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  • does the order a composite key is defined matter?

    I have a table with (col1,col2) as a composite primary key. create table twokeytable(col1 int,col2 int,constraint twokeytable_pk primary key (col1,col2)); and another table with col3,col4 collumns witha composite foreign key(col3,col4) which references the(col1,col2) primary key. For some processing I need to drop the foreign key and primary constraints .While restoring the constraints does order of the keys matter?. are these same? create table fktwokeytable(col3 int,col4 int,constraint fkaddfaa_fk foreign key(col4,col3) references twokeytable(col1,col2)) and create table fktwokeytable(col3 int,col4 int,constraint fkaddfaa_fk foreign key(col3,col4) references twokeytable(col1,col2))

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  • [rails] do we need database level constraints

    - by shrimpy
    i have the same problem as in the following post http://stackoverflow.com/questions/1451570/ruby-on-rails-database-migration-not-creating-foreign-keys-in-mysql-tables so i am wondering, why rails do not support generate foreign key by default??? it is not necessary??? or we suppose to do it manually?

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  • Problems getting foreign keys working in MySQL

    - by thehuby
    I've been trying to get a delete to cascade and it just doesn't seem to work. I'm sure I am missing something obvious, can anyone help me find it? I would expect a delete on the 'articles' table to trigger a delete on the corresponding rows in the 'article_section_lt' table. CREATE TABLE articles ( id INTEGER UNSIGNED PRIMARY KEY AUTO_INCREMENT, url_stub VARCHAR(255) NOT NULL UNIQUE, h1 VARCHAR(60) NOT NULL UNIQUE, title VARCHAR(60) NOT NULL, description VARCHAR(150) NOT NULL, summary VARCHAR(150) NOT NULL DEFAULT "", html_content TEXT, date DATE NOT NULL, updated TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP )ENGINE=INNODB; CREATE TABLE article_sections ( /* blog, news etc */ id INTEGER UNSIGNED PRIMARY KEY AUTO_INCREMENT, url_stub VARCHAR(255) NOT NULL UNIQUE, h1 VARCHAR(60) NOT NULL, title VARCHAR(60) NOT NULL, description VARCHAR(150) NOT NULL, summary VARCHAR(150) NOT NULL DEFAULT "", html_content TEXT NOT NULL DEFAULT "" )ENGINE=INNODB; CREATE TABLE article_section_lt ( fk_article_id INTEGER UNSIGNED NOT NULL REFERENCES articles(id) ON DELETE CASCADE, fk_article_section_id INTEGER UNSIGNED NOT NULL )ENGINE=INNODB;

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  • Type casting in TPC inheritance

    - by Mohsen Esmailpour
    I have several products like HotelProduct, FlightProduct ... which derived from BaseProduct class. The table of these products will be generated in TPC manner in database. There is OrderLine class which has a BaseProduct. My problem is when i select an OrderLine with related product i don't know how cast BaseProduct to derived product. for example i have this query: var order = (from odr in _context.Orders join orderLine in _context.OrderLines on odr.Id equals orderLine.OrderId join hotel in _context.Products.OfType<HotelProduct>() on orderLine.ProductId equals hotel.Id where odr.UserId == userId && odr.Id == orderId orderby odr.OrderDate descending select odr).SingleOrDefault(); In OrderLine i have BaseProduct properties not properties of HotelProduct. Is there any way to cast BaseProduct to derived class in OrderLine or any other solutions ?

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  • SQL - Two foreign keys that have a dependency between them

    - by Brian
    The current structure is as follows: Table RowType: RowTypeID Table RowSubType: RowSubTypeID FK_RowTypeID Table ColumnDef: FK_RowTypeID FK_RowSubTypeID (nullable) In short, I'm mapping column definitions to rows. In some cases, those rows have subtype(s), which will have column definitions specific to them. Alternatively, I could hang those column definitions that are specific to subtypes off their own table, or I could combine the data in RowType and RowSubType into one table and work with a single ID, but I'm not sure either is a better solution (if anything, I'd lean towards the latter, as we mostly end up pulling ColumnDefs for a given RowType/RowSubType). Is the current design SQL Blasphemy? If I keep the current structuree, how do I maintain that if RowSubTypeID is specified in ColumnDef, that it must correspond to the RowType specified by RowTypeID? Should I try to enforce this with a trigger or am I missing a simple redesign that would solve the problem?

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  • I want define tables from a part of my ER Diagram.

    - by M R Jafari
    I have a ER-Diagram (Show in http://www.4freeimagehost.com/show.php?i=f82997ca4d5d.png). In the diagram you see 2 entities and a 1:N relataion together. Project has 2 columns as ProjectID, ProjectName. Employee has 3 colums as EmployeeID, EmployeeName and ProjectID. A project has ONLY 1 project-manager and project-manager is a employee. What columns add them?

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  • In this example, would Customer or AccountInfo properly be the entity group parent?

    - by Badhu Seral
    In this example, the Google App Engine documentation makes the Customer the entity group parent of the AccountInfo entity. Wouldn't AccountInfo encapsulate Customer rather than the other way around? Normally I would think of an AccountInfo class as including all of the information about the Customer. import javax.jdo.annotations.IdGeneratorStrategy; import javax.jdo.annotations.PersistenceCapable; import javax.jdo.annotations.Persistent; import javax.jdo.annotations.PrimaryKey; import com.google.appengine.api.datastore.Key; import com.google.appengine.api.datastore.KeyFactory; @PersistenceCapable public class AccountInfo { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key key; public void setKey(Key key) { this.key = key; } } // ... KeyFactory.Builder keyBuilder = new KeyFactory.Builder(Customer.class.getSimpleName(), "custid985135"); keyBuilder.addChild(AccountInfo.class.getSimpleName(), "acctidX142516"); Key key = keyBuilder.getKey(); AccountInfo acct = new AccountInfo(); acct.setKey(key); pm.makePersistent(acct);

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  • [Database] How to model this one-to-one relation?

    - by pbean
    I have several entities which respresent different types of users who need to be able to log in to a particular system. Additionally, they have different types of information associated with them. For example: a "general user", which has an e-mail address and "admin user", which has a workstation number (note that this a hypothetical case). Both entities also share common properties like first name, surname, address and telephone number. Finally, they naturally need to have a (unique) user name and a password to log in. In the application, the user just has to fill in his user name and password, and the functionality of the application changes slightly according to the type of the user. You can imagine that the username needs to be unique for this work. How should I model this effectively? I can't just create two tables, because then I can't force a unique constaint on the user name. I also can't put them all in just one table, because they have different types of specific information associated to them. I think I might need 3 seperate tables, one for "users" (with user name and password), one for the "general users" and another one for the "admin users", but how would the relations between these work? Or is there another solution? (By the way, the target DBMS is MySQL, so I don't think generalization is supported in the database system itself).

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  • How to test if a doctrine records has any relations that are used

    - by murze
    Hi, I'm using a doctrine table that has several optional relations (of types Doctrine_Relation_Association and Doctrine_Relation_ForeignKey) with other tables. How can I test if a record from that table has connections with records from the related table. Here is an example to make my question more clear. Assume that you have a User and a user has a many to many relation with Usergroups and a User can have one Userrole How can I test if a give user is part of any Usergroups or has a role. The solution starts I believe with $relations = Doctrine_Core::getTable('User')->getRelations(); $user = Doctrine_Core::getTable('User')->findOne(1); foreach($relations as $relation) { //here should go a test if the user has a related record for this relation if ($relation instanceof Doctrine_Relation_Association) { //here the related table probably has more then one foreign key (ex. user_id and group_id) } if ($relation instanceof Doctrine_Relation_ForeignKey) { //here the related table probably has the primary key of this table (id) as a foreign key (user_id) } } //true or false echo $result I'm looking for a general solution that will work no matter how many relations there are between user and other tables. Thanks!

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  • How to propose Asp.Net Mvc over other technologies to client?

    - by Arnis L.
    How to show benefits of adopting asp.net mvc to client? I mean - we as developers can understand benefits of easier implementation of automated testing, better control over rendered html etc., but what would be strongest motives for client to accept usage of asp.net mvc? Maybe there's some more nice looking examples built with asp.net mvc (excluding stackoverflow) to show? p.s. Please, do not start flame war. In this case - it doesn't matter if asp.net mvc is better than x or vica versa.

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  • How does Hibernate detect dirty state of an entity object?

    - by ???'Lenik
    Is it using some kind of byte codes modification to the original classes? Or, maybe Hibernate get the dirty state by compare the given object with previously persisted version? I'm having a problem with hashCode() and equals() methods for complicated objects. I feel it would be very slow to compute hash code if the object has collection members, and cyclic references are also a problem. If Hibernate won't use hashCode()/equals() to check the dirty state, I guess I should not use equals()/hashCode() for the entity object (not value object), but I'm also afraid if the same operator (==) is not enough. So, the questions are: How does Hibernate know if a property of an object is changed? Do you suggest to override the hashCode()/equals() methods for complicated objects? What if they contains cyclic references? And, also, Would hashCode()/equals() with only the id field be enough?

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  • Hibernate not saving foreign key, but with junit it's ok

    - by Leonardo
    Hi All, I have this strange problem. In a J2ee webapp with spring, smartgwt and hibernate, it happens that I have a class A wich has a set of class B, both of them mapped to table A and table B. I wrote a simple test case for testing the service manager which is supposed to do insert, update, delete and everything work as expected especially during insert. In the end I have one record in A and records in B with foreign key to A. But when I try to call the service from the web app, the entity in B are saved without a foreign key reference. I am sure that the service is the same. One thing I noticed is that enabling hibernate logging, seems that when the service is called from the application, one more update is made: insert A insert B update A update B update B (foreign key only) update A <--- ??? update B <--- ??? Instead, when junit test case is run, the update is as follows: insert A insert B update A update B update B (foreign key only) I suppose the latest update is what is causing the erroe, maybe it is overwriting values. Considering that the app is using spring, with the well known mechanism of DAO + Manager, where can I investigate to solve this issue ? Someone told me that the session is not closed, so hibernate would do one more update before release the objects by itself. I am pretty sure that all the configuration hbm, xml, and the rest are fine...but I maybe wrong. thanks

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  • How to design this simple database?

    - by Vafello
    I have 2 tables - one storing user information (id, username, password) and the second one storing information about events (id, name, description, date, username(represents the user who created the event)). I would like to implement 'favourite events' functionality. This would allow the user to store his favourite events and later display them in a list. I am not sure how to implement this in terms of design. I need a simple solution. Something like storing the IDs of favourite events in a field in the user table. I am using mysql and php. Can anyone point me to the right direction?

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  • Non-normalized association with legacy tables in Rails and ActiveRecord

    - by Thomas Holmström
    I am building a Rails application accessing a legacy system. The data model contains Customers which can have one or more Subscriptions. A Subscription always belong to one and only one Customer. Though not needed, this association is represented through a join table "subscribes", which do not have an id column: Column | Type | Modifiers -----------------+---------+----------- customer_id | integer | not null subscription_id | integer | not null I have this coded as a has_and_belongs_to_many declarations in both Customer and Subscription class Customer < Activerecord::Base has_and_belongs_to_many :subscriptions, :join_table => "subscribes", :foreign_key => "customer_id", :association_foreign_key => "subscription_id" end class Subscription < Activerecord::Base has_and_belongs_to_many :customers, :join_table => "subscribes", :foreign_key => "subscription_id", :association_foreign_key => "customer_id" end The problem I have is that there can only ever be one customer for each subscription, not many, and the join table will always contain at most one row with a certain customer_id. And thus, I don't want the association "customers" on a Subscription which returns an array of (at most one) Customer, I really do want the relation "customer" which returns the Customer associated. Is there any way to force ActiveRecord to make this a 1-to-N relation even though the join table itself seems to make it an N-to-M relation? --Thomas

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  • EntityManager does not update on flush()

    - by Sara
    Java EJB's EntityManager does not update data from a Consumer. A Consumer logs into a shop, buys some stuff and wants to look at his shopping-history. Everything is displayed but his last purchase. If he logs out and in, it shows. I have used JPA to persist buys/purchases (that are mapped to the Consumer)to DB. It seems like purchases from this session can't be detected. Code: public Buys buyItem(Consumer c, int amount) { Buys b = new Buys(); b.setConsumerId(c); b.setContent("DVD"); b.setPrice(amount); em.persist(b); em.flush(); return b; } public Collection getAllBuysFromUser(Consumer consumer) { Collection collection = consumer.getBuysCollection(); return collection; } Help!? Flush does not do the trick...

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  • Creating a Group of Groups in Django

    - by Greg
    I'm creating my own Group model; I'm not referring to the builtin Group model. I want each hroup to be a member of another group (it's parent), but there is the one "top" group that doesn't have a parent group. The admin interface won't let me create a group without entering a parent. I get the error personnel_group.parent_id may not be NULL. My Group model looks like this: class Group(models.Model): name = models.CharField(max_length=50) parent = models.ForeignKey('self', blank=True, null=True) order = models.IntegerField() icon = models.ImageField(upload_to='groups', blank=True, null=True) description = models.TextField(blank=True, null=True) How can I accomplish this? Thanks.

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  • Help needed with Linq To Sql Query

    - by fearofawhackplanet
    I have the concept of valid/ordered transitions. So for example, it's not possible to move to status In progress from status Complete. Current and Next in table StatusTransition are FK (StatusType.Id). The Linq generator has created the following relations: Child Property Name: StatusTransitions1 Parent Property Name: StatusType1 Participating Properties: StatusType.Id -> StatusTransition.Next Child Property Name: StatusTransitions Parent Property Name: StatusType Participating Properties: StatusType.Id -> StatusTransition.Current I'm normally ok with Linq but I'm having difficulty getting the list of valid Next StatusTypes from the Current status. public List<StatusType> GetValidStatusTransitions(int statusId) { // trying to write something like the following // (obviously not correct) return _statusRepository .Where(s => s.Id == statusId) .Next.StatusTypes; }

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  • Multiple has_many's of the same model

    - by Koning Baard
    I have these models: Person has_many :messages_form_person, :foreign_key => :from_user_id, :class_name => :messages has_many :messages_to_person, :foreign_key => :to_user_id, :class_name => :messages Message belongs_to :to_person, :foreign_key => :to_user_id, :class_name => :person belongs_to :from_person, :foreign_key => :to_user_id, :class_name => :person And this view: person#show <% @person.messages_to_person.each do |message| %> <%=h message.title %> <% end %> But I get this error: TypeError in People#show Showing app/views/people/show.html.erb where line #26 raised: can't convert Symbol into String Extracted source (around line #26): 23: <%=h @person.biography %> 24: </p> 25: 26: <% @person.messages_to_person.each do |message| %> 27: 28: <% end %> 29: I basicly want that people can send eachother messages. Can anyone help me? Thanks.

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  • Circular database relationships. Good, Bad, Exceptions?

    - by jim
    I have been putting off developing this part of my app for sometime purely because I want to do this in a circular way but get the feeling its a bad idea from what I remember my lecturers telling me back in school. I have a design for an order system, ignoring the everything that doesn't pertain to this example I'm left with: CreditCard Customer Order I want it so that, Customers can have credit cards (0-n) Customers have orders (1-n) Orders have one customer(1-1) Orders have one credit card(1-1) Credit cards can have one customer(1-1) (unique ids so we can ignore uniqueness of cc number, husband/wife may share cc instances ect) Basically the last part is where the issue shows up, sometimes credit cards are declined and they wish to use a different one, this needs to update which their 'current' card is but this can only change the current card used for that order, not the other orders the customer may have on disk. Effectively this creates a circular design between the three tables. Possible solutions: Either Create the circular design, give references: cc ref to order, customer ref to cc customer ref to order or customer ref to cc customer ref to order create new table that references all three table ids and put unique on the order so that only one cc may be current to that order at any time Essentially both model the same design but translate differently, I am liking the latter option best at this point in time because it seems less circular and more central. (If that even makes sense) My questions are, What if any are the pros and cons of each? What is the pitfalls of circular relationships/dependancies? Is this a valid exception to the rule? Is there any reason I should pick the former over the latter? Thanks and let me know if there is anything you need clarified/explained. --Update/Edit-- I have noticed an error in the requirements I stated. Basically dropped the ball when trying to simplify things for SO. There is another table there for Payments which adds another layer. The catch, Orders can have multiple payments, with the possibility of using different credit cards. (if you really want to know even other forms of payment). Stating this here because I think the underlying issue is still the same and this only really adds another layer of complexity.

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  • Problem in mutiple :dependent=> :destroy when multiple polymorphic is true

    - by piemesons
    I have four models question, answer, comment and vote.Consider it same as stackoverflow. Question has_many comments Answers has_many comments Questions has_many votes answers has_many votes comments has_many votes Here are the models (only relevant things) class Comment < ActiveRecord::Base belongs_to :commentable, :polymorphic => true has_many :votes, :as => :votable, :dependent => :destroy end class Question < ActiveRecord::Base has_many :comments, :as => :commentable, :dependent => :destroy has_many :answers, :dependent => :destroy has_many :votes, :as => :votable, :dependent => :destroy end class Vote < ActiveRecord::Base belongs_to :votable, :polymorphic => true end class Answer < ActiveRecord::Base belongs_to :question, :counter_cache => true has_many :comments, :as => :commentable , :dependent => :destroy end Now the problem is whenever i am trying to delete any question/answer/comment its giving me an error NoMethodError in QuestionsController#destroy undefined method `each' for 0:Fixnum if i remove this line from any of the model (question/answer/comment) has_many :votes, :as => :votable, :dependent => :destroy then it works perfectly. It seems there is a problem while deleting the records active record is not able to find out the proper path because of multiple joins within the tables.

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  • IPhone CoreData: How should I relate many child entities to thier parents

    - by Robert
    I am trying to import data from a database that uses primary key / forign key relations to a core data database in Xcode. I have code that creates hundreds of child entities in a managed object context: Each child has an ID that corresponds to a parent. child1 parentID = 3 child2 parentID = 17 child3 parentID = 17 ... childn parentID = 5 I now need to relate each child to its parent. The parents are all stored in persistent memory. My first thought was to preform a fetch for each child to get its parent. However, I think this would be slow. Am I correct? How should I do this instead?

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