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  • ODI 12c - Aggregating Data

    - by David Allan
    This posting will look at the aggregation component that was introduced in ODI 12c. For many ETL tool users this shouldn't be a big surprise, its a little different than ODI 11g but for good reason. You can use this component for composing data with relational like operations such as sum, average and so forth. Also, Oracle SQL supports special functions called Analytic SQL functions, you can use a specially configured aggregation component or the expression component for these now in ODI 12c. In database systems an aggregate transformation is a transformation where the values of multiple rows are grouped together as input on certain criteria to form a single value of more significant meaning - that's exactly the purpose of the aggregate component. In the image below you can see the aggregate component in action within a mapping, for how this and a few other examples are built look at the ODI 12c Aggregation Viewlet here - the viewlet illustrates a simple aggregation being built and then some Oracle analytic SQL such as AVG(EMP.SAL) OVER (PARTITION BY EMP.DEPTNO) built using both the aggregate component and the expression component. In 11g you used to just write the aggregate expression directly on the target, this made life easy for some cases, but it wan't a very obvious gesture plus had other drawbacks with ordering of transformations (agg before join/lookup. after set and so forth) and supporting analytic SQL for example - there are a lot of postings from creative folks working around this in 11g - anything from customizing KMs, to bypassing aggregation analysis in the ODI code generator. The aggregate component has a few interesting aspects. 1. Firstly and foremost it defines the attributes projected from it - ODI automatically will perform the grouping all you do is define the aggregation expressions for those columns aggregated. In 12c you can control this automatic grouping behavior so that you get the code you desire, so you can indicate that an attribute should not be included in the group by, that's what I did in the analytic SQL example using the aggregate component. 2. The component has a few other properties of interest; it has a HAVING clause and a manual group by clause. The HAVING clause includes a predicate used to filter rows resulting from the GROUP BY clause. Because it acts on the results of the GROUP BY clause, aggregation functions can be used in the HAVING clause predicate, in 11g the filter was overloaded and used for both having clause and filter clause, this is no longer the case. If a filter is after an aggregate, it is after the aggregate (not sometimes after, sometimes having).  3. The manual group by clause let's you use special database grouping grammar if you need to. For example Oracle has a wealth of highly specialized grouping capabilities for data warehousing such as the CUBE function. If you want to use specialized functions like that you can manually define the code here. The example below shows the use of a manual group from an example in the Oracle database data warehousing guide where the SUM aggregate function is used along with the CUBE function in the group by clause. The SQL I am trying to generate looks like the following from the data warehousing guide; SELECT channel_desc, calendar_month_desc, countries.country_iso_code,       TO_CHAR(SUM(amount_sold), '9,999,999,999') SALES$ FROM sales, customers, times, channels, countries WHERE sales.time_id=times.time_id AND sales.cust_id=customers.cust_id AND   sales.channel_id= channels.channel_id  AND customers.country_id = countries.country_id  AND channels.channel_desc IN   ('Direct Sales', 'Internet') AND times.calendar_month_desc IN   ('2000-09', '2000-10') AND countries.country_iso_code IN ('GB', 'US') GROUP BY CUBE(channel_desc, calendar_month_desc, countries.country_iso_code); I can capture the source datastores, the filters and joins using ODI's dataset (or as a traditional flow) which enables us to incrementally design the mapping and the aggregate component for the sum and group by as follows; In the above mapping you can see the joins and filters declared in ODI's dataset, allowing you to capture the relationships of the datastores required in an entity-relationship style just like ODI 11g. The mix of ODI's declarative design and the common flow design provides for a familiar design experience. The example below illustrates flow design (basic arbitrary ordering) - a table load where only the employees who have maximum commission are loaded into a target. The maximum commission is retrieved from the bonus datastore and there is a look using employees as the driving table and only those with maximum commission projected. Hopefully this has given you a taster for some of the new capabilities provided by the aggregate component in ODI 12c. In summary, the actions should be much more consistent in behavior and more easily discoverable for users, the use of the components in a flow graph also supports arbitrary designs and the tool (rather than the interface designer) takes care of the realization using ODI's knowledge modules. Interested to know if a deep dive into each component is interesting for folks. Any thoughts? 

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  • Derby 10.9.1.0 released

    - by kah
    Earlier today, the release of Apache Derby 10.9.1.0 was announced. In addition to the usual chunk of bug fixes, this release includes the following new features: NATIVE authentication, a new authentication mechanism with better support for managing credentials. See this section of the developer's guide for an introduction. JDBC 4.1 escape syntax completes Derby's support for JDBC 4.1. Allow multi-column subqueries in EXISTS predicates (SQL:2003 Feature T501, Enhanced EXISTS predicate) to support auto-generated SQL from some persistence frameworks. Download it now and try it out!

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  • BIT of a Problem

    The BIT data type is an awkward fit for a SQL database. It doesn't have just two values, and it can do unexpected things in expressions. What is worse, it is a flag rather than a predicate, and so its overuse, along with bit masks, is a prime candidate for being listed as a 'SQL Code Smell'. Joe Celko makes the case. Free trial of SQL Backup™“SQL Backup was able to cut down my backup time significantly AND achieved a 90% compression at the same time!” Joe Cheng. Download a free trial now.

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  • What is the most handy function you've ever came across? [closed]

    - by Viniyo Shouta
    Obviously everything is 'handy' when it comes to programming terms, but some get a highlight spot, like containers, matrix trasnformation functions and many others. But in this case please mention the one it was more handy to you, saved you from sparing hours resolving a problem, or even the one you like more, What is it and what does it does? I'll start with an example. Language: C++ Function: std::sort (STL) What does it does: Arranges the elements in a specified range into a nondescending order or according to an ordering criterion specified by a binary predicate. (It arranges a container in decreasing order) Why of this question? Because I want to learn how to if possible make my own implementations of these functions for pure studying purposes, to enhance knowledge

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  • NSFetchedResultsController crashing on performFetch: when using a cache

    - by Oliver
    I make use of NSFetchedResultsController to display a bunch of objects, which are sectioned using dates. On a fresh install, it all works perfectly and the objects are displayed in the table view. However, it seems that when the app is relaunched I get a crash. I specify a cache when initialising the NSFetchedResultsController, and when I don't it works perfectly. Here is how I create my NSFetchedResultsController: - (NSFetchedResultsController *)results { // If we are not nil, stop here if (results != nil) return results; // Create the fetch request, entity and sort descriptors NSFetchRequest *fetch = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Event" inManagedObjectContext:self.managedObjectContext]; NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:@"utc_start" ascending:YES]; NSArray *descriptors = [[NSArray alloc] initWithObjects:descriptor, nil]; // Set properties on the fetch [fetch setEntity:entity]; [fetch setSortDescriptors:descriptors]; // Create a fresh fetched results controller NSFetchedResultsController *fetched = [[NSFetchedResultsController alloc] initWithFetchRequest:fetch managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"day" cacheName:@"Events"]; fetched.delegate = self; self.results = fetched; // Release objects and return our controller [fetched release]; [fetch release]; [descriptor release]; [descriptors release]; return results; } These are the messages I get when the app crashes: FATAL ERROR: The persistent cache of section information does not match the current configuration. You have illegally mutated the NSFetchedResultsController's fetch request, its predicate, or its sort descriptor without either disabling caching or using +deleteCacheWithName: *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'FATAL ERROR: The persistent cache of section information does not match the current configuration. You have illegally mutated the NSFetchedResultsController's fetch request, its predicate, or its sort descriptor without either disabling caching or using +deleteCacheWithName:' I really have no clue as to why it's saying that, as I don't believe I'm doing anything special that would cause this. The only potential issue is the section header (day), which I construct like this when creating a new object: // Set the new format [formatter setDateFormat:@"dd MMMM"]; // Set the day of the event [event setValue:[formatter stringFromDate:[event valueForKey:@"utc_start"]] forKey:@"day"]; Like I mentioned, all of this works fine if there is no cache involved. Any help appreciated!

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  • Exception with Linq2SQL Query

    - by Hadi Eskandari
    I am running a query using Linq2SQL that comes down to following query: DateTime? expiration = GetExpirationDate(); IQueryable<Persons> persons = GetPersons(); IQueryable<Items> subquery = from i in db.Items where i.ExpirationDate >= expiration select i; return persons.Where(p = p.Items != null && p.Items.Any(item => subquery.Contains(item))); When I evaluate the result of the function, I get a NullReferenceException and here's the stack trace. Any idea what I'm doing wrong?! Basically I want to select all the persons and filter them by item expiration date. at System.Data.Linq.SqlClient.SqlFactory.Member(SqlExpression expr, MemberInfo member) at System.Data.Linq.SqlClient.QueryConverter.VisitMemberAccess(MemberExpression ma) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) at System.Data.Linq.SqlClient.QueryConverter.VisitBinary(BinaryExpression b) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) at System.Data.Linq.SqlClient.QueryConverter.VisitBinary(BinaryExpression b) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) at System.Data.Linq.SqlClient.QueryConverter.VisitWhere(Expression sequence, LambdaExpression predicate) at System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitContains(Expression sequence, Expression value) at System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) at System.Data.Linq.SqlClient.QueryConverter.VisitQuantifier(SqlSelect select, LambdaExpression lambda, Boolean isAny) at System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) at System.Data.Linq.SqlClient.QueryConverter.VisitBinary(BinaryExpression b) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) at System.Data.Linq.SqlClient.QueryConverter.VisitWhere(Expression sequence, LambdaExpression predicate) at System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.ConvertOuter(Expression node) at System.Data.Linq.SqlClient.SqlProvider.BuildQuery(Expression query, SqlNodeAnnotations annotations) at System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query) at System.Data.Linq.DataQuery`1.System.Collections.Generic.IEnumerable.GetEnumerator() at System.Linq.SystemCore_EnumerableDebugView`1.get_Items()

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  • Prolog - ASSERT and RETRACT

    - by KP65
    I was wondering, I am aware you can use assert to add facts or rules or whatever if you have declared the predicate to be -:dynamic, but this only allows the changes that are made to be kept in that session only, e.g. if you close the prolog window then the database changes are lost. So I was wondering, is there any way of making it so that the assert and retract predicates can make permanent changes to the prolog .pl file? Thanks

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  • Filtering a collection based on filtering rules

    - by Mike
    I have an observable collection of Entities, with each entity having a status added, deleted, modified and cancelled. I have four buttons (toggle) when clicked should filter my collection as below: If I select the button Added, then my collection should contain entities with status added. If I select the button Deleted and Added, then my collection should contain entities with status Deleted AND entities with status Added, none of the rest. If I select the button Deleted,Added and Modified, then my collection should contain entities with status Deleted, Added AND Modified. . . so on. If I unselect one of the buttons, it should remove those entities from the collection with that status. For example if I unselect Deleted, but select Added and Modified, then my collection should contain items with Added and Modified status and NOT Deleted ones. For implementing this I have created a master collection and a filtered collection. The Filter collection gets filtered based on the selections and unselections. The following is my code: private bool _clickedAdded; public bool ClickedAdded { get { return _clickedAdded; } set { _clickedAdded = value; if(!_clickedAdded) FilterAny(typeof(Added)); } } private bool _clickedDeleted; public bool ClickedDeleted { get { return _clickedDeleted; } set { _clickedDeleted = value; if (!_clickedDeleted) FilterAny(typeof(Deleted)); } } private bool _clickedModified; public bool ClickedModified { get { return _clickedModified; } set { _clickedModified = value; if (!_clickedModified) FilterAny(typeof(Modified)); } } private void FilterAny(Type status) { Func<Entity, bool> predicate = entity => entity.Status.GetType() != status; var filteredItems = MasterEntites.Where(predicate); FilteredEntities = new ObservableCollection<Entity>(filteredItems); } This however breaks the above rules - for example if I have all selected, and then I remove Added followed by deleted then it still shows the list of Added, Modified and Cancelled. It should be just Modified and Cancelled in the filtered collection. Can you please help me in solving this issue? Also do I need 2 different list to solve this. Please note that I'm using .NET 3.5.

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  • RDF of sentences

    - by Lily
    Hi, I need to classify sentences as a RDF format. In other words "John likes coke" would be automatically represented as Subject : John Predicate : Likes Object : Coke does nyone know where I should start? Are there any programs which can do this automatically or would I need to do everything from scratch? Any help would be appreciated thanks!

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  • What are 'len', 'dir', 'vars' named?

    - by johannix
    I was wondering what language to use when talking about a function that takes in a specific object, acts on it and returns something else. Clearly they're functions, but I was wondering if there's a more specific term. A couple examples of Python built-in functions that fit this spec are: 'len', 'dir', 'vars' I thought it was 'predicate', but apparently that's specific to functions that return a boolean value.

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  • java.lang.ClassNotFoundException using google commons

    - by pie154
    I have two classes inside a package. Both call a method from another class, one works perfectly fine and the other gives the error java.lang.ClassNotFoundException and the error java.lang.NoClassDefFoundError: com/google/common/base/Predicate The class path should be the same for both as they are in he same package so I can't figure out why one has access to the class and the other doesn't? thanks in advance for any help given.

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  • Linq to SQL Repository ~theory~ - Generic but now uses Linq to Objects?

    - by Matt Tolliday
    The project I am currently working on used Linq to SQL as an ORM data access technology. Its an MVC3 Web app. The problem I faced was primarily due to the inability to mock (for testing) the DataContext which gets autogenerated by the DBML designer. So to solve this issue (after much reading) I refactored the repository system which was in place - single repository with seperate and duplicated access methods for each table which ended up with something like 300 methods only 10 of which were unique - into a single repository with generic methods taking the table and returning more generic types to the upper reaches of the application. My question revolves more around the design I've used to get thus far and the differences I'm noticing in the structure of the app. 1) Having refactored the code from the dark ages which used classic Linq to SQL queries: public Billing GetBilling(int id) { var result = ( from bil in _bicDc.Billings where bil.BillingId == id select bil).SingleOrDefault(); return (result); } it now looks like: public T GetRecordWhere<T>(Expression<Func<T, bool>> predicate) where T : class { T result; try { result = _dataContext.GetTable<T>().Where(predicate).SingleOrDefault(); } catch (Exception ex) { throw ex; } return result; } and is used by the controller with a query along the lines of: _repository.GetRecordWhere<Billing>(x => x.BillingId == 1); which is fine, and precisely what I wanted to achieve. ...however.... I'm also having to do the following to get precisely the result set i require in the controller class (the highest point of the app in essence)... viewModel.RecentRequests = _model.GetAllRecordsWhere<Billing>(x => x.BillingId == 1) .Where(x => x.BillingId == Convert.ToInt32(BillingType.Submitted)) .OrderByDescending(x => x.DateCreated). Take(5).ToList(); This - as far as my understanding is correct - is now using Linq to Objects rather than the Linq to SQL queries I was previously? Is this okay practise? It feels wrong to me but I dont know why. Probably because the logic of the queries is in the very highest tier of the app, rather than the lowest, but... I defer to you good people for advice. One of the issues I considered was bringing the entire table into memory but I understand that using the Iqeryable return type the where clause is taken to the database and evaluated there. Thus returning only the resultset i require... i may be wrong. And if you've made it this far, well done. Thank you, and if you have any advice it is very much appreciated!!

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  • What would be the good name for this operation?

    - by Rogach
    I see that Scala standard library misses the method to get ranges of objects in the collection, that satisfy the predicate: def <???>(p: A => Boolean): List[List[A]] = { val buf = collection.mutable.ListBuffer[List[A]]() var elems = this.dropWhile(e => !p(e)) while (elems.nonEmpty) { buf += elems.takeWhile(p) elems = elems.dropWhile(e => !p(e)) } buf.toList } What would be the good name for such method? And is my implementation good enough?

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  • what's the way to determine if an Int a perfect square in Haskell?

    - by valya
    I need a simple function is_square :: Int -> Bool which determines if an Int N a perfect square (is there an integer x such that x*x = N). Of course I can just write something like is_square n = sq * sq == n where sq = floor $ sqrt $ (fromIntegral n::Double) but it looks terrible! Maybe there is a common simple way to implement such predicate?

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  • translating specifications into query predicates

    - by Jeroen
    I'm trying to find a nice and elegant way to query database content based on DDD "specifications". In domain driven design, a specification is used to check if some object, also known as the candidate, is compliant to a (domain specific) requirement. For example, the specification 'IsTaskDone' goes like: class IsTaskDone extends Specification<Task> { boolean isSatisfiedBy(Task candidate) { return candidate.isDone(); } } The above specification can be used for many purposes, e.g. it can be used to validate if a task has been completed, or to filter all completed tasks from a collection. However, I want to re-use this, nice, domain related specification to query on the database. Of course, the easiest solution would be to retrieve all entities of our desired type from the database, and filter that list in-memory by looping and removing non-matching entities. But clearly that would not be optimal for performance, especially when the entity count in our db increases. Proposal So my idea is to create a 'ConversionManager' that translates my specification into a persistence technique specific criteria, think of the JPA predicate class. The services looks as follows: public interface JpaSpecificationConversionManager { <T> Predicate getPredicateFor(Specification<T> specification, Root<T> root, CriteriaQuery<?> cq, CriteriaBuilder cb); JpaSpecificationConversionManager registerConverter(JpaSpecificationConverter<?, ?> converter); } By using our manager, the users can register their own conversion logic, isolating the domain related specification from persistence specific logic. To minimize the configuration of our manager, I want to use annotations on my converter classes, allowing the manager to automatically register those converters. JPA repository implementations could then use my manager, via dependency injection, to offer a find by specification method. Providing a find by specification should drastically reduce the number of methods on our repository interface. In theory, this all sounds decent, but I feel like I'm missing something critical. What do you guys think of my proposal, does it comply to the DDD way of thinking? Or is there already a framework that does something identical to what I just described?

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  • NSSortDescriptor for NSFetchRequestController causes crash when value of sorted attribute is changed

    - by AJ
    I have an Core Data Entity with a number of attributes, which include amount(float), categoryTotal(float) and category(string) The initial ViewController uses a FethchedResultsController to retrieve the entities, and sorts them based on the category and then the categoryTotal. No problems so far. NSManagedObjectContext *moc = [self managedObjectContext]; NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Transaction" inManagedObjectContext:moc]; NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease]; [request setEntity:entityDescription]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(dateStamp >= %@) AND (dateStamp =< %@)", startDate, endDate]; [request setPredicate:predicate]; NSSortDescriptor *sortByCategory = [[NSSortDescriptor alloc] initWithKey:@"category" ascending:sortOrder]; NSSortDescriptor *sortByTotals = [[NSSortDescriptor alloc] initWithKey:@"categoryTotal" ascending:sortOrder]; NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortByTotals, sortByCategory, nil]; [request setSortDescriptors:sortDescriptors]; NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:managedObjectContext sectionNameKeyPath:@"category" cacheName:nil]; aFetchedResultsController.delegate = self; self.fetchedResultsController = aFetchedResultsController; On selecting a row (tableView:didSelectRowAtIndexPath), another view controller is loaded that allows editing of the amount field for the selected entity. Before returning to the first view, categoryTotal is updated by the new ‘amount’. The problem comes when returning to the first view controller, the app bombs with *Serious application error. Exception was caught during Core Data change processing: Invalid update: invalid number of rows in section 0. The number of rows contained in an existing section after the update (1) must be equal to the number of rows contained in that section before the update (1), plus or minus the number of rows inserted or deleted from that section (0 inserted, 1 deleted). with userInfo (null) Program received signal: “EXC_BAD_ACCESS”.* This seems to be courtesy of NSSortDescriptor *sortByTotals = [[NSSortDescriptor alloc] initWithKey:@"categoryTotal" ascending:sortOrder]; If I remove this everything works as expected, but obviously without the sorting I want. I'm guessing this is to do with the sorting order changing due to categoryTotal changing (deletion / insertion) but can't find away fix this. I've verified that values are being modified correctly in the second view, so it appears down to the fetchedResultsController being confused. If the categoryAmount is changed to one that does not change the sort order, then no error is generated I'm not physically changing (ie deleting) the number of items the fetchedResultsController is returning ... the only other issue I can find that seem to generate this error Any ideas would be most welcome Thanks, AJ

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  • What are the pros and cons of using manual list iteration vs recursion through fail

    - by magus
    I come up against this all the time, and I'm never sure which way to attack it. Below are two methods for processing some season facts. What I'm trying to work out is whether to use method 1 or 2, and what are the pros and cons of each, especially large amounts of facts. methodone seems wasteful since the facts are available, why bother building a list of them (especially a large list). This must have memory implications too if the list is large enough ? And it doesn't take advantage of Prolog's natural backtracking feature. methodtwo takes advantage of backtracking to do the recursion for me, and I would guess would be much more memory efficient, but is it good programming practice generally to do this? It's arguably uglier to follow, and might there be any other side effects? One problem I can see is that each time fail is called, we lose the ability to pass anything back to the calling predicate, eg. if it was methodtwo(SeasonResults), since we continually fail the predicate on purpose. So methodtwo would need to assert facts to store state. Presumably(?) method 2 would be faster as it has no (large) list processing to do? I could imagine that if I had a list, then methodone would be the way to go.. or is that always true? Might it make sense in any conditions to assert the list to facts using methodone then process them using method two? Complete madness? But then again, I read that asserting facts is a very 'expensive' business, so list handling might be the way to go, even for large lists? Any thoughts? Or is it sometimes better to use one and not the other, depending on (what) situation? eg. for memory optimisation, use method 2, including asserting facts and, for speed use method 1? season(spring). season(summer). season(autumn). season(winter). % Season handling showseason(Season) :- atom_length(Season, LenSeason), write('Season Length is '), write(LenSeason), nl. % ------------------------------------------------------------- % Method 1 - Findall facts/iterate through the list and process each %-------------------------------------------------------------- % Iterate manually through a season list lenseason([]). lenseason([Season|MoreSeasons]) :- showseason(Season), lenseason(MoreSeasons). % Findall to build a list then iterate until all done methodone :- findall(Season, season(Season), AllSeasons), lenseason(AllSeasons), write('Done'). % ------------------------------------------------------------- % Method 2 - Use fail to force recursion %-------------------------------------------------------------- methodtwo :- % Get one season and show it season(Season), showseason(Season), % Force prolog to backtrack to find another season fail. % No more seasons, we have finished methodtwo :- write('Done').

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