Search Results

Search found 30246 results on 1210 pages for 'object persistence'.

Page 15/1210 | < Previous Page | 11 12 13 14 15 16 17 18 19 20 21 22  | Next Page >

• javascript - query object graph?

  - by Scott

  Given an object like this: var obj = { first:{ second:{ third:'hi there' } } }; And a key like this "first.second.third" How can I get the value of the nested object "hi there"? I think maybe the Array.reduce function could help, but not sure.

  Read the article

• What is a simple way to get ACID transactions with persistence on the local file system (in Java)?

  - by T.R.

  I'm working on a small (java) project where a website needs to maintain a (preferably comma-separated) list of registered e-mail addresses, nothing else, and be able to check if an address is in the list. I have no control over the hosting or the server's lack of database support. Prevayler seemed a good solution, but the website is a ghost town, with example code missing from just about everywhere it's supposed to be, so I'm a little wary. What other options are recommended for such a task?

  Read the article

• Jquery draggable persistence either through mysql or saving cookie in the database?

  - by Muhammad Jehanzaib

  I want to know that how can I persist the divs dropped on a draggable. I have been trying since long but stuck at this point. Actually you can see the demo here. I have to save the user designed wedding floor. So whenever user logins next time he/ she is able to see the last design saved. The code is shown below: $(document).ready(function() { $("#droppable").droppable({ accept: '.draggable', drop: function(event, ui) { $(this).append($(ui.draggable).clone()); $("#droppable .draggable").addClass("objects"); $(".objects").removeClass("ui-draggable draggable"); $(".objects").draggable({ containment: 'parent', }); } }); $(".draggable").draggable({ helper: 'clone', tolerance: 'touch', cursor:'move' }); });

  Read the article

• Java programming accessing object variables

  - by Haxed

  Helo, there are 3 files, CustomerClient.java, CustomerServer.java and Customer.java PROBLEM: In the CustomerServer.java file, i get an error when I compile the CustomerServer.java at line : System.out.println(a[k].getName()); ERROR: init: deps-jar: Compiling 1 source file to C:\Documents and Settings\TLNA\My Documents\NetBeansProjects\Server\build\classes C:\Documents and Settings\TLNA\My Documents\NetBeansProjects\Server\src\CustomerServer.java:44: cannot find symbol symbol : method getName() location: class Customer System.out.println(a[k].getName()); 1 error BUILD FAILED (total time: 0 seconds) CustomerClient.java import java.io.*; import java.net.*; import java.awt.*; import java.awt.event.*; import javax.swing.*; import javax.swing.border.*; public class CustomerClient extends JApplet { private JTextField jtfName = new JTextField(32); private JTextField jtfSeatNo = new JTextField(32); // Button for sending a student to the server private JButton jbtRegister = new JButton("Register to the Server"); // Indicate if it runs as application private boolean isStandAlone = false; // Host name or ip String host = "localhost"; public void init() { JPanel p1 = new JPanel(); p1.setLayout(new GridLayout(2, 1)); p1.add(new JLabel("Name")); p1.add(jtfName); p1.add(new JLabel("Seat No.")); p1.add(jtfSeatNo); add(p1, BorderLayout.CENTER); add(jbtRegister, BorderLayout.SOUTH); // Register listener jbtRegister.addActionListener(new ButtonListener()); // Find the IP address of the Web server if (!isStandAlone) { host = getCodeBase().getHost(); } } /** Handle button action */ private class ButtonListener implements ActionListener { public void actionPerformed(ActionEvent e) { try { // Establish connection with the server Socket socket = new Socket(host, 8000); // Create an output stream to the server ObjectOutputStream toServer = new ObjectOutputStream(socket.getOutputStream()); // Get text field String name = jtfName.getText().trim(); String seatNo = jtfSeatNo.getText().trim(); // Create a Student object and send to the server Customer s = new Customer(name, seatNo); toServer.writeObject(s); } catch (IOException ex) { System.err.println(ex); } } } /** Run the applet as an application */ public static void main(String[] args) { // Create a frame JFrame frame = new JFrame("Register Student Client"); // Create an instance of the applet CustomerClient applet = new CustomerClient(); applet.isStandAlone = true; // Get host if (args.length == 1) { applet.host = args[0]; // Add the applet instance to the frame } frame.add(applet, BorderLayout.CENTER); // Invoke init() and start() applet.init(); applet.start(); // Display the frame frame.pack(); frame.setVisible(true); } } CustomerServer.java import java.io.*; import java.net.*; public class CustomerServer { private String name; private int i; private ObjectOutputStream outputToFile; private ObjectInputStream inputFromClient; public static void main(String[] args) { new CustomerServer(); } public CustomerServer() { Customer[] a = new Customer[30]; try { // Create a server socket ServerSocket serverSocket = new ServerSocket(8000); System.out.println("Server started "); // Create an object ouput stream outputToFile = new ObjectOutputStream( new FileOutputStream("student.dat", true)); while (true) { // Listen for a new connection request Socket socket = serverSocket.accept(); // Create an input stream from the socket inputFromClient = new ObjectInputStream(socket.getInputStream()); // Read from input //Object object = inputFromClient.readObject(); for (int k = 0; k <= 2; k++) { if (a[k] == null) { a[k] = (Customer) inputFromClient.readObject(); // Write to the file outputToFile.writeObject(a[k]); //System.out.println("A new student object is stored"); System.out.println(a[k].getName()); break; } if (k == 2) { //fully booked outputToFile.writeObject("All seats are booked"); break; } } } } catch (ClassNotFoundException ex) { ex.printStackTrace(); } catch (IOException ex) { ex.printStackTrace(); } finally { try { inputFromClient.close(); outputToFile.close(); } catch (Exception ex) { ex.printStackTrace(); } } } } Customer.java public class Customer implements java.io.Serializable { private String name; private String seatno; public Customer(String name, String seatno) { this.name = name; this.seatno = seatno; } public String getName() { return name; } public String getSeatNo() { return seatno; } }

  Read the article

• SQL SERVER – Validating Spatial Object as NULL using IsNULL

  - by pinaldave

  Follow up questions are the most fun part of writing a blog post. Earlier I wrote about SQL SERVER – Validating Spatial Object with IsValidDetailed Function and today I received a follow up question on the same subject. The question was mainly about how NULL is handled by spatial functions. Well, NULL is NULL. It is very easy to work with NULL. There are two different ways to validate if the passed in the value is NULL or not. 1) Using IsNULL Function IsNULL function validates if the object is null or not, if object is not null it will return you value 0 and if object is NULL it will return you the value NULL. DECLARE @p GEOMETRY = 'Polygon((2 2, 3 3, 4 4, 5 5, 6 6, 2 2))' SELECT @p.ISNULL ObjIsNull GO DECLARE @p GEOMETRY = NULL SELECT @p.ISNULL ObjIsNull GO 2) Using IsValidDetailed Function IsValidateDetails function validates if the object is valid or not. If the object is valid it will return 24400: Valid but if the object is not valid it will give message with the error number. In case object is NULL it will return the value as NULL. DECLARE @p GEOMETRY = 'Polygon((2 2, 3 3, 4 4, 5 5, 6 6, 2 2))' SELECT @p.IsValidDetailed() IsValid GO DECLARE @p GEOMETRY = NULL SELECT @p.IsValidDetailed() IsValid GO When to use what? Now you can see that there are two different ways to validate the NULL values. I personally have no preference about using one over another. However, there is one clear difference between them. In case of the IsValidDetailed Function the return value is nvarchar(max) and it is not always possible to compare the value with nvarchar(max). Whereas the ISNULL function returns the bit value of 0 when the object is null and it is easy to determine if the object is null or not in the case of ISNULL function. Additionally, ISNULL function does not check if the object is valid or not and will return the value 0 if the object is not NULL. Now you know even though either of the function can be used in place of each other both have very specific use case. Use the one which fits your business case. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Spatial Database, SQL Spatial

  Read the article

• Ways to ensure unique instances of a class?

  - by Peanut

  I'm looking for different ways to ensure that each instance of a given class is a uniquely identifiable instance. For example, I have a Name class with the field name. Once I have a Name object with name initialised to John Smith I don't want to be able to instantiate a different Name object also with the name as John Smith, or if instantiation does take place I want a reference to the orginal object to be passed back rather than a new object. I'm aware that one way of doing this is to have a static factory that holds a Map of all the current Name objects and the factory checks that an object with John Smith as the name doesn't already exist before passing back a reference to a Name object. Another way I could think of off the top of my head is having a static Map in the Name class and when the constructor is called throwing an exception if the value passed in for name is already in use in another object, however I'm aware throwing exceptions in a constructor is generally a bad idea. Are there other ways of achieving this?

  Read the article

• How can we protect the namespace of an object in Javascript?

  - by Eduard Florinescu

  Continuing from my previous question: Javascript simple code to understand prototype-based OOP basics Let's say we run into console this two separate objects(even if they are called child and parent there is no inheritance between them): var parent = { name: "parent", print: function(){ console.log("Hello, "+this.name); } }; var child = { name: "child", print: function(){ console.log("Hi, "+this.name); } }; parent.print() // This will print: Hello, parent child.print() // This will print: Hi, child temp =parent; parent = child; child = temp; parent.print() // This will now print: Hi, child child.print() // This will now print: Hello, parent Now suppose that parent is a library, as a HTML5 application in a browser this cannot do much harm because is practically running sandboxed, but now with the advent of the ChromeOS, FirefoxOS and other [Browser] OS they will also be linked to a native API, that would be a head out of the „sandbox”. Now if someone changes the namespace it would be harder for a code reviewer (either automated or not ) to spot an incorrect use if the namespaces changes. My question would be: Are there many ways in which the above situation can be done and what can be done to protect this namespaces? (Either in the javascript itself or by some static code analysis tool)

  Read the article

• If I define a property to prototype appears in the constructor of object, why?

  - by Eduard Florinescu

  I took the example from this question modified a bit: What is the point of the prototype method? function employee(name,jobtitle,born) { this.name=name; this.jobtitle=jobtitle; this.born=born; this.status="single" } employee.prototype.salary=10000000; var fred=new employee("Fred Flintstone","Caveman",1970); console.log(fred.salary); fred.salary=20000; console.log(fred.salary) And the output in console is this: What is the difference salary is in constructor but I still can access it with fred.salary, how can I see if is in constructor from code, status is still employee property how can I tell for example if name is the one of employee or has been touch by initialization? Why is salary in constructor, when name,jobtitle,born where "touched" by employee("Fred Flintstone","Caveman",1970); «constructor»?

  Read the article

• Should main method be only consists of object creations and method calls?

  - by crucified soul

  A friend of mine told me that, the best practice is class containing main method should be named Main and only contains main method. Also main method should only parse inputs, create other objects and call other methods. The Main class and main method shouldn't do anything else. Basically what he is saying that class containing main method should be like: public class Main { public static void main(String[] args) { //parse inputs //create other objects //call methods } } Is it the best practice?

  Read the article

• Design in "mixed" languages: object oriented design or functional programming?

  - by dema80

  In the past few years, the languages I like to use are becoming more and more "functional". I now use languages that are a sort of "hybrid": C#, F#, Scala. I like to design my application using classes that correspond to the domain objects, and use functional features where this makes coding easier, more coincise and safer (especially when operating on collections or when passing functions). However the two worlds "clash" when coming to design patterns. The specific example I faced recently is the Observer pattern. I want a producer to notify some other code (the "consumers/observers", say a DB storage, a logger, and so on) when an item is created or changed. I initially did it "functionally" like this: producer.foo(item => { updateItemInDb(item); insertLog(item) }) // calls the function passed as argument as an item is processed But I'm now wondering if I should use a more "OO" approach: interface IItemObserver { onNotify(Item) } class DBObserver : IItemObserver ... class LogObserver: IItemObserver ... producer.addObserver(new DBObserver) producer.addObserver(new LogObserver) producer.foo() //calls observer in a loop Which are the pro and con of the two approach? I once heard a FP guru say that design patterns are there only because of the limitations of the language, and that's why there are so few in functional languages. Maybe this could be an example of it? EDIT: In my particular scenario I don't need it, but.. how would you implement removal and addition of "observers" in the functional way? (I.e. how would you implement all the functionalities in the pattern?) Just passing a new function, for example?

  Read the article

• How can I explain object-oriented programming to someone who's only coded in Fortran 77?

  - by Zonedabone

  My mother did her college thesis in Fortran, and now (over a decade later) needs to learn c++ for fluids simulations. She is able to understand all of the procedural programming, but no matter how hard I try to explain objects to her, it doesn't stick. (I do a lot of work with Java, so I know how objects work) I think I might be explaining it in too high-level ways, so it isn't really making sense to someone who's never worked with them at all and grew up in the age of purely procedural programming. Is there any simple way I can explain them to her that will help her understand?

  Read the article

• Print all values in a value object

  - by SKDev

  I have to debug an issue which requires me to print all the values of a Value Object that is returned by a web service call. The Value object is a complex object in the sense, it has another object as its member which in turn has another object. Printing all the values by using get methods is cumbersome. So was wondering if there is a way to break down the value object by any way to get to a primitive level like String or int or Date and print them all using one API? I had a look at the below question but my prob is that i don't have access to the source code of the value object. The sources are in obfuscated jar. http://stackoverflow.com/questions/2413001/how-to-print-values-of-an-object-in-java

  Read the article

• Recommended design pattern for object with optional and modifiable attributtes? [on hold]

  - by Ikuzen

  I've been using the Builder pattern to create objects with a large number of attributes, where most of them are optional. But up until now, I've defined them as final, as recommended by Joshua Block and other authors, and haven't needed to change their values. I am wondering what should I do though if I need a class with a substantial number of optional but non-final (mutable) attributes? My Builder pattern code looks like this: public class Example { //All possible parameters (optional or not) private final int param1; private final int param2; //Builder class public static class Builder { private final int param1; //Required parameters private int param2 = 0; //Optional parameters - initialized to default //Builder constructor public Builder (int param1) { this.param1 = param1; } //Setter-like methods for optional parameters public Builder param2(int value) { param2 = value; return this; } //build() method public Example build() { return new Example(this); } } //Private constructor private Example(Builder builder) { param1 = builder.param1; param2 = builder.param2; } } Can I just remove the final keyword from the declaration to be able to access the attributes externally (through normal setters, for example)? Or is there a creational pattern that allows optional but non-final attributes that would be better suited in this case?

  Read the article

• Implement DDD and drawing the line between the an Entity and value object

  - by William

  I am implementing an EMR project. I would like to apply a DDD based approach to the problem. I have identified the "Patient" as being the core object of the system. I understand Patient would be an entity object as well as an aggregrate. I have also identified that every patient must have a "Doctor" and "Medical Records". The medical records would encompass Labs, XRays, Encounter.... I believe those would be entity objects as well. Let us take a Encounter for example. My implementation currently has a few fields as "String" properties, which are the complaint, assessment and plan. The other items necessary for an Encounter are vitals. I have implemented vitals as a value object. Given that it will be necessary to retrieve vitals without haveing to retrieve each Encounter then do vitals become part of the Encounter aggregate and patient aggregrate. I am assuming I could view the Encounter as an aggregrate, because other items are spwaned from the Encounter like prescriptions, lab orders, xrays. Is approach right that I am taking in identifying my entities and aggregates. In the case of vitals, they are specific to a patient, but outside of that there is not any other identity associated with them.

  Read the article

• Getting an Error Trying to Create an Object in Python

  - by Nick Rogers

  I am trying to create an object from a class in python but I am getting an Error, "e_tank = EnemyTank() TypeError: 'Group' object is not callable" I am not sure what this means, I have tried Google but I couldn't get a clear answer on what is causing this error. Does anyone understand why I am unable to create an object from my EnemyTank Class? Here is my code: #Image Variables bg = 'bg.jpg' bunk = 'bunker.png' enemytank = 'enemy-tank.png' #Import Pygame Modules import pygame, sys from pygame.locals import * #Initializing the Screen pygame.init() screen = pygame.display.set_mode((640,360), 0, 32) background = pygame.image.load(bg).convert() bunker_x, bunker_y = (160,0) class EnemyTank(pygame.sprite.Sprite): e_tank = pygame.image.load(enemytank).convert_alpha() def __init__(self, startpos): pygame.sprite.Sprite.__init__(self, self.groups) self.pos = startpos self.image = EnemyTank.image self.rect = self.image.get_rect() def update(self): self.rect.center = self.pos class Bunker(pygame.sprite.Sprite): bunker = pygame.image.load(bunk).convert_alpha() def __init__(self, startpos): pygame.spriter.Sprite.__init__(self, self.groups) self.pos = startpos self.image = Bunker.image self.rect = self.image.get_rect() def getCollisionObjects(self, EnemyTank): if (EnemyTank not in self._allgroup, False): return False self._allgroup.remove(EnemyTank) result = pygame.sprite.spritecollide(EnemyTank, self._allgroup, False) self._allgroup.add(EnemyTank) def update(self): self.rect.center = self.pos #Setting Up The Animation x = 0 clock = pygame.time.Clock() speed = 250 allgroup = pygame.sprite.Group() EnemyTank = allgroup Bunker = allgroup e_tank = EnemyTank() bunker = Bunker()5 #Main Loop while True: for event in pygame.event.get(): if event.type == QUIT: pygame.quit() sys.exit() screen.blit(background, (0,0)) screen.blit(bunker, (bunker_x, bunker_y)) screen.blit(e_tank, (x, 0)) pygame.display.flip() #Animation milli = clock.tick() seconds = milli/1000. dm = seconds*speed x += dm if x>640: x=0 #Update the Screen pygame.display.update()

  Read the article

• Save Jquery Object without losing its binding

  - by Ahmad Satiri

  Hi I have object created using jquery where each object has it's own binding. function closeButton(oAny){ var div = create_div(); $(div).attr("id","btn_"+$(oAny).attr("id")); var my_parent = this; $(div).html("<img src='"+ my_parent._base_url +"/assets/images/close.gif'>"); $(div).click(function(){ alert("do some action here"); }); return div; } var MyObject = WindowObject(); var btn = closeButton(MyObject); $(myobject).append(btn); $("body").append(myobject); //at this point button will work as i expected //save to array for future use ObjectCollections[0] = myobject; //remove $(myobject).remove(); $(body).append(ObjectCollections[0]); // at this point button will not work For the first time i can show my object and close button is working as i expected. But if i save myobject to any variable for future use. It will loose its binding. Anybody ever try to do this ? Is there any work around ? or It is definitely a bad idea ? .And thanks for answering my question.

  Read the article

• Is it possible to restrict instantiation of an object to only one other (parent) object in VB.NET?

  - by Casey

  VB 2008 .NET 3.5 Suppose we have two classes, Order and OrderItem, that represent some type of online ordering system. OrderItem represents a single line item in an Order. One Order can contain multiple OrderItems, in the form of a List(of OrderItem). Public Class Order Public Property MyOrderItems() as List(of OrderItem) End Property End Class It makes sense that an OrderItem should not exist without an Order. In other words, an OrderItem class should not be able to be instantiated on its own, it should be dependent on an Order class to contain it and instantiate it. However, the OrderItem should be public in scope so that it's properties are accessible to other objects. So, the requirements for OrderItem are: Can not be instantiated as a stand alone object; requires Order to exist. Must be public so that any other object can access it's properties/methods through the Order object. e.g. Order.OrderItem(0).ProductID. OrderItem should be able to be passed to other subs/functions that will operate on it. How can I achieve these goals? Is there a better approach?

  Read the article

• Adding array to an object breaks the array

  - by DisgruntledGoat

  I have an array like this (output from print_r): Array ( [price] => 700.00 [room_prices] => Array ( [0] => [1] => [2] => [3] => [4] => ) [bills] => Array ( [0] => Gas ) ) I'm running a custom function to convert it to an object. Only the top-level should be converted, the sub-arrays should stay as arrays. The output comes out like this: stdClass Object ( [price] => 700.00 [room_prices] => Array ( [0] => Array ) [bills] => Array ( [0] => Array ) ) Here is my conversion function. All it does is set the value of each array member to an object: function array_to_object( $arr ) { $obj = new stdClass; if ( count($arr) == 0 ) return $obj; foreach ( $arr as $k=>$v ) $obj->$k = $v; return $obj; } I can't figure this out for the life of me!

  Read the article

• object / class methods serialized as well?

  - by Mat90

  I know that data members are saved to disk but I was wondering whether object's/class' methods are saved in binary format as well? Because I found some contradictionary info, for example: Ivor Horton: "Class objects contain function members as well as data members, and all the members, both data and functions, have access specifiers; therefore, to record objects in an external file, the information written to the file must contain complete specifications of all the class structures involved." and: Are methods also serialized along with the data members in .NET? Thus: are method's assembly instructions (opcodes and operands) stored to disk as well? Just like a precompiled LIB or DLL? During the DOS ages I used assembly so now and then. As far as I remember from Delphi and the following site (answer by dan04): Are methods also serialized along with the data members in .NET? sizeof(<OBJECT or CLASS>) will give the size of all data members together (no methods/procedures). Also a nice C example is given there with data and members declared in one class/struct but at runtime these methods are separate procedures acting on a struct of data. However, I think that later class/object implementations like Pascal's VMT may be different in memory.

  Read the article

• Strange behavior with large Object Types

  - by Peter Lang

  I recognized that calling a method on an Oracle Object Type takes longer when the instance gets bigger. The code below just adds rows to a collection stored in the Object Type and calls the empty dummy-procedure in the loop. Calls are taking longer when more rows are in the collection. When I just remove the call to dummy, performance is much better (the collection still contains the same number of records): Calling dummy: Not calling dummy: 11 0 81 0 158 0 Code to reproduce: Create Type t_tab Is Table Of VARCHAR2(10000); Create Type test_type As Object( tab t_tab, Member Procedure dummy ); Create Type Body test_type As Member Procedure dummy As Begin Null; --# Do nothing End dummy; End; Declare v_test_type test_type := New test_type( New t_tab() ); Procedure run_test As start_time NUMBER := dbms_utility.get_time; Begin For i In 1 .. 200 Loop v_test_Type.tab.Extend; v_test_Type.tab(v_test_Type.tab.Last) := Lpad(' ', 10000); v_test_Type.dummy(); --# Removed this line in second test End Loop; dbms_output.put_line( dbms_utility.get_time - start_time ); End run_test; Begin run_test; run_test; run_test; End; I tried with both 10g and 11g. Can anyone explain/reproduce this behavior?

  Read the article

• How to Object Array to List

  - by Peter Black

  (C#) I have 2 classes. 1 is called Employee. The other is my "main". I am trying to take a list and assign each value in list to an array of Employee object. //Inside "Main" class int counter = NameList.Count; Employee[] employee = new Employee[counter]; for (int i = 0; i <= counter; i++) { employee[i].Name = NameList[i]; employee[i].EmpNumber = EmpNumList[i]; employee[i].DateOfHire = DOHList[i]; employee[i].Salary = SalaryList[i]; employee[i].JobDescription = JobDescList[i]; employee[i].Department = DeptList[i]; } This returns the error: An unhandled exception of type 'System.NullReferenceException' occurred in Pgm4.exe Additional information: Object reference not set to an instance of an object. I think this means that I am not calling the list properly. Any help would be much appreciated. Thank you.

  Read the article

• java /TableModel of Objects/Update Object"

  - by Tomás Ó Briain

  I've a collection of Stock objects that I'm updating about 10/15 variables for in real-time. I'm accessing each Stock by its ID in the collection. I'm also trying to display this in a JTable and have implemented an AbstractTablemodel. It's not working too well. I've a RowMap that I add each ID to as Stocks are added to the TableModel. To update the prices and variables of all the stocks in the TableModel, I want to send a Stock object to an updateModel(Stock s) method. I can find the relevant row by searching the map, but how do I handle this nicely, so I don't have to start iterating through table columns and comparing the values of the cells to the variables of the object to see whether there are any differences?? Basically, i want to send a Stock object to the TableModel and update cells if there are changes and do nothing if there aren't. Any ideas about how to implement a TableModel that might do this? Any pointeres at all would be appreciated. Thanks.

  Read the article

• what is the difference between loose coupling and tight coupling in obect oriented paradigm?

  - by Jim

  Hi, can any one describe the exact difference between loose coupling and tight coupling in Object oriented paradigm?? I am too much confused on this. Thanks, Jim.

  Read the article

• How to create PHP method linking?

  - by Kerry

  I've seen other objects that do this: $obj->method1()->method2(); How do I do that? Is each function just modifying the pointer of an object or returning a pointer? I don't know the proper term for this style -- if anyone could help me with that, it would be great.

  Read the article

• ORM Persistence by Reachability violates Aggregate Root Boundaries?

  - by Johannes Rudolph

  Most common ORMs implement persistence by reachability, either as the default object graph change tracking mechanism or an optional. Persistence by reachability means the ORM will check the aggregate roots object graph and determines wether any objects are (also indirectly) reachable that are not stored inside it's identity map (Linq2Sql) or don't have their identity column set (NHibernate). In NHibernate this corresponds to cascade="save-update", for Linq2Sql it is the only supported mechanism. They do both, however only implement it for the "add" side of things, objects removed from the aggregate roots graph must be marked for deletion explicitly. In a DDD context one would use a Repository per Aggregate Root. Objects inside an Aggregate Root may only hold references to other Aggregate Roots. Due to persistence by reachability it is possible this other root will be inserted in the database event though it's corresponding repository wasn't invoked at all! Consider the following two Aggregate Roots: Contract and Order. Request is part of the Contract Aggregate. The object graph looks like Contract->Request->Order. Each time a Contractor makes a request, a corresponding order is created. As this involves two different Aggregate Roots, this operation is encapsulated by a Service. //Unit Of Work begins Request r = ...; Contract c = ContractRepository.FindSingleByKey(1); Order o = OrderForRequest(r); // creates a new order aggregate r.Order = o; // associates the aggregates c.Request.Add(r); ContractRepository.SaveOrUpdate(c); // OrderAggregate is reachable and will be inserted Since this Operation happens in a Service, I could still invoke the OrderRepository manually, however I wouldn't be forced to!. Persistence by reachability is a very useful feature inside Aggregate Roots, however I see no way to enforce my Aggregate Boundaries.

  Read the article

< Previous Page | 11 12 13 14 15 16 17 18 19 20 21 22  | Next Page >