extends relationship - Page 13

Making a many-to-many relationship using DataRelations object

- by dotnetdev

Hi, I have about 200 tables which need to relate to another table in a many-to-many fashion. I have the tables (including the intersection table) ready IN SQL Server. How can I write code using the data relation object to make the relationship? The tables are: PartStatPartName PartsMaterialsIntersection << Materials The materials table needs to have a foreign key from the PartStatPartName table. I tried various approaches using the DataRelation class but the change did not sync to SQL Server, despite being connected and adding the relation, and then calling AcceptChanges() on the dataset. Any guidance much appreciated. I have seen some threads covering the same problem but need an example in code so I can follow the right method. Thanks

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One-to-many relationship related to many tables

- by Andrey

I have a scenario where: there are two (or more) tables that represent independent items. lets say Users and Companies Both of these tables need addresses stored. Each one can have one or more address In a normal 1 to many scenario Addresses table woudl just have a UserId or a CompanyId creating a normal 1 to many relationship. In this case i have a few approaches i can think of the Addresses table could have both a UserId and a CompanyId and only one would be used for each record. 2 keys could be used ObjectId and ObjectType So Object id would have a UserId or a CompanyId, and ObjectType woudl be User or Company Create an ObjectTable and add ObjectId to Users and Companies. Addresses would then have an OjbectId I do not really like any of these solutions. i am wondering what is the best approach here. On another note i will most likely user linqtosql for my data access layer.

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

- by user569139

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

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Many-to-many relationship in oop

- by Manu

what is best way to model many-to-many relationship? lets say we have a two classes , Team and Player any given Player can be in multiple Team s any Team can have as many Player s as they like I like to call methods like playerX.getTeamList() to get the list of all the Team s he/she is in teamY.getPlayerList() to get the list of all the Player s in the team (or have some other way to do this effectively) I can think of two ways of doing this , but they just don't feels like good oop pattens. can you think of any good ways , perhaps a design patten ?

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Drupal Views: Render Null Result for Relationship as 0

- by Kyle S

I have a View configured in Drupal to return nodes, sorting them by their average vote in descending order. For the purpose of the View, the value of the average votes is a Relationship. I noticed that nodes with no votes are displayed after nodes with a negative average. Nodes with no votes should have an average of 0, but I believe the MySQL JOIN is causing NULL values to be returned (as there are no matching rows in the joined table, since a row is created after the first vote is cast for that item). I discovered that with MySQL it is possible to output all values that are NULL in a column as another value with IFNULL(column_name,'other value'). I feel like I would need to modify the Views module in order to obtain this functionality, but I'm hoping that there is some sort of option that returns NULL values in a relation (a relation doesn't exist for the item) as 0 instead of NULL, so that I can properly sort the nodes. The modules I am using include Views, Voting API, Vote Up/Down, and CTools. Thanks.

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Using iPhone Core Data to many Relationship

- by BLeB

When I define a to many relationship between entities in Xcode and then generate the data class from the entity I get a header with the following methods defined: @interface PriceList (CoreDataGeneratedAccessors) - (void)addItemsObject:(PriceListItem *)value; - (void)removeItemsObject:(PriceListItem *)value; - (void)addItems:(NSSet *)value; - (void)removeItems:(NSSet *)value; @end When I attempt to call addItemsObject with the following code a doesNotRecognizeSelector exception is thrown. PriceListItem *item = [NSEntityDescription insertNewObjectForEntityForName:@"PriceListItem" inManagedObjectContext:managedObjectContext]; item.cat = [attributeDict valueForKey:@"c"]; item.sel = [attributeDict valueForKey:@"s"]; [self addItemsObject:item]; From what I have read I do not have to implement these methods and that they are generated at runtime. Any ideas?

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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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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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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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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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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 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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Mapping composite foreign keys in a many-many relationship in Entity Framework

- by Kirk Broadhurst

I have a Page table and a View table. There is a many-many relationship between these two via a PageView table. Unfortunately all of these tables need to have composite keys (for business reasons). Page has a primary key of (PageCode, Version), View has a primary key of (ViewCode, Version). PageView obviously enough has PageCode, ViewCode, and Version. The FK to Page is (PageCode, Version) and the FK to View is (ViewCode, Version) Makes sense and works, but when I try to map this in Entity framework I get Error 3021: Problem in mapping fragments...: Each of the following columns in table PageView is mapped to multiple conceptual side properties: PageView.Version is mapped to (PageView_Association.View.Version, PageView_Association.Page.Version) So clearly enough, EF is having a complain about the Version column being a common component of the two foreign keys. Obviously I could create a PageVersion and ViewVersion column in the join table, but that kind of defeats the point of the constraint, i.e. the Page and View must have the same Version value. Has anyone encountered this, and is there anything I can do get around it? Thanks!

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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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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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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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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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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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