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• Please suggest me the best way to design my database.

  - by Raymond Ho

  I have a table named "Pages" and a table named "Categories". Each entry of the table "Pages" is linked to the table "Categories". The "Categories" table have 5 entries, they are: "Car", "Websites", "Technology", "Mobile Phones", and "Interest". So each time I put an entry to the "Pages" table, I need to map it to the "Categories" table so are arranged properly. Here's my table: Pages ______ id [PK] name url Categories ______ id [PK] Categoryname Pages2Categories ______ Pages.id Categories.id So my question is, is this the most efficient way to create this kind of relationships between tables? It seems very amateur

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• SQL Server (2008) Creating link tables with unique rows

  - by peteski22

  Hi guys, I'm having trouble getting in touch with SQL Server Managemen Studio 2008! I want to create a link-table that will link an Event to many Audiences (EventAudience). An example of the data that could be contained: EventId | AudienceId 4 1 5 1 4 2 However, I don't want this: EventId | AudienceId 4 1 4 1 I've been looking at relationships and constraints.. but no joy so far! As a sneaky second part to the question, I would like to set up the Audience table such that if a row is deleted from Audience, it will clear down the EventAudience link table in a cascading manner. As always, ANY help/advice appreciated! Thanks Pete

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• Design ideas for a versioned db schema with related tables also versioned

  - by vfilby

  Here is the drill, I want to version a database. I have done this before using multiple rows where the table primary key becomes a combination of the row id and either a datestamp or a version #. Now I want to version a table that depends on many other small tables. Versioning each table will be a giant PITA, so I am looking for good options to verion a schema where the data to be versioned spreads over multiple tables. All related tables are properly keyed with foreign key relationships. The database is currently on Sql Server 2005.

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• How To Query Many-to-Many Table (one table's values becomes column headers)

  - by CRice

  Given this table structure, I want to flatten out the many-to-many relationships and make the values in the Name field of one table into column headers and the quantities from the same table into column values. The current idea which will work is to put the values into a Dictionary (hashtable) and represent this data in code but im wondering if there is a SQL way to do this. I am also using Linq-to-SQL for data access so a Linq-to-SQL solution would be ideal. [TableA] (int Id) [TableB] (int id, string Name) [TableAB] (int tableAId, int tableBId, int Quantity) fk: TableA.Id joins to TableAB.tableAId fk: TableB.Id joins to TableAB.tableBId Is there a way I can query the three tables and return one result for example: TableA [Id] 1 TableB [Id], [Name] 1, "Red" 2, "Green" 3, "Blue" TableAB [TableAId], [TableBId], [Quantity] 1 1 5 1 2 6 1 3 7 Query Result: [TableA.Id], [Red], [Green], [Blue] 1, 5, 6, 7

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• has_many relation doesn't seems right or logical, some thing like belongs_to_many looks right

  - by Vijendra

  My situation is like this. Company has many users and users may belongs to many companies. And current implementation is something like below. class Company has_many :employments has_many :users, :through = :employments end class Employment belongs_to :company belongs_to :user end class User has_many :employments has_many :companies, :through = :employments #This doesn't looks correct end User has many companies doesn't looks logically meaningful.It must be some thing like belongs_to_many companies. Do I need to use has_and_belongs_to_many? But that also will gives the same meaning. Can some one please suggest the right way for representing these relationships?

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• Facebook user_id as MongoDB BSON ObjectId?

  - by MattDiPasquale

  I'm rebuilding Lovers on Facebook with Sinatra & Redis. I like Redis because it doesn't have the long (12-byte) BSON ObjectIds and I am storing sets of Facebook user_ids for each user. The sets are requests_sent, requests_received, & relationships, and they all contain Facebook user ids. I'm thinking of switching to MongoDB because I want to use it's geospatial indexing. If I do, I'd want to use the FB user ids as the _id field because I want the sets to be small and I want the JSON responses to be small. But, is the BSON ObjectId better (more efficient for MongoDB) to use than just an integer (fb user_id)?

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• Foreign key on table A --> B, AND foreign key on table B --> A. How is this done?

  - by unclaimedbaggage

  Hi, I have two tables - 'business' and 'business_contacts'. The business_contact table has a many-to-one relationship with the business table. Furthermore, each business has a 'primary contact' field - which I'd assume is a one-to-many relationship with the business_contacts table. The problem, of course, is that this creates a catch-22 for data insertion. Since neither field can be null, I can't insert a business_contact until I have a corresponding business, but I can't insert a business until I have a corresponding business_contact. If anyone could help me get my head around how mutual one-to-many relationships are supposed to be dealt with I'd be most appreciative. (Project being done in MySQL if it makes any difference)

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• Rails architecture questions

  - by justinbach

  I'm building a Rails site that, among other things, allows users to build their own recipe repository. Recipes are entered either manually or via a link to another site (think epicurious, cooks.com, etc). I'm writing scripts that will scrape a recipe from these sites given a link from a user, and so far (legal issues notwithstanding) that part isn't giving me any trouble. However, I'm not sure where to put the code that I'm writing for these scraper scripts. My first thought was to put it in the recipes model, but it seems a bit too involved to go there; would a library or a helper be more appropriate? Also, as I mentioned, I'm building several different scrapers for different food websites. It seems to me that the elegant way to do this would be to define an interface (or abstract base class) that determines a set of methods for constructing a recipe object given a link, but I'm not sure what the best approach would be here, either. How might I build out these OO relationships, and where should the code go?

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• Many-to-many relationship on same table with association object

  - by Nicholas Knight

  Related (for the no-association-object use case): http://stackoverflow.com/questions/1889251/sqlalchemy-many-to-many-relationship-on-a-single-table Building a many-to-many relationship is easy. Building a many-to-many relationship on the same table is almost as easy, as documented in the above question. Building a many-to-many relationship with an association object is also easy. What I can't seem to find is the right way to combine association objects and many-to-many relationships with the left and right sides being the same table. So, starting from the simple, naïve, and clearly wrong version that I've spent forever trying to massage into the right version: t_groups = Table('groups', metadata, Column('id', Integer, primary_key=True), ) t_group_groups = Table('group_groups', metadata, Column('parent_group_id', Integer, ForeignKey('groups.id'), primary_key=True, nullable=False), Column('child_group_id', Integer, ForeignKey('groups.id'), primary_key=True, nullable=False), Column('expires', DateTime), ) mapper(Group_To_Group, t_group_groups, properties={ 'parent_group':relationship(Group), 'child_group':relationship(Group), }) What's the right way to map this relationship?

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• NSFetchedResultsChangeInsert reported when only updates are taking place

  - by niblha

  I have a class that acts as a NSFetchedResultsControllerDelegate which is receiving messages to -(void)controller:didChangeObject:atIndexPath:forChangeType:newIndexPath: with change type NSFetchedResultsChangeInsert, but the actual object which is the subject has with certainty not been newly inserted, only updated. So I would expect to get a change message with type NSFetchedResultsChangeUpdate, should I not? If i check the value of isInserted on the object, it yields false (as expected from the logic in my program). So my question is, why is this reported as an insert when it is only a change/update? They only thing I can think of is that part of the changes that are taking place is that objects of another entity type are inserted with relationships to objects of the entity type that the NSFetchedResultsController is set up to fetch.

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• Assign values from same table

  - by Reddy S R

  I have a database table with parent child relationships between different rows. 1 parent can have any number of children. Children do not have children. I want to copy 'Message' from 'Parent Category' to child categories. CategoryID Name Value Message ParentID DeptId 1 Books 9 Specials 1 2 Music 7 1 3 Paperback 25 1 1 4 PDFs 26 1 2 5 CDs 35 2 1 If that was sample data, Paperback should have Specials as it's Message after the query is run. I have gotten the child rows (the query runs very slow, don't know why), but how do I get the data and assign it to appropriate child rows? --@DeptId = 1 select * from Categories where ParentID in( select CategoryID from Categories where DeptID = @DeptId ) I would like to see a solution that would not use cursors. Thanks

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• What is an algorithm for minimizing some D distances between N items?

  - by Ross

  A classmate printed out a diagram of a database for class, the kind with lines representing relationships between tables. However, his lines crossed all over the place and it looked ugly. So I got to thinking about a way to move the tables to minimize the total line distance, and I couldn't think of a way to do it, other than just moving them all on top of each other. So basically: Given N items on some 2d coordinate space and some amount of connections between pairs of those items, how do you move the items so that the total distance between pairs is minimal, but that no distance is smaller than S? (so that the tables would not be too close together) Is there some algorithm for this? (I realize that smallest total distance won't necessarily make the layout less ugly; lines might still cross. But the table layout is just what got me thinking)

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• How to create relationship mapping via Entity framework

  - by James

  I have following domain model: User { int Id; } City { int Id; } UserCity { int UserId, int CityId, dateTime StartDate } In the function where I have to attach a user to a city, the following code is working for me: UserCity uc = new UserCity(); //This is a db hit uc.User = MyEntityFrameworkDBContext.User.FirstOrDefault(u => u.ID == currentUserId); //this is a db hit uc.City = MyEntityFrameworkDBContext.City.FirstOrDefault(c => c.ID == currentCityId); uc.StartDate = userCityStartDate; //this is a db hit MyEntityFrameworkDBContext.SaveChanges(); Is there any way I can create relationships with just one single DB hit? The first two db hits are not required, actually.

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• In Entity framework, we can use Model first, DB first, Code first but how can we create table programmatically

  - by AukI

  In entity framework we can use 3 approaches model first , code first , database first but each one of them needs manual hand touch(means creating database or create model or write the POCO class codes or entity class codes) before proceeding to the next step ( using EF in context ). What if I want to create database and tables and table relationships programatically and still want to have to features of EntityFramework 4.3. To be more specific , from this example http://support.microsoft.com/kb/307283 we can create database , tables and everything using SQL command but we can't have the advantages of entity framework. So if we want to have that what should we do?

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• Creating a view linking three different node types with two node references

  - by mikesir87

  I have the following content types: Camp - the top level type Registration Information - contains node reference to Camp called Camp Medical Release Form - contains node reference to registration information called Camper I would like to create a View that takes the nid for the Camp, and pulls out all the fields for the Registration Info and Medical Release Form. I'm having trouble figuring out how to set up the various arguments/relationships. I haven't done something that's referenced more than two types. I know it would be smart/best to just combine the Registration Info and Medical Release Form, since it's a 1:1 mapping, but we can't. So... any help would be appreciated!

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• database modeling for google app engine for multiple revison of entity.

  - by iamgopal

  hi, in my application ( kind of wiki clone ) - an article is frequently changing. and i need to track all changes that are done on that article. { text only. } one crude way i have done it, is to add a datetime property and create a new entity everytime something change. which is too much database wasting. { and also un-necessary index waste too. } and also need to re-create parent-child and entity relationships. i also have log which can show changes -- but i want some thing easier , so that jumping from one version to another version could be easier. ideas ? thanks.

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• jpa join query on a subclass

  - by Brian

  I have the following relationships in JPA (hibernate). Object X has two subclasses, Y and Z. Object A has a manyToOne relationship to object X. (Note, this is a one-sided relationship so object X cannot see object A). Now, I want to get the max value of a column in object A, but only where the relationship is of a specific subtype, ie...Y. So, that equates to...get the max value of column1 in object A, across all instances of A where they have a relationship with Y. Is this possible? I'm a bit lost as how to query it. I was thinking of something like: String query = "SELECT MAX(a.columnName) FROM A a join a.x; Query query = super.entityManager.createQuery(query); query.execute(); However that doesn't take account of the subclass of X...so I'm a bit lost. Any help would be much appreciated.

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• has_many relation doesn't seems right or logical in business perceptive, needed some thing like belo

  - by Vijendra

  My situation is like this. Company has many users and users may belongs to many companies. And current implementation is something like below. class Company has_many :employments has_many :users, :through = :employments end class Employment belongs_to :company belongs_to :user end class User has_many :employments has_many :companies, :through = :employments #This doesn't looks correct end It works, but "user has many companies" doesn't looks logically meaningful. It must be some thing like belongs_to_many companies. Do I need to use has_and_belongs_to_many? Can some one please suggest the right way for representing these relationships?

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• Missing something with Entity Framework for .NET 3.5?

  - by AC

  Is it not possible to have EF create the necessary entities when I have two related tables linked with a FK in .NET3.5SP1? I see where the checkbox to support this is disabled but it is available in .NET4. I've got a DB that has only tables with relationships in it. I need to build a Silverlight app (SL4) that allows management of the data within this app. I can't use .NET4 on the server... only .NET3.5SP1 so FK relationship bit in EF4 isn't available to me. Looking to avoid building as much of the plumbing to get back to the DB from the SL4 app as possible...

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• Hibernate - why use many-to-one to represent a one-to-one?

  - by aberrant80

  I've seen people use many-to-one mappings to represent one-to-one relationships. I've also read this in a book by Gavin King and on articles. For example, if a customer can have exactly one shipping address, and a shipping address can belong to only one customer, the mapping is given as: <class name="Customer" table="CUSTOMERS"> ... <many-to-one name="shippingAddress" class="Address" column="SHIPPING_ADDRESS_ID" cascade="save-update" unique="true"/> ... </class> The book reasons as (quoting it): "You don't care what's on the target side of the association, so you can treat it like a to-one association without the many part." My question is, why use many-to-one and not one-to-one? What is it about a one-to-one that makes it a less desirable option to many-to-one? Thanks.

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• How do you manage web navigation info in your application?

  - by Dave

  I’m building an application where different users will have different menu items available to them depending on what they’ve paid for. There will also be multiple levels to the menu hierarchy. What’s the best approach to this problem? I’m assuming I need a database table that represents the menu hierarchy, including the parent-child relationships of the nodes in the navigation as well as the sorting of the items. Then another table which I use to manage whether a user is authorized to access a particular item in that table. When I render the view, I’d reference the menus, and the access rights of the user to output the menu, and I’d also need a function to check that same authorization from each controller in case a user manually types in a URL of a controller they’re not supposed to have access to. Is this the right approach? Any suggestions for caching this to prevent the constant look-ups of this type of info? I’m open to any suggestions on how you may have approached this type of requirement.

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• Pre loaded database on iPhone?

  - by Julian

  Hi, I have recently developed an app using core data as the storage db. The app allowed the user to read and write to the db. I am now developing a new app which the user doesnt need to write anything to the db, instead the app just needs to read the data. The data has relationships etc so cannot just use a plist or something similar. My question is should I use core data for such a requirement and if so how would i go about entering the data and then releasing the app. Would I have to code the data entry which would populate the db then remove all this code (as I dont want the database to repopulate every time the user opens the app)?? Is there a way to create a core data model using sql commands as with sqlite ie insert into..... etc? Any ideas/thoughts would be very helpful. Many thanks Jules

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• Query to add a column depending of outcome of there columns

  - by Tam

  I have a user table 'users' that has fields like: id first_name last_name ... and have another table that determines relationships: user_id friend_id user_accepted friend_accepted .... I would like to generate a query that selects all the users but also add another field/column say 'network_status' that depends on the values of user_accepted and fiend_accepted. For example, if user_accepted is true friend_accepted is false I want the 'network_status' field to say 'request sent'. Can I possibly do this in one query? (I would prefer not to user if/else inside the query but if that's the only way so be it)

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• Microsoft Access - Enter Parameter Value why?

  - by Jane Doe

  I am encountering a problem for my database. Here is the relationships of the database And tried to do the query for how many transactions have movie "Harry_Potter"? so I used SQL query: SELECT COUNT(td.movie) AS number_of_occurrence, td.transaction_number FROM TransactionDetails td, MovieDetails md WHERE md.movie = Harry_Potter But it asks for Harry_Potter enter parameter value why? The relevant SQL statements are CREATE TABLE TransactionDetails ( transaction_number INTEGER PRIMARY KEY, movie VARCHAR(30) NOT NULL, date_of_transaction DATE NOT NULL, member_number INTEGER NOT NULL ) CREATE TABLE MovieDetails ( movie VARCHAR(30) PRIMARY KEY, movie_type VARCHAR(3) NOT NULL, movie_genre VARCHAR(10) NOT NULL ) ALTER TABLE TransactionDetails ADD CONSTRAINT member_number_fk FOREIGN KEY (member_number) REFERENCES LimelightMemberDetails(member_number); ALTER TABLE TransactionDetails ADD CONSTRAINT transaction_number_drink_fk FOREIGN KEY (transaction_number) REFERENCES DrinkTransactionDetails(transaction_number); ALTER TABLE TransactionDetails ADD CONSTRAINT transaction_number_food_fk FOREIGN KEY (transaction_number) REFERENCES FoodTransactionDetails(transaction_number); ALTER TABLE TransactionDetails ADD CONSTRAINT movie_fk FOREIGN KEY (movie) REFERENCES MovieDetails (movie); Thank you for your help! If there is anything wrong with my database design please let me know! thank you!

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• how do I integrate the aspnet_users table that comes with asp.net membership into my existing databa

  - by ooo

  i have a database that already has a users table COLUMNS: userID - int loginName - string First - string Last - string i just installed the asp.net membership table. Right now all of my tables are joined into my users table foreign keyed into the "userId" field How do i integrate asp.net_users table into my schema? here are the ideas i thought of: Add a membership_id field to my users table and on new inserts, include that new field in my users table. This seems like the cleanest way as i dont need to break any existing relationships. break all existing relationship and move all of the fields in my user table into the asp.net_users table. This seems like a pain but ultimately will lead to the most simple, normalized solution any thoughts?

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