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  • JPA: what is the proper pattern for iterating over large result sets?

    - by Caffeine Coma
    Let's say I have a table with millions of rows. Using JPA, what's the proper way to iterate over a query against that table, such that I don't have all an in-memory List with millions of objects? I suspect that the following will blow up if the table is large: List<Model> models = entityManager().createQuery("from Model m", Model.class).getResultList(); for (Model model : models) { // do something with model } Is pagination (looping and manually updating setFirstResult()/setMaxResult()) really the best solution?

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  • How can I embed the result of a rails view in another website?

    - by NotDan
    I would like to allow users to call my ruby on rails app as a service which returns a 'div' with html content in it, and embed that div into their app (which will not be a rails application). For example, assume someone has their own php website that has a header/footer template that gets rendered, and a content area of the page that they need to fill based on some html I generate in my rails app. I would like to allow them, from php, to call to my website, get the 'div' I generate, and embed that as html in their php page. What I'm trying to do is host a service on my site that returns some html content, but actually show that content as part of another site, so that the end user only sees the other site and never really knows about mine. Is this possible?

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  • does entity framework or mysql provider swallows timeout exceptions on enumeration of result?!

    - by Freddy Rios
    I'm trying to make sense of a situation I have using entity framework on .net 3.5 sp1 + MySQL 6.1.2.0 as the provider. It involves the following code: Response.Write("Products: " + plist.Count() + "<br />"); var total = 0; foreach (var p in plist) { //... some actions total++; //... other actions } Response.Write("Total Products Checked: " + total + "<br />"); Basically the total products is varying on each run, and it isn't matching the full total in plist. Its varies widely, from ~ 1/5th to half. There isn't any control flow code inside the foreach i.e. no break, continue, try/catch, conditions around total++, anything that could affect the count. As confirmation, there are other totals captured inside the loop related to the actions, and those match the lower and higher total runs. I don't find any reason to the above, other than something in entity framework or the mysql provider that causes it to end the foreach when retrieving an item. The body of the foreach can have some good variation in time, as the actions involve file & network access, my best shot at the time is that when it takes beyond certain threshold there is some type of timeout in the underlying framework/provider and instead of causing an exception it is silently reporting no more items for enumeration. Can anyone give some light in the above scenario and/or confirm if the entity framework/mysql provider has the above behavior?

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  • Trailing comments after variable assignment subvert comparison

    - by nobar
    In GNU make, trailing comments appended to variable assignments prevent subsequent comparison (via ifeq) from working correctly. Here's the Makefile... A = a B = b ## trailing comment C = c RESULT := ifeq "$(A)" "a" RESULT += a endif ifeq "$(B)" "b" RESULT += b endif ifeq "$(C)" "c" RESULT += c endif rule: @echo RESULT=\"$(RESULT)\" @echo A=\"$(A)\" @echo B=\"$(B)\" @echo C=\"$(C)\" Here's the output... $ make RESULT=" a c" A="a" B="b " C="c" As you can see from the displayed value of RESULT, the ifeq was affected by the presence of the comment in the assignment of B. Echoing the variable B, shows that the problem is not the comment, but the intervening space. The obvious solution is to explicitly strip the whitespace prior to comparison like so... ifeq "$(strip $(B))" "b" RESULT += b endif However this seems error prone. Since the strip operation is not needed unless/until a comment is used, you can leave out the strip and everything will initially work just fine -- so chances are you won't always remember to add the strip. Later, if someone adds a comment when setting the variable, the Makefile no longer works as expected. Note: There is a closely related issue, as demonstrated in this question, that trailing whitespace can break string compares even if there is no comment. Question: Is there a more fool-proof way to deal with this issue?

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  • How to sum up a fetched result's number property based on the object's category?

    - by mr_kurrupt
    I have a NSFetchRequest that is returning all my saved objects (call them Items) and storing them in an NSMutableArray. Each of these Items have a category, an amount, and some other properties. My goal is to check the category of each Item and store the sum of the amounts for objects of the same category. So if I had these Items: Red; 10.00 Blue; 20.00 Green; 5.00 Red; 5.00 Green; 15.00 then I would have an array or other type of container than has: Red; 15.00 Blue; 20.00 Green; 20.00 What would be the best way to organize the data in such a manner? I was going to create a object class (call it Totals) that just has the category and amount. As I traverse through the fetch results in a for-loop, add Items with the same category in a Totals object an store them in a NSMutableArray. The problem I ran into with that is that I'm not sure how to check if an array contains a Totals object with a specific property. Specifically, a category that already exists. So if 'Red' exists, add the amount to it, otherwise create a new Totals object with category 'Red' and a the first Item's amount. Thanks.

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  • Python: why does this code take forever (infinite loop?)

    - by Rosarch
    I'm developing an app in Google App Engine. One of my methods is taking never completing, which makes me think it's caught in an infinite loop. I've stared at it, but can't figure it out. Disclaimer: I'm using http://code.google.com/p/gaeunitlink text to run my tests. Perhaps it's acting oddly? This is the problematic function: def _traverseForwards(course, c_levels): ''' Looks forwards in the dependency graph ''' result = {'nodes': [], 'arcs': []} if c_levels == 0: return result model_arc_tails_with_course = set(_getListArcTailsWithCourse(course)) q_arc_heads = DependencyArcHead.all() for model_arc_head in q_arc_heads: for model_arc_tail in model_arc_tails_with_course: if model_arc_tail.key() in model_arc_head.tails: result['nodes'].append(model_arc_head.sink) result['arcs'].append(_makeArc(course, model_arc_head.sink)) # rec_result = _traverseForwards(model_arc_head.sink, c_levels - 1) # _extendResult(result, rec_result) return result Originally, I thought it might be a recursion error, but I commented out the recursion and the problem persists. If this function is called with c_levels = 0, it runs fine. The models it references: class Course(db.Model): dept_code = db.StringProperty() number = db.IntegerProperty() title = db.StringProperty() raw_pre_reqs = db.StringProperty(multiline=True) original_description = db.StringProperty() def getPreReqs(self): return pickle.loads(str(self.raw_pre_reqs)) def __repr__(self): return "%s %s: %s" % (self.dept_code, self.number, self.title) class DependencyArcTail(db.Model): ''' A list of courses that is a pre-req for something else ''' courses = db.ListProperty(db.Key) def equals(self, arcTail): for this_course in self.courses: if not (this_course in arcTail.courses): return False for other_course in arcTail.courses: if not (other_course in self.courses): return False return True class DependencyArcHead(db.Model): ''' Maintains a course, and a list of tails with that course as their sink ''' sink = db.ReferenceProperty() tails = db.ListProperty(db.Key) Utility functions it references: def _makeArc(source, sink): return {'source': source, 'sink': sink} def _getListArcTailsWithCourse(course): ''' returns a LIST, not SET there may be duplicate entries ''' q_arc_heads = DependencyArcHead.all() result = [] for arc_head in q_arc_heads: for key_arc_tail in arc_head.tails: model_arc_tail = db.get(key_arc_tail) if course.key() in model_arc_tail.courses: result.append(model_arc_tail) return result Am I missing something pretty obvious here, or is GAEUnit acting up?

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  • Strange sql query result from Mysql and from PHP mysqli_query!

    - by qinHaiXiang
    this is the query command echo from php web page: SELECT DISTINCT FT.file_type_name AS type,FT.file_type_en AS tp,FT.file_type_id AS fti, MATCH(keywords) AGAINST ('words <2' IN BOOLEAN MODE ) AS score FROM movie AS M,file_type AS FT WHERE MATCH (keywords) AGAINST ('words <2' IN BOOLEAN MODE ) AND M.type_cn = FT.file_type_id HAVING score >=1 ORDER BY FT.file_type_order; I am running above query in MySQL tools HeidiSQL and got only tow row records which score are 1.66666 and 2. If I remove the HAVING clause I would got three row records with one's score less than 1. But the same query I get from PHP mysqli_query() were all the three records and the one which score less than 1 became 1. What is the problem. Any tips will be pleasure. Thank you very much!!

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  • Why is this statement treated as a string instead of its result?

    - by reve_etrange
    I am trying to perform some composition-based filtering on a large collection of strings (protein sequences). I wrote a group of three subroutines in order to take care of it, but I'm running into trouble in two ways - one minor, one major. The minor trouble is that when I use List::MoreUtils 'pairwise' I get warnings about using $a and $b only once and them being uninitialized. But I believe I'm calling this method properly (based on CPAN's entry for it and some examples from the web). The major trouble is an error "Can't use string ("17/32") as HASH ref while "strict refs" in use..." It seems like this can only happen if the foreach loop in &comp is giving the hash values as a string instead of evaluating the division operation. I'm sure I've made a rookie mistake, but can't find the answer on the web. The first time I even looked at perl code was last Wednesday... use List::Util; use List::MoreUtils; my @alphabet = ( 'A', 'R', 'N', 'D', 'C', 'Q', 'E', 'G', 'H', 'I', 'L', 'K', 'M', 'F', 'P', 'S', 'T', 'W', 'Y', 'V' ); my $gapchr = '-'; # Takes a sequence and returns letter = occurrence count pairs as hash. sub getcounts { my %counts = (); foreach my $chr (@alphabet) { $counts{$chr} = ( $[0] =~ tr/$chr/$chr/ ); } $counts{'gap'} = ( $[0] =~ tr/$gapchr/$gapchr/ ); return %counts; } # Takes a sequence and returns letter = fractional composition pairs as a hash. sub comp { my %comp = getcounts( $[0] ); foreach my $chr (@alphabet) { $comp{$chr} = $comp{$chr} / ( length( $[0] ) - $comp{'gap'} ); } return %comp; } # Takes two sequences and returns a measure of the composition difference between them, as a scalar. # Originally all on one line but it was unreadable. sub dcomp { my @dcomp = pairwise { $a - $b } @{ values( %{ comp( $[0] ) } ) }, @{ values( %{ comp( $[1] ) } ) }; @dcomp = apply { $_ ** 2 } @dcomp; my $dcomp = sqrt( sum( 0, @dcomp ) ) / 20; return $dcomp; } Much appreciation for any answers or advice!

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  • Can piping of screen to file change the result of a C++ code?

    - by Biga
    I am having this very weird behaviour with a C++ code: It gives me different results when running with and without piping the screen to a file (reproducible in cygwin and linux). I mean, if I get the same executable and run it like './run' or run it like './run out.log', I get different results! I use std::cout to output to screen, all lines ending with endl; I use ifstream for the input file; I use ofstream for output, all lines ending with endl. I am using g++ 4. Any idea what is going on? UPDATE: I have hard-coded the input data, so 'ifstream' is not used, and problem persists. UPDATE 2: That's getting interesting. I have output three variables that are computed initially, and that's what I get with and without piping direct to screen: 0 -0.02 0 piped: 0 -0.02 1.04083e-17 So there's a round-off difference with and without piping the output! Now, why piping would interefere with an internal computation of the code?

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  • Joining two tables (through a link), one which may yield multiple rows, together into one result.

    - by Eikern
    Lets say I've got a table listing car brands or models: Cars: Id | Brand ----------- 1 | BMW 2 | Audi 3 | Volvo And I've also got another table which links features. Link: Id | carid | featureid ----------------------- 1 | 1 | 1 2 | 1 | 2 3 | 2 | 2 4 | 3 | 1 5 | 3 | 2 6 | 3 | 3 And I've got the table listing the features. Features: Id | Feature ----------- 1 | A/C 2 | 4WD 3 | Heated seats I want to list these results on my front page like this: BMW A/C 4WD Audi 4WD Volvo A/C 4WD Heated seats What's the best/most efficient way of doing this (using PHP and MySQL)?

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  • Can redirection of screen output to file change the result of a C++ code?

    - by Biga
    I am having this very weird behaviour with a C++ code: It gives me different results when running with and without redirecting the screen output to a file (reproducible in cygwin and linux). I mean, if I get the same executable and run it like ./run or run it like ./run >out.log, I get different results! I use std::cout to output to screen, all lines ending with endl; I use ifstream for the input file; I use ofstream for output, all lines ending with endl. I am using g++ 4. Any idea what is going on? UPDATE: I have hard-coded the input data, so 'ifstream' is not used, and problem persists. UPDATE 2: That's getting interesting. I have probed three variables that are computed initially, and that's what I get when using with and without redirecting the output to file redirected to file: 0 -0.02 0 direct to screen: 0 -0.02 1.04083e-17 So there's a round-off difference in the code variables with and without redirecting the output! Now, why redirecting would interefere with an internal computation of the code? UPDATE 3: If I redirect to /dev/null, I get the sam behaviour as outputing direct to screen, instead of redirecting to file.

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  • MySql selecting default value if there are no result?

    - by Kenan
    i'm having 2 tables: members and comments. I select all members, and then join comments. But in comments I'm selecting some SUM of points, and if user never commented, I can't get that user in listing?! So how to select default value for SUM, or some other solution: SELECT c.comment_id AS item_id, m.member_id AS member_id, m.avatar, SUM(c.vote_value) AS vote_value, SUM(c.best) AS best, SUM(c.vote_value) + SUM(c.najbolji)*10 AS total FROM members m LEFT JOIN comments c ON m.member_id = c.author_id GROUP BY c.author_id ORDER BY m.member_id DESC LIMIT {$sql_start}, {$sql_pokazi}

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  • Unable to write to a text file

    - by chrissygormley
    Hello, I am running some tests and need to write to a file. When I run the test's the open = (file, 'r+') does not write to the file. The test script is below: class GetDetailsIP(TestGet): def runTest(self): self.category = ['PTZ'] try: # This run's and return's a value result = self.client.service.Get(self.category) mylogfile = open("test.txt", "r+") print >>mylogfile, result result = ("".join(mylogfile.readlines()[2])) result = str(result.split(':')[1].lstrip("//").split("/")[0]) mylogfile.close() except suds.WebFault, e: assert False except Exception, e: pass finally: if 'result' in locals(): self.assertEquals(result, self.camera_ip) else: assert False When this test run's, no value has been entered into the text file and a value is returned in the variable result. I havw also tried mylogfile.write(result). If the file does not exist is claim's the file does not exist and doesn't create one. Could this be a permission problem where python is not allowed to create a file? I have made sure that all other read's to this file are closed so I the file should not be locked. Can anyone offer any suggestion why this is happening? Thanks

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  • Why does this C++ code result in a segmentation fault?

    - by user69514
    I keep getting a segmentation fault when the readAuthor() method is called. Does anybody know why this happens? I am supposed to use dynamic arrays, I know this would be so easy if I was using static array. #include <iostream> #include <string> #include <cstring> #include <cstdlib> using namespace std; /** declare arrays **/ int* isbnArr = new int[25]; char* authorArr = new char[25]; char* publisherArr = new char[25]; char* titleArr = new char[25]; int* editionArr = new int[25]; int* yearArr = new int[25]; int* pagesArr = new int[25]; float* retailPriceArr = new float[25]; float* discountedPriceArr = new float[25]; int* stockArr = new int[25]; /** function prototypes **/ int readIsbn(); char* readAuthor(); char* readPublisher(); char* readTitle(); int readEdition(); int readYear(); int readPages(); float readMsrp(); float readDiscountedPrice(); int readStockAmount(); void readonebook(int* isbn, char* author, char* title, char* publisher, int* edition, int* year, int* pages, float* msrp, float* discounted, int* inventory); int main() { bool stop = false; //flag when to stop loop int ind = 0; //index for current book while( !stop ){ cout << "Add book: press A: "; cout << "another thing here "; char choice; cin >> choice; if( choice == 'a' || choice == 'A' ){ readonebook(&isbnArr[ind], &authorArr[ind], &titleArr[ind], &publisherArr[ind], &editionArr[ind], &yearArr[ind], &pagesArr[ind], &retailPriceArr[ind], &discountedPriceArr[ind], &stockArr[ind]); test(&authorArr[ind]); ind++; } } return 0; } /** define functions **/ int readIsbn(){ int isbn; cout << "ISBN: "; cin >> isbn; return isbn; } char* readAuthor(){ char* author; cout << "Author: "; cin >> author; return author; } char* readPublisher(){ char* publisher = NULL; cout << "Publisher: "; cin >> publisher; return publisher; } char* readTitle(){ char* title = NULL; cout << "Title: "; cin >> title; return title; } int readEdition(){ int edition; cout << "Edition: "; cin >> edition; return edition; } int readYear(){ int year; cout << "Year: "; cin >> year; return year; } int readPages(){ int pages; cout << "Pages: "; cin >> pages; return pages; } float readMsrp(){ float price; cout << "Retail Price: "; cin >> price; return price; } float readDiscountedPrice(){ float price; cout << "Discounted Price: "; cin >> price; return price; } int readStockAmount(){ int amount; cout << "Stock Amount: "; cin >> amount; return amount; } void readonebook(int* isbn, char* author, char* title, char* publisher, int* edition, int* year, int* pages, float* msrp, float* discounted, int* inventory){ *isbn = readIsbn(); author = readAuthor(); title = readTitle(); publisher = readPublisher(); *edition = readEdition(); *year = readYear(); *pages = readPages(); *msrp = readMsrp(); *discounted = readDiscountedPrice(); *inventory = readStockAmount(); }

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  • Button to add value to array and then compare result with another array on IPhone.

    - by slickplaid
    I have ten buttons that each correspond to a different number. I'm looking to record the order that these buttons are pressed and enter them into an array and then compare it to another array that is static in the app. The check should be done on the Nth button press, where N equals the number of items in the other, static array. How do I A) have a button press add a value to an array B) stop after Nth button press equal to amount of numbers in the array I'm checking against and C) compare this array to the other array?

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  • Why am I not getting correct result when I calculate exponent with ^ in C++?

    - by xbonez
    I am using Bode's formuala to calculate distance of nth planet from sun dist = (4 + 3*(2^(n-2)))/10 If I calculate the distance this way, I get the right values: dist[2] = ((4 + 3*1)/10.0) ; dist[3] = ((4 + 3*2)/10.0) ; dist[4] = ((4 + 3*4)/10.0) ; But doing it this way, gives me incorrect values: vector <double> dist(5); for (unsigned int i = 2; i < 5; i++) { dist[i] = ((4 + 3*(2^(3-2)))/10.0) ; } Why so?

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  • How can I "merge" or "flatten" results from a query which returns multiple rows into a single result

    - by dsm
    I have a simple query over a table, which returns results like the following: id id_type id_ref 2702 5 31 2702 16 14 2702 17 3 2702 40 1 2702 26 4 And I would like to merge the results into a single row, for instance: id concatenation 2702 5,16,17,40,26:31,14,3,1,4 Is there any way to do this within a trigger? NB: I know I can use a cursor, but I would really prefer not to unless there is no better way.

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  • C++ arrays as parameters, EDIT: now includes variable scoping

    - by awshepard
    Alright, I'm guessing this is an easy question, so I'll take the knocks, but I'm not finding what I need on google or SO. I'd like to create an array in one place, and populate it inside a different function. I define a function: void someFunction(double results[]) { for (int i = 0; i<100; ++i) { for (int n = 0; n<16; ++n) //note this iteration limit { results[n] += i * n; } } } That's an approximation to what my code is doing, but regardless, shouldn't be running into any overflow or out of bounds issues or anything. I generate an array: double result[16]; for(int i = 0; i<16; i++) { result[i] = -1; } then I want to pass it to someFunction someFunction(result); When I set breakpoints and step through the code, upon entering someFunction, results is set to the same address as result, and the value there is -1.000000 as expected. However, when I start iterating through the loop, results[n] doesn't seem to resolve to *(results+n) or *(results+n*sizeof(double)), it just seems to resolve to *(results). What I end up with is that instead of populating my result array, I just get one value. What am I doing wrong? EDIT Oh fun, I have a typo: it wasn't void someFunction(double results[]). It was: void someFunction(double result[])... So perhaps this is turning into a scoping question. If my double result[16] array is defined in a main.cpp, and someFunction is defined in a Utils.h file that's included by the main.cpp, does the result variable in someFunction then wreak havoc on the result array in main?

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  • Please Help to locate the error

    - by jagdeep
    using System; using System.Collections; using System.Configuration; using System.Data; using System.Linq; using System.Web; using System.Web.Security; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.WebControls.WebParts; using System.Xml.Linq; public partial class expt2 : System.Web.UI.Page { double result ; protected void Page_Load(object sender, EventArgs e) { if (!Page.IsPostBack) result = 0.0; protected void Chkbxbd_CheckedChanged(object sender, EventArgs e) { if (Chkbxbd.Checked) { txtbxttl.Text = "" + 10000; result += double.Parse(txtbxttl.Text); } else result = result - 10000; } protected void Chkbxsfa_CheckedChanged(object sender, EventArgs e) { if (Chkbxsfa.Checked) { txtbxttl.Text = "" + 15000; result += double.Parse(txtbxttl.Text); } else result = result - 15000; } protected void btnttl_Click(object sender, EventArgs e) { txtbxttl.Text = "" + result; } } In this code the individual value for checkbox is ok but when the total is made it becomes 0. Please help me to fix it.

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  • Will an optimizing compiler remove calls to a method whose result will be multiplied by zero?

    - by Tim R.
    Suppose you have a computationally expensive method, Compute(p), which returns some float, and another method, Falloff(p), which returns another float from zero to one. If you compute Falloff(p) * Compute(p), will Compute(p) still run when Falloff(p) returns zero? Or would you need to write a special case to prevent Compute(p) from running unnecessarily? Theoretically, an optimizing compiler could determine that omitting Compute when Falloff returns zero would have no effect on the program. However, this is kind of hard to test, since if you have Compute output some debug data to determine whether it is running, the compiler would know not to omit it because of that debug info, resulting in sort of a Schrodinger's cat situation. I know the safe solution to this problem is just to add the special case, but I'm just curious.

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