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• iPhone Development - Query related records using CoreData

  - by Mustafa

  I have a case where i have three entities with one-to-many and one-to-many relationships: Entity A (Entity B relationhip), Entity B (Entity A relationship, Entity C relationship), Entity C (Entity B relationhip) I have the reference of Entity A, and now i want to fetch all the related Entity C records. How can i do that? (with least amount of code) Edit: Here's another way to put it. Can we perform joins with CoreData. For example, (and this is a very crude example), We have a following entity-relationship: Grand Parent (1)---(m) Parent Parent (1)---(m) Child So, now if i have "Albert" the Grand Parent, and i want to get all his grand children, how can i do that?

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• Memory Profiling: How to detect which application/package is consuming too much memory

  - by malvim

  Hi, I have a situation here at work where we run a JEE server with several applications deployed on it. Lately, we've been having frequent OutOfMemoryException's. We suspect some of the apps might be behaving badly, maybe leaking, or something. The problem is, we can't really tell which one. We have run some memory profilers (like YourKit), and they're pretty good at telling what classes use the most memory. But they don't show relationships between classes, so that leaves us with a situation like this: We see that there are, say, lots of Strings and int arrays and HashMap entries, but we can't really tell which application or package they come from. Is there a way of knowing where these objects come from, so we can try to pinpoint the packages (or apps) that are allocating the most memory? Thank you in advance.

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• Faking a dynamic schema in Core Data?

  - by Gouldsc

  From reading the Apple Docs on Core Data, I've learned that you should not use Core Data when you need a dynamic schema. If I wanted to provide the user the ability to create their own properties, in a core data model would it work if I created some "dummy" attributes like "custom decimal 1", "custom decimal 2", "custom text 1", "custom text 2" etc that the user could name and use for their own purposes? Obviously this won't work for relationships, but for simple properties it seems like a reasonable workaround. Will creating a bunch of dummy attributes on my entities that go unused by most users noticeably decrease performance for them? Have any of you tried something like this? Thanks!

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• When and how should custom hierarchies be used in clojure?

  - by Rob Lachlan

  Clojure's system for creating an ad hoc hierarchy of keywords is familiar to most people who have spent a bit of time with the language. For example, most demos and presentations of the language include examples such as (derive ::child ::parent) and they go on to show how this can be used for multi-method dispatch. In all of the slides and presentations that I've seen, they use the global hierarchy. But it is possible to keyword relationships in custom hierarchies. Some questions, therefore: Are there any guidelines on when this is useful or necessary? Are there any functions for manipulating hierarchies? Merging is particularly useful, so I do this: (defn merge-h [& hierarchies] (apply merge-with (cons #(merge-with clojure.set/union %1 %2) hierarchies)) But I was wondering if such functions already exist somewhere.

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• How to do this NHibernate one-to-one mapping?

  - by JMSA

  This is a problem of unidirectional one-to-one mapping in NHibernate. Student.cs public class Student { public int ID { get; set; } public int Roll { get; set; } public int RegNo { get; set; } public string Name { get; set; } public StudentDetail StudentDetail { get; set; } } StudentDetail.cs public class StudentDetail { public int ID { get; set; } public string Father { get; set; } public string Mother { get; set; } } How can I map these classes (how do the hbm mapping files look like) to the following two distinct cases of one-to-one relationships? 1st case: 2nd case:

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• What are the "Navigation Properties" in this data model for?

  - by d03boy

  I've been wondering how to properly set up many-to-many relationships in ASP.NET MVC 2 using Linq2Sql for quite some time now. I found this blog post that seems to have a similar model layout as mine. If you take a look at the first screenshot showing the data model you can see that each model has "Navigation Properties" at the bottom of it. What exactly is this and why don't my models have them? I have the proper foreign keys put in to place. Most specifically, I am looking at the relationship between the Article and Category models since that is the only many-to-many relationship that I see and that's what I'm trying to model. Obviously I use an intermediary joining table between these two tables but I am having trouble understanding the proper methodology for modeling that relationship and I'm not finding this information anywhere on The Google.

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• Limit a user to view only associated records in rails

  - by trobrock

  I have an application with three Models (Profile - SubModel - SubSubModel) chained together with has many relationships. I am trying to limit a user, after logging in, to only retrieving records that are associated with their Profile. I am very new to rails and this is what I had been trying in the Profile model has_many :submodels, :conditions => {:profile_id => self.id} but this is returning an empty data set when calling with Profile.find_by_id(1).submodels, how else could I achieve what I am trying to do. Or should I handle this in the controller or view instead, I thought it sounded well suited for the model to handle this.

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• EJB 3 Session Bean Design for Simple CRUD

  - by sdoca

  I am writing an application that's sole purpose in life is to do CRUD operations for maintaining records in database. There are relationships between some of the tables/entities. Most examples I've seen for creating session beans deals with complex business logic/operations that interact with many entities which I don't have. Since my application is so very basic, what would be the best design for the session bean(s)? I was thinking of having one session bean per entity which had CRUD the methods defined. Then I thought of combining all of those session beans into a single session bean. And then I found this blog entry which is intriguing, but I must admit I don't understand all of it (what is a ServiceFacade?). I'm leaning towards session bean/entity class, but would like to hear more experienced opinions. Thanks.

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• Rails: Polymorphic User Table a good idea with AuthLogic?

  - by sscirrus

  Hi everyone, I have a system where I need to login three user types: customers, companies, and vendors from one login form on the home page. I have created one User table that works according to AuthLogic's example app at http://github.com/binarylogic/authlogic_example. I have added a field called "User Type" that currently contains either 'Customer', 'Company', or 'Vendor'. Note: each user type contains many disparate fields so I'm not sure if Single Table Inheritance is the best way to go (would welcome corrections if this conclusion is invalid). Is this a polymorphic association where each of the three types is 'tagged' with a User record? How should my models look so I have the right relationships between my User table and my user types Customer, Company, Vendor? Thanks very much!

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• CodeIgniter model debugging errors

  - by Jono

  I am new to CodeIgniter, and I need a way to get more meaningful error messages. Specifically I am having trouble with some model relationships, but the error is vague. I am willing to try/install anything since I dont know how to fix this relationship. Is there a way to specify how verbose an error message is? Also, this could be related to DataMapper, but I cant tell. I dont care if they are logged or in the browser. In my browser error reads: An Error Was Encountered Unable to relate X with Y. Any more info would be great... which class, line number, a stacktrace. Increasing the log threshold did not help.

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• Generate Info (wrapper) Class from stored procedure

  - by Adem

  Hello everybody I am in a crucial project and I am trying to speed up the development phase by using codesmith for generating the business class DAL and info class for the tables of my project. There are about 50 tables with relationships parent child many to many and for retrieving data I have to code several inner joins in stored procedures. I have to combine fields from many tables and this makes working with the info class difficult. Is there anyway to generate info class from stored procedures or to be more exact is there a way to parse the result set of the stored procedure and to generate the info class with properties for every column in that result set. Please if anyone can give me some advice and tell me how to achieve this. Best Regards

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• insertNewObjectForEntityForName: inManagedObjectContext: returning NSNumber bug?

  - by beinstein

  I'm relatively well versed in CoreData and have been using it for several years with little or no difficulty. All of a sudden I'm now dumbfounded by an error. For the life of me, I can't figure out why insertNewObjectForEntityForName:inManagedObjectContext: is all of a sudden returning some sort of strange instance of NSNumber. GDB says the returned object is of the correct custom subclass of NSManagedObject, but when I go to print a description of the NSManagedObject itself, I get the following error: *** -[NSCFNumber objectID]: unrecognized selector sent to instance 0x3f26f50 What's even stranger, is that I'm able to set some relationships and attributes using setValue:forKey: and all is good. But when I try to set once specific relationship, I get this error: *** -[NSCFNumber entity]: unrecognized selector sent to instance 0x3f26f50 Has anyone ever encountered anything like this before? I've tried clean all targets, restarting everything, even changing the model to the relationship in question is a to-one instead of a to-many. Nothing makes any difference.

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• Alright to truncate database tables when also using Hibernate?

  - by Marcus

  Is it OK to truncate tables while at the same time using Hibernate to insert data? We parse a big XML file with many relationships into Hibernate POJO's and persist to the DB. We are now planning on purging existing data at certain points in time by truncating the tables. Is this OK? It seems to work fine. We don't use Hibernate's second level cache. One thing I did notice, which is fine, is that when inserting we generate primary keys using Hibernate's @GeneratedValue where Hibernate just uses a key value one greater than the highest value in the table - and even though we are truncating the tables, Hibernate remembers the prior value and uses prior value + 1 as opposed to starting over at 1. This is fine, just unexpected. Note that the reason we do truncate as opposed to calling delete() on the Hibernate POJO's is for speed. We have gazillions of rows of data, and truncate is just so much faster.

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• Is there a declarative language for data definitions?

  - by Jekke

  Reading about WPF and thinking about my application's data store at the same time led me to wonder if there are any languages or tools that allow you to define relational data in a declarative way? A shallow Google search suggests no such thing exists. Yet it seems so obviously useful. The kind of tool I have in mind would declaratively describe (at least) entities, relationships and views is a platform-agnostic way that would act as an abstraction layer between data-driven applications and their datastores. Does any such tool exist?

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• Create a Models Diagram Using Railroad

  - by SeeBees

  Railroad is a great UML tool for Ruby on Rails. It can automatically generate class diagrams of models and controllers. For models, a railroad-generated class diagram shows attributes of each model and the associations between one model and another. A sample diagram can be found here. It is very useful for a developer to see attributes and associations of models. While attributes and associations reveal the inner states and relationships of models, methods specify their behaviours. They are all desirable in a class diagram. I would like railroad to generate a class diagram that also lists methods for models, which will help me to know what each model does. I know methods are displayed in a diagram that is generated for controllers, but I don't see such an option for a diagram of models. Does someone know how to do that with railroad? Or is that possible? Thanks!

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• LINQ to SQL Web Application Best Practices

  - by derek

  In my experience building web applications, I've always used a n-tier approach. A DAL that gets data from the db and populates the objects, and BLL that gets objects from the DAL and performs any business logic required on them, and the website that gets it's display data from the BLL. I've recently started learning LINQ, and most of the examples show the queries occurring right from the Web Application code-behinds(it's possible that I've only seen overly simplified examples). In the n-tier architectures, this was always seen as a big no-no. I'm a bit unsure of how to architect a new Web Application. I've been using the Server Explorer and dbml designer in VS2008 to create the dbml and object relationships. It seems a little unclear to me if the dbml would be considered the DAL layer, if the website should call methods within a BLL, which then would do the LINQ queries, etc. What are some general architecture best practices, or approaches to creating a Web Application solution using LINQ to SQL?

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• Entity Framework, what's so bad and what's so good?

  - by AverageJoe719

  Hi all, I am curious as to what your opinions are in Entity Framework? I have read some things like the first version of it is super horrible because it doesn't handle many to many relationships (though many ORMs don't and I've never seen the issue with just making a linking table). Also is LINQ to Entities the same as Entity Framework? I think it is, but it seems like one term is used or the other. I have used Linq to SQL before, what are the advantages of it compared to that? In terms of coding preference I like to build everything from the ground up so I can fully understand it/be in control of the code I write. So I have heard that Entity Framework is harder and I know LinqToSQL handles a lot of stuff automatically, but specifically what are the differences? I appreciate your responses, Thanks =)

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• Action Controller: Exception - ID not found

  - by Danny McClelland

  Hi Everyone, I am slowly getting the hang of Rails and thanks to a few people I now have a basic grasp of the database relations and associations etc. You can see my previous questions here: http://stackoverflow.com/questions/2714621/rails-database-relationships I have setup my applications models with all of the necessary has_one and has_many :through etc. but when I go to add a kase and choose from a company from the drop down list - it doesnt seem to be assigning the company ID to the kase. You can see a video of the the application and error here: http://screenr.com/BHC You can see a full breakdown of the application and relevant source code at the Git repo here: http://github.com/dannyweb/surveycontrol If anyone could shed some light on my mistake I would be appreciate it very much! Thanks, Danny

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• Specialization hierarchy in a domain-model

  - by devoured elysium

  I'm trying to make the domain model of a management system. I have the following kinds of persons in this system: employee manager top mananger I decided to define a User, from where employee, manager and top manager will specialize from. What I don't know is what kind of specialization hierarchy I should choose from. I thought of two ways: or Which might be preferable and why? As a long time coder, every time I try to do a domain-model, I have to fight against the idea of trying to think in how I'm going to code this. From what I've understood, I should not think about those matters in the domain-model, only in object relationships. I don't have to think of code duplication or any of these kind of details here, so I can't really pick any of the options over the other. Thanks

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• insertNewObjectForEntityForName:inManagedObjectContext: returning NSNumber bug?

  - by beinstein

  I'm relatively well versed in CoreData and have been using it for several years with little or no difficulty. For the life of me, I can't figure out why insertNewObjectForEntityForName:inManagedObjectContext: is all of a sudden returning some sort of strange instance of NSNumber. GDB says the returned object is of the correct custom subclass of NSManagedObject, but when I go to print a description of the NSManagedObject itself, I get the following error: *** -[NSCFNumber objectID]: unrecognized selector sent to instance 0x3f26f50 What's even stranger, is that I'm able to set some relationships and attributes using setValue:forKey: and all is good. But when I try to set one specific relationship, I get this error: *** -[NSCFNumber entity]: unrecognized selector sent to instance 0x3f26f50 I've tried everything from clean all targets, to restarting both mac and iPhone, even editing the model so that the relationship in question is to-one instead of to-many. No matter what I do, the same problem appears. Has anyone ever seen anything like this before?

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• ORM solutions (JPA; Hibernate) vs. JDBC

  - by Grasper

  I need to be able to insert/update objects at a consistent rate of at least 8000 objects every 5 seconds in an in-memory HSQL database. I have done some comparison performance testing between Spring/Hibernate/JPA and pure JDBC. I have found a significant difference in performance using HSQL.. With Spring/Hib/JPA, I can insert 3000-4000 of my 1.5 KB objects (with a One-Many and a Many-Many relationship) in 5 seconds, while with direct JDBC calls I can insert 10,000-12,000 of those same objects. I cannot figure out why there is such a huge discrepancy. I have tweaked the Spring/Hib/JPA settings a lot trying to get close in performance without luck. I want to use Spring/Hib/JPA for future purposes, expandability, and because the foreign key relationships (one-many and many-many) are difficult to maintain by hand; but the performance requirements seem to point towards using pure JDBC. Any ideas of why there would be such a huge discrepancy?

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• How to think in data stores instead of databases?

  - by Jim

  As an example, Google App Engine uses data stores, not a database, to store data. Does anybody have any tips for using data stores instead of databases? It seems I've trained my mind to think 100% in object relationships that map directly to table structures, and now it's hard to see anything differently. I can understand some of the benefits of data stores (e.g. performance and the ability to distribute data), but some good database functionality is sacrificed (e.g. joins). Does anybody who has worked with data stores like BigTable have any good advice to working with them?

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• LINQ DataLoadOptions - Retrieval of data via Fulltext/Broken Foreign Key Relationship

  - by Alex

  I've hit a brick wall: I have an SQL Function: FUNCTION [dbo].[ContactsFTS] (@searchtext nvarchar(4000)) RETURNS TABLE AS RETURN SELECT * FROM Contacts INNER JOIN CONTAINSTABLE(Contacts, *, @searchtext) AS KEY_TBL ON Contacts.Id = KEY_TBL.[KEY] which I am calling via LINQ public IQueryable<ContactsFTSResult> SearchByFullText(String searchText) { return db.ContactsFTS(searchText); } I am projecting the ContactsFTSResult collection into a List<Contact> which is then given to my viewmodel. Here is the problem: My Contacts table (and therefore the Contact object created via LINQ to SQL) has multiple FK relationships to other information, such as Contact.BillingAddressId is an FK to an Address.Id. That information is missing after I do the fulltext search (e.g. if I try to access Contact.BillingAddress it is null). Can I add this information somehow via DataLoadOptions? I tried LoadWith<Contact>(c => c.BillingAddress) but this doesn't work, I assume because of the fact that I'm calling the function instead of doing the whole query via LINQ.

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• strategies for learning complex software packages

  - by Tom

  I am a fairly novice Java programmer and I am currently working on a project to extend a piece of software that has been developed over a few years. So it has pretty big code base and the previous developers knew it well, so extending it is not going to be easy without a thorough understanding of the structure and function. 1) I had begun by trying to tackle small parts of the system and document them with mindmap. (particularly I am trying to document the interactions with external systems) 2) I have the book "code complete", which I am working through. 3) I have pointed some tools like "tattletale" at the code to get some diagrams of dependency relationships. What other strategies should I employ, should I focus on one particular aspect?

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• free public databases with non-trivial table structures?

  - by Caffeine Coma

  I'm looking for some sample database data that I can use for testing and demonstrating a DB tool I am working on. I need a DB that has (preferably) many tables, and many foreign key relationships between the tables. Ideally the data would be in SQL dump format, or at least in something that maintains the foreign key references, and could be easily import into an RDBMS (MySQL or H2). The dataset itself doesn't have to be huge (in fact, best if it's not). I thought about using the Stackoverflow Data Dump, but it's only about 5 tables.

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