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• Color space - RGB and YCbCr question

  - by HardCoder1986

  Hello! I am now trying to understand how JPEG encoding works and everything seems fine except the color transformation part. Before attempting to do a DCT in JPEG algorithm, the image is transformed into YCbCr color space. To me this essentially means that we just (comparing to initial RGB image) take a chunk of color information and dispose it while applying the RGB -> YCbCr transformation. So, our encoding steps look generally like RGB -> YCbCr -> DCT -> Huffman. The decoding means inversing this process. And my question is - why does the image (for example, created and exported to JPEG) remain the same in terms of color, although we have to make inverse YCbCr -> RGB transform. Where does the disposed part of color information comes from or how is it handled?

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• How to iterate javascript object properties in the order they were written.

  - by Jenea

  Hi. I identified a bug in my code which I hope to solve with minimal refactoring effort. This bug occurs in Chrome and Opera browsers. Problem: var obj = {23:"AA",12:"BB"}; //iterating through obj's properties for(i in obj) document.write("Key: "+i +" "+"Value: "+obj[i]); Output in FF,IE Key: 23 Value: AA Key: 12 Value: BB Output in Opera and Chrome (Wrong) Key: 12 Value BB Key: 23 Value AA I attempted to make an inverse ordered object like this var obj1={"AA":23,"BB":12}; for(i in obj1) document.write("Key: "+obj[i] +" "+"Value: "+i); However the output is the same. Is there a way to get for all browser the same behaviour with small changes?

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• What wording in the C++ standard allows static_cast<non-void-type*>(malloc(N)); to work?

  - by ben

  As far as I understand the wording in 5.2.9 Static cast, the only time the result of a void*-to-object-pointer conversion is allowed is when the void* was a result of the inverse conversion in the first place. Throughout the standard there is a bunch of references to the representation of a pointer, and the representation of a void pointer being the same as that of a char pointer, and so on, but it never seems to explicitly say that casting an arbitrary void pointer yields a pointer to the same location in memory, with a different type, much like type-punning is undefined where not punning back to an object's actual type. So while malloc clearly returns the address of suitable memory and so on, there does not seem to be any way to actually make use of it, portably, as far as I have seen.

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• is this a correct way to generate rsa keys?

  - by calccrypto

  is this code going to give me correct values for RSA keys (assuming that the other functions are correct)? im having trouble getting my program to decrypt properly, as in certain blocks are not decrypting properly this is in python: import random def keygen(bits): p = q = 3 while p == q: p = random.randint(2**(bits/2-2),2**(bits/2)) q = random.randint(2**(bits/2-2),2**(bits/2)) p += not(p&1) # changes the values from q += not(q&1) # even to odd while MillerRabin(p) == False: # checks for primality p -= 2 while MillerRabin(q) == False: q -= 2 n = p * q tot = (p-1) * (q-1) e = tot while gcd(tot,e) != 1: e = random.randint(3,tot-1) d = getd(tot,e) # gets the multiplicative inverse while d<0: # i can probably replace this with mod d = d + tot return e,d,n one set of keys generated: e = 3daf16a37799d3b2c951c9baab30ad2d d = 16873c0dd2825b2e8e6c2c68da3a5e25 n = dc2a732d64b83816a99448a2c2077ced

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• Core Data: Fetch all entities in a to-many-relationship of a particular object?

  - by Björn Marschollek

  Hi there, in my iPhone application I am using simple Core Data Model with two entities (Item and Property): Item name properties Property name value item Item has one attribute (name) and one one-to-many-relationship (properties). Its inverse relationship is item. Property has two attributes the according inverse relationship. Now I want to show my data in table views on two levels. The first one lists all items; when one row is selected, a new UITableViewController is pushed onto my UINavigationController's stack. The new UITableView is supposed to show all properties (i.e. their names) of the selected item. To achieve this, I use a NSFetchedResultsController stored in an instance variable. On the first level, everything works fine when setting up the NSFetchedResultsController like this: -(NSFetchedResultsController *) fetchedResultsController { if (fetchedResultsController) return fetchedResultsController; // goal: tell the FRC to fetch all item objects. NSFetchRequest *fetch = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Item" inManagedObjectContext:self.moContext]; [fetch setEntity:entity]; NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES]; [fetch setSortDescriptors:[NSArray arrayWithObject:sort]]; [fetch setFetchBatchSize:10]; NSFetchedResultsController *frController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetch managedObjectContext:self.moContext sectionNameKeyPath:nil cacheName:@"cache"]; self.fetchedResultsController = frController; fetchedResultsController.delegate = self; [sort release]; [frController release]; [fetch release]; return fetchedResultsController; } However, on the second-level UITableView, I seem to do something wrong. I implemented the fetchedresultsController in a similar way: -(NSFetchedResultsController *) fetchedResultsController { if (fetchedResultsController) return fetchedResultsController; // goal: tell the FRC to fetch all property objects that belong to the previously selected item NSFetchRequest *fetch = [[NSFetchRequest alloc] init]; // fetch all Property entities. NSEntityDescription *entity = [NSEntityDescription entityForName:@"Property" inManagedObjectContext:self.moContext]; [fetch setEntity:entity]; // limit to those entities that belong to the particular item NSPredicate *predicate = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"item.name like '%@'",self.item.name]]; [fetch setPredicate:predicate]; // sort it. Boring. NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES]; [fetch setSortDescriptors:[NSArray arrayWithObject:sort]]; NSError *error = nil; NSLog(@"%d entities found.",[self.moContext countForFetchRequest:fetch error:&error]); // logs "3 entities found."; I added those properties before. See below for my saving "problem". if (error) NSLog("%@",error); // no error, thus nothing logged. [fetch setFetchBatchSize:20]; NSFetchedResultsController *frController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetch managedObjectContext:self.moContext sectionNameKeyPath:nil cacheName:@"cache"]; self.fetchedResultsController = frController; fetchedResultsController.delegate = self; [sort release]; [frController release]; [fetch release]; return fetchedResultsController; } Now it's getting weird. The above NSLog statement returns me the correct number of properties for the selected item. However, the UITableViewDelegate method tells me that there are no properties: -(NSInteger) tableView:(UITableView *)table numberOfRowsInSection:(NSInteger)section { id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section]; NSLog(@"Found %d properties for item \"%@\". Should have found %d.",[sectionInfo numberOfObjects], self.item.name, [self.item.properties count]); // logs "Found 0 properties for item "item". Should have found 3." return [sectionInfo numberOfObjects]; } The same implementation works fine on the first level. It's getting even weirder. I implemented some kind of UI to add properties. I create a new Property instance via Property *p = [NSEntityDescription insertNewObjectForEntityForName:@"Property" inManagedObjectContext:self.moContext];, set up the relationships and call [self.moContext save:&error]. This seems to work, as error is still nil and the object gets saved (I can see the number of properties when logging the Item instance, see above). However, the delegate methods are not fired. This seems to me due to the possibly messed up fetchRequest(Controller). Any ideas? Did I mess up the second fetch request? Is this the right way to fetch all entities in a to-many-relationship for a particular instance at all?

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• Highlight polygon and tint rest of map using Google Maps

  - by Haes

  Hi, I'd like to display a highlighted polygon using Google Maps. The idea is that the polygon in question would be displayed normally and the rest of the map should be darkened a little bit. Here's an example image what I would like to accomplish with a polygon from Austria: Unfortunately, I'm a complete rookie when it comes to Google Maps API's and map stuff in general. So, is this even possible do this with Google Map API's? If yes, with what version (v2, v3)? Would it be easier to do it with other map toolkits, like openlayers? PS: One idea I had, was to build an inverse polygon (in this example, the whole world minus the shape of austria) and then display a black colored overlay with transparency using this inverted polygon. But that seems to be quite complicated to me.

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• Fluent nHibernate - How to map a non-key column on an association table?

  - by The Matt

  Taking an example that is provided on the Fluent nHibernate website, I need to extend it slightly: I need to add a 'Quantity' column to the StoreProduct table. How would I map this using nHibernate? An example mapping is provided for the given scenario above, but I'm not sure how I would get the Quantity column to map: public class StoreMap : ClassMap<Store> { public StoreMap() { Id(x => x.Id); Map(x => x.Name); HasMany(x => x.Employee) .Inverse() .Cascade.All(); HasManyToMany(x => x.Products) .Cascade.All() .Table("StoreProduct"); } }

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• Hibernate without primary keys generated by db?

  - by Michael Jones

  I'm building a data warehouse and want to use InfiniDB as the storage engine. However, it doesn't allow primary keys or foreign key constraints (or any constraints for that matter). Hibernate complains "The database returned no natively generated identity value" when I perform an insert. Each table is relational, and contains a unique integer column that was previously used as the primary key - I want to keep that, but just not have the constraint in the db that the column is the primary key. I'm assuming the problem is that Hibernate expects the db to return a generated key. Is it possible to override this behaviour so I can set the primary key field's value myself and keep Hibernate happy? -- edit -- Two of the mappings are as follows: <?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <!-- Generated Jun 1, 2010 2:49:51 PM by Hibernate Tools 3.2.1.GA --> <hibernate-mapping> <class name="com.example.project.Visitor" table="visitor" catalog="orwell"> <id name="id" type="java.lang.Long"> <column name="id" /> <generator class="identity" /> </id> <property name="firstSeen" type="timestamp"> <column name="first_seen" length="19" /> </property> <property name="lastSeen" type="timestamp"> <column name="last_seen" length="19" /> </property> <property name="sessionId" type="string"> <column name="session_id" length="26" unique="true" /> </property> <property name="userId" type="java.lang.Long"> <column name="user_id" /> </property> <set name="visits" inverse="true"> <key> <column name="visitor_id" /> </key> <one-to-many class="com.example.project.Visit" /> </set> </class> </hibernate-mapping> and: <?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <!-- Generated Jun 1, 2010 2:49:51 PM by Hibernate Tools 3.2.1.GA --> <hibernate-mapping> <class name="com.example.project.Visit" table="visit" catalog="orwell"> <id name="id" type="java.lang.Long"> <column name="id" /> <generator class="identity" /> </id> <many-to-one name="visitor" class="com.example.project.Visitor" fetch="join" cascade="all"> <column name="visitor_id" /> </many-to-one> <property name="visitId" type="string"> <column name="visit_id" length="20" unique="true" /> </property> <property name="startTime" type="timestamp"> <column name="start_time" length="19" /> </property> <property name="endTime" type="timestamp"> <column name="end_time" length="19" /> </property> <property name="userAgent" type="string"> <column name="user_agent" length="65535" /> </property> <set name="pageViews" inverse="true"> <key> <column name="visit_id" /> </key> <one-to-many class="com.example.project.PageView" /> </set> </class> </hibernate-mapping>

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• How to handle this type of model validation in Ruby on Rails

  - by randombits

  I have a controller/model hypothetically named Pets. Pets has the following declarations: :belongs_to owner :has_many dogs :has_many cats Not the best example, but again, it demonstrates what I'm trying to solve. Now when a request comes in as an HTTP POST to http://127.0.0.1/pets, I want to create an instance of Pets. The restriction here is, if the user doesn't submit at least one dog or one cat, it should fail validation. It can have both, but it can't be missing both. How does one handle this in Ruby on Rails? Dogs don't care if cats exists and the inverse is also true. Can anyone show some example code of what the Pets model would look like to ensure that one or the other exists, or fail otherwise? errors.add also takes an attribute, in this case, there is no particular attribute that's failing. It's almost a 'virtual' combination that's missing.

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• Django: Extending User Model - Inline User fields in UserProfile

  - by Jack Sparrow

  Is there a way to display User fields under a form that adds/edits a UserProfile model? I am extending default Django User model like this: class UserProfile(models.Model): user = models.OneToOneField(User, unique=True) about = models.TextField(blank=True) I know that it is possible to make a: class UserProfileInlineAdmin(admin.TabularInline): and then inline this in User ModelAdmin but I want to achieve the opposite effect, something like inverse inlining, displaying the fields of the model pointed by the OneToOne Relationship (User) in the page of the model defining the relationship (UserProfile). I don't care if it would be in the admin or in a custom view/template. I just need to know how to achieve this. I've been struggling with ModelForms and Formsets, I know the answer is somewhere there, but my little experience in Django doesn't allow me to come up with the solution yet. A little example would be really helpful!

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• custom helpers inside each block

  - by Unspecified

  myArray = [{name: "name1", age: 20}, {name: "name2", age:22}]; {{#each person in myArray}} {{#myHelper person}} Do something {{/myHelper}} {{/each}} Handlebars.registerHelper(function(context, options){ if(context.age > 18){ return options.fn(this); }else{ return options.inverse(this); } }) In the above code when I tried to debug my custom helper it shows the context="person" while I want the context to be the person object, what's wrong with my code ? I found a similar question here but did not get it either...

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• VST plugin : using FFT on audio input buffer with arbitrary size, how ?

  - by Led

  I'm getting interested in programming a VST plugin, and I have a basic knowledge of audio dsp's and FFT's. I'd like to use VST.Net, and I'm wondering how to implement an FFT-based effect. The process-code looks like public override void Process(VstAudioBuffer[] inChannels, VstAudioBuffer[] outChannels) If I'm correct, normally the FFT would be applied on the input, some processing would be done on the FFT'd data, and then an inverse-FFT would create the processed soundbuffer. But since the FFT works on a specified buffersize that will most probably be different then the (arbitrary) amount of input/output-samples, how would you handle this ?

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• Rounding a positive number to a power of another number

  - by Sagekilla

  I'm trying to round a number to the next smallest power of another number. The number I'm trying to round is always positive. I'm not particular on which direction it rounds, but I prefer downwards if possible. I would like to be able to round towards arbitrary bases, but the ones I'm most concerned with at the moment is base 2 and fractional powers of 2 like 2^(1/2), 2^(1/4), and so forth. Here's my current algorithm for base 2. The log2 I multiply by is actually the inverse of log2: double roundBaseTwo(double x) { return 1.0 / (1 << (int)((log(x) * log2)) } Any help would be appreciated!

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• Extending fluent nhibernate mappings in another assembly

  - by Jarek

  Hi, I'm using NHibernate with my ASP.Net MVC application. I'm writing some extensions (plugins) for my application. And I'm loading those plugin dynamically (from different assemblies). In my base application I have many entities and mappings defined (User, Group, etc...) I need to create new entities in my extensions, so i.e. I'm creating News module, so I need to create News mapping. In database News table has a foreign key to User table. Is there any way I can modify my User mapping, so it will have: HasMany(x => x.Courses) .KeyColumn("GroupId") .Inverse(); Or the only way to do it is to change code in my User class and recompile project ? I'm not NHibernate advanced user, so any help will be appreciated. TIA.

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• Is there a fast concat method for linked list in Java?

  - by rocker

  How can I concat two linked lists in O(1) with Java via jdk, google or apache commons collection or whatever? E.g. in jdk there is only the addAll method which is O(n). Another feature I miss is to concat two lists where each of them could be in inverse order. To illustrate this assume two lists a-b-c and e-f-g could merged into a-b-c-e-f-g a-b-c-g-f-e c-b-a-e-f-g c-b-a-g-f-e Do you know of such a list implemenation or do I have to implement my own linked list? It would be also helpful to know how to tweak existing solutions (e.g. the jdk LinkedList has a lot of private methods only). These features seems to me very obvious, hopefully I am not missing something stupid.

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• Fluent nHibernate - How to map a non-key column on a junction table?

  - by The Matt

  Taking an example that is provided on the Fluent nHibernate website, I need to extend it slightly: I need to add a 'Quantity' column to the StoreProduct table. How would I map this using nHibernate? An example mapping is provided for the given scenario above, but I'm not sure how I would get the Quantity column to map to a property on the Product class: public class StoreMap : ClassMap<Store> { public StoreMap() { Id(x => x.Id); Map(x => x.Name); HasMany(x => x.Employee) .Inverse() .Cascade.All(); HasManyToMany(x => x.Products) .Cascade.All() .Table("StoreProduct"); } }

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• Python. Draw rectangle in basemap

  - by user2928318

  I need to add several rectangles in my basemap. I nee four rectangles with lat and log ranges as below. 1) llcrnrlon=-10, urcrnrlon=10, llcrnrlat=35,urcrnrlat=60 2) llcrnrlon=10.5, urcrnrlon=35, llcrnrlat=35,urcrnrlat=60 3) llcrnrlon=35.5, urcrnrlon=52, llcrnrlat=30,urcrnrlat=55 4) llcrnrlon=-20, urcrnrlon=35, llcrnrlat=20,urcrnrlat=34.5 My script is below. I found "polygon" packages to add lines but I do not exactly know how to do. Please help me!! Thanks a lot for your help in advance! from mpl_toolkits.basemap import Basemap m=basemaputpart.Basemap(llcrnrlon=-60, llcrnrlat=20, urcrnrlon=60, urcrnrlat=70, resolution='i', projection='cyl', lon_0=0, lat_0=45) lon1=np.array([[-180.+j*0.5 for j in range(721)] for i in range(181)]) lat1=np.array([[i*0.5 for j in range(721)] for i in range(181) ]) Nx1,Ny1=m(lon1,lat1,inverse=False) toplot=data[:,:] toplot[data==0]=np.nan toplot=np.ma.masked_invalid(toplot) plt.pcolor(Nx1,Ny1,np.log(toplot),vmin=0, vmax=5) cbar=plt.colorbar() m.drawcoastlines(zorder=2) m.drawcountries(zorder=2) plt.show()

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• Java Hibernate Lazy=false

  - by Noor

  When setting Lazy=false, then hibernate will automatically loads the objects into the required sets e.g. <set name="Options" table="ATTRIBUTEOPTION" inverse="false" cascade="all" lazy="false"> <key> <column name="ATTRIBUTEID" /> </key> <one-to-many class="com.BiddingSystem.Models.AttributeOption" /> </set> but if in my xml mapping, I place lazy=true and in some place in my application i decide that i want to load all attribute options, should i do it manually, or is there a technique which lets tells hibernate that now i want to set lazy=false??

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• Pseudorandom Number Generation with Specific Non-Uniform Distributions

  - by carnun

  Hello all, I'm writing a program that simulates various random walks (with differing distributions). At each timestep, I need randomly generated, two dimensional step distances and angles from the distribution of the random walk. I'm hoping someone can check my understanding of how to generate these random numbers. As I understand it I can use Inverse Transform Sampling as follows: If f(x) is the pdf of our random walk that has a non-uniform distribution, and y is a random number from a uniform distribution. Then if we let f(x) = y and solve to find x then we have a random number from the non-uniform distribution. Is this a feasible solution?

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• Ruby Hash.merge with specified keys only

  - by ba

  I'm pretty sure I saw on a Rails related site something along the lines of: def my_function(*opts) opts.require_keys(:first, :second, :third) end And if one of the keys in require_keys weren't specified, or if there were keys that weren't specified, an exception was raised. I've been looking through ActiveSupport and I guess I might be looking for something like the inverse of except. I like to try and use as much of the framework as possible compared to writing my own code, that's the reason I'm asking when I know how to make the same functionality on my own. :) At the moment I'm doing it through the normal merge routine and making sure that I have what I need with some IFs.

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• how to force nhibernate to set the foreign key of the child item?

  - by npeBeg

  i have a collection in the mapping: <bag name="Values" cascade="all-delete-orphan" lazy="false" inverse="true"> <key column="[TemplateId]"/> <one-to-many class="MyNamespace.Value, MyLib"/> </bag> the Value object has a foreign key [TemplateId]. both entities has their generator set to "identity". when i call session.Save() for the parent Template object, the Value objects has their [TemplateId] (the foreign key) set to zero, so an SQL exception appears. how do i forse nhibernate to set the FK value for the child items to the value of the inserted parent object?

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• Strange profiler behavior: same functions, different performances

  - by arthurprs

  I was learning to use gprof and then i got weird results for this code: int one(int a, int b) { return a / (b + 1); } int two(int a, int b) { return a / (b + 1); } int main() { for (int i = 1; i < 30000000; i++) { two(i, i * 2); one(i, i * 2); } return 0; } and this is the profiler output % cumulative self self total time seconds seconds calls ns/call ns/call name 48.39 0.90 0.90 29999999 30.00 30.00 one(int, int) 40.86 1.66 0.76 29999999 25.33 25.33 two(int, int) 10.75 1.86 0.20 main If i call one then two the result is the inverse, two takes more time than one both are the same functions, but the first calls always take less time then the second Why is that? Note: The assembly code is exactly the same and code is being compiled with no optimizations

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• undo or reverse argsort(), python

  - by Vincent

  Given an array 'a' I would like to sort the array by columns "a.sort(axis=0)" do some stuff to the array and then undo the sort. By that I don't mean re sort but basically reversing how each element was moved. I assume argsort() is what I need but it is not clear to me how to sort an array with the results of argsort() or more importantly apply the reverse/inverse of argsort() Here is a little more detail I have an array a, shape(a) = rXc I need to sort each column aargsort = a.argsort(axis=0) # May use this later aSort = a.sort(axis=0) now average each row aSortRM = asort.mean(axis=1) now replace each col in a row with the row mean. is there a better way than this aWithMeans = ones_like(a) for ind in range(r) # r = number of rows aWithMeans[ind]* aSortRM[ind] Now I need to undo the sort I did in the first step. ????

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• SQL Server: Find Values that don't exist in a table

  - by MacAnthony

  I have a list or set of values that I would like to know which ones do not currently exist in a table. I know I can find out which ones do exist with: SELECT * FROM Table WHERE column1 IN (x,x,x,x,x) The set is the values I am checking against. Is there a way to find out which values in that set do not exist in column1? Basically, I'm looking for the inverse of the sql statement above. This is for a report, so all I need is the values that don't exist to be returned back. I have and could do this with a left join and putting the values in another table, but the values I check are always different and was hoping to find a solution that didn't involve clearing a table and inserting data first. Trying to find a better solution for me if one exists.

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• Hibernate: delete many-to-many association

  - by Bar

  I have two tables with the many-to-many association. — DB fragment: loads Id Name sessions Id Date sessionsloads LoadId SessionId — Hibernate mapping fragments: /* loads.hbm.xml */ <set name="sessions" table="sessionsloads" inverse="true"> <key column="LoadId" /> <many-to-many column="SessionId" class="Session" /> </set> … /* sessions.hbm.xml */ <set name="loads" table="sessionsloads"> <key column="SessionId" /> <many-to-many column="LoadId" class="Load" /> </set> In order to remove one entry from the association table sessionsloads, I execute this code: Session session = sessionDao.getObject(sessionId); Load load = loadDao.getObject(loadId); load.getSessions().remove(session); loadDao.saveObject(load); But, after launching, this code change nothing. What's the right way to remove an association?

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