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  • MongoDB index/RAM relationship

    - by Tegan Clark
    I'm about to adopt MongoDB for a new project and I've chosen it for flexibility, not scalability. From the documentation and web posts I keep reading that all indexes are in RAM. This just isn't making sense to me as my indexes will easily be larger than the amount of available RAM. Can anyone share some insight on the index/RAM relationship and what happens when both an individual index and all of my indexes exceed the size of available RAM?

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  • Correct way to model recursive relationship in Django

    - by Yuval A
    My application has two node types: a parent node which can hold recursive child nodes. Think of it like the post-comment system in SO, but comments can be recursive: parent_1 child_11 child_12 child_121 child_3 parent_2 child_21 child_211 child_2111 Important to note that the parent nodes have different attributes and behavior than the child nodes. What is the correct (and presumably most efficient) way of modeling this relationship in Django?

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  • Entity Framework foreign relationship issue

    - by Doug Hope
    I've had an entity framework model working for some time. Yesterday, it suddenly started complaining about a foreign key relationship issue during an insert. I've checked the fields and can do a manual insert using the exact field values. But the EF continues to complain. Any ideas what could have happened?

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  • Model a Zero or One to Many Relationship

    - by John
    How should I model a zero or one to a many relationship in the database? For example, a user record may or may not have a parent. So should my user table have a t_user.parent_id or should I have an associative table called t_user_hierarchy with the columns t_user_hierarchy.parent_id and t_user_hierarchy.user_id?

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  • Can't destroy record in many-to-many relationship

    - by Dmart
    I'm new to Rails, so I'm sure I've made a simple mistake. I've set up a many-to-many relationship between two models: User and Group. They're connected through the junction model GroupMember. Here are my models (removed irrelevant stuff): class User < ActiveRecord::Base has_many :group_members has_many :groups, :through => :group_members end class GroupMember < ActiveRecord::Base belongs_to :group belongs_to :user end class Group < ActiveRecord::Base has_many :group_members has_many :users, :through => :group_members end The table for GroupMembers contains additional information about the relationship, so I didn't use has_and_belongs_to_many (as per the Rails "Active Record Associations" guide). The problem I'm having is that I can't destroy a GroupMember. Here's the output from rails console: irb(main):006:0> m = GroupMember.new => #<GroupMember group_id: nil, user_id: nil, active: nil, created_at: nil, updated_at: nil> irb(main):007:0> m.group_id =1 => 1 irb(main):008:0> m.user_id = 16 => 16 irb(main):009:0> m.save => true irb(main):010:0> m.destroy NoMethodError: undefined method `eq' for nil:NilClass from /usr/local/lib/ruby/gems/1.8/gems/activesupport-3.0.4/lib/active_support/whiny_nil.rb:48:in `method_missing' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/persistence.rb:79:in `destroy' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/locking/optimistic.rb:110:in `destroy' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/callbacks.rb:260:in `destroy' from /usr/local/lib/ruby/gems/1.8/gems/activesupport-3.0.4/lib/active_support/callbacks.rb:413:in `_run_destroy_callbacks' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/callbacks.rb:260:in `destroy' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:235:in `destroy' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:292:in `with_transaction_returning_status' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/connection_adapters/abstract/database_statements.rb:139:in `transaction' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:207:in `transaction' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:290:in `with_transaction_returning_status' from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:235:in `destroy' from (irb):10 This is driving me crazy, so any help would be greatly appreciated.

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  • Why One-to-one relationship dosen't work?

    - by eugenn
    I'm trying to create a very simple relationship between two objects. Can anybody explain me why I can't find the Company object via findBy method? class Company { String name String desc City city static constraints = { city(unique: true) } } class City { String name static constraints = { } } class BootStrap { def init = { servletContext -> new City(name: 'Tokyo').save() new City(name: 'New York').save() new Company(name: 'company', city: City.findByName('New York')).save() def c = Company.findByName('company') // Why c=null????! } def destroy = { } }

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  • What is the relationship between a R.V N(0,1) and others continuous random variables

    - by calejero
    Hello. I have a question. I need to kwon what is the relationship between a Random Variable with Normal distribuation (N(0,1)) and others continuous random variables. Can you write to me an example? Thank You Hola a todos. Necesito saber qué relación existe entre una variable aleatoria Normal (0,1) y cualquier variable aleatoria continua. Además, me vendría bien un ejemplo. Gracias por vuestra ayuda

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  • Appengine Model SelfReferenceProperty and parent child relationship

    - by GeekTantra
    I have a scenario in which I need a self reference property as follow: class Post(db.Model): creator = db.UserProperty() post_title = db.StringProperty(required=True) post_status = db.StringProperty(required=True, choices=['draft', 'published']) post_parent = db.SelfReferenceProperty() Now, I want ensure that an entity shouldn't be its own parent and a child of an entity cannot be its parent. How can I ensure this kind of a relationship in the PostForm model form and the Post model.

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  • What is the relationship between programming and music?

    - by pheze
    Who here is both a musician and a programmer? I would also be curious to know which instruments you play, the ages at which you started programming and playing music, your personal experiences, etc. Perhaps we can find a relationship between these two things. I'll begin: Piano since 10, Computer since 12, I am 21. Note: Question originally from pheze.myopenid.com. Related: Jazz Programmer

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  • The Relationship Between Activities and View Objects - Android

    - by Greenhouse Gases
    I am attempting to learn how to develop on the Android platform but do not quite understand the relationship between Activities and Views, because according to the documentation an Activity is link to a UI object that the user can interact with, but if this is the case where does the whole idea of Views come in? There is probably a very basic explanation but I would appreciate a few pointers all the same. Thanks

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  • insert with many to many relationship

    - by Luca Romagnoli
    hi, i have 2 object: user, group that have a relationship many to many i want create a user and associate some groups to it. How can i do it? thanks I've tried with this. but it's wrong: user = new User(); List<int> gruppi = new List<int>() {1,2}; utente.Group =db.Group.Where(p => gruppi.Contains(p.GruppoID)

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  • Relationship problem?

    - by dilip
    I have four tables Tag=id,tag_name Image=Id,Image_name TagImage=Id,tag_id,Image_id ImageStudent=id,Image_id,student_id And I want to find a record using student id and tag name. What relationship do I use?

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  • acts_as_list with has_and_belongs_to_many relationship

    - by mculp
    I've found an old plugin called acts_as_habtm_list - but it's for Rails 1.0.0. Is this functionality built in acts_as_list now? I can't seem to find any information on it. Basically, I have an artists_events table - no model. The relationship is handled through those two models specifying :has_and_belongs_to_many How can I specify order in this situation?

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  • ruby on rails- nested attributes for 'has_one' relationship

    - by Kum
    Hello, I need some help concerning nested attributes in models with 'has_one' relationship. Model Survey has 1 question Model Question has 1 answer How do i build the 'answer' in the code below def new @survey = Survey.new @survey.build_question # build one question @survey.question.answer.build #this part is not working end Please can anybody tell me how to build the answer as the code "@survey.question.answer.build" is not correct. Many many thanks for your help

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  • How to explain to someone that a data structure should not draw itself, explaining separation of con

    - by leeand00
    I have another programmer who I'm trying to explain why it is that a UI component should not also be a data-structure. For instance say that you get a data-structure that contains a record-set from the "database", and you wish to display that record-set in a UI component within your application. According to this programmer (who will remain nameless, he's young and I'm teaching him...), we should subclass the data-structure into a class that will draw the UI component within our application!!!!!! And thus according to this logic, the record-set should manage the drawing of the UI. **Head Desk*** I know that asking a record-set to draw itself is wrong, because, if you wish to render the same data-structure on more than one type of component on your UI, you are going to have a real mess on your hands; you'll need to extend yet another class for each and every UI component that you render from the base-class of your record-set; I am well aware of the "cleanliness" of the of the MVC pattern (and by that what I really mean is you don't confuse your data (the Model) with your UI (the view) or the actions that take place on the data (the Controller more or less...okay not really the API should really handle that...and the Controller should just make as few calls to it as it can, telling it which view to render)) But it's certainly alot cleaner than using data-structures to render UI components! Is there any other advice I could send his way other than the example above? I understand that when you first learn OOP you go through "a stage" where you where just want to extend everything. Followed by a stage when you think that Design Patterns are the solution every single problem...which isn't entirely correct either...thanks Jeff. Is there a way that I can gently nudge this kid in the right direction? Do you have any more examples that might help explain my point to him?

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  • Casting a object to a base class , return the extented object??

    - by CrazyJoe
    My Code: public class Contact { public string id{ get; set; } public string contact_type_id { get; set; } public string value{ get; set; } public string person_id { get; set; } public Contact() { } } public class Contact:Base.Contact { public ContactType ContactType { get; set; } public Person Person {get; set;} public Contact() { ContactType = new ContactType(); Person = new Person(); } } And: Contact c = new Contact(); Base.Contact cb = (Base.Contact)c; The Problem: The **cb** is set to **Contac** and not to **Base.Contact**. Have any trick to do that????

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  • Scala parser combinator runs out of memory

    - by user3217013
    I wrote the following parser in Scala using the parser combinators: import scala.util.parsing.combinator._ import scala.collection.Map import scala.io.StdIn object Keywords { val Define = "define" val True = "true" val False = "false" val If = "if" val Then = "then" val Else = "else" val Return = "return" val Pass = "pass" val Conj = ";" val OpenParen = "(" val CloseParen = ")" val OpenBrack = "{" val CloseBrack = "}" val Comma = "," val Plus = "+" val Minus = "-" val Times = "*" val Divide = "/" val Pow = "**" val And = "&&" val Or = "||" val Xor = "^^" val Not = "!" val Equals = "==" val NotEquals = "!=" val Assignment = "=" } //--------------------------------------------------------------------------------- sealed abstract class Op case object Plus extends Op case object Minus extends Op case object Times extends Op case object Divide extends Op case object Pow extends Op case object And extends Op case object Or extends Op case object Xor extends Op case object Not extends Op case object Equals extends Op case object NotEquals extends Op case object Assignment extends Op //--------------------------------------------------------------------------------- sealed abstract class Term case object TrueTerm extends Term case object FalseTerm extends Term case class FloatTerm(value : Float) extends Term case class StringTerm(value : String) extends Term case class Identifier(name : String) extends Term //--------------------------------------------------------------------------------- sealed abstract class Expression case class TermExp(term : Term) extends Expression case class UnaryOp(op : Op, exp : Expression) extends Expression case class BinaryOp(op : Op, left : Expression, right : Expression) extends Expression case class FuncApp(funcName : Term, args : List[Expression]) extends Expression //--------------------------------------------------------------------------------- sealed abstract class Statement case class ExpressionStatement(exp : Expression) extends Statement case class Pass() extends Statement case class Return(value : Expression) extends Statement case class AssignmentVar(variable : Term, exp : Expression) extends Statement case class IfThenElse(testBody : Expression, thenBody : Statement, elseBody : Statement) extends Statement case class Conjunction(left : Statement, right : Statement) extends Statement case class AssignmentFunc(functionName : Term, args : List[Term], body : Statement) extends Statement //--------------------------------------------------------------------------------- class myParser extends JavaTokenParsers { val keywordMap : Map[String, Op] = Map( Keywords.Plus -> Plus, Keywords.Minus -> Minus, Keywords.Times -> Times, Keywords.Divide -> Divide, Keywords.Pow -> Pow, Keywords.And -> And, Keywords.Or -> Or, Keywords.Xor -> Xor, Keywords.Not -> Not, Keywords.Equals -> Equals, Keywords.NotEquals -> NotEquals, Keywords.Assignment -> Assignment ) def floatTerm : Parser[Term] = decimalNumber ^^ { case x => FloatTerm( x.toFloat ) } def stringTerm : Parser[Term] = stringLiteral ^^ { case str => StringTerm(str) } def identifier : Parser[Term] = ident ^^ { case value => Identifier(value) } def boolTerm : Parser[Term] = (Keywords.True | Keywords.False) ^^ { case Keywords.True => TrueTerm case Keywords.False => FalseTerm } def simpleTerm : Parser[Expression] = (boolTerm | floatTerm | stringTerm) ^^ { case term => TermExp(term) } def argument = expression def arguments_aux : Parser[List[Expression]] = (argument <~ Keywords.Comma) ~ arguments ^^ { case arg ~ argList => arg :: argList } def arguments = arguments_aux | { argument ^^ { case arg => List(arg) } } def funcAppArgs : Parser[List[Expression]] = funcEmptyArgs | ( Keywords.OpenParen ~> arguments <~ Keywords.CloseParen ^^ { case args => args.foldRight(List[Expression]()) ( (a,b) => a :: b ) } ) def funcApp = identifier ~ funcAppArgs ^^ { case funcName ~ argList => FuncApp(funcName, argList) } def variableTerm : Parser[Expression] = identifier ^^ { case name => TermExp(name) } def atomic_expression = simpleTerm | funcApp | variableTerm def paren_expression : Parser[Expression] = Keywords.OpenParen ~> expression <~ Keywords.CloseParen def unary_operation : Parser[String] = Keywords.Not def unary_expression : Parser[Expression] = operation(0) ~ expression(0) ^^ { case op ~ exp => UnaryOp(keywordMap(op), exp) } def operation(precedence : Int) : Parser[String] = precedence match { case 0 => Keywords.Not case 1 => Keywords.Pow case 2 => Keywords.Times | Keywords.Divide | Keywords.And case 3 => Keywords.Plus | Keywords.Minus | Keywords.Or | Keywords.Xor case 4 => Keywords.Equals | Keywords.NotEquals case _ => throw new Exception("No operations with this precedence.") } def binary_expression(precedence : Int) : Parser[Expression] = precedence match { case 0 => throw new Exception("No operation with zero precedence.") case n => (expression (n-1)) ~ operation(n) ~ (expression (n)) ^^ { case left ~ op ~ right => BinaryOp(keywordMap(op), left, right) } } def expression(precedence : Int) : Parser[Expression] = precedence match { case 0 => unary_expression | paren_expression | atomic_expression case n => binary_expression(n) | expression(n-1) } def expression : Parser[Expression] = expression(4) def expressionStmt : Parser[Statement] = expression ^^ { case exp => ExpressionStatement(exp) } def assignment : Parser[Statement] = (identifier <~ Keywords.Assignment) ~ expression ^^ { case varName ~ exp => AssignmentVar(varName, exp) } def ifthen : Parser[Statement] = ((Keywords.If ~ Keywords.OpenParen) ~> expression <~ Keywords.CloseParen) ~ ((Keywords.Then ~ Keywords.OpenBrack) ~> statements <~ Keywords.CloseBrack) ^^ { case ifBody ~ thenBody => IfThenElse(ifBody, thenBody, Pass()) } def ifthenelse : Parser[Statement] = ((Keywords.If ~ Keywords.OpenParen) ~> expression <~ Keywords.CloseParen) ~ ((Keywords.Then ~ Keywords.OpenBrack) ~> statements <~ Keywords.CloseBrack) ~ ((Keywords.Else ~ Keywords.OpenBrack) ~> statements <~ Keywords.CloseBrack) ^^ { case ifBody ~ thenBody ~ elseBody => IfThenElse(ifBody, thenBody, elseBody) } def pass : Parser[Statement] = Keywords.Pass ^^^ { Pass() } def returnStmt : Parser[Statement] = Keywords.Return ~> expression ^^ { case exp => Return(exp) } def statement : Parser[Statement] = ((pass | returnStmt | assignment | expressionStmt) <~ Keywords.Conj) | ifthenelse | ifthen def statements_aux : Parser[Statement] = statement ~ statements ^^ { case st ~ sts => Conjunction(st, sts) } def statements : Parser[Statement] = statements_aux | statement def funcDefBody : Parser[Statement] = Keywords.OpenBrack ~> statements <~ Keywords.CloseBrack def funcEmptyArgs = Keywords.OpenParen ~ Keywords.CloseParen ^^^ { List() } def funcDefArgs : Parser[List[Term]] = funcEmptyArgs | Keywords.OpenParen ~> repsep(identifier, Keywords.Comma) <~ Keywords.CloseParen ^^ { case args => args.foldRight(List[Term]()) ( (a,b) => a :: b ) } def funcDef : Parser[Statement] = (Keywords.Define ~> identifier) ~ funcDefArgs ~ funcDefBody ^^ { case funcName ~ funcArgs ~ body => AssignmentFunc(funcName, funcArgs, body) } def funcDefAndStatement : Parser[Statement] = funcDef | statement def funcDefAndStatements_aux : Parser[Statement] = funcDefAndStatement ~ funcDefAndStatements ^^ { case stmt ~ stmts => Conjunction(stmt, stmts) } def funcDefAndStatements : Parser[Statement] = funcDefAndStatements_aux | funcDefAndStatement def parseProgram : Parser[Statement] = funcDefAndStatements def eval(input : String) = { parseAll(parseProgram, input) match { case Success(result, _) => result case Failure(m, _) => println(m) case _ => println("") } } } object Parser { def main(args : Array[String]) { val x : myParser = new myParser() println(args(0)) val lines = scala.io.Source.fromFile(args(0)).mkString println(x.eval(lines)) } } The problem is, when I run the parser on the following example it works fine: define foo(a) { if (!h(IM) && a) then { return 0; } if (a() && !h()) then { return 0; } } But when I add threes characters in the first if statement, it runs out of memory. This is absolutely blowing my mind. Can anyone help? (I suspect it has to do with repsep, but I am not sure.) define foo(a) { if (!h(IM) && a(1)) then { return 0; } if (a() && !h()) then { return 0; } } EDIT: Any constructive comments about my Scala style is also appreciated.

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  • Adding fields to a proxied class in Clojure

    - by mikera
    I'm using "proxy" to extend various Swing classes in a Clojure GUI application, generally with code that looks something like: (def ^JPanel mypanel (proxy [JPanel] [] (paintComponent [#^Graphics g] (.drawImage g background-image 0 0 nil)))) This works well but I can't figure out how to add additional fields to the newly extended class, for example making the background-image a field that could be subsequently updated. This would be pretty easy and common practice in Java. Is there a good way to do this in Clojure? Or is there another preferred method to achieve the same effect?

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