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• Processing large recordsets in Rails

  - by japancheese

  Hello, I'm trying to perform a daily operation on a larger than normal dataset (2m+ records). However, Rails seems to take a very long time performing operations on such a dataset. Operations like Dataset.all.each do |data| ... end take a very long time to complete (I assume this is because it can't fit all the items into memory at once, right?). Does anyone have any strategies on how I could handle this situation? I know SQL would probably speed up the process, but I'm looking to use the Rails environment as I can do many more complicated things to the data than I can with just SQL statements.

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• Select from parent table return ID = 0 column values for child objects

  - by SaD

  Entities: public class Person { public Person(){} public virtual long ID { get; set; } } public class Employee : Person { public Employee(){} public virtual long ID { get; set; } public virtual string Appointment { get; set; } } Mappings: public class PersonMap : ClassMap<Person> { public PersonMap() { Id(x => x.ID) .GeneratedBy.Identity(); } } public class EmployeeMap : SubclassMap<Employee> { public EmployeeMap() { KeyColumn("ID"); Map(x => x.Appointment) .Not.Nullable() .Length(50); } } 2 items in Person table 1 item in Employee table (1 in base class, 1 in child class) Query:var list = Session.CreateQuery("from Person").List<Person>(); Return: 0 | ID = 1 1 | ID = 0, Appointment = "SomeAppointment"

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• how to convert big-endian numbers to native numbers delphi

  - by steve0

  hi all i want to know how to convert big endian numbers to native numbers in delphi i am porting some c++ code in that i came accross this part unsigned long blockLength = *blockLengthPtr++ << 24; blockLength |= *blockLengthPtr++ << 16; blockLength |= *blockLengthPtr++ << 8; blockLength |= *blockLengthPtr; unsigned long dataLength = *dataLengthPtr++ << 24; dataLength |= *dataLengthPtr++ << 16; dataLength |= *dataLengthPtr++ << 8; dataLength |= *dataLengthPtr; i am not familiar with c++ ,so i didnt understand what those operators doing can any one help ? regards

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• Converting a C++ Checksum function to Java

  - by user1897599

  I'm trying to convert this C++ checksum to Java but for the time being I've failed. What am I doing wrong? What is it supposed to do? It is supposed to return a positive checksum for a buffer in OpenGL Here's the C part. DWORD QuickChecksum(DWORD *data, int size){ if(!data) { return 0x0; } DWORD sum; DWORD tmp; sum = *data; for(int i = 1; i < (size/4); i++) { tmp = data[i]; tmp = (DWORD)(sum >> 29) + tmp; tmp = (DWORD)(sum >> 17) + tmp; sum = (DWORD)(sum << 3) ^ tmp; } return sum; } And here is what I have tried in Java. As far As I know DWORD is 32bit so I use int in a long to get a unsigned int which should be done in java with ? I've been looking at this problem so much now that I've grown blind to it. public static long getChecksum(byte[] data, int size) { long sum, tmp; sum = getInt(new byte[]{data[0], data[1], data[2], data[3]},true) & 0xFF; for(int I = 4; I < data.length; I += 4) { tmp = getInt(new byte[]{data[I],data[I+1],data[I+2],data[I+3]},true) & 0xFF; tmp = (sum >>> 29) + tmp; tmp = (sum >>> 17) + tmp; sum = (sum << 3) ^ tmp; } return sum & 0xFF; } private static int getInt(byte[] bytes, boolean big) { ByteBuffer bb = ByteBuffer.wrap(bytes); return bb.getInt(); } Thank you all for your help!

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• size of structures in .NET

  - by redpaladin

  My problem is very simple. My problem is to send a structure between a program in C to a C# program. I made a struct in C#: public struct NetPoint { public float lat; // 4 bytes public float lon; // 4 bytes public int alt; // 4 bytes public long time; // 8 bytes } Total size of the struct must be 20 bytes. When I do a sizeof() of this struct: System.Diagnostics.Debug.WriteLine("SizeOf(NetPoint)=" + System.Runtime.InteropServices.Marshal.SizeOf(new NetPoint())); The debug console shows: SizeOf(NetPoint)=24 But I expected to have 20 bytes. Why do I see a difference?

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• I am using jquery ajax using text() but any html written in the XML doesn't render?

  - by Xtian

  So I have Jquery Ajax working real nice, but an issue I am having is in my XML if I want to bold a work or Italicize a sentence, if I do it in the XML using HTML tags it will not show up. I am pretty sure it is due to using the .text(). Any suggestions on a work around for this? $(document).ready(function(){ $.ajax({ type: "GET", url: "xml/sites.xml", dataType: "xml", success: function(xml) { $(xml).find('site').each(function(){ $(this).find('desc').each(function(){ var brief = $(this).find('brief').text(); var long = $(this).find('long').text(); var url = $(this).find('url').text(); $('<div class="brief"></div>').html(brief).appendTo('#link_'+id);

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• Excel VBA: Alternate Row Color in Range

  - by Kurt

  I spent a VERY long time today looking up a method to alternate row colors within a specified range. There really isn't a lot out there and to be honest what I found just looked over-complicated. So, I decided to stop acting like a shameless 'script-kiddy' and put the below sample together: Sub AlternateRowColors() Dim lastRow as Long lastRow = Range("A1").End(xlDown).Row For Each Cell In Range("A1:A" & lastRow) ''change range accordingly If Cell.Row Mod 2 = 1 Then ''highlights row 2,4,6 etc|= 0 highlights 1,3,5 Cell.Interior.ColorIndex = 15 ''color to preference Else Cell.Interior.ColorIndex = xlNone ''color to preference End If Next Cell End Sub Now I know that works, but I was wondering if there's a simpler method? If so, please do tell because I'm very eager to learn simplification as I have a tendency to write verbose code at present. If not, then may this entry find it's way to page 1 of Google for it's search term(s), because it took me absolutely ages to find anything even remotely useful. Comments left for script-kiddies' benefit.

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• Mass data store with SQL SERVER

  - by Leo

  We need management 10,000 GPS devices, each GPS device upload a GPS data every 30 seconds, these data need to store in the database(MS SQL Server 2005). Each GPS device daily data quantity is: 24 * 60 * 2 = 2,880 10 000 10,000 GPS devices daily data quantity is: 10000 * 2880 = 28,800,000 Each GPS data approximately 160Byte, the amount of data per day is: 28,800,000 * 160 = 4.29GB We need hold at least 3 months of GPS data in the database, My question is: 1, whether SQL Server 2005 can support such a large amount of data store? 2, How to plan data table? (all GPS data storage in one table? Daily table? Each GPS device with a GPS data table?) The GPS data: GPSID varchar(21), RecvTime datetime, GPSTime datetime, IsValid bit, IsNavi bit, Lng float, Lat float, Alt float, Spd smallint, Head smallint, PulseValue bigint, Oil float, TSW1 bigint, TSW1Mask bigint, TSW2 bigint, TSW2Mask, BSW bigint, StateText varchar(200), PosText varchar(200), UploadType tinyint

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• Unique identification string in php

  - by NardCake

  Currently me and my friend are developing a website, for what we will call 'projects' we just have a basic auto increment id in the database used to navigate to projects such as oururl.com/viewproject?id=1 but we started thinking, if we have alot of posted projects thats going to be a LONG url. So we need to somehow randomly generate a alphanumerical string about 6 characters long. We want the chance of the string being duplicated being extremely low and of course we will query the database before assigning an identifier. Thanks for anyhelp, means alot!

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• Pass a parameter from one jsp to another using form.action

  - by Ntz

  I have an ID that I need in the next jsp once the user click a button. I am trying to do the following: FirstJSP.jsp: function getSecond() { var frm = document.getElementById("frm"); frm.action = "**second.jsp?id=myId;"** frm.submit(); } ... form id="frm" ..... input type="button" value="Next" onclick="getSecond()"/ ...... This code takes me to my second page, but if I tried to access the id, it gives me an error since the id is null. I access the id in the second page by: final Long passedId = Long.parseLong(request.getParameter("id")); I think I am not passing the parameter correctly, but I don't know how to do it. Any ideas? Thank you so much!

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• Not a statement?

  - by abelenky

  I have a simple little code fragment that is frustrating me: HashSet<long> groupUIDs = new HashSet<long>(); groupUIDs.Add(uid)? unique++ : dupes++; At compile time, it generates the error: Only assignment, call, increment, decrement, and new object expressions can be used as a statement HashSet.Add is documented to return a bool, so the ternary (?) operator should work, and this looks like a completely legitimate way to track the number of unique and duplicate items I add to a hash-set. When I reformat it as a if-then-else, it works fine. Can anyone explain the error, and if there is a way to do this as a simple ternary operator?

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• cannot convert ‘mcontext_t*’ to ‘sigcontext*’ in assignment

  - by user353573

  i have checked asm/ucontext.h it should be sigcontext, but why pop up the error message cannot convert ‘mcontext_t*’ to ‘sigcontext*’ in assignment #include <stdio.h> #include <signal.h> #include <asm/ucontext.h> static unsigned long target; void handler(int signum, siginfo_t *siginfo, void *uc0){ struct ucontext *uc; struct sigcontext *sc; uc = (struct ucontext *)uc0; sc = &uc->uc_mcontext; sc->eip = target; } struct ucontext { unsigned long uc_flags; struct ucontext *uc_link; stack_t uc_stack; struct sigcontext uc_mcontext; sigset_t uc_sigmask; /* mask last for extensibility */ };

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• What's the reason behind the jumping GeneratedValue(strategy=GenerationType.TABLE) when not specifyi

  - by joeduardo

  Why do I need to add allocationSize=1 when using the @TableGenerator to ensure that the id wouldn't jump from 1, 2,... to 32,xxx, 65,xxx,... after a jvm restart? Is there a design reason for the need to specify the allocationSize? This snippet would produce the jumping ids @Id @GeneratedValue(strategy = GenerationType.TABLE) private Long id; Here's the modified snippet that produces the properly sequenced ids @Id @GeneratedValue(strategy = GenerationType.TABLE, generator = "account_generator") @TableGenerator(name = "account_generator", initialValue = 1, allocationSize = 1) private Long id;

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• PHP - MySQL - Select runs indefinitely

  - by John

  I have three tables listings: id, pid, beds, baths, etc, etc, etc, db locations: id, pid, zip, lat, lon, etc, etc, etc, db images id, pid, height, width, raw, etc, etc, db id, pid & db are indexed. db just references the mls provider a particular item came from. in images the raw column holds raw image data there are about 15k rows in listings/locations, and about 120k rows in images so there are multiple rows that have the same pid. when i do "select pid from listings" or "select pid from locations" the query completes successfully in about 100ms. when i do "select pid from images" it just hangs in sqlyog and never completes... i was thinking since the raw column contains alot of information that it might be trying to select that too, but my query doesn't try to select that so I can't imagine why it's taking so long... any idea why this is happening??

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• Efficient bitshifting an array of int?

  - by nn

  Hi, To be on the same page, let's assume sizeof(int)=4 and sizeof(long)=8. Given an array of integers, what would be an efficient method to bitshift the array to either the left or right? I am contemplating an auxiliary variable such as a long, that will compute the bitshift for the first pair of elements (index 0 and 1) and set the first element (0). Continuing in this fashion the bitshift for elements (index 1 and 2) will be computer, and then index 1 will be set. I think this is actually a fairly efficient method, but there are drawbacks. I cannot bitshift greater than 32 bits. I think using multiple auxiliary variables would work, but I'm envisioning recursion somewhere along the line.

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• Hot to get rid of memory allocations/deallocations in swig wrappers?

  - by Dmitriy Matveev

  I want to use swig for generation of read-only wrappers for a complex object. The object which I want to wrap will always be existent while I will read it. And also I will only use my wrappers at the time that object is existent, thus I don't need any memory management from SWIG. For following swig interface: %module test %immutable; %inline %{ struct Foo { int a; }; struct Bar { int b; Foo f; }; %} I will have a wrappers which will have a lot of garbage in generated interfaces and do useless work which will reduce performance in my case. Generated java wrapper for Bar class will be like this: public class Bar { private long swigCPtr; protected boolean swigCMemOwn; protected Bar(long cPtr, boolean cMemoryOwn) { swigCMemOwn = cMemoryOwn; swigCPtr = cPtr; } protected static long getCPtr(Bar obj) { return (obj == null) ? 0 : obj.swigCPtr; } protected void finalize() { delete(); } public synchronized void delete() { if (swigCPtr != 0) { if (swigCMemOwn) { swigCMemOwn = false; testJNI.delete_Bar(swigCPtr); } swigCPtr = 0; } } public int getB() { return testJNI.Bar_b_get(swigCPtr, this); } public Foo getF() { return new Foo(testJNI.Bar_f_get(swigCPtr, this), true); } public Bar() { this(testJNI.new_Bar(), true); } } I don't need 'swigCMemOwn' field in my wrapper since it always will be false. All code related to this field will also be useless. There are also unnecessary logic in native code: SWIGEXPORT jlong JNICALL Java_some_testJNI_Bar_1f_1get(JNIEnv *jenv, jclass jcls, jlong jarg1, jobject jarg1_) { jlong jresult = 0 ; struct Bar *arg1 = (struct Bar *) 0 ; Foo result; (void)jenv; (void)jcls; (void)jarg1_; arg1 = *(struct Bar **)&jarg1; result = ((arg1)->f); { Foo * resultptr = (Foo *) malloc(sizeof(Foo)); memmove(resultptr, &result, sizeof(Foo)); *(Foo **)&jresult = resultptr; } return jresult; } I don't need these calls to malloc and memmove. I want to force swig to resolve both of these problems, but don't know how. Is it possible?

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• How to implement a private virtual function within derived classes?

  - by Dane

  Hi, I know why I want to use private virtual functions, but how exactly can I implement them? For example: class Base{ [...] private: virtual void func() = 0; [...] } class Derived1: puplic Base{ void func() { //short implementation is ok here } } class Derived2: puplic Base{ void func(); //long implementation elsewhere (in cpp file) } [...] void Derived2::func() { //long implementation } The first version is ok but not always possible. Isn't the second version simply name hiding? How do you define the Base::func() of Derived2, if you cannot do it within the class declaration of Dereived2? Thanks

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• Doesn't Matlab optimize the following?

  - by kloop

  I have a very long vector 1xr v, and a very long vector w 1xs, and a matrix A rxs, which is sparse (but very big in dimensions). I was expecting the following to be optimized by Matlab so I won't run into trouble with memory: A./(v'*w) but it seems like Matlab is actually trying to generate the full v'*w matrix, because I am running into Out of memory issue. Is there a way to overcome this? Note that there is no need to calculate all v'*w because many values of A are 0. EDIT: If that were possible, one way to do it would be to do A(find(A)) ./ (v'*w)(find(A)); but you can't select a subset of a matrix (v'*w in this case) without first calculating it and putting it in a variable.

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• Is it possible with dynamic TSQL query ?

  - by eugeneK

  I have very long select query which i need to filter based on some params, i'm trying to avoid having different stored procedures or if statements inside of single stored procedure by using partly dynamic TSQL... I will avoid long select just for example sake select a from b where c=@c or d=@d @c and @d are filter params, only one can filter at the same time but also both filters could be disabled. 0 for each of these means param is disables so i can create nvarchar with where statement in it... How do i integrate in here dynamic query so 'where' can be added to normal query. I cannot add all the query as big nvarchar because there is too many things in it which will require changes ( ie. when's, subqueries, joins)

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• How to map a search object to a class with more fields with JPA annotations

  - by Moli

  Hi all, I'm a newbie with JPA. I need to map a search object to a table. The search object has only and id, name. The big object has more fileds id, name, adress and more. I use this as big object view plaincopy to clipboardprint? I use this as big object @Entity @Table(name="users") public class User { @Id @GeneratedValue(strategy = GenerationType.AUTO) private long id; private String name; private String adress; private String keywords; } //this is my search object @XXX public class UserSearch { @Id @GeneratedValue(strategy = GenerationType.AUTO) private long id; private String name; } What annotations I need to use to map the search object to the table users? I'm using spring+struts2+hibernate+JPA. Help is appreciated! Thanks!

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• new operator overwriting an existing object

  - by dvpdiner2

  I have a custom FastStack class, implemented as a fixed size array and an index into that array. In my copy constructor, I allocate the array and then assign each object from the copy's array into the new array. There's some refcounting in the objects on the stack, hence assignment is used rather than a simple copy. The problem is that when allocating the array, it sometimes overwrites part of the other stack's array. As can be expected, this leads to eventual segmentation faults when that data is dereferenced. class FastStack { private: int m_size, m_ptr; ObjectRef* m_stack; public: FastStack(int size) : m_size(size), m_ptr(-1) { m_stack = new ObjectRef[m_size]; } FastStack(const FastStack& copy) : m_size(copy.m_size), m_ptr(copy.m_ptr) { long a = (long)copy.m_stack[0]; m_stack = new ObjectRef[m_size]; if ((long)copy.m_stack[0] != a) fprintf(stderr, "\nWe have a serious problem!\n\n"); for (int i = 0; i <= m_ptr; i++) m_stack[i] = copy.m_stack[i]; } ~FastStack() { delete[] m_stack; } }; class ObjectRef { private: DataObj* m_obj; public: ObjectRef() : m_obj(0) { } ObjectRef(DataObj* obj) : m_obj(obj) { if (m_obj) m_obj->addRef(); } ObjectRef(const ObjectRef& obj) : m_obj(obj.m_obj) { if (m_obj) m_obj->addRef(); } ~ObjectRef() { if (m_obj) m_obj->delRef(); } ObjectRef& operator=(DataObj* obj) { if (obj) obj->addRef(); if (m_obj) m_obj->delRef(); m_obj = obj; return *this; } ObjectRef& operator=(const ObjectRef& obj) { if (obj.m_obj) obj.m_obj->addRef(); if (m_obj) m_obj->delRef(); m_obj = obj.m_obj; return *this; } }; I see that "We have a serious problem!" line shortly before a segfault, and stepping through it with gdb I can see that one of the ObjectRefs created by new has the same address as the other stack's array. My first instinct is to say that new should never be allocating memory that is already in use, but that clearly seems to be the case here and I am at a complete loss as to what can be done. Added: At the time that I see this happen, m_size = 2 and m_ptr = 0.

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• Fitting place names into map shapes

  - by Old Man

  I'm drawing shapes using GDI+ using a list of lat/lon floats, and I need to place the name of the place within the borders of the polygon. Simply centering the text in the bounding rectangle doesn't work for irregular shapes. I have the text and the font so I can get the size of the rectangle that the text will need to fit in, but at that point I'm stuck. This seems like a common problem that all mapping software solves, as well as the kind of thing you would find in an algorithm or computer graphics textbook. So, given a list of floats for a polygon and a rectangle, is there a way to get the best possible point to place the text, using: 1) GDI+; 2) SQL Server Geospatial; or 3) c# code (or c, pseudocode, etc)

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• How to print size_t variable portably?

  - by ArunSaha

  I have a variable of type size_t, and I want to print it using printf(). What format specifier do I use to print it portably? In 32-bit machine, %u seems right. I compiled with g++ -g -W -Wall -Werror -ansi -pedantic, and there was no warning. But when I compile that code in 64-bit machine, it produces warning. size_t x = <something>; printf( "size = %u\n", x ); warning: format '%u' expects type 'unsigned int', but argument 2 has type 'long unsigned int' The warning goes away, as expected, if I change that to %lu. The question is, how can I write the code, so that it compiles warning free on both 32- and 64- bit machines? Edit: I guess one answer might be to "cast" the variable into an unsigned long, and print using %lu. That would work in both cases. I am looking if there is any other idea. (C, C++)

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• Importing data from a text file using python

  - by Will

  I have a text file containing data in rows and columns (~17000 rows in total). Each column is a uniform number of characters long, with the 'unused' characters filled in by spaces. For example, the first column is 11 characters long, but the last four characters in that column are always spaces (so that it appears to be a nice column when viewed with a text editor). Sometimes it's more than four if the entry is less than 7 characters. The columns are not otherwise separated by commas, tabs, or spaces. They are also not all the same number of characters (the first two are 11, the next two are 8 and the last one is 5 - but again, some are spaces). What I want to do is import the entires (which are numbers) in the last two columns if the second column contains the string 'OW' somewhere in it. Any help would be greatly appreciated.

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• Do encryption algorithms provide really unique results?

  - by Mikulas Dite

  I was wondering whether md5, sha1 and anothers return unique values. For example, sha1() for test returns a94a8fe5ccb19ba61c4c0873d391e987982fbbd3, which is 40 characters long. So, sha1 for strings larger than 40 chars must be the same (of course it's scrambled, because the given input may contain whitespaces and special chars etc.). Due to this, when we are storing users' passwords, they can enter either their original password or some super-long one, which nobody knows. Is this right, or do these hash algorithms provide really unique results - I'm quite sure it's hardly possible.

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