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• Entity Framework v4 examples and tutorials of conceptual model mapping

  - by Rody van Sambeek

  In an application I'm writing I have a fairly complicated Database model. I'd like to use EF4 to map this to a whole lot nicer conceptual model. However all the tutorials I've read are with samples of 2 or 3 tables which all map 1 on 1 to the conceptual model. I'd like to learn how to correctly map the database model to a different conceptual model using VS 2010. However I can't find any good tutorials or (preferabally) instruction video's. Somebody got any tips, links or even books?

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• Javascript Object Database

  - by Narven

  Hi, is there any javascript object database?? Something like http://www.db4o.com/ but for javascript? thanks

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• How to draw a graph in LaTeX?

  - by Amir Rachum

  First of all, let me say I'm using LyX, though I have no problem using ERT. Secondly, what is the most simplest way to draw a simple graph like this in Latex? I've seen some documents with graphs and I've seen some examples, but I couldn't figure out how to just draw a simple graph - what packages do I need, etc?

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• Throughput measurements

  - by dotsid

  I wrote simple load testing tool for testing performance of Java modules. One problem I faced is algorithm of throughput measurements. Tests are executed in several thread (client configure how much times test should be repeated), and execution time is logged. So, when tests are finished we have following history: 4 test executions 2 threads 36ms overall time - idle * test execution 5ms 9ms 4ms 13ms T1 |-*****-*********-****-*************-| 3ms 6ms 7ms 11ms T2 |-***-******-*******-***********-----| <-----------------36ms---------------> For the moment I calculate throughput (per second) in a following way: 1000 / overallTime * threadCount. But there is problem. What if one thread will complete it's own tests more quickly (for whatever reason): 3ms 3ms 3ms 3ms T1 |-***-***-***-***----------------| 3ms 6ms 7ms 11ms T2 |-***-******-*******-***********-| <--------------32ms--------------> In this case actual throughput is much better because of measured throughput is bounded by the most slow thread. So, my question is how should I measure throughput of code execution in multithreaded environment.

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• Conditional relation

  - by Lowgain

  I've got a model like this: Stem -id -etc And then I have Stemrelation -stem_id -related_stem_id -active I can get the related stems with the following relations class Stem < ActiveRecord::Base has_many :stemrelations has_many :related_stems, :through => :stemrelations end class Stemrelation < ActiveRecord::Base belongs_to :stem belongs_to :related_stem, :class_name => "Stem", :foreign_key => "related_stem_id" end But now I'd only like to get the active relations. I tried adding this to the Stem model: has_many :active_related, :through => :stemrelations, :source => :related_stem, :conditions => {:active => true} but this gives me an error becasue it tries to check the active flag on the stem model instead of the stemrelation. What do I change here? Thanks!

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• Can Haskell's Parsec library be used to implement a recursive descent parser with backup?

  - by Thor Thurn

  I've been considering using Haskell's Parsec parsing library to parse a subset of Java as a recursive descent parser as an alternative to more traditional parser-generator solutions like Happy. Parsec seems very easy to use, and parse speed is definitely not a factor for me. I'm wondering, though, if it's possible to implement "backup" with Parsec, a technique which finds the correct production to use by trying each one in turn. For a simple example, consider the very start of the JLS Java grammar: Literal: IntegerLiteral FloatingPointLiteral I'd like a way to not have to figure out how I should order these two rules to get the parse to succeed. As it stands, a naive implementation like this: literal = do { x <- try (do { v <- integer; return (IntLiteral v)}) <|> (do { v <- float; return (FPLiteral v)}); return(Literal x) } Will not work... inputs like "15.2" will cause the integer parser to succeed first, and then the whole thing will choke on the "." symbol. In this case, of course, it's obvious that you can solve the problem by re-ordering the two productions. In the general case, though, finding things like this is going to be a nightmare, and it's very likely that I'll miss some cases. Ideally, I'd like a way to have Parsec figure out stuff like this for me. Is this possible, or am I simply trying to do too much with the library? The Parsec documentation claims that it can "parse context-sensitive, infinite look-ahead grammars", so it seems like something like I should be able to do something here.

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• Gaining information from nodes of tree

  - by jainp

  I am working with the tree data structure and trying to come up with a way to calculate information I can gain from the nodes of the tree. I am wondering if there are any existing techniques which can assign higher numerical importance to a node which appears less frequently at lower level (Distance from the root of the tree) than the same nodes appearance at higher level and high frequency. To give an example, I want to give more significance to node Book, at level 2 appearing once, then at level 3 appearing thrice. Will appreciate any suggestions/pointers to techniques which achieve something similar. Thanks, Prateek

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• How do I create a good evaluation function for a new board game?

  - by A. Rex

  I write programs to play board game variants sometimes. The basic strategy is standard alpha-beta pruning or similar searches, sometimes augmented by the usual approaches to endgames or openings. I've mostly played around with chess variants, so when it comes time to pick my evaluation function, I use a basic chess evaluation function. However, now I am writing a program to play a completely new board game. How do I choose a good or even decent evaluation function? The main challenges are that the same pieces are always on the board, so a usual material function won't change based on position, and the game has been played less than a thousand times or so, so humans don't necessarily play it enough well yet to give insight. (PS. I considered a MoGo approach, but random games aren't likely to terminate.) Any ideas? Game details: The game is played on a 10-by-10 board with a fixed six pieces per side. The pieces have certain movement rules, and interact in certain ways, but no piece is ever captured. The goal of the game is to have enough of your pieces in certain special squares on the board. The goal of the computer program is to provide a player which is competitive with or better than current human players.

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• How do I left join tables in unidirectional many-to-one in Hibernate?

  - by jbarz

  I'm piggy-backing off of http://stackoverflow.com/questions/2368195/how-to-join-tables-in-unidirectional-many-to-one-condition. If you have two classes: class A { @Id public Long id; } class B { @Id public Long id; @ManyToOne @JoinColumn(name = "parent_id", referencedColumnName = "id") public A parent; } B - A is a many to one relationship. I understand that I could add a Collection of Bs to A however I do not want that association. So my actual question is, Is there an HQL or Criteria way of creating the SQL query: select * from A left join B on (b.parent_id = a.id) This will retrieve all A records with a Cartesian product of each B record that references A and will include A records that have no B referencing them. If you use: from A a, B b where b.a = a then it is an inner join and you do not receive the A records that do not have a B referencing them. I have not found a good way of doing this without two queries so anything less than that would be great. Thanks.

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• Git dirctet acyclic graph - children know their parents but not the other way around

  - by dayscott

  Git is implemented as a directed acyclic graph. Children know their parents but not the other way round. This makes sense because i can reach every commit only through a branch or a tag ( generally speaking through a reference). That's how i traverse the tree. What other reasons had the developers of Git to make "the children know their parents but not the other way around"?/ What are the key benefits of this?

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• count of distinct acyclic paths from A[a,b] to A[c,d]?

  - by Sorush Rabiee

  I'm writing a sokoban solver for fun and practice, it uses a simple algorithm (something like BFS with a bit of difference). now i want to estimate its running time ( O and omega). but need to know how to calculate count of acyclic paths from a vertex to another in a network. actually I want an expression that calculates count of valid paths, between two vertices of a m*n matrix of vertices. a valid path: visits each vertex 0 or one times. have no circuits for example this is a valid path: but this is not: What is needed is a method to find count of all acyclic paths between the two vertices a and b. comments on solving methods and tricks are welcomed.

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• What is the "owning side" in an ORM mapping?

  - by Yousui

  Hi guys, I'm new to JPA. Now I have a question that what exactly is the owning side mean? I only have a rough idea of it. Can someone give me an explanation with some mapping examples(one to many, one to one, many to one) please? Great thanks. ps, the following text is excerpt from the decription of @OneToOne in java EE 6 documentation. You can see the concept owning side in it. Defines a single-valued association to another entity that has one-to-one multiplicity. It is not normally necessary to specify the associated target entity explicitly since it can usually be inferred from the type of the object being referenced. If the relationship is bidirectional, the non-owning side must use the mappedBy element of the OneToOne annotation to specify the relationship field or property of the owning side.

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• What is an XYZ-complete problem?

  - by TheMachineCharmer

  EDIT: Diagram: http://www.cs.umass.edu/~immerman/complexity_theory.html There must be some meaning to the word "complete" its used every now and then. Look at the diagram. I tried reading previous posts about NP- My question is what does the word "COMPLETE" mean? Why is it there? What is its significance? N- Non-deterministic - makes sense' P- Polynomial - makes sense but the "COMPLETE" is still a mystery for me.

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• What is Turing Complete?

  - by david

  What does the expression Turing Complete means? Can you give a simple explanation, without going into too much theoretical details?

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• Examples of useful or non-trival dual interfaces

  - by Scott Weinstein

  Recently Erik Meijer and others have show how IObservable/IObserver is the dual of IEnumerable/IEnumerator. The fact that they are dual means that any operation on one interface is valid on the other, thus providing a theoretical foundation for the Reactive Extentions for .Net Do other dual interfaces exist? I'm interested in any example, not just .Net based.

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• SQL: How do I INSERT primary key values from two tables INTO a master table.

  - by Stefan

  Hello, I would appreciate some help with an SQL statement I really can't get my head around. What I want to do is fairly simple, I need to take the values from two different tables and copy them into an master table when a new row is inserted into one of the two tables. The problem is perhaps best explained like this: I have three tables, productcategories, regioncategories and mastertable. --------------------------- TABLE: PRODUCTCATEGORIES --------------------------- COLUMNS: CODE | DESCRIPTION --------------------------- VALUES: BOOKS | Books --------------------------- --------------------------- TABLE: REGIONCATEGORIES --------------------------- COLUMNS: CODE | DESCRIPTION --------------------------- VALUES: EU | European Union --------------------------- --------------------------- TABLE: MASTERTABLE --------------------------- COLUMNS: REGION | PRODUCT --------------------------- VALUES: EU | BOOKS --------------------------- I want the values to be inserted like this when a new row is created in either productcategories or regioncategories. New row is created. --------------------------- TABLE: PRODUCTCATEGORIES --------------------------- COLUMNS: CODE | DESCRIPTION --------------------------- VALUES: BOOKS | Books --------------------------- VALUES: DVD | DVDs --------------------------- And a SQL statement copies the new values into the mastertable. --------------------------- TABLE: MASTERTABLE --------------------------- COLUMNS: REGION | PRODUCT --------------------------- VALUES: EU | BOOKS --------------------------- VALUES: EU | DVD --------------------------- The same goes if a row is created in the regioncategories. New row. --------------------------- TABLE: REGIONCATEGORIES --------------------------- COLUMNS: CODE | DESCRIPTION --------------------------- VALUES: EU | European Union --------------------------- VALUES: US | United States --------------------------- Copied to the mastertable. --------------------------- TABLE: MASTERTABLE --------------------------- COLUMNS: REGION | PRODUCT --------------------------- VALUES: EU | BOOKS --------------------------- VALUES: EU | DVD --------------------------- VALUES: US | BOOKS --------------------------- VALUES: US | DVD --------------------------- I hope it makes sense. Thanks, Stefan

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• What is a data structure for quickly finding non-empty intersections of a list of sets?

  - by Andrey Fedorov

  I have a set of N items, which are sets of integers, let's assume it's ordered and call it I[1..N]. Given a candidate set, I need to find the subset of I which have non-empty intersections with the candidate. So, for example, if: I = [{1,2}, {2,3}, {4,5}] I'm looking to define valid_items(items, candidate), such that: valid_items(I, {1}) == {1} valid_items(I, {2}) == {1, 2} valid_items(I, {3,4}) == {2, 3} I'm trying to optimize for one given set I and a variable candidate sets. Currently I am doing this by caching items_containing[n] = {the sets which contain n}. In the above example, that would be: items_containing = [{}, {1}, {1,2}, {2}, {3}, {3}] That is, 0 is contained in no items, 1 is contained in item 1, 2 is contained in itmes 1 and 2, 2 is contained in item 2, 3 is contained in item 2, and 4 and 5 are contained in item 3. That way, I can define valid_items(I, candidate) = union(items_containing[n] for n in candidate). Is there any more efficient data structure (of a reasonable size) for caching the result of this union? The obvious example of space 2^N is not acceptable, but N or N*log(N) would be.

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• Software to find dependencys in a database that not have them as restrictions

  - by Tomas Friden

  I have a database in SQL server 2005 that originaly comes fom an old mainframe. All relations was set in the surrounding software and there are non i the database. I need to find the relations, not by field name but by actual contence in the registers. (as suggestions, I realize I'l have to check them up) It would be nice with some extras, like finding motherless posts etc. but not a primary demand. There are some 200 registers with max 2 000 000 posts in any register. Does any one know of a software that can help me with this? The software I can find presuposes that relations are set in the database :(

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• rails: has_many :through validation?

  - by ramonrails

  Rails 2.1.0 (Cannot upgrade for now due to several constraints) I am trying to achieve this. Any hints? A project has many users through join model A user has many projects through join model Admin class inherits User class. It also has some Admin specific stuff. Admin like inheritance for Supervisor and Operator Project has one Admin, One supervisor and many operators. Now I want to 1. submit data for project, admin, supervisor and operator in a single project form 2. validate all and show errors on the project form. Project has_many :projects_users ; has_many :users, :through => :projects_users User has_many :projects_users ; has_many :projects, :through => :projects_users ProjectsUser = :id integer, :user_id :integer, :project_id :integer, :user_type :string ProjectUser belongs_to :project, belongs_to :user Admin < User # User has 'type:string' column for STI Supervisor < User Operator < User Is the approach correct? Any and all suggestions are welcome.

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• has_many through a habtm relationship in Rails

  - by macek

  I'm trying to define a has_many X, :through => Y where Y is a habtm relationship. Rails is throwing a fit about this. See comment in user model: class User < ActiveRecord::Base has_many :posts # I want to display a list of all tags this user is involved in has_many :tags, :through => :posts # ERROR end class Post < ActiveRecord::Base has_and_belongs_to_many :tags end class Tag < ActiveRecord::Base has_and_belongs_to_many :posts end What can I do to fix this?

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• SOA design principles with regards to database relationships

  - by Eitan

  If I were to extricate my current membership provider from my solution, i.e. as a dll and expose it as a web service with it's own db, how would I model the relationships with regards to SOA design. For example I have a table: USER id, name, lastname, username, password, role. and table PRODUCT id, name, price, createdate, userid the foreign key being userid to table user. How would I model the relationship and/or query the db. If I wanted to get all products that were uploaded today for example, before I would query: SELECT u.name, u.lastname, u.username, p.* FROM PRODUCT p INNER JOIN USER u ON p.userid = u.id WHERE createdate = '05/05/2010' Now that I don't have the table within the database how would I perform this query? Thanks.

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• What exactly are administrative redexes after CPS conversion?

  - by eljenso

  In the context of Scheme and CPS conversion, I'm having a little trouble deciding what administrative redexes (lambdas) exactly are: all the lambda expressions that are introduced by the CPS conversion only the lambda expressions that are introduced by the CPS conversion but you wouldn't have written if you did the conversion "by hand" or through a smarter CPS-converter If possible, a good reference would be welcome.

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• How to force grails GORM to respect DB scheme ?

  - by fabien-barbier

  I have two domains : class CodeSet { String id String owner String comments String geneRLF String systemAPF static hasMany = [cartridges:Cartridge] static constraints = { id(unique:true,blank:false) } static mapping = { table 'code_set' version false columns { id column:'code_set_id', generator: 'assigned' owner column:'owner' comments column:'comments' geneRLF column:'gene_rlf' systemAPF column:'system_apf' } } and : class Cartridge { String id String code_set_id Date runDate static belongsTo = CodeSet static constraints = { id(unique:true,blank:false) } static mapping = { table 'cartridge' version false columns { id column:'cartridge_id', generator: 'assigned' code_set_id column:'code_set_id' runDate column:'run_date' } } Actually, with those models, I get tables : - code_set, - cartridge, - and table : code_set_cartridge (two fields : code_set_cartridges_id, cartridge_id) I would like to not have code_set_cartridge table, but keep relationship : code_set -- 1:n -- cartridge In other words, how can I keep association between code_set and cartridge without intermediate table ? (using code_set_id as primary key in code_set and code_set_id as foreign key in cartridge). Mapping with GORM can be done without intermediate table?

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• Rating System Database Structure

  - by Harsha M V

  I have two entity groups. Restaurants and Users. Restaurants can be rated (1-5) by users. And rating fromeach user should be retrievable. Resturant(id, name, ..... , total_number_of_votes, total_voting_points ) User (id, name ...... ) Rating (id, restaurant_id, user_id, rating_value) Do i need to store the avg value so that it need not be calculated every time ? which table is the best place to store avg_rating, total_no_of_votes, total_voting_points ?

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• Can information encoded with a one time pad be distinguished from random noise?

  - by Robert

  I understand that the cyphertext from a properly used one time pad cypher reveals absolutely no data about the encrypted message. Does this mean that there is no way to distinguish a message encrypted with a one time pad from completely random noise? Or is there some theoretical way to determine that there is a message, even though you can't learn anything about it?

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