.VehicleId = Trips.VehicleId and Faults.FaultTime between Trips.TripStartTime and Trips.TripEndTime where Faults.FaultTime between :p0 and :p1 Do you have any ideas how to achieve it? Note 1: Currently the application shouldn't write to the database, so persistence is not a must, although if the mapping supports persistence, it may help at some point in the future. Note 2: I know it's a tough one, so if you give me a great answer, you will be properly rewarded :) Thank you for reading this long question, and now I only hope for the best :)

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