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  • An Array returned by a model association is not an Array?

    - by Warren
    We have a model association that looks something like this: class Example < ActiveRecord::Base has_many :others, :order => 'others.rank' end The rank column is an integer type. The details of these particular models are not really important though as we have found the same problem with other has_many associations between other models. We have also added to the Enumerable module: module Enumerable def method_missing(name) super unless name.to_s[0..7] == 'collect_' method = name.to_s[8..-1] collect{|element| element.send(method)} end end This adds a collect_id method that we can use to get an array of record ids from an array of ActiveRecord objects. So if we use a normal ActiveRecord find :all, we get a nice array which we can then use collect_id on but if we use Example.others.collect_id, we get NoMethodError: undefined method `collect_id' for #<Class:0x2aaaac0060a0> Example.others.class returns "Array" so is it lying or confused? Our solution thus far has been to use it this way: Example.others.to_a.collect_id This works but this seems a bit strange. Why would you have to do that? We are on Ruby 1.8.7 and Rails 2.3.4

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  • Difference between macros and functions in C in relation to instruction memory and speed

    - by DAHANS
    To my understanding the difference between a macro and a function is, that a macro-call will be replaced by the instruction in the definition, and a function does the whole push, branch and pop -thing. Is this right, or have I understand something wrong? Additionally, if this is right, it would mean, that macros would take more space, but would be faster (because of the lack of the push,branch and pop instructions.), wouldn't it?

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  • difference between where and nested queries

    - by Chris H
    I'm not able to figure out the difference between these queries. I'm pretty sure that the first one is an equi-join. I'm not sure how the second one ISN'T the same as the first. The sub query in #2 selects all Ids from S, and then it returns all R's that also have those ID's, no? SELECT R.cname FROM R, S, WHERE R.Id = S.Id SELECT R.cname FROM R WHERE R.Id IN (SELECT S.Id FROM S)

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  • Difference between "and" and "where" in joins

    - by Midhat
    Whats the difference between SELECT DISTINCT field1 FROM table1 cd JOIN table2 ON cd.Company = table2.Name and table2.Id IN (2728) and SELECT DISTINCT field1 FROM table1 cd JOIN table2 ON cd.Company = table2.Name where table2.Id IN (2728) both return the same result and both have the same explain output

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  • what is the difference between MVC1 and MVC2

    - by Alaa
    I am using MVC design pattern in jsp-servlet web application, and want to what is the exact difference between MVC1 and MVC2 , can someone help? EDIT newly I hear that there is 2 versions of using MVC in servlet programming, I hear that in MVC1 there is kind of coupling between controller and view , but in MVC2 they overtake it, if someone know whether this is right or wrong I'll be very thankful.

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  • What is the difference between these two statements (asp.net/c#/entity framework)

    - by user318573
    IEnumerable<Department> myQuery = (from D in myContext.Departments orderby D.DeptName select D); var myQuery = (from D in myContext.Departments orderby D.DeptName select D); What is the difference between these two statements above? In my little asp.net/C#/ EF4.0 app I can write them either way, and as far as how I want to use them, they both work, but there has to be a reason why I would choose one over the other?

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  • Date difference in SQL Server 2005

    - by naveen
    Hi, I have two dates of the form Start Date: 2007-03-24, End Date: 2009-06-26 Now I need to find the difference between these two in the below form: 2 years, 3 months and 2 days Can someone please … in SQL Server 2005

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  • PreferenceFragment - Difference between getPreferenceManager() and getPreferenceScreen()?

    - by Zynga Liker
    I've implemented my own PreferenceFragment subclass (detailed here), and want to listen for preference changes within it. PreferenceFragment provides you with two ways of doing this: getPreferenceManager().getSharedPreferences().registerOnSharedPreferenceChangeListener(this); and getPreferenceScreen().getSharedPreferences().registerOnSharedPreferenceChangeListener(this); Which one should be used? What's the difference? I don't really understand the distinction made in the Android docs.

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  • Can reducing index length in Javascript associative array save memory

    - by d777
    I am trying to build a large Associative Array in JavaScript (22,000 elements). Do I need to worry about the length of the indices with regards to memory usage? In other words, which of the following options saves memory? or are they the same in memory consumption? Option 1: var student = new Array(); for (i=0; i<22000; i++) student[i] = { "studentName": token[0], "studentMarks": token[1], "studentDOB": token[2] }; Option 2: var student = new Array(); for (i=0; i<22000; i++) student[i] = { "n": token[0], "m": token[1], "d": token[2] }; I tried to test this on Google Chrome DevTools, but the numbers are inconsistent to make a decision. My best guess is that because the Array indices repeat, the browser can optimize memory usage by not repeating them for each student[i], but that is just a guess. Thanks.

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  • Using rowDiffs() to calculate difference in values in matrix

    - by user1723765
    I'm using the rowDiffs() command to calculate the step by step difference in 116 rows in a matrix. I get the following error: Error in r[i1] - r[-length(r):-(length(r) - lag + 1L)] : non-numeric argument to binary operator I have no idea why this is happening. I could take the diff() separately for each row and it would work. Any ideas? Here's the data: https://dl.dropbox.com/u/22681355/data.csv Code: a=rowDiffs(data)

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  • Difference between INSERT INTO and INSERT ALL INTO

    - by emily soto
    While I was inserting some records in table i found that.. INSERT INTO T_CANDYBAR_DATA SELECT CONSUMER_ID,CANDYBAR_NAME,SURVEY_YEAR,GENDER,1 AS STAT_TYPE,OVERALL_RATING FROM CANDYBAR_CONSUMPTION_DATA UNION SELECT CONSUMER_ID,CANDYBAR_NAME,SURVEY_YEAR,GENDER,2 AS STAT_TYPE,NUMBER_BARS_CONSUMED FROM CANDYBAR_CONSUMPTION_DATA; 79 rows inserted. INSERT ALL INTO t_candybar_data VALUES (consumer_id,candybar_name,survey_year,gender,1,overall_rating) INTO t_candybar_data VALUES (consumer_id,candybar_name,survey_year,gender,2,number_bars_consumed) SELECT * FROM candybar_consumption_data 86 rows inserted. I have read somewhere that INSERT ALL INTO automatically unions then why those difference is showing.

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