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• Help identify the pattern for reacting on updates

  - by Mike

  There's an entity that gets updated from external sources. Update events are at random intervals. And the entity has to be processed once updated. Multiple updates may be multiplexed. In other words there's a need for the most current state of entity to be processed. There's a point of no-return during processing where the current state (and the state is consistent i.e. no partial update is made) of entity is saved somewhere else and processing goes on independently of any arriving updates. Every consequent set of updates has to trigger processing i.e. system should not forget about updates. And for each entity there should be no more than one running processing (before the point of no-return) i.e. the entity state should not be processed more than once. So what I'm looking for is a pattern to cancel current processing before the point of no return or abandon processing results if an update arrives. The main challenge is to minimize race conditions and maintain integrity. The entity sits mainly in database with some files on disk. And the system is in .NET with web-services and message queues. What comes to my mind is a database queue-like table. An arriving update inserts row in that table and the processing is launched. The processing gathers necessary data before the point of no-return and once it reaches this barrier it looks into the queue table and checks whether there're more recent updates for the entity. If there are new updates the processing simply shuts down and its data is discarded. Otherwise the processing data is persisted and it goes beyond the point of no-return. Though it looks like a solution to me it is not quite elegant and I believe this scenario may be supported by some sort of middleware. If I would use message queues for this then there's a need to access the queue API in the point of no-return to check for the existence of new messages. And this approach also lacks elegance. Is there a name for this pattern and an existing solution?

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• Is it a good approach to rely on 3rd party software ( not library )?

  - by gunbuster363

  We have program using a call to a winzip program or 7zip commandline tool to zip some files. Once I accidentally uninstall winzip on my computer and making one of our program( created by the programmer already left ) crashed. So we cannot uninstall the winzip program. Now I've come to a point which I need to decide a external tool for gzip in windows or I make a java program which I can call to gzip the file. Obviously a external tool such as 7z is convenient and we can avoid some extra coding with java. On the contrary, if 7z is uninstalled accidentally, our program will crash. What do you think?

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• Service Layer - how broad should it be, and should it also be on the local application?

  - by BornToCode

  Background: I need to build a desktop application with some operations (CRUD and more) (=winforms), I need to make another application which will re-use some of the functions of the main application (=webforms). I understood that using service layer is the best approach here. If I understood correctly the service should be calling the function on the BL layer (correct me if I'm wrong) The dilemma: In my main winform UI - should I call the functions from the BL, or from the service? (please explain why) Should I create a service for every single function on the BL even if I need some of the functions only in one UI? for example - should I create services for all the CRUD operations, even though I need to re-use only update operation in the webform? YOUR HELP IS MUCH APPRECIATED

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• How many tiers should my models have in a DB driven web app?

  - by Hanno Fietz

  In my experience, the "Model" in MVC is often not really a single layer. I would regularly have "backend" models and "frontend" models, where the backend ones would have properties that I want to hide from the UI code, and the frontend ones have derived or composite properties which are more meaningful in the context of the UI. Recently, I have started to introduce a third layer in between when database normalization created tables that did not really match the conceptual domain objects anymore. In those projects I have model classes that are equivalent with the DB structure, these become components of objects that represent the domain model, and finally these are filtered and amended for displaying information to the user. Are there patterns or guidelines for how, when and why to organize the data model across application layers?

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• Concurrency pattern of logger in multithreaded application

  - by Dipan Mehta

  The context: We are working on a multi-threaded (Linux-C) application that follows a pipeline model. Each module has a private thread and encapsulated objects which do processing of data; and each stage has a standard form of exchanging data with next unit. The application is free from memory leak and is threadsafe using locks at the point where they exchange data. Total number of threads is about 15- and each thread can have from 1 to 4 objects. Making about 25 - 30 odd objects which all have some critical logging to do. Most discussion I have seen about different levels as in Log4J and it's other translations. The real big questions is about how the overall logging should really happen? One approach is all local logging does fprintf to stderr. The stderr is redirected to some file. This approach is very bad when logs become too big. If all object instantiate their individual loggers - (about 30-40 of them) there will be too many files. And unlike above, one won't have the idea of true order of events. Timestamping is one possibility - but it is still a mess to collate. If there is a single global logger (singleton) pattern - it indirectly blocks so many threads while one is busy putting up logs. This is unacceptable when processing of the threads are heavy. So what should be the ideal way to structure the logging objects? What are some of the best practices in actual large scale applications? I would also love to learn from some of the real designs of large scale applications to get inspirations from!

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• How to verify the Liskov substitution principle in an inheritance hierarchy?

  - by Songo

  Inspired by this answer: Liskov Substitution Principle requires that Preconditions cannot be strengthened in a subtype. Postconditions cannot be weakened in a subtype. Invariants of the supertype must be preserved in a subtype. History constraint (the "history rule"). Objects are regarded as being modifiable only through their methods (encapsulation). Since subtypes may introduce methods that are not present in the supertype, the introduction of these methods may allow state changes in the subtype that are not permissible in the supertype. The history constraint prohibits this. I was hoping if someone would post a class hierarchy that violates these 4 points and how to solve them accordingly. I'm looking for an elaborate explanation for educational purposes on how to identify each of the 4 points in the hierarchy and the best way to fix it. Note: I was hoping to post a code sample for people to work on, but the question itself is about how to identify the faulty hierarchies :)

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• share distribution question

  - by facebook-100000781341887

  Hi, I just developed a facebook game(mifia like), but the graphic I make is not good, because it is reference with some existing photo, trace with AI, and coloring it. Therefore, I invite my friend to join me, he is a graphic designer, own a company with his friend (I know both of them), for the share, I expect at least 70% for me, and at most 30% for them (both of them want to join). Therefore, they give me a counter offer, 60% for me and 40% for them, of course, I feel their counter offer is unacceptable because they only build the image in part time, and all the other work just like coding, webhosting...etc, is what I do in full time. Why they said they worth 40% is that they will make a good graphic, they can provide a advertise channel(on local magazine), etc... Actually, I don't think the game need advertisement on local magazine because the game is not target for local... Please give me some comments on this issue(is the share fair? what is the importance of the image of the game, is it worth more than 30%), or can anyone share the experience on this. Thanks in advance.

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• Should I close database connections after use in PHP?

  - by Sprottenwels

  I wonder if I should close any unnecessary database connection inside of my PHP scripts. I am aware of the fact that database connections are closed implicitly when the block stops executing and 'manually' closing the connections could kinda bloat the codebase with unnecessary code. But shouldn't I do so in order to make by code as readable and as easy understandable as possible, while also preventing several possible issues during run time? Also, if I would do, would it be enough to unset() my database object?

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• Designing exceptions for conversion failures

  - by Mr.C64

  Suppose there are some methods to convert from "X" to "Y" and vice versa; the conversion may fail in some cases, and exceptions are used to signal conversion errors in those cases. Which would be the best option for defining exception classes in this context? A single XYConversionException class, with an attribute (e.g. an enum) specifying the direction of the conversion (e.g. ConversionFromXToY, ConversionFromYToX). A XYConversionException class, with two derived classes ConversionFromXToYException and ConversionFromYToXException. ConversionFromXToYException and ConversionFromYToXException classes without a common base class.

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• Why do old programming languages continue to be revised?

  - by SunAvatar

  This question is not, "Why do people still use old programming languages?" I understand that quite well. In fact the two programming languages I know best are C and Scheme, both of which date back to the 70s. Recently I was reading about the changes in C99 and C11 versus C89 (which seems to still be the most-used version of C in practice and the version I learned from K&R). Looking around, it seems like every programming language in heavy use gets a new specification at least once per decade or so. Even Fortran is still getting new revisions, despite the fact that most people using it are still using FORTRAN 77. Contrast this with the approach of, say, the typesetting system TeX. In 1989, with the release of TeX 3.0, Donald Knuth declared that TeX was feature-complete and future releases would contain only bug fixes. Even beyond this, he has stated that upon his death, "all remaining bugs will become features" and absolutely no further updates will be made. Others are free to fork TeX and have done so, but the resulting systems are renamed to indicate that they are different from the official TeX. This is not because Knuth thinks TeX is perfect, but because he understands the value of a stable, predictable system that will do the same thing in fifty years that it does now. Why do most programming language designers not follow the same principle? Of course, when a language is relatively new, it makes sense that it will go through a period of rapid change before settling down. And no one can really object to minor changes that don't do much more than codify existing pseudo-standards or correct unintended readings. But when a language still seems to need improvement after ten or twenty years, why not just fork it or start over, rather than try to change what is already in use? If some people really want to do object-oriented programming in Fortran, why not create "Objective Fortran" for that purpose, and leave Fortran itself alone? I suppose one could say that, regardless of future revisions, C89 is already a standard and nothing stops people from continuing to use it. This is sort of true, but connotations do have consequences. GCC will, in pedantic mode, warn about syntax that is either deprecated or has a subtly different meaning in C99, which means C89 programmers can't just totally ignore the new standard. So there must be some benefit in C99 that is sufficient to impose this overhead on everyone who uses the language. This is a real question, not an invitation to argue. Obviously I do have an opinion on this, but at the moment I'm just trying to understand why this isn't just how things are done already. I suppose the question is: What are the (real or perceived) advantages of updating a language standard, as opposed to creating a new language based on the old?

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• Naming a class that processes orders

  - by p.campbell

  I'm in the midst of refactoring a project. I've recently read Clean Code, and want to heed some of the advice within, with particular interest in Single Responsibility Principle (SRP). Currently, there's a class called OrderProcessor in the context of a manufacturing product order system. This class is currently performs the following routine every n minutes: check database for newly submitted + unprocessed orders (via a Data Layer class already, phew!) gather all the details of the orders mark them as in-process iterate through each to: perform some integrity checking call a web service on a 3rd party system to place the order check status return value of the web service for success/fail email somebody if web service returns fail constantly log to a text file on each operation or possible fail point I've started by breaking out this class into new classes like: OrderService - poor name. This is the one that wakes up every n minutes OrderGatherer - calls the DL to get the order from the database OrderIterator (? seems too forced or poorly named) - OrderPlacer - calls web service to place the order EmailSender Logger I'm struggling to find good names for each class, and implementing SRP in a reasonable way. How could this class be separated into new class with discrete responsibilities?

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• Who can change the View in MVC?

  - by Luke

  I'm working on a thick client graph displaying and manipulation application. I'm trying to apply the MVC pattern to our 3D visualization component. Here is what I have for the Model, View, and Controller: Model - The graph and it's metadata. This includes vertices, edges, and the attributes of each. It does not contain position information, icons, colors, or anything display related. View - This would commonly be called a scene graph. It includes the 3D display information, texture information, color information, and anything else that is related specifically to the visualization of the model. Controller - The controller takes the view and displays it in a Window using OpenGL (but it could potentially be any 3D graphics package). The application has various "layouts" that change the position of the vertices in the display. For instance, one layout may arrange the vertices in a circle. Is it common for these layouts to access and change the view directly? Should they go through the Controller to access the View? If they go through the Controller, should they just ask for direct access to the View or should each change go through the controller? I realize this is a bit different from the standard MVC example where there a finite number of Views. In this case, the View can change in an infinite number of ways. Perhaps I'm shattering some basic principle of MVC here. Thanks in advance!

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• How to make an Actor follow my finger

  - by user48352

  I'm back with another question that may be really simple. I've a texture drawn on my spritebatch and I'm making it move up or down (y-axis only) with Libgdx's Input Handler: touchDown and touchUp. @Override public boolean touchDown(int screenX, int screenY, int pointer, int button) { myWhale.touchDownY = screenY; myWhale.isTouched = true; return true; } @Override public boolean touchUp(int screenX, int screenY, int pointer, int button) { myWhale.isTouched = false; return false; } myWhale is an object from Whale Class where I move my texture position: public void update(float delta) { this.delta = delta; if(isTouched){ dragWhale(); } } public void dragWhale() { if(Gdx.input.getY(0) - touchDownY < 0){ if(Gdx.input.getY(0)<position.y+height/2){ position.y = position.y - velocidad*delta; } } else{ if(Gdx.input.getY(0)>position.y+height/2){ position.y = position.y + velocidad*delta; } } } So the object moves to the center of the position where the person is pressing his/her finger and most of the time it works fine but the object seems to take about half a second to move up or down and sometimes when I press my finger it wont move. Maybe there's another simplier way to do this. I'd highly appreciate if someone points me on the right direction.

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• Expiring timed actions a good idea?

  - by Bart van Heukelom

  We have an online game where players sometimes have to wait a while (say 30 minutes) before a process they intiated completes. This encourages them to come back later. An example of this is growing crops in Farmville or basically any action in the Sims Play4Free. Now, however, there is the idea to let these processes expire, so if the player doesn't 'reap' them in time (e.g. within 4 hours) they are aborted. I'm a bit sceptical about this. How will this make players come back more often? Is not the reward of reaping the process enough for that? Can we expect players to fit their daily schedule around our game, maybe even set the alarm clock at night? Won't this just cause players to give up on starting these processes in the first place? I realise this may be too subjective for this site, so I'll end with a concrete question: Do (m)any other online free-to-play games employ this technique?

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• two-part dice pool mechanic

  - by bythenumbers

  I'm working on a dice mechanic/resolution system based off of the Ghost/Echo (hereafter shortened to G/E) tabletop RPG. Specifically, since G/E can be a little harsh with dealing out consequences and failure, I was hoping to soften the system and add a little more player control, as well as offer the chance for players to evolve their characters into something unique, right from creation. So, here's the mechanic: Players roll 2d12 against the two statistics for their character (each is a number from 2-11, and may be rolled above or below depending on the nature of the action attempted, rolling your stat exactly always fails). Depending on the success for that roll, they add dice to the pool rolled for a modified G/E style action. The acting player gets two dice anyhow, and I am debating offering a bonus die for each success, or a single bonus die for succeeding on both of the statistic-compared rolls. One the size of the dice pool is set, the entire pool is rolled, and the players are allowed to assign rolled dice to a goal and a danger. Assigned results are judged as follows: 1-4 means the attempted goal fails, or the danger comes true. 5-8 is a partial success at the goal, or partially avoiding the danger. 9-12 means the goal is achieved, or the danger avoided. My concerns are twofold: Firstly, that the two-stage action is too complicated, with two rolls to judge separately before anything can happen. Secondly, that the statistics involved go too far in softening the game. I've run some basic simulations, and the approximate statistics follow: 2 dice (up to) 3 dice (up to) 4 dice failure ~33% ~25% ~20% partial ~33% ~35% ~35% success ~33% ~40% ~45% I'd appreciate any advice that addresses my concerns or offers to refine my simulation (right now the first roll is statistically modeled as sign(1d12-1d12), where 0 is a success).

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• Truly useful UML diagrams

  - by eversor

  UML has a jungle of Diagrams. Profile Diagrams, Class Diagrams, Package Diagrams... However, (IMH-and-not-too-experienced-O) I quite see that doing each and every diagram is overkill. Therefore, which UML Diagrams are more suitable in a web context, more expecificly a blog (we want to build it from scratchs). I understand that just because I used UML Diagrams does not imply that our code would be great and brilliant... but, it certainly would be better than just unplanified code...

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• Algorithms or patterns for a linked question and answer cost calculator

  - by kmc

  I've been asked to build an online calculator in PHP (and the Laravel framework). It will take the answers to a series of questions to estimate the cost of a home extension. For example, a couple of questions may be: What is the lie of your property? Flat, slightly inclined, heavily inclined. (these suggestive values could have specific values in the underlying calculator like, 0 degrees, 5 degrees, 10 degrees. What is your current flooring system? Wooden, or concrete? These would then impact the results of other questions. Once the size of the extension has been input, the lie of the land will affect how much site works will cost, and how much rubbish collection will cost. The second question will impact the cost of the extensions flooring, as stumping and laying floorboards is a different cost to laying foundations and a concrete slab. It will also influence what heating and cooling systems are available in the calculator. So it's VERY interlinked. The answer to any question can influence the options of other questions, and the end result. I'm having trouble figuring out an approach to this that will allow new options and questions to be plugged in at a later stage without having things too coupled. The Observer pattern, or Laravel's events may be handy, but currently the sheer breadth of the calculator has me struggling to gather my thoughts and see a sensible implementation. Are there any patterns or OO approaches that may help? Thanks!

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• Identifying which pattern fits better.

  - by Daniel Grillo

  I'm developing a software to program a device. I have some commands like Reset, Read_Version, Read_memory, Write_memory, Erase_memory. Reset and Read_Version are fixed. They don't need parameters. Read_memory and Erase_memory need the same parameters that are Length and Address. Write_memory needs Lenght, Address and Data. For each command, I have the same steps in sequence, that are something like this sendCommand, waitForResponse, treatResponse. I'm having difficulty to identify which pattern should I use. Factory, Template Method, Strategy or other pattern. Edit I'll try to explain better taking in count the given comments and answers. I've already done this software and now I'm trying to refactoring it. I'm trying to use patterns, even if it is not necessary because I'm taking advantage of this little software to learn about some patterns. Despite I think that one (or more) pattern fits here and it could improve my code. When I want to read version of the software of my device, I don't have to assembly the command with parameters. It is fixed. So I have to send it. After wait for response. If there is a response, treat (or parse) it and returns. To read a portion of the memory (maximum of 256 bytes), I have to assembly the command using the parameters Len and Address. So I have to send it. After wait for response. If there is a response, treat (or parse) it and returns. To write a portion in the memory (maximum of 256 bytes), I have to assembly the command using the parameters Len, Address and Data. So I have to send it. After wait for response. If there is a response, treat (or parse) it and returns. I think that I could use Template Method because I have almost the same algorithm for all. But the problem is some commands are fixes, others have 2 or 3 parameters. I think that parameters should be passed on the constructor of the class. But each class will have a constructor overriding the abstract class constructor. Is this a problem for the template method? Should I use other pattern?

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• How to had operation with character/items on binary with concrete operations on C++?

  - by Piperoman

  I have the next problem. A item can had a lot of states: NORMAL = 0000000 DRY = 0000001 HOT = 0000010 BURNING = 0000100 WET = 0001000 COLD = 0010000 FROZEN = 0100000 POISONED= 1000000 A item can had some states at same time but not all of them Is impossible to be dry and wet at same time. If you COLD a WET item, it turns into FROZEN. If you HOT a WET item, it turns into NORMAL A item can be BURNING and POISON Etc. I have try to set binary flags to states, and use AND to set operation to combine different states, checking before if is possible or not to do it, or change to another status. Exist a concrete patron to solve this problem efficiently without had a interminable switch that check every states with everynew states? It is relative easy to check 2 different states, but if exist a third state it is not trivial to do.

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• Options for Application Registry

  - by Matt Felzani

  I work for a small software company (about 200 people building 8-10 applications) and I was hoping to get some advice on products that might be out there to manage the information of which clients are using which versions of our products? The most fundamental relationship would be that a "product" has "versions" and a given "version" is used by a "client." Uses would be: Determine which clients use which products Determine which clients are on which versions of a product Determine which clients are exposed to which vulnerabilities because of the version they use Determine which clients cannot move to a new version because of a vulnerability in the new version that they may hit Determine which clients should be approached for an upgrade Any thoughts or product reviews would be greatly appreciated! Thanks in advance.

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• How to fix this navigation issue in my site?

  - by David

  First off I use webs.com for the creation of my site. I have a very basic layout. List of links of the left and content on the right with a heading up top. Now in my list of links every link is an article that I wrote, I have about 25 links going down the left hand side of my site. Problem is when I try out new themes that support horizontal navigation as opposed to vertical navigation I get either a messy overflow of links Or a link called "more" which lists the rest of the articles in a drop down-list across my site. What I wish I had was a simple horizontal navigation like" "home, about, articles" and when the user clicks on articles it would then bring them to a page containing all my articles there. I would prefer it to be in a table like display. That way is not a long list. Anyways any ideas on how I can fix this issue im having? Please let me know if you need more information.

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• How should I architect a personal schedule manager that runs 24/7?

  - by Crawford Comeaux

  I've developed an ADHD management system for myself that's attempting to change multiple habits at once. I know this is counter to conventional wisdom, but I've tried the conventional for years & am now trying it my way. (just wanted to say that to try and prevent it from distracting people from the actual question) Anyway, I'd like to write something to run on a remote server that monitors me, helps me build/avoid certain habits, etc. What this amounts to is a system that: runs 24/7 may have multiple independent tasks to run at once may have tasks that require other tasks to run first lets tasks be scheduled by specific time, recurrence (ie. "run every 5 mins"), or interval (ie. "run from 2pm to 3pm") My first naive attempt at this was just a single PHP script scheduled to run every minute by cron (language was chosen in order to use a certain library, but no longer necessary). The logic behind when to run this or that portion of code got hairy pretty quick. So my question is how should I approach this from here? I'm not tied to any one language, though I'm partial to python/javascript. Thoughts: Could be done as a set of scripts that include a scheduling mechanism with one script per bit of logic...but the idea just feels wrong to me. Building it as a daemon could be helpful, but still unsure what to do about dozens of if-else statements for detecting the current time

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• I need an approach to the problem of preventing inserting duplicate records into the database

  - by Maurice

  Apologies is this question is asked on the incorrect "stack" A webservice that I call returns a list of data. The data from the webservice is updated periodically, so a call to the webservice done in one hour could return the same data as a call done in an hour. Also, the data is returned based on a start and end date. We have multiple users that can run the webservice search, and duplicate data is most likely to be returned (especially for historical data). However I don't want to insert this duplicate data in the database. I've created a db table in which the data is stored (most important columns are) Id int autoincrement PK Date date not null --The date to which the data set belongs. LastUpdate date not null --The date the data set was last updated. UserName varchar(50) --The name of the user doing the search. I use sql server 2008 express with c# 4.0 and visual studio 2010. Entity Framework is used as the ORM. If stored procedures could be avoided in the proposed solution, then that will be a plus. Another way of looking interpreting what I'm asking a solution for is as follows: I have a million unique records in my table. A user does a new search. The search results from the user contains around 300k of the data that is already in the db. An efficient solution to finding an inserting only the unique records is needed.

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• How common are circular references? Would reference-counting GC work just fine?

  - by user9521

  How common are circular references? The less common they are, the fewer hard cases you have if you are writing in a language with only reference counting-GC. Are there any cases where it wouldn't work well to make one of the references a "weak" reference so that reference counting still works? It seems like you should be able to have a language only use reference counting and weak references and have things work just fine most of the time, with the goal of efficiency. You could also have tools to help you detect memory leaks caused by circular references. Thoughts, anyone? It seems that Python uses references counting (I don't know if it uses a tracing collector occasionally or not for sure) and I know that Vala uses reference counting with weak references; I know that it's been done before, but how well would it work?

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• Nested Entities and calculation on leaf entity property - SQL or NoSQL approach

  - by Chandu

  I am working on a hobby project called Menu/Recipe Management. This is how my entities and their relations look like. A Nutrient has properties Code and Value An Ingredient has a collection of Nutrients A Recipe has a Collection of Ingredients and occasionally can have a collection of other recipes A Meal has a Collection of Recipes and Ingredients A Menu has a Collection of Meals The relations can be depicted as In one of the pages, for a selected menu I need to display the effective nutrients information calculated based on its constituents (Meals, Recipes, Ingredients and the corresponding nutrients). As of now am using SQL Server to store the data and I am navigating the chain from my C# code, starting from each meal of the menu and then aggregating the nutrient values. I think this is not an efficient way as this calculation is being done every time the page is requested and the constituents change occasionally. I was thinking about a having a background service that maintains a table called MenuNutrients ({MenuId, NutrientId, Value}) and will populate/update this table with the effective nutrients when any of the component (Meal, Recipe, Ingredient) changes. I feel that a GraphDB would be a good fit for this requirement, but my exposure to NoSQL is limited. I want to know what are the alternative solutions/approaches to this requirement of displaying the nutrients of a given menu. Hope my description of the scenario is clear.

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