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• Short snippet summarizing a webpage?

  - by Legend

  Is there a clean way of grabbing the first few lines of a given link that summarizes that link? I have seen this being done in some online bookmarking applications but have no clue on how they were implemented. For instance, if I give this link, I should be able to get a summary which is roughly like: I'll admit it, I was intimidated by MapReduce. I'd tried to read explanations of it, but even the wonderful Joel Spolsky left me scratching my head. So I plowed ahead trying to build decent pipelines to process massive amounts of data Nothing complex at first sight but grabbing these is the challenging part. Just the first few lines of the actual post should be fine. Should I just use a raw approach of grabbing the entire html and parsing the meta tags or something fancy like that (which obviously and unfortunately is not generalizable to every link out there) or is there a smarter way to achieve this? Any suggestions? Update: I just found InstaPaper do this but am not sure if it is getting the information from RSS feeds or some other way.

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• How can i create an n-dimensional array in c

  - by shortCircuit

  I was thinking of making a function that would accept the size of array as a parameter and create a n dimensional array. My room-mate took the liberty of making it complex. He said lets write a function that takes n parameters and returns an n-dimensional array using those parameters as the dimensions. Now i realize an one-day and d array is easy to implement with pointers. For 2d array the snippet would be something like (standard way) : int** x; int* temp; x = (int**)malloc(m * sizeof(int*)); temp = (int*)malloc(m*n * sizeof(int)); for (int i = 0; i < m; i++) { x[i] = temp + (i * n); } where the array is of size m*n; But the problem lies how do we find the nested loop parameters for a n-dimensional array? Is there any way to optimize the code?

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• How to cancel a deeply nested process

  - by Mystere Man

  I have a class that is a "manager" sort of class. One of it's functions is to signal that the long running process of the class should shut down. It does this by setting a boolean called "IsStopping" in class. public class Foo { bool isStoping void DoWork() { while (!isStopping) { // do work... } } } Now, DoWork() was a gigantic function, and I decided to refactor it out and as part of the process broke some of it into other classes. The problem is, Some of these classes also have long running functions that need to check if isStopping is true. public class Foo { bool isStoping void DoWork() { while (!isStopping) { MoreWork mw = new MoreWork() mw.DoMoreWork() // possibly long running // do work... } } } What are my options here? I have considered passing isStopping by reference, which I don't really like because it requires there to be an outside object. I would prefer to make the additional classes as stand alone and dependancy free as possible. I have also considered making isStopping a property, and then then having it call an event that the inner classes could be subscribed to, but this seems overly complex. Another option was to create a "Process Cancelation Token" class, similar to what .net 4 Tasks use, then that token be passed to those classes. How have you handled this situation? EDIT: Also consider that MoreWork might have a EvenMoreWork object that it instantiates and calls a potentially long running method on... and so on. I guess what i'm looking for is a way to be able to signal an arbitrary number of objects down a call tree to tell them to stop what they're doing and clean up and return.

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• Reusing named_scope to define another named_scope

  - by Sergei Kozlov

  The problem essence as I see it One day, if I'm not mistaken, I have seen an example of reusing a named_scope to define another named_scope. Something like this (can't remember the exact syntax, but that's exactly my question): named_scope :billable, :conditions => ... named_scope :billable_by_tom, :conditions => { :billable => true, :user => User.find_by_name('Tom') } The question is: what is the exact syntax, if it's possible at all? I can't find it back, and Google was of no help either. Some explanations Why I actually want it, is that I'm using Searchlogic to define a complex search, which can result in an expression like this: Card.user_group_managers_salary_greater_than(100) But it's too long to be put everywhere. Because, as far as I know, Searchlogic simply defines named_scopes on the fly, I would like to set a named_scope on the Card class like this: named_scope from_big_guys, { user_group_managers_salary_greater_than(100) } - this is where I would use that long Searchlogic method inside my named_scope. But, again, what would be the syntax? Can't figure it out. Resume So, is named_scope nesting (and I do not mean chaining) actually possible?

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• Concept: Information Into Memory Location.

  - by Richeve S. Bebedor

  I am having troubles conceptualizing an algorithm to be used to transform any information or data into a specific appropriate and reasonable memory location in any data structure that I will be devising. To give you an idea, I have a JPanel object instance and I created another Container type object instance of any subtype (note this is in Java because I love this language), then I collected those instances into a data structure not specifically just for those instances but also applicable to any type of object. Now my procedure for fetching those data again is to extract the object specific features similar in category to all object in that data structure and transform it into a integer data memory location (specifically as much as possible) or any type of data that will pertain to this transformation. And I can already access that memory location without further sorting or applications of O(n) time complex algorithms (which I think preferable but I wanted to do my own way XD). The data structure is of any type either binary tree, linked list, arrays or sets (and the like XD). What is important is I don't need to have successive comparing and analysis of data just to locate information in big structures. To give you a technical idea, I have to an array DS that contains JLabel object instance with a specific name "HelloWorld". But array DS contains other types of object (in multitude). Now this JLabel object has a location in the array at index [124324] (which is if you do any type of searching algorithm just to arrive at that location is conceivably slow because added to it the data structure used was an array *note please disregard the efficiency of the data structure to be used I just want to explain to you my concept XD). Now I want to equate "HelloWorld" to 124324 by using a conceptually made function applicable to all data types. So that I can do a direct search by doing this DS[extractLocation("HelloWorld")] just to get that JLabel instance. I know this may sound crazy but I want to test my concept of non-sorting feature extracting search algorithm for any data structure wherein my main problem is how to transform information to be stored into memory location of where it was stored.

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• Cross-browser method for getting width and height of a DIV?

  - by thinkthank

  This is my first post, so please go easy on me. I'm sure I'm doing everything wrong. However, I couldn't find any posts that answered the question above. I use jQuery. I'm trying to find a way to get the current width and height of a DIV element, even if they're set to "auto". I've found many ways to do this, but no method returns the same width in IE. It is important that this method is cross-browser, as it will break the layout of the page if different numbers are returned in different browsers. .width() and .height() do not work because in IE, padding is subtracted (e.g. width() returns 25 where width is 30 and padding is 5). .outerWidth() and .outerHeight() are not consistent either. While they work IE (believe it or not) in FF, the padding is added again to the full width (e.g. outerWidth() returns 110 in FF where width is 100px and padding is 10px). Is there any way out of this mess without writing complex browser checks? Thanks!

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• Custom Android layout that handles its children

  - by Gromix

  Hi, I'm trying to create a custom Android control to emulate a LinearLayout with a fancier display. Basically, I want the exact behaviour of a LinearLayout, but also borders, a background, ... I could do it all in XML (works great) but since I have dozens of occurences in my app it's getting hard to maintain. I thought it would be nicer to have something like this: /* Main.xml */ <MyFancyLayout> <TextView /> <ImageView /> </MyfancyLayout> My problem is, I don't want to have to re-write LinearLayout, so is there a way to only change its appearance? I got as far as this, which doesn't work... can anyone think of a better approach? /* MyFancyLayout.xml */ <merge> ... the complex hierarchy to make it look like what I want ... with background attributes etc </merge> and /* MyFancyLayout.java */ public class MyFancyLayout extends LinearLayout { // inflate the XML // move all the real children (as given by main.xml) to the inflated layout // do I still need to override onMeasure and onLayout? } Cheers! Romain

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• Typical Search, Result and Detail Workflow Staying Within an Android Tab

  - by Justin

  So, I've been banging my head looking for a good solution for a few days and am stuck. I have a search screen (Activity) in a tab, and after the user enters a value and clicks "search" I would like the results to come back in that same tab, and then if an item from the results is selected, to show more detailed results, in that same tab. I have it all working now in separate activities, and even the first step working in a tab, but as soon as I call the activity to process he search results... i.e. startActivity(i); for the results Activity, the results displayed are not in the tab! I am having a very difficult time getting this flow to work all under a tab. Any thoughts on how to make this happen? I keep hearing that Android views should be used instead of activities, but am I then to assume that all the logic I have right now for 3 activity needs to go inside 1 activity and then I need to handle setting the content and state for each of these cases? Plus, won't the history stack not work as pressing the back button will take the user out of the application, instead of taking them from say the search result to the search screen, or the details to the search results, etc. This seems like a mess. Can anyone show a more complex example of tabs or how one might have a simple search, result and detail workflow staying in a tab? I have seen a few questions on this concept of keeping activities "within a tab", but no good resolution. Please help.

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• Stable/repeatable random sort (MySQL, Rails)

  - by Matt Rogish

  I'd like to paginate through a randomly sorted list of ActiveRecord models (rows from MySQL database). However, this randomization needs to persist on a per-session basis, so that other people that visit the website also receive a random, paginate-able list of records. Let's say there are enough entities (tens of thousands) that storing the randomly sorted ID values in either the session or a cookie is too large, so I must temporarily persist it in some other way (MySQL, file, etc.). Initially I thought I could create a function based on the session ID and the page ID (returning the object IDs for that page) however since the object ID values in MySQL are not sequential (there are gaps), that seemed to fall apart as I was poking at it. The nice thing is that it would require no/minimal storage but the downsides are that it is likely pretty complex to implement and probably CPU intensive. My feeling is I should create an intersection table, something like: random_sorts( sort_id, created_at, user_id NULL if guest) random_sort_items( sort_id, item_id, position ) And then simply store the 'sort_id' in the session. Then, I can paginate the random_sorts WHERE sort_id = n ORDER BY position LIMIT... as usual. Of course, I'd have to put some sort of a reaper in there to remove them after some period of inactivity (based on random_sorts.created_at). Unfortunately, I'd have to invalidate the sort as new objects were created (and/or old objects being removed, although deletion is very rare). And, as load increases the size/performance of this table (even properly indexed) drops. It seems like this ought to be a solved problem but I can't find any rails plugins that do this... Any ideas? Thanks!!

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• What wrapper class in C++ should I use for automated resource management?

  - by Vilx-

  I'm a C++ amateur. I'm writing some Win32 API code and there are handles and weirdly compositely allocated objects aplenty. So I was wondering - is there some wrapper class that would make resource management easier? For example, when I want to load some data I open a file with CreateFile() and get a HANDLE. When I'm done with it, I should call CloseHandle() on it. But for any reasonably complex loading function there will be dozens of possible exit points, not to mention exceptions. So it would be great if I could wrap the handle in some kind of wrapper class which would automatically call CloseHandle() once execution left the scope. Even better - it could do some reference counting so I can pass it around in and out of other functions, and it would release the resource only when the last reference left scope. The concept is simple - but is there something like that in the standard library? I'm using Visual Studio 2008, by the way, and I don't want to attach a 3rd party framework like Boost or something.

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• Are workflows good for web service business logic?

  - by JL

  I have a series of complex web services that are getting used in my SOA application. I am generally happy with the overall design of the application, but as the complexity grows, I was wondering if Windows Workflow might be the way to go. My motivations for this are that you can get a graphic representation of the applications functionality, so it would be easier to maintain the code by its business function, rather than what I have now ( a standard 3 tier class library structure). My concerns are: I would be inducing an abstraction in my code, and I don't want to spend time having to deal with possible WF quirks or bugs. I've never worked with WF, is it a solid technology? I don't want to hit any WF limitations that prevent me from developing my solution. Is a WF even the right solution for the task? Simply put I am considering writing my next web service in this app to call a WF, and in this work flow manage the tasks the web service needs to carry out. I think it will be much neater and easier to maintain than a regular c# class library (maintainable by namespaces, classes ). Do you think this is the right thing to do? I'm hoping for positive feedback on WF (.net 4), but brutal honestly at the end of the day would help more. Thanks

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• Generating all possible subsets of a given QuerySet in Django

  - by Glen

  This is just an example, but given the following model: class Foo(models.model): bar = models.IntegerField() def __str__(self): return str(self.bar) def __unicode__(self): return str(self.bar) And the following QuerySet object: foobar = Foo.objects.filter(bar__lt=20).distinct() (meaning, a set of unique Foo models with bar <= 20), how can I generate all possible subsets of foobar? Ideally, I'd like to further limit the subsets so that, for each subset x of foobar, the sum of all f.bar in x (where f is a model of type Foo) is between some maximum and minimum value. So, for example, given the following instance of foobar: >> print foobar [<Foo: 5>, <Foo: 10>, <Foo: 15>] And min=5, max=25, I'd like to build an object (preferably a QuerySet, but possibly a list) that looks like this: [[<Foo: 5>], [<Foo: 10>], [<Foo: 15>], [<Foo: 5>, <Foo: 10>], [<Foo: 5>, <Foo: 15>], [<Foo: 10>, <Foo: 15>]] I've experimented with itertools but it doesn't seem particularly well-suited to my needs. I think this could be accomplished with a complex QuerySet but I'm not sure how to start.

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• Expanders inside listbox leaving blank space on collapse

  - by siz

  We have a rather complex UI that is presenting some problems for us. I have a ListBox that contains a set of DataItems. The DataTemplate for each item is an Expander. The header is text, the content of the Expander is a ListBox. The ListBox contains SubDataItems. The DataTemplate for each SubDataItem is an Expander. Here is a simplified XAML in which I reproduce the issue: <ListBox ItemsSource="{Binding Items}"> <ListBox.ItemTemplate> <DataTemplate> <Expander Header="{Binding Header}"> <ListBox ItemsSource="{Binding SubItems}"> <ListBox.ItemTemplate> <DataTemplate> <Expander Header="{Binding SubHeader}"> <Grid Height="40"> <TextBlock Text="{Binding SubText}" /> </Grid> </Expander> </DataTemplate> </ListBox.ItemTemplate> </ListBox> </Expander> </DataTemplate> </ListBox.ItemTemplate> </ListBox> There is a problem with how the layout is produced. If any Expander corresponding to the SubDataItem is expanded, the ListBoxItem containing this ListBox (the Expander.Content in the parent DataTemplate) correctly requests more space. So I can expand all SubDataItems and correctly see my data. However, when I collapse, the space I previously asked to expand, remains blank, instead of being reclaimed by the ListBoxItem. This is a problem because if I have say 10 SubDataItems and happen to expand all of them at the same time and then collapse, there is a significant amount of white space wasting my real estate. How can I force WPF to resize the ListBoxItem to the correct state?

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• Windows Workflow Foundation 4.0 Designer Rehosting with Custom Activities

  - by Robert

  I have several WF 4.0 workflows that I have created for an application my company is developing. Some of these workflows are simple, and some are very complex (i.e. many steps, several different types of activities, custom activities). For many of these workflows, I have created several custom code activities to support some internal process types. The workflows work great and we have had very few problems when it comes to maintaining them within VS 2010. We now want to move that responsibility off to our business users, so I have created a WPF application to rehost the WF designer (according to the MS samples). My problem is that when I open one of the workflows that contains custom code activities, those activities are represented as red boxes with the error message of "Activity could not be loaded because of errors in XAML." I have done research and have found several posts that mention that this is usually a problem with namespacing and referencing. The rehosted designer is in a namespace similar to this: Company.Application.Workflow.Designer And the custom code activities are contained within a separate custom workflow library, which I have included as a reference in the designer project. The library's namespace is similar to this: Company.Application.Workflow.Data.Activities As I have mentioned, the library is set as a reference in the designer's project, and I see it being copied to the output when I build the project. I have also included the reference in the XAML of the main designed application. What am I missing?

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• LINQ to SQL - Lightweight O/RM?

  - by CoffeeAddict

  I've heard from some that LINQ to SQL is good for lightweight apps. But then I see LINQ to SQL being used for Stackoverflow, and a bunch of other .coms I know (from interviewing with them). Ok, so is this true? for an e-commerce site that's bringing in millions and you're typically only doing basic CRUDs most the time with the exception of an occasional stored proc for something more complex, is LINQ to SQL complete enough and performance-wise good enough or able to be tweaked enough to run happily on an e-commerce site? I've heard that you just need to tweak performance on the DB side when using LINQ to SQL for a better approach. So there are really 2 questions here: 1) Meaning/scope/definition of a "Lightweight" O/RM solution: What the heck does "lightweight" mean when people say LINQ to SQL is a "lightweight O/RM" and is that true??? If this is so lightweight then why do I see a bunch of huge .coms using it? Is it good enough to run major .coms (obviously it looks like it is) and what determines what the context of "lightweight" is...it's such a generic statement. 2) Performance: I'm working on my own .com and researching different O/RMs. I'm not really looking at the Entity Framework (yet), just want to figure out the LINQ to SQL basics here and determine if it will be efficient enough for me. The problem I think is you can't tweak or control the SQL it generates...

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• Asp.net MVC - Model binding image button

  - by big dave

  I've got a very complex form and i'm using the MVC model binding to capture all the information I've got it set up to capture all the different submissions that can happen as there are about 10 different submit buttons on the form, and there are also 2 image buttons I tried to get a bit clever (or so i thought) with capturing the image button submissions, and have created a child class so that i can capture the x value that's returned public class ImageButtonViewData { public int x { get; set; } public string Value { get; set; } } The parent class looks something like this public class ViewDataObject { public ImageButtonViewData ImageButton { get; set; } public ViewDataObject(){ this.ImageButton = new ImageButton(); } } The html for the image button then looks like <input type="image" id="ViewDataObject_ImageButton" name="ViewDataObject.ImageButton" /> This works fine in all browsers except for Chrome. When i debug it in chrome, the Request.Form object contains the values that i would expect, but after the model binding has occurred, the ImageButton property on the ViewDataObject has been set to null The only difference that i can see between the submission values is that Chrome passes the x as lower case (ViewDataObject.ImageButton.x) and IE passes it as upper case (ViewDataObject.ImageButton.X) but i didn't think that model binding took any notice of casing on property names Does anyone have any ideas ?

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• Query crashes MS Access

  - by user284651

  THE TASK: I am in the process of migrating a DB from MS Access to Maximizer. In order to do this I must take 64 tables in MS ACCESS and merge them into one. The output must be in the form of a TAB or CSV file. Which will then be imported into Maximizer. THE PROBLEM: Access is unable to perform a query that is so complex it seems, as it crashes any time I run the query. ALTERNATIVES: I have thought about a few alternatives, and would like to do the least time-consuming one, out of these, while also taking advantage of any opportunities to learn something new. Export each table into CSVs and import into SQLight and then make a query with it to do the same as what ACCESS fails to do (merge 64 tables). Export each table into CSVs and write a script to access each one and merge the CSVs into a single CSV. Somehow connect to the MS ACCESS DB (API), and write a script to pull data from each table and merge them into a CSV file. QUESTION: What do you recommend?

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• How to Bind a Command in WPF

  - by MegaMind

  Sometimes we used complex ways so many times, we forgot the simplest ways to do the task. I know how to do command binding, but i always use same approach. Create a class that implements ICommand interface and from the view model i create new instance of that class and binding works like a charm. This is the code that i used for command binding public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); DataContext = this; testCommand = new MeCommand(processor); } ICommand testCommand; public ICommand test { get { return testCommand; } } public void processor() { MessageBox.Show("hello world"); } } public class MeCommand : ICommand { public delegate void ExecuteMethod(); private ExecuteMethod meth; public MeCommand(ExecuteMethod exec) { meth = exec; } public bool CanExecute(object parameter) { return false; } public event EventHandler CanExecuteChanged; public void Execute(object parameter) { meth(); } } But i want to know the basic way to do this, no third party dll no new class creation. Do this simple command binding using a single class. Actual class implements from ICommand interface and do the work.

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• CSS - Positioning images next to text

  - by jpjoki

  Hi, I'm doing a site in which images need to presented next to textual content - a sort of pseudo two-column layout, as the images and text come from a single html source. I've found quite a simple way to do this by putting the images as their own paragraphs and floating them. Would there still be a more simpler way (in regards to html) to do this without these extra paragraphs and by only attributing extra css to images? If the floated image is in the same paragraph than the text, then paragraphs with and without images would be different in width. EDIT: Basically, I'm looking for as simple HTML markup as possible to position images like this. The CSS can be complex ;) CSS: p { width: 500px; } p.image { float: right; width: 900px; } Current HTML: <p class="image"><img src="image.jpg" /></p> <p>Some text here.</p> Is the above possible with this HTML? <p><img src="image.jpg" /></p>

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• Coldfusion 8 and HTTP PUT - is there a way to PUT an object?

  - by ciaranarcher

  Hi all We are using EHCache with CF 8 to cache stuff on a central server using a RESTful interface over HTTP. I am trying to cache a cfquery object to the cache server. I can get this to work if I call EHCache direct (i.e. store it in a local cache) but if I try to cache on a remote server over HTTP I am running into problems. The code I am using is as follows: <cfhttp url="http://localhost:8080/myCache/myKey" method="put" result="r" timeout="2" throwonerror="true" > <cfhttpparam type="body" value="#ARGUMENTS.item#" /> </cfhttp> CF doesn't like this reference to #ARGUMENTS.item# and it complains Complex object types cannot be converted to simple values. Can anyone give me an example of how to put an object over http using CF? If this is not possible with CF then a Java example would be the next best thing. Many thanks in advance! PS: I do not want to use serialization to text/JSON etc. as this approach has issues with data integrity and most importantly it's not fast enough.

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• Is there a Designer for MFC in Visual Studio like for windows forms in .NET?

  - by claws

  I'm a .NET programmer. I've never developed anything in MFC. Currently I had to write a C++ application (console) for some image processing task. I finished writing it. But the point is I need to design GUI also for this. Well, there won't be anything complex. Just a window with few Buttons, RadioButtons, Check Boxes, PicturesBox & few sliders. thats it. I'm using VS 2008 and was expecting a .NET style form designer. Just to test, I created a MFC project (with all default configuration) and these files were created by default: ChildFrm.cpp MainFrm.cpp mfc.cpp mfcDoc.cpp mfcView.cpp stdafx.cpp Now, I'm unable to find a Designer. There is no View Designer. I've opened all the above *.cpp and in the code editor right clicked to see "Designer View". ToolBox is just empty because I'm in code editor mode. When I built the project. This is the window I get. How to open a designer?

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• Modeling Buyers & Sellers in a Rails Ecommerce App

  - by MikeH

  I'm building a Rails app that has Etsy.com style functionality. In other words, it's like a mall. There are many buyers and many sellers. I'm torn about how to model the sellers. Key facts: There won't be many sellers. Perhaps less than 20 sellers in total. There will be many buyers. Hopefully many thousands :) I already have a standard user model in place with account creation and roles. I've created a 'role' of 'seller', which the admin will manually apply to the proper users. Since we'll have very few sellers, this is not an issue. I'm considering two approaches: (1) Create a 'store' model, which will contain all the relevant store information. Products would :belong_to :store, rather than belonging to the seller. The relationship between the user and store models would be: user :has_one store. My main problem with this is that I've always found has_one associations to be a little funky, and I usually try to avoid them. The app is fairly complex, and I'm worried about running into a cascade of problems connected to the has_one association as I get further along into development. (2) Simply include the relevant 'store' information as part of the user model. But in this case, the store-related db columns would only apply to a very small percentage of users since very few users will also be sellers. I'm not sure if this is a valid concern or not. It's very possible that I'm thinking about this incorrectly. I appreciate any thoughts. Thanks.

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• 2-column table with two foreign keys. Performance/design question.

  - by Emanuel

  Hello everyone! I recently ran into a quite complex problem and after looking around a lot I couldn't find a solution to it. I've found answers to my questions many times before on stackoverflow.com, so I decided to post here. So I'm making a user/group managment system for a web-based project, and I'm storing all related data into a postgreSQL database. This system relies on three tables: USERS GROUPS GROUP_USERS The two first tables simply define all the users and all the groups on the site, and the last table, GROUP_USERS, stores the groups every user is part of. It only has two columns: USER_ID GROUP_ID Since every user can be a member of several groups, I decided to make a separate table for this purpose, rather than storing a comma separated column in the USERS-table. Now, both columns are foreign keys, and I want to make them both primary keys as well, this since each combination of USER_ID and GROUP_ID has to be unique, and if I give them the constraint UNIQUE pgAdmin tells me that each table should have at least one Primary key. But now I am stuck with what seems to be a lot of indexes and relations to a very small table only containing numbers. In the end, I want this table to be as fast as possible, even if containing tens of thousands of rows. Size on disk shouldn't be a problem since its just all numbers anyway, but it feels quite stupid to have a full-sized index refering to a smaller table. Should I stick with my current solution, store comma-separated values in a column in the USERS-table or is there any other solution I should be aware of. PS. I don't want to use an array-column, even if they are supported by postgreSQL. I want to be as generic as possible so I can switch database later on, if necessary. EDIT: I other words, will using a compound primary key and two foreign keys in one table with only two columns have a negative impact on performance rather than the opposite due to the size of the generated index? Thank you!

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• How can I spot subtle Lisp syntax mistakes?

  - by Marius Andersen

  I'm a newbie playing around with Lisp (actually, Emacs Lisp). It's a lot of fun, except when I seem to run into the same syntax mistakes again and again. For instance, here's something I've encountered several times. I have some cond form, like (cond ((foo bar) (qux quux)) ((or corge (grault warg)) (fred) (t xyzzy))) and the default clause, which returns xyzzy, is never carried out, because it's actually nested inside the previous clause: (cond ((foo bar) (qux quux)) ((or corge (grault warg)) (fred)) (t xyzzy)) It's difficult for me to see such errors when the difference in indentation is only one space. Does this get easier with time? I also have problems when there's a large distance between the (mal-)indented line and the line it should be indented against. let forms with a lot of complex bindings, for example, or an unless form with a long conditional: (defun test () (unless (foo bar (qux quux) (or corge (grault warg) (fred)))) xyzzy) It turns out xyzzy was never inside the unless form at all: (defun test () (unless (foo bar (qux quux) (or corge (grault warg) (fred))) xyzzy)) I auto-indent habitually and use parenthesis highlighting to avoid counting parentheses. For the most part it works like a breeze, but occasionally, I discover my syntax mistakes only by debugging. What can I do?

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• Passing C++ object to C++ code through Python?

  - by cornail

  Hi all, I have written some physics simulation code in C++ and parsing the input text files is a bottleneck of it. As one of the input parameters, the user has to specify a math function which will be evaluated many times at run-time. The C++ code has some pre-defined function classes for this (they are actually quite complex on the math side) and some limited parsing capability but I am not satisfied with this construction at all. What I need is that both the algorithm and the function evaluation remain speedy, so it is advantageous to keep them both as compiled code (and preferrably, the math functions as C++ function objects). However I thought of glueing the whole simulation together with Python: the user could specify the input parameters in a Python script, while also implementing storage, visualization of the results (matplotlib) and GUI, too, in Python. I know that most of the time, exposing C++ classes can be done, e.g. with SWIG but I still have a question concerning the parsing of the user defined math function in Python: Is it possible to somehow to construct a C++ function object in Python and pass it to the C++ algorithm? E.g. when I call f = WrappedCPPGaussianFunctionClass(sigma=0.5) WrappedCPPAlgorithm(f) in Python, it would return a pointer to a C++ object which would then be passed to a C++ routine requiring such a pointer, or something similar... (don't ask me about memory management in this case, though :S) The point is that no callback should be made to Python code in the algorithm. Later I would like to extend this example to also do some simple expression parsing on the Python side, such as sum or product of functions, and return some compound, parse-tree like C++ object but let's stay at the basics for now. Sorry for the long post and thx for the suggestions in advance.

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