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  • Can someone describe the nested set model from a C#/LINQ perspective?

    - by Chad
    I know the nested set model doesn't pertain to the C# language or LINQ directly... it's what I'm using to develop my web app. For hierarchical data (categories with sub-categories in my case), I'm currently using something similar to the Adjacency List model. At the moment, I've only got 2 levels of categories, but I'd like to take it further and allow for n levels of categories using the nested set model. I'm not quite clear on how to use it in a C# context. Here's the article I'm reading on the nested set model. Though this article cleared up my confusion some, I still have a big ?? in my head: - Is inserting, updating or deleting categories tedious? It looks like the left and right numbers would require re-numbering... what would the LINQ queries look like for the following scenarios? Delete a child node (re-number all node's left/right values) Delete a parent node (what do you do with the orphans?) Move a child node to a different parent node (renumber again) If my understanding is correct, at all times the child node's left/right values will always be between the parent node's left/right values, am I correct? Seems easy enough, if only the categories were static... most likely I need to spend more time to get my head around the concept. Any help is greatly appreciated!

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  • How to map IEnumerable<SelectListItem> to IList<> for ListBox

    - by Superhuman
    I have two classes. Class1 and Class2. public class Class1{ ... public virtual IList<Class2> Class2s{get;set;} ... } public class Class2{ ... public virtual IList<Class1> Class1s{get;set;} ... } The view contains <%=Html.ListBox("Class2s", ViewData.Model.Class2s.Select( x => new SelectListItem { Text = x.Name, Value = x.Id.ToString(), Selected = ViewData.Model.Class1.Class2s.Any(y => y.Id == x.Id) }) They have many to many mapping. I have a ListBox in Class1 view which displays Class2. How to map the output of the ListBox back to IList Class2s property of Class1? I am able to display the values in the ListBox but unable to map back the SelectListItem to IList.

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  • Graph Algorithm To Find All Paths Between N Arbitrary Vertices

    - by russtbarnacle
    I have an graph with the following attributes: Undirected Not weighted Each vertex has a minimum of 2 and maximum of 6 edges connected to it. Vertex count will be < 100 I'm looking for paths between a random subset of the vertices (at least 2). The paths should simple paths that only go through any vertex once. My end goal is to have a set of routes so that you can start at one of the subset vertices and reach any of the other subset vertices. Its not necessary to pass through all the subset nodes when following a route. All of the algorithms I've found (Dijkstra,Depth first search etc.) seem to be dealing with paths between two vertices and shortest paths. Is there a known algorithm that will give me all the paths (I suppose these are subgraphs) that connect these subset of vertices?

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  • Doctrine does not export relation properly

    - by iggnition
    Hi, I've got a MySQL 5.1.41 database which i'm trying to fill with doctrine, but doctrine does not insert the relations correctly. My YAML is: Locatie: connection: doctrine tableName: locatie columns: loc_id: type: integer(4) fixed: false unsigned: false primary: true autoincrement: true org_id: type: integer(4) fixed: false unsigned: false primary: false notnull: false autoincrement: false naam: type: string(30) fixed: false unsigned: false primary: false notnull: true autoincrement: false straat: type: string(30) fixed: false unsigned: false primary: false notnull: true autoincrement: false huisnummer: type: integer(4) fixed: false unsigned: false primary: false notnull: true autoincrement: false huisnummer_achtervoegsel: type: string(3) fixed: false unsigned: false primary: false notnull: false autoincrement: false plaats: type: string(25) fixed: false unsigned: false primary: false notnull: true autoincrement: false postcode: type: string(6) fixed: false unsigned: false primary: false notnull: true autoincrement: false telefoon: type: string(12) fixed: false unsigned: false primary: false notnull: true autoincrement: false opmerking: type: string() fixed: false unsigned: false primary: false notnull: false autoincrement: false inloggegevens: type: string() fixed: false unsigned: false primary: false notnull: false autoincrement: false relations: Organisatie: local: org_id foreign: org_id type: one onDelete: CASCADE onUpdate: CASCADE Organisatie: connection: doctrine tableName: organisatie columns: org_id: type: integer(4) fixed: false unsigned: false primary: true autoincrement: true naam: type: string(30) fixed: false unsigned: false primary: false notnull: true autoincrement: false straat: type: string(30) fixed: false unsigned: false primary: false notnull: true autoincrement: false huisnummer: type: integer(4) fixed: false unsigned: false primary: false notnull: true autoincrement: false huisnummer_achtervoegsel: type: string(3) fixed: false unsigned: false primary: false notnull: false autoincrement: false plaats: type: string(25) fixed: false unsigned: false primary: false notnull: true autoincrement: false postcode: type: string(6) fixed: false unsigned: false primary: false notnull: true autoincrement: false telefoon: type: string(12) fixed: false unsigned: false primary: false notnull: true autoincrement: false opmerking: type: string(255) fixed: false unsigned: false primary: false notnull: false autoincrement: false relations: Locatie: local: org_id foreign: org_id type: many Now if a make an organisation and then create a location which has a foreignkey to organisation everything is fine. but when i try to update the org_id with phpmyadmin i get a contraint error. If i manually set the foreign key to ON_UPDATE CASCADE it does work. Why does doctrine not set this option? I got it to work in Propel, but i really want to use doctrine for this.

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  • integer division properties

    - by aaa
    hi. does the following integer arithmetic property hold? (m/n)/l == m/(n*l) At first I thought I knew answer (does not hold), but now am not sure. Does it hold for all numbers or only for certain conditions, i.e. n > l?

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  • What is the exact problem with multiple inheritance?

    - by Totophil
    I can see people asking all the time whether multiple inheritance should be included into the next version of C# or Java and C++ folks, who are fortunate enough to have this ability, say that this is like giving someone a rope to eventually hang themselves. What’s the matter with the multiple inheritance? Are there any concrete samples?

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  • Amazing families of algorithms over implicit graphs

    - by Diego de Estrada
    Dynamic programming is, almost by definition, to find a shortest/longest path on an implicit dag. Every DP algorithm just does this. An Holographic algorithm can be loosely described as something that counts perfect matchings in implicit planar graphs. So, my question is: are there any other families of algorithms that use well-known algorithms over implicit graphs to achieve a considerable speedup?

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  • Should we have a database independent SQL like query language in Django? [closed]

    - by Yugal Jindle
    Note : I know we have Django ORM already that keeps things database independent and converts to the database specific SQL queries. Once things starts getting complicated it is preferred to write raw SQL queries for better efficiency. When you write raw sql queries your code gets trapped with the database you are using. I also understand its important to use the full power of your database that can-not be achieved with the django orm alone. My Question : Until I use any database specific feature, why should one be trapped with the database. For instance : We have a query with multiple joins and we decided to write a raw sql query. Now, that makes my website postgres specific. Even when I have not used any postgres specific feature. I feel there should be some fake sql language which can translate to any database's sql query. Even Django's ORM can be built over it. So, that if you go out of ORM but not database specific - you can still remain database independent. I asked the same question to Jacob Kaplan Moss (In person) : He advised me to stay with the database that I like and endure its whole power, to which I agree. But my point was not that we should be database independent. My point is we should be database independent until we use a database specific feature. Please explain, why should be there a fake sql layer over the actual sql ?

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  • Should this even be a has_many :through association?

    - by GoodGets
    A Post belongs_to a User, and a User has_many Posts. A Post also belongs_to a Topic, and a Topic has_many Posts. class User < ActiveRecord::Base has_many :posts end class Topic < ActiveRecord::Base has_many :posts end class Post < ActiveRecord::Base belongs_to :user belongs_to :topic end Well, that's pretty simple and very easy to set up, but when I display a Topic, I not only want all of the Posts for that Topic, but also the user_name and the user_photo of the User that made that Post. However, those attributes are stored in the User model and not tied to the Topic. So how would I go about setting that up? Maybe it can already be called since the Post model has two foreign keys, one for the User and one for the Topic? Or, maybe this is some sort of "one-way" has_many through assiociation. Like the Post would be the join model, and a Topic would has_many :users, :through = :posts. But the reverse of this is not true. Like a User does NOT has_many :topics. So would this even need to be has_many :though association? I guess I'm just a little confused on what the controller would look like to call both the Post and the User of that Post for a give Topic. Edit: Seriously, thank you to all that weighed in. I chose tal's answer because I used his code for my controller; however, I could have just as easily chosen either j.'s or tim's instead. Thank you both as well. This was so damn simple to implement, and I think today marks the day that I'm beginning to fall in love with rails.

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  • finding shortest valid path in a colored-edge graphs

    - by user1067083
    Given a directed graph G, with edges colored either green or purple, and a vertex S in G, I must find an algorithm that finds the shortest path from s to each vertex in G so the path includes at most two purple edges (and green as much as needed). I thought of BFS on G after removing all the purple edges, and for every vertex that the shortest path is still infinity, do something to try to find it, but I'm kinda stuck, and it takes alot of the running time as well... Any other suggestions? Thanks in advance

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  • Find optimal/good-enough strategy and AI for the game 'Proximity'?

    - by smci
    'Proximity' is a strategy game of territorial domination similar to Othello, Go and Risk. Two players, uses a 10x12 hex grid. Game invented by Brian Cable in 2007. Seems to be a worthy game for discussing a) optimal algorithm then b) how to build an AI. Strategies are going to be probabilistic or heuristic-based, due to the randomness factor, and the insane branching factor (20^120). So it will be kind of hard to compare objectively. A compute time limit of 5s per turn seems reasonable. Game: Flash version here and many copies elsewhere on the web Rules: here Object: to have control of the most armies after all tiles have been placed. Each turn you received a randomly numbered tile (value between 1 and 20 armies) to place on any vacant board space. If this tile is adjacent to any ally tiles, it will strengthen each tile's defenses +1 (up to a max value of 20). If it is adjacent to any enemy tiles, it will take control over them if its number is higher than the number on the enemy tile. Thoughts on strategy: Here are some initial thoughts; setting the computer AI to Expert will probably teach a lot: minimizing your perimeter seems to be a good strategy, to prevent flips and minimize worst-case damage like in Go, leaving holes inside your formation is lethal, only more so with the hex grid because you can lose armies on up to 6 squares in one move low-numbered tiles are a liability, so place them away from your main territory, near the board edges and scattered. You can also use low-numbered tiles to plug holes in your formation, or make small gains along the perimeter which the opponent will not tend to bother attacking. a triangle formation of three pieces is strong since they mutually reinforce, and also reduce the perimeter Each tile can be flipped at most 6 times, i.e. when its neighbor tiles are occupied. Control of a formation can flow back and forth. Sometimes you lose part of a formation and plug any holes to render that part of the board 'dead' and lock in your territory/ prevent further losses. Low-numbered tiles are obvious-but-low-valued liabilities, but high-numbered tiles can be bigger liabilities if they get flipped (which is harder). One lucky play with a 20-army tile can cause a swing of 200 (from +100 to -100 armies). So tile placement will have both offensive and defensive considerations. Comment 1,2,4 seem to resemble a minimax strategy where we minimize the maximum expected possible loss (modified by some probabilistic consideration of the value ß the opponent can get from 1..20 i.e. a structure which can only be flipped by a ß=20 tile is 'nearly impregnable'.) I'm not clear what the implications of comments 3,5,6 are for optimal strategy. Interested in comments from Go, Chess or Othello players. (The sequel ProximityHD for XBox Live, allows 4-player -cooperative or -competitive local multiplayer increases the branching factor since you now have 5 tiles in your hand at any given time, of which you can only play one. Reinforcement of ally tiles is increased to +2 per ally.)

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  • Database design grouping contacts by lists and companies

    - by Serge
    Hi, I'm wondering what would be the best way to group contacts by their company. Right now a user can group their contacts by custom created lists but I'd like to be able to group contacts by their company as well as store the contact's position (i.e. Project Manager of XYZ company). Database wise this is what I have for grouping contacts into lists contact [id_contact] [int] PK NOT NULL, [lastName] [varchar] (128) NULL, [firstName] [varchar] (128) NULL, ...... contact_list [id_contact] [int] FK, [id_list] [int] FK, list [id_list] [int] PK [id_user] [int] FK [list_name] [varchar] (128) NOT NULL, [description] [TEXT] NULL Should I implement something similar for grouping contacts by company? If so how would I store the contact's position in that company and how can I prevent data corruption if a user modifies a contact's company name. For instance John Doe changed companies but the other co-workers are still in the old company. I doubt that will happen often (might not even happen at all) but better be safe than sorry. I'm also keeping an audit trail so in a way the contact would still need to be linked to the old company as well as the new one but without confusing what company he's actually working at the moment. I hope that made sense... Has anyone encountered such a problem? UPDATE Would something like this make sense contact_company [id_contact_company] [int] PK [id_contact] [int] FK [id_company] [int] FK [contact_title] [varchar] (128) company [id_company] [int] PK NOT NULL, [company_name] [varchar] (128) NULL, [company_description] [varchar] (300) NULL, [created_date] [datetime] NOT NULL This way a contact can work for more than one company and contacts can be grouped by companies

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  • GORM ID generation and belongsTo association ?

    - by fabien-barbier
    I have two domains : class CodeSetDetail { String id String codeSummaryId static hasMany = [codes:CodeSummary] static constraints = { id(unique:true,blank:false) } static mapping = { version false id column:'code_set_detail_id', generator: 'assigned' } } and : class CodeSummary { String id String codeClass String name String accession static belongsTo = [codeSetDetail:CodeSetDetail] static constraints = { id(unique:true,blank:false) } static mapping = { version false id column:'code_summary_id', generator: 'assigned' } } I get two tables with columns: code_set_detail: code_set_detail_id code_summary_id and code_summary: code_summary_id code_set_detail_id (should not exist) code_class name accession I would like to link code_set_detail table and code_summary table by 'code_summary_id' (and not by 'code_set_detail_id'). Note : 'code_summary_id' is define as column in code_set_detail table, and define as primary key in code_summary table. To sum-up, I would like define 'code_summary_id' as primary key in code_summary table, and map 'code_summary_id' in code_set_detail table. How to define a primary key in a table, and also map this key to another table ?

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  • Big O complexity of simple for not always linear?

    - by i30817
    I'm sure most of you know that a nested loop has O(n^2) complexity if the function input size is n for(int i = 0; i < n; i++){ for(int j = 0; j < n; j++){ ... } } I think that this is similar, by a analogous argument, but i'm not sure can anyone confirm? for(int i = 0, max = n*n; i < max; i++{ ... } If so i guess that there is some kinds of code whose big O mapping is not immediately obvious besides recursion and subroutines.

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  • SimpleDB to ActiveResource. Rails

    - by Victor P
    Im looking for a way to map an ActiveResource to SimpleDB I want to avoid plugins/gems as all I have used are outdated/buggy/not mantained It doesnt seem hard, I wonder if any of you have succesfully implemented a rails app with simpleDB as an Active Resource. How did you do it? Thanks.

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  • Calculate shortest path through a grocery store

    - by Bart
    Hi, I'm trying to find a way to find the shortest path through a grocery store, visiting a list of locations (shopping list). The path should start at a specified startposition and can end at multiple endpositions (there are multiple checkout counters). Also, I have some predefined constraints on the path, such as "item x on the shopping list needs to be the last, second last, or third last item on the path". There is a function that will return true or false for a given path. Finally, this needs to be calculated with limited cpu power (on a smartphone) and within a second or so. If this isn't possible, then an approximation to the optimal path is also ok. Is this possible? So far I think I need to start by calculating the distance between every item on the list using something like A* or Dijkstra's. After that, should I treat it like the travelling salesman problem? Because in my problem there is a specified startnode, specified endnodes, and some constraints, which are not in the travelling salesman problem. Any help would be appreciated :)

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  • Finding the Reachability Count for all vertices of a DAG

    - by ChrisH
    I am trying to find a fast algorithm with modest space requirements to solve the following problem. For each vertex of a DAG find the sum of its in-degree and out-degree in the DAG's transitive closure. Given this DAG: I expect the following result: Vertex # Reacability Count Reachable Vertices in closure 7 5 (11, 8, 2, 9, 10) 5 4 (11, 2, 9, 10) 3 3 (8, 9, 10) 11 5 (7, 5, 2, 9, 10) 8 3 (7, 3, 9) 2 3 (7, 5, 11) 9 5 (7, 5, 11, 8, 3) 10 4 (7, 5, 11, 3) It seems to me that this should be possible without actually constructing the transitive closure. I haven't been able to find anything on the net that exactly describes this problem. I've got some ideas about how to do this, but I wanted to see what the SO crowd could come up with.

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  • Can you find a pattern to sync files knowing only dates and filenames?

    - by Robert MacLean
    Imagine if you will a operating system that had the following methods for files Create File: Creates (writes) a new file to disk. Calling this if a file exists causes a fault. Update File: Updates an existing file. Call this if a file doesn't exist causes a fault. Read File: Reads data from a file. Enumerate files: Gets all files in a folder. Files themselves in this operating system only have the following meta data: Created Time: The original date and time the file was created, by the Create File method. Modified Time: The date and time the file was last modified by the Update File method. If the file has never been modified, this will equal the Create Time. You have been given the task of writing an application which will sync the files between two directories (lets call them bill and ted) on a machine. However it is not that simple, the client has required that The application never faults (see methods above). That while the application is running the users can add and update files and those will be sync'd next time the application runs. Files can be added to either the ted or bill directories. File names cannot be altered. The application will perform one sync per time it is run. The application must be almost entirely in memory, in other words you cannot create a log of filenames and write that to disk and then check that the next time. The exception to point 6 is that you can store date and times between runs. Each date/time is associated with a key labeled A through J (so you have 10 to use) so you can compare keys between runs. There is no way to catch exceptions in the application. Answer will be accepted based on the following conditions: First answer to meet all requirements will be accepted. If there is no way to meet all requirements, the answer which ensures the smallest amount of missed changes per sync will be accepted. A bounty will be created (100 points) as soon as possible for the prize. The winner will be selected one day before the bounty ends. Please ask questions in the comments and I will gladly update and refine the question on those.

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  • Rails model relations depending on count of nested relations

    - by Lowgain
    I am putting together a messaging system for a rails app I am working on. I am building it in a similar fashion to facebook's system, so messages are grouped into threads, etc. My related models are: MsgThread - main container of a thread Message - each message/reply in thread Recipience - ties to user to define which users should subscribe to this thread Read - determines whether or not a user has read a specific message My relationships look like class User < ActiveRecord::Base #stuff... has_many :msg_threads, :foreign_key => 'originator_id' #threads the user has started has_many :recipiences has_many :subscribed_threads, :through => :recipiences, :source => :msg_thread #threads the user is subscribed to end class MsgThread < ActiveRecord::Base has_many :messages has_many :recipiences belongs_to :originator, :class_name => "User", :foreign_key => "originator_id" end class Recipience < ActiveRecord::Base belongs_to :user belongs_to :msg_thread end class Message < ActiveRecord::Base belongs_to :msg_thread belongs_to :author, :class_name => "User", :foreign_key => "author_id" end class Read < ActiveRecord::Base belongs_to :user belongs_to :message end I'd like to create a new selector in the user sort of like: has_many :updated_threads, :through => :recipiencies, :source => :msg_thread, :conditions => {THREAD CONTAINS MESSAGES WHICH ARE UNREAD (have no 'read' models tying a user to a message)} I was thinking of either writing a long condition with multiple joins, or possibly writing giving the model an updated_threads method to return this, but I'd like to see if there is an easier way first. Any ideas? Also, if there is something fundamentally wrong with my structure for this functionality let me know! Thanks!!

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  • Integrating Pentaho/Talend/etc. with an OR Mapper

    - by DaDaDom
    We have an application (Java) with an own OR mapper. Within this system we have what can be compared to Hibernate's interceptors (we call it triggers): Do specific actions just before saving data in the database, after it's deleted and so on. The underlying database is MySQL. Now we would like to use tools such as Pentaho Data Integration or Talend to convert data to put it into our system. It's no problem to do that directly on the SQL level, but by doing so we loose the built-in power of our triggers. Is there a way to somehow integrate any of the Data Integration solutions into our existing application? It would be great if there was a way to write into instances of our classes instead of writing into the database directly. Any hints welcome :-)

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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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