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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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• Designing and refactoring of payment logic

  - by jokklan

  Im currently working on an application that helps users to coordinate dinner clubs and all related accounting. (A dinner club is where people in a group, take turns to cook for the rest and then you pay a small amount to participate. This is pretty normal in dorms and colleges where im from). However there is some different models that all have a price and the accounting aspect is therefore a little spread. We both have DinnerClub, ShoppingItem and are about to implement the third Payment when users pay their debts (or get refunded for expenses). Each of these have a "price" attribute and a users expense (that he or she needs refunded) is calculated by the total of these "prices" minus what other users have bought and he or she have used/participated in. My question is then if someone have some hints to refactor this bring all this behavior together in one place? For now have i thought about a Transaction class that are responsible for this behaviour, but I'm a little worried about the performance impact on having to query for another polymorphic record each time i want to show the price on dinner clubs and shopping items (i have a standard index page with a list for both so it's a lot of extra records being queried)...

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• Calculate travel time on road map with semaphores

  - by Ivansek

  I have a road map with intersections. At intersections there are semaphores. For each semaphore I generate a red light time and green light time which are represented with syntax [R:T1, G:T2], for example: 119 185 250 A ------- B: [R:6, G:4] ------ C: [R:5, G:5] ------ D I want to calculate a car travel time from A - D. Now I do this with this pseudo code: function get_travel_time(semaphores_configuration) { time = 0; for( i=1; i<path.length;i++) { prev_node = path[i-1]; next_node = path[i]); cost = cost_between(prev_node, next_node) time += (cost/movement_speed) // movement_speed = 50px per second light_times = get_light_times(path[i], semaphore_configurations) lights_cycle = get_lights_cycle(light_times) // Eg: [R,R,R,G,G,G,G], where [R:3, G:4] lights_sum = light_times.green_time+light_times.red_light; // Lights cycle time light = lights_cycle[cost%lights_sum]; if( light == "R" ) { time += light_times.red_light; } } return time; } So for distance 119 between A and B travel time is, 119/50 = 2.38s ( exactly mesaured time is between 2.5s and 2.6s), then we add time if we came at a red light when at B. If we came at a red light is calculated with lines: lights_cycle = get_lights_cycle(light_times) // Eg: [R,R,R,G,G,G,G], where [R:3, G:4] lights_sum = light_times.green_time+light_times.red_light light = lights_cycle[cost%lights_sum]; if( light == "R" ) { time += light_times.red_light; } This pseudo code doesn't calculate exactly the same times as they are mesaured, but the calculations are very close to them. Any idea how I would calculate this?

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• What is the best database design for managing historical information? [closed]

  - by Emmad Kareem

  Say you have a Person table with columns such as: ID, FirstName, LastName, BirthCountry, ...etc. And you want to keep track of changes on such a table. For example, the user may want to see previous names of a person or previous addresses, etc. The normalized way is to keep names in separate table, addresses in a separate table,...etc. and the main person table will contain only the information that you are not interested in monitoring changes for (such information will be updated in place). The problem I see here, aside form the coding hassle due to the extensive number of joins required in a real-life situation, is that I have never seen this type of design in any real application (maybe because most did not provide this feature!). So, is there a better way to design this? Thanks.

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• How to achieve selection of a tile from a tile sheet based on an ID?

  - by Bugster

  Let's say I have a tile sheet that contains 8 sprites per sheet. Each sprite is a tile of 30x30. I wrote my own custom map parser/map loader however I'm having trouble extracting a certain tile sprite from the file. I'll describe my problem better in order for everyone to understand. I wrote an enum of materials, each material has a value according to it's location relative to the tile sheet. For example void is 1, grass is 2, rock is 3, etc. So in my tile sheet they are represented as such: +---+---+---+---+---+ | 1 | 2 | 3 | 4 | 5 | +---+---+---+---+---+ Which is equivalent to: +------+-------+-------+ | void | grass | stone | +------+-------+-------+ Basically when rendering, I created a tile class, each tile has 2 coordinates: X and Y (They are calculated automatically) and a material which can be represented either as a number, either as a value (ID). When rendering, I have a vector of sprites which are all taken from 1 file called tilesheet.png, however each of them must only draw a certain portion of the tile sheet, for example say I have something like this: tile coordinateBounds(topLeftX, topLeftY, tileWidth, tileHeight); During the initialization of the map I calculate an array of tiles, and I give each of them their position, their materials based on the values in a map file and a few other variables such as collision. I need to apply the coordinateBounds to each of them according to their material value. For example if the material is grass it should only take the grass sprite from the tilesheet. I must also mention I'm using SFML, and there are no borders or spacing between the tiles.

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• Understanding dot notation

  - by Starkers

  Here's my interpretation of dot notation: a = [2,6] b = [1,4] c = [0,8] a . b . c = (2*6)+(1*4)+(0*8) = 12 + 4 + 0 = 16 What is the significance of 16? Apparently it's a scalar. Am I right in thinking that a scalar is the number we times a unit vector by to get a vector that has a scaled up magnitude but the same direction as the unit vector? So again, what is the relevance of 16? When is it used? It's not the magnitude of all the vectors added up. The magnitude of all of them is calculated as follows: sqrt( ax * ax + ay * ay ) + sqrt( bx * bx + by * by ) + sqrt( cx * cx + cy * cy) sqrt( 2 * 2 + 6 * 6 ) + sqrt( 1 * 1 + 4 * 4 ) + sqrt( 0 * 0 + 8 * 8) sqrt( 4 + 36 ) + sqrt( 1 + 16 ) + sqrt( 0 + 64) sqrt( 40 ) + sqrt( 17 ) + sqrt( 64) 6.3 + 4.1 + 8 10.4 + 8 18.4 So I don't really get this diagram: Attempting with sensible numbers: a = [1,0] b = [4,3] a . b = (1*0) + (4*3) = 0 + 12 = 12 So what exactly is a . b describing here? The magnitude of that vector? Because that isn't right: the 'a.b' vector = [4,0] sqrt( x*x + y*y ) sqrt( 4*4 + 0*0 ) sqrt( 16 + 0 ) 4 So what is 12 describing?

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• filtering dates in a data view webpart when using webservices datasource

  - by Patrick Olurotimi Ige

  I was working on a data view web part recently and i had  to filter the data based on dates.Since the data source was web services i couldn't use  the Offset which i blogged about earlier.When using web services to pull data in sharepoint designer you would have to use xpath.So for example this is the soap that populates the rows<xsl:variable name="Rows" select="/soap:Envelope/soap:Body/ddw1:GetListItemsResponse/ddw1:GetListItemsResult/ddw1:listitems/rs:data/z:row/>But you would need to add some predicate [] and filter the date nodes.So you can do something like this (marked in red)<xsl:variable name="Rows" select="/soap:Envelope/soap:Body/ddw1:GetListItemsResponse/ddw1:GetListItemsResult/ddw1:listitems/rs:data/z:row[ddwrt:FormatDateTime(string(@ows_Created),1033,'yyyyMMdd') &gt;= ddwrt:FormatDateTime(string(substring-after($fd,'#')),1033,'yyyyMMdd')]"/>For the filtering to work you need to have the date formatted  above as yyyyMMdd.One more thing you must have noticed is the $fd variable.This variable is created by me creating a calculated column in the list so something like this [Created]-2So basically that the xpath is doing is get me data only when the Created date  is greater than or equal to the Created date -2 which is 2 date less than the created date.Also not that when using web services in sharepoint designer and try to use the default filtering you won't get to see greater tha or less than in the option list comparison.:(Hope this helps.

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• I'm having trouble understanding these exercises wording.

  - by KasHKoW

  Exercise 1-20. Write a program detab that replaces tabs in the input with the proper number of blanks to space to the next tab stop. Assume a fixed set of tab stops, say every n columns. Should n be a variable or a symbolic parameter? Exercise 1-21. Write a program entab that replaces strings of blanks by the minimum number of tabs and blanks to achieve the same spacing. Use the same tab stops as for detab. When either a tab or a single blank would suffice to reach a tab stop, which should be given preference? could you paraphrase these for me. thanks

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• Using Microsoft&apos;s Chart Controls In An ASP.NET Application: Serializing Chart Data

  In most usage scenarios, the data displayed in a Microsoft Chart control comes from some dynamic source, such as from a database query. The appearance of the chart can be modified dynamically, as well; past installments in this article series showed how to programmatically customize the axes, labels, and other appearance-related settings. However, it is possible to statically define the chart's data and appearance strictly through the control's declarative markup. One of the demos examined in the <a href="http://www.4guysfromrolla.com/articles/072209-1.aspx">Getting Started</a> article rendered a column chart with seven columns whose labels and values were defined statically in the <code>&lt;asp:Series&gt;</code> tag's

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• Attention All Procurement Buyers!

  - by LuciaC

  Have you discovered the power of the Buyer Work Center?   Released in Procurement 12.0 the Professional Buyer Work Center (BWC) is a web based interface that provides a central 'launch pad' from which you can efficiently perform your daily tasks, including:  You can manage your requisitions and create them to Purchase Orders (like manual autocreate) Create new standard purchase orders, blanket purchase agreements, or contract purchase agreements Create and maintain supplier information If Oracle Sourcing is licensed and implemented, you can create buyer's auctions or sourcing RFQs If Oracle Services Procurement is licensed and implemented you can create and maintain purchase orders for complex work payments If Oracle Procurement Contracts is licensed and implemented you can handle author contract terms and manage deliverables Globally for the BWC: Create and personalize your own document views including list of columns, where conditions and sort sequences. You can additionally use predefined document views. Accessed from the Purchasing responsibility as we see in the screenshot here, the Buyer Work Center has links to launch to the areas you want to access. See these documents for more information on the BWC: Doc ID 1301969.1: FAQ - Buyer Work CenterDoc ID 1394392.1: Assistant: Oracle Purchasing Purchasing Buyer Work Center Search Helper.

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• A simple example of movement prediction

  - by Daniel

  I've seen lots of examples of theory about the reason for client-side prediction, but I'm having a hard time converting it into code. I was wondering if someone knows of some specific examples that share some of the code, or can share their knowledge to shed some light into my situation. I'm trying to run some tests to get a the movement going (smoothly) between multiple clients. I'm using mouse input to initiate movement. I'm using AS3 and C# on a local Player.IO server. Right now I'm trying to get the Client side working, as I'm only forwarding position info with the client. I have 2 timers, one is an onEnterFrame and the other is a 100ms Timer, and one on mouseClick listener. When I click anywhere with a mouse, I update my player class to give it a destination point On every enterFrame Event for the player, it moves towards the destination point At every 100ms it sends a message to the server with the position of where it should be in a 100ms. The distance traveled is calculated by taking the distance (in Pixels) that the player can travel in one second, and dividing it by the framerate for the onEnterFrame handler, and by the update frequency (1/0.100s) for the server update. For the other Players, the location is interpolated and animated on every frame based on the new location. Is this the right way of doing it?

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• Are there design patterns or generalised approaches for particle simulations?

  - by romeovs

  I'm working on a project (for college) in C++. The goal is to write a program that can more or less simulate a beam of particles flying trough the LHC synchrotron. Not wanting to rush into things, me and my team are thinking about how to implement this and I was wondering if there are general design patterns that are used to solve this kind of problem. The general approach we came up with so far is the following: there is a World that holds all objects you can add objects to this world such as Particle, Dipole and Quadrupole time is cut up into discrete steps, and at each point in time, for each Particle the magnetic and electric forces that each object in the World generates are calculated and summed up (luckily electro-magnetism is linear). each Particle moves accordingly (using a simple estimation approach to solve the differential movement equations) save the Particle positions repeat This seems a good approach but, for instance, it is hard to take into account symmetries that might be present (such as the magnetic field of each Quadrupole) and is this thus suboptimal. To take into account such symmetries as that of the Quadrupole field, it would be much easier to (also) make space discrete and somehow store form of the Quadrupole field somewhere. (Since 2532 or so Quadrupoles are stored this should lead to a massive gain of performance, not having to recalculate each Quadrupole field) So, are there any design patterns? Is the World-approach feasible or is it old-fashioned, bad programming? What about symmetry, how is that generally taken into acount?

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• How does this circle collision detection math work?

  - by Griffin

  I'm going through the wildbunny blog to learn about collision detection. I'm confused about how the vectors he's talking about come into play. Here's the part that confuses me: p = ||A-B|| – (r1+r2) The two spheres are penetrating by distance p. We would also like the penetration vector so that we can correct the penetration once we discover it. This is the vector that moves both circles to the point where they just touch, correcting the penetration. Importantly it is not only just a vector that does this, it is the only vector which corrects the penetration by moving the minimum amount. This is important because we only want to correct the error, not introduce more by moving too much when we correct, or too little. N = (A-B) / ||A-B|| P = N*p Here we have calculated the normalised vector N between the two centres and the penetration vector P by multiplying our unit direction by the penetration distance. I understand that p is the distance by which the circles penetrate, but I don't get what exactly N and P are. It seems to me N is just the coordinates of the 3rd point of the right trianlge formed by point A and B (A-B) then being divided by the hypotenuse of that triangle or distance between A and B (||A-B||). What's the significance of this? Also, what is the penetration vector used for? It seems to me like a movement that one of the circles would perform to get un-penetrated.

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• Web application interacts bi-directional with server program?

  - by Roelof Berkepeis

  I want to write a web application to play chess against the engine Crafty. I'm not new to PHP and javascript, but must learn how to interact with a server process : how can a web application and/or (jQuery) ajax interact bi-directionally with a (linux) program running on the server? At this moment i am developing on (Apache) local host. Crafty is installed on my Ubuntu PC. This well-known chess engine has no GUI, it runs in terminal by the command $ /usr/games/crafty and so you can play chess against it and even see it's calculations. I can make Crafty run by PHP, using the functions proc_open() or exec(), and most documentation i found states that the output stream should be a file .. But i think i don't want such setup, because then the webpage should be constanty polling that file (eg. by ajax) to see if some new data was appended, right? How can Crafty talk to the web page directly, saying "i have calculated another variation" or "i have decided a move" etc, then display this info on the web page and let the user give some counter move, just like in terminal. Isn't it possible to use some session / stream / listener? I have no clue at all, can anybody point me in a right direction?

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• Figuring our complex REST queries for SharePoint

  - by Sahil Malik

  SharePoint 2010 Training: more information A little while ago, I showed the REST query for a relatively complex query. Some readers have emailed me about how to figure out further queries, and especially for complex insert/delete/update scenarios. Well it is quite easy to figure out almost any query for SharePoint REST API. Okay, this is not just about SharePoint – you can apply what you read here for any REST API interface supported by Microsoft, like WCF data services. But, sometimes when you have many columns, or complex update operations, or are working with weird providers, it is tough to figure out the specific HTTP request you need to craft, error free, using REST. Well fear not, there is hope. As an example, what I did is, I created a SharePoint site at http://sp2010.winsmarts.internal/sampledata with 3 lists in it - 1. Artists (with one Column, Title) Read full article ....

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• Trouble with Collada bones

  - by KyleT

  I have a Collada file with a rigged mesh. I've read the node tags in the library_visual_scenes tag and extracted the matrix for each node and stored everything in a hierarchical bone structure. My Matrix container is "row major", so I'd store the first float of a matrix tag in the 1st row, 1st column, the second in the 1st row, 2nd column, etc. From what I gather this is the Bind Pose Matrix. After that I went through the tag and extracted the float array in the source tag of the skin tag of the controller for the mesh. I stored each matrix from this float array in their corresponding Bone as the Inverse Bind Matrix. I also extracted the bind-shape-matrix and stored it. Now I'd like to draw the skeleton with OpenGL to see if everything is working correctly before I go about skinning. I iterate once over my bones and multiply a bone's Bind Pose Matrix by it's parents and store that. After that I iterate again over the bones and multiply the result of the previous matrix multiplication by the Inverse Bind Matrix and then by the Bind Shape Matrix. The results look something like this: [0.2, 9.2, 5.8, 1.2 ] [4.6, -3.3, -0.2, -0.1 ] [-1.8, 0.2, -4.2, -3.9 ] [0, 0, 0, 1 ] I've had to go to various sources to get the little understanding of Collada I have and books about 3d transform matricies can get pretty intense. I've hit a brick wall and if you could please read through this and see if there is something I'm doing wrong, and how I'd go about getting an X,Y,Z to draw a point for each of these joints once I've calculated the final transform, I'd really appreciate it.

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• Advice on reconciling discordant data

  - by Justin

  Let me support my question with a quick scenario. We're writing an app for family meal planning. We'll produce daily plans with a target calorie goal and meals to achieve it for our nuclear family. Our calorie goal will be calculated for each person from their attributes (gender, age, weight, activity level). The weight attribute is the simplest example here. When Dad (the fascist nerd who is inflicting this on his family) first uses the application he throws approximate values into it for Daughter. He thinks she is 5'2" (157 cm) and 125 lbs (56kg). The next day Mom sits down to generate the menu and looks back over what the bumbling Dad did, quietly fumes that he can never recall anything about the family, and says the value is really 118 lbs! This is the first introduction of the discord. It seems, in this scenario, Mom is probably more correct that Dad. Though both are only an approximation of the actual value. The next day the dear Daughter decides to use the program and sees her weight listed. With the vanity only a teenager could muster she changes the weight to 110 lbs. Later that day the Mom returns home from a doctor's visit the Daughter needed and decides that it would be a good idea to update her Daughter's weight in the program. Hooray, another value, this time 117 lbs. Now how do you reconcile these data points? Measurement error, confidence in parties, bias, and more all confound the data. In some idealized world we'd have a weight authority of some nature providing the one and only truth. How about in our world though? And the icing on the cake is that this single data point changes over time. How have you guys solved or managed this conflict?

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• Is it possible to use 3G internet for a TCP/IP game server?

  - by Amit Ofer

  I'm working on a turned based multiplayer android game with a friend. I started working on the game server and client using socket programming. I found a few tutorials on how to implement a basic chat on android and I started extending that example to suit my needs. Basically the game is really simple and the communication only include sending a few string from the client to the server every turn and sending the calculated scores back to all the clients after each turn. the idea is that one of the players creates the game and thus initialize the server, and each player connects to this client using ip. I tried this solution and it seems to work great when all the players are using the same wifi connection or by using router port forwarding. The problem is when trying to use 3G internet for the server, I guess the problem is that 3G ip address isn't global and you can't use port forwarding there, correct me if I'm wrong here. Is there a way to overcome this issue? or the only solution is to limit my game to wifi only or think of a different solution than the standard socket programming solution? I.E web server etc. what do you think would be the best approach here? Thanks.

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• Retrieve data from an ASP.Net application using Ado.Net 2.0 disconnected model

  - by nikolaosk

  This is the second post in a series of posts regarding to ADO.Net 2.0. Have a look at the first post if you like. In this post I am going to investigate the "Disconnected" model. When I say "Disconnected" I mean Datasets . Datasets are in memory representations of tables in a particular database. A Dataset contains a Table collection and each Table collection contains a Row collection and each Row collection contains a Columns collection. So initially you connect to the database, get the data to...(read more)

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• Speaking in Omaha: December 7, 2011

  - by Bill Graziano

  I’m presenting in Omaha on Writing Faster SQL at 6PM on December 7th.  You can find meeting details on the Omaha SQL Server User Group page. The meeting location requires an RSVP so building security has a list of attendees. The presentation is a series of suggestions on improving performance.  It ranges from simple things like comparing indexed columns to scalar values up to tips for reducing query compiles and asynchronous processing patterns.  Nearly all of these come from specific issues I’ve encountered working on poorly performing SQL Servers.

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• Using ConcurrentQueue for thread-safe Performance Bookkeeping.

  - by Strenium

  Just a small tidbit that's sprung up today. I had to book-keep and emit diagnostics for the average thread performance in a highly-threaded code over a period of last X number of calls and no more. Need of the day: a thread-safe, self-managing stats container. Since .NET 4.0 introduced new thread-safe 'Collections.Concurrent' objects and I've been using them frequently - the one in particular seemed like a good fit for storing each threads' performance data - ConcurrentQueue. But I wanted to store only the most recent X# of calls and since the ConcurrentQueue currently does not support size constraint I had to come up with my own generic version which attempts to restrict usage to numeric types only: unfortunately there is no IArithmetic-like interface which constrains to only numeric types – so the constraints here here aren't as elegant as they could be. (Note the use of the Average() method, of course you can use others as well as make your own).   FIFO FixedSizedConcurrentQueue using System;using System.Collections.Concurrent;using System.Linq; namespace xxxxx.Data.Infrastructure{    [Serializable]    public class FixedSizedConcurrentQueue<T> where T : struct, IConvertible, IComparable<T>    {        private FixedSizedConcurrentQueue() { }         public FixedSizedConcurrentQueue(ConcurrentQueue<T> queue)        {            _queue = queue;        }         ConcurrentQueue<T> _queue = new ConcurrentQueue<T>();         public int Size { get { return _queue.Count; } }        public double Average { get { return _queue.Average(arg => Convert.ToInt32(arg)); } }         public int Limit { get; set; }        public void Enqueue(T obj)        {            _queue.Enqueue(obj);            lock (this)            {                T @out;                while (_queue.Count > Limit) _queue.TryDequeue(out @out);            }        }    } }   The usage case is straight-forward, in this case I’m using a FIFO queue of maximum size of 200 to store doubles to which I simply Enqueue() the calculated rates: Usage var RateQueue = new FixedSizedConcurrentQueue<double>(new ConcurrentQueue<double>()) { Limit = 200 }; /* greater size == longer history */   That’s about it. Happy coding!

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• Storage of leftover values in a situation of having to round down

  - by jt0dd

  I'm writing an app (client and server side) where the number of sales required by each employee must be kept track of in round-number form. Each month, the employees are required to sell a certain number, and this app needs to keep track of how many sales must be made for each 12 hour interval during the work week. Because I have to round the values down to a whole number, I must keep track of leftovers in the rounding process and ensure that they are always carried over. My method must ensure the storage of the leftover value even when client and server side crash, restart, close, etc. Right now, I'm working on doing this by storing the leftovers in a field in the user's account row in the database each time a value is rounded, reading the stored value, removing any portion that is used (when a whole number is reached, most of the leftover is used up), and storing the new value. This practice seems weird because while the leftovers are calculated on the client side, it's the same number for each employee, and every employee using the app is storing a copy of the same leftover data. Alternatively, I could have all clients store the data at once into the same data field on a general table, but this is just as weird. Is there a better way that this can be handled or is my method correct?

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• How to make a table structure for products to be available for both wholesale and retail?

  - by kmy

  Ignoring the different column details like colors, shapes, and sizes, I already have an idea of dealing with that, I'm more interested in dealing with retail pricing, whole pricing (with or without a table), and possibly discount. If anything, I want to know what I should also take account for. Will it just be adding a quantity column, two pricing cols, and two discount columns, and a quantity limit? If I were to add a pricing table it would be inserted as a json file, would this be a bad idea? Please give any insight about this.

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• Should I build a multi-threaded system that handles events from a game and sorts them, independently, into different threads based on priority?

  - by JonathonG

  Can I build a multi-threaded system that handles events from a game and sorts them, independently, into different threads based on priority, and is it a good idea? Here's more info: I am about to begin work on porting a mid-sized game from Flash/AS3 to Java so that I can continue development with multi-threading capabilities. Here's a small bit of background about the game: The game contains numerous asynchronous activities, such as "world updating" (the game environment is constantly changing based on a set of natural laws and forces), procedural generation of terrain, NPCs, quests, items, etc., and on top of that, the effects of all of the player's interactions with his environment are programmatically calculated in real time, based on a set of constantly changing "stats" and once again, natural laws and forces. All of these things going on at once, in an asynchronous manner, seem to lend themselves to multi-threading very well. My question is: Can I build some kind of central engine that handles the "stacking" of all of these events as they are triggered, and dynamically sorts them out amongst the available threads, and would it be a good idea? As an example: Essentially, every time something happens (IE, a magic missile being generated by a spell, or a bunch of plants need to grow to their next stage), instead of just processing that task right then and adding the new object(s) to a list of managed objects, send a reference to that event to a core "event handler" that throws it into a stack of all other currently queued events, which then sorts them out and orders them according to urgency, splits them between a number of available threads for as-fast-as-possible multithreaded execution.

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• Local LINQtoSQL Database For Your Windows Phone 7 Application

  - by Tim Murphy

  There aren’t many applications that are of value without having some for of data store.  In Windows Phone development we have a few options.  You can store text directly to isolated storage.  You can also use a number of third party libraries to create or mimic databases in isolated storage.  With Mango we gained the ability to have a native .NET database approach which uses LINQ to SQL.  In this article I will try to bring together the components needed to implement this last type of data store and fill in some of the blanks that I think other articles have left out. Defining A Database The first things you are going to need to do is define classes that represent your tables and a data context class that is used as the overall database definition.  The table class consists of column definitions as you would expect.  They can have relationships and constraints as with any relational DBMS.  Below is an example of a table definition. First you will need to add some assembly references to the code file. using System.ComponentModel;using System.Data.Linq;using System.Data.Linq.Mapping; You can then add the table class and its associated columns.  It needs to implement INotifyPropertyChanged and INotifyPropertyChanging.  Each level of the class needs to be decorated with the attribute appropriate for that part of the definition.  Where the class represents the table the properties represent the columns.  In this example you will see that the column is marked as a primary key and not nullable with a an auto generated value. You will also notice that the in the column property’s set method It uses the NotifyPropertyChanging and NotifyPropertyChanged methods in order to make sure that the proper events are fired. [Table]public class MyTable: INotifyPropertyChanged, INotifyPropertyChanging{ public event PropertyChangedEventHandler PropertyChanged; private void NotifyPropertyChanged(string propertyName) { if(PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); } } public event PropertyChangingEventHandler PropertyChanging; private void NotifyPropertyChanging(string propertyName) { if(PropertyChanging != null) { PropertyChanging(this, new PropertyChangingEventArgs(propertyName)); } } private int _TableKey; [Column(IsPrimaryKey = true, IsDbGenerated = true, DbType = "INT NOT NULL Identity", CanBeNull = false, AutoSync = AutoSync.OnInsert)] public int TableKey { get { return _TableKey; } set { NotifyPropertyChanging("TableKey"); _TableKey = value; NotifyPropertyChanged("TableKey"); } } The last part of the database definition that needs to be created is the data context.  This is a simple class that takes an isolated storage location connection string its constructor and then instantiates tables as public properties. public class MyDataContext: DataContext{ public MyDataContext(string connectionString): base(connectionString) { MyRecords = this.GetTable<MyTable>(); } public Table<MyTable> MyRecords;} Creating A New Database Instance Now that we have a database definition it is time to create an instance of the data context within our Windows Phone app.  When your app fires up it should check if the database already exists and create an instance if it does not.  I would suggest that this be part of the constructor of your ViewModel. db = new MyDataContext(connectionString);if(!db.DatabaseExists()){ db.CreateDatabase();} The next thing you have to know is how the connection string for isolated storage should be constructed.  The main sticking point I have found is that the database cannot be created unless the file mode is read/write.  You may have different connection strings but the initial one needs to be similar to the following. string connString = "Data Source = 'isostore:/MyApp.sdf'; File Mode = read write"; Using you database Now that you have done all the up front work it is time to put the database to use.  To make your life a little easier and keep proper separation between your view and your viewmodel you should add a couple of methods to the viewmodel.  These will do the CRUD work of your application.  What you will notice is that the SubmitChanges method is the secret sauce in all of the methods that change data. private myDataContext myDb;private ObservableCollection<MyTable> _viewRecords;public ObservableCollection<MyTable> ViewRecords{ get { return _viewRecords; } set { _viewRecords = value; NotifyPropertyChanged("ViewRecords"); }}public void LoadMedstarDbData(){ var tempItems = from MyTable myRecord in myDb.LocalScans select myRecord; ViewRecords = new ObservableCollection<MyTable>(tempItems);}public void SaveChangesToDb(){ myDb.SubmitChanges();}public void AddMyTableItem(MyTable newScan){ myDb.LocalScans.InsertOnSubmit(newScan); myDb.SubmitChanges();}public void DeleteMyTableItem(MyTable newScan){ myDb.LocalScans.DeleteOnSubmit(newScan); myDb.SubmitChanges();} Updating existing database What happens when you need to change the structure of your database?  Unfortunately you have to add code to your application that checks the version of the database which over time will create some pollution in your codes base.  On the other hand it does give you control of the update.  In this example you will see the DatabaseSchemaUpdater in action.  Assuming we added a “Notes” field to the MyTable structure, the following code will check if the database is the latest version and add the field if it isn’t. if(!myDb.DatabaseExists()){ myDb.CreateDatabase();}else{ DatabaseSchemaUpdater dbUdater = myDb.CreateDatabaseSchemaUpdater(); if(dbUdater.DatabaseSchemaVersion < 2) { dbUdater.AddColumn<MyTable>("Notes"); dbUdater.DatabaseSchemaVersion = 2; dbUdater.Execute(); }} Summary This approach does take a fairly large amount of work, but I think the end product is robust and very native for .NET developers.  It turns out to be worth the investment. del.icio.us Tags: Windows Phone,Windows Phone 7,LINQ to SQL,LINQ,Database,Isolated Storage

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