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• Code Contracts: validating arrays and collections

  - by DigiMortal

  Validating collections before using them is very common task when we use built-in generic types for our collections. In this posting I will show you how to validate collections using code contracts. It is cool how much awful looking code you can avoid using code contracts. Failing code Let’s suppose we have method that calculates sum of all invoices in collection. We have class Invoice and one of properties it has is Sum. I don’t introduce here any complex calculations on invoices because we have another problem to solve in this topic. Here is our code. public static decimal CalculateTotal(IList<Invoice> invoices) {     var sum = invoices.Sum(p => p.Sum);     return sum; } This method is very simple but it fails when invoices list contains at least one null. Of course, we can test if invoice is null but having nulls in lists like this is not good idea – it opens green way for different coding bugs in system. Our goal is to react to bugs ASAP at the nearest place they occur. There is one more way how to make our method fail. It happens when invoices is null. I thing it is also one common bugs during development and it even happens in production environments under some conditions that are usually hardly met. Now let’s protect our little calculation method with code contracts. We need two contracts: invoices cannot be null invoices cannot contain any nulls Our first contract is easy but how to write the second one? Solution: Contract.ForAll Preconditions in code are checked using Contract.Ensures method. This method takes boolean value as argument that sais if contract holds or not. There is also method Contract.ForAll that takes collection and predicate that must hold for that collection. Nice thing is ForAll returns boolean. So, we have very simple solution. public static decimal CalculateTotal(IList<Invoice> invoices) {     Contract.Requires(invoices != null);     Contract.Requires(Contract.ForAll<Invoice>(invoices, p => p != null));       var sum = invoices.Sum(p => p.Sum);     return sum; } And here are some lines of code you can use to test the contracts quickly. var invoices = new List<Invoice>(); invoices.Add(new Invoice()); invoices.Add(null); invoices.Add(new Invoice()); //CalculateTotal(null); CalculateTotal(invoices); If your code is covered with unit tests then I suggest you to write tests to check that these contracts hold for every code run. Conclusion Although it seemed at first place that checking all elements in collection may end up with for-loops that does not look so nice we were able to solve our problem nicely. ForAll method of contract class offered us simple mechanism to check collections and it does it smoothly the code-contracts-way. P.S. I suggest you also read devlicio.us blog posting Validating Collections with Code Contracts by Derik Whittaker.

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• SQL SERVER – Puzzle #1 – Querying Pattern Ranges and Wild Cards

  - by Pinal Dave

  Note: Read at the end of the blog post how you can get five Joes 2 Pros Book #1 and a surprise gift. I have been blogging for almost 7 years and every other day I receive questions about Querying Pattern Ranges. The most common way to solve the problem is to use Wild Cards. However, not everyone knows how to use wild card properly. SQL Queries 2012 Joes 2 Pros Volume 1 – The SQL Queries 2012 Hands-On Tutorial for Beginners Book On Amazon | Book On Flipkart Learn SQL Server get all the five parts combo kit Kit on Amazon | Kit on Flipkart Many people know wildcards are great for finding patterns in character data. There are also some special sequences with wildcards that can give you even more power. This series from SQL Queries 2012 Joes 2 Pros® Volume 1 will show you some of these cool tricks. All supporting files are available with a free download from the www.Joes2Pros.com web site. This example is from the SQL 2012 series Volume 1 in the file SQLQueries2012Vol1Chapter2.2Setup.sql. If you need help setting up then look in the “Free Videos” section on Joes2Pros under “Getting Started” called “How to install your labs” Querying Pattern Ranges The % wildcard character represents any number of characters of any length. Let’s find all first names that end in the letter ‘A’. By using the percentage ‘%’ sign with the letter ‘A’, we achieve this goal using the code sample below: SELECT * FROM Employee WHERE FirstName LIKE '%A' To find all FirstName values beginning with the letters ‘A’ or ‘B’ we can use two predicates in our WHERE clause, by separating them with the OR statement. Finding names beginning with an ‘A’ or ‘B’ is easy and this works fine until we want a larger range of letters as in the example below for ‘A’ thru ‘K’: SELECT * FROM Employee WHERE FirstName LIKE 'A%' OR FirstName LIKE 'B%' OR FirstName LIKE 'C%' OR FirstName LIKE 'D%' OR FirstName LIKE 'E%' OR FirstName LIKE 'F%' OR FirstName LIKE 'G%' OR FirstName LIKE 'H%' OR FirstName LIKE 'I%' OR FirstName LIKE 'J%' OR FirstName LIKE 'K%' The previous query does find FirstName values beginning with the letters ‘A’ thru ‘K’. However, when a query requires a large range of letters, the LIKE operator has an even better option. Since the first letter of the FirstName field can be ‘A’, ‘B’, ‘C’, ‘D’, ‘E’, ‘F’, ‘G’, ‘H’, ‘I’, ‘J’ or ‘K’, simply list all these choices inside a set of square brackets followed by the ‘%’ wildcard, as in the example below: SELECT * FROM Employee WHERE FirstName LIKE '[ABCDEFGHIJK]%' A more elegant example of this technique recognizes that all these letters are in a continuous range, so we really only need to list the first and last letter of the range inside the square brackets, followed by the ‘%’ wildcard allowing for any number of characters after the first letter in the range. Note: A predicate that uses a range will not work with the ‘=’ operator (equals sign). It will neither raise an error, nor produce a result set. --Bad query (will not error or return any records) SELECT * FROM Employee WHERE FirstName = '[A-K]%' Question: You want to find all first names that start with the letters A-M in your Customer table and end with the letter Z. Which SQL code would you use? a. SELECT * FROM Customer WHERE FirstName LIKE 'm%z' b. SELECT * FROM Customer WHERE FirstName LIKE 'a-m%z' c. SELECT * FROM Customer WHERE FirstName LIKE 'a-m%z' d. SELECT * FROM Customer WHERE FirstName LIKE '[a-m]%z' e. SELECT * FROM Customer WHERE FirstName LIKE '[a-m]z%' f. SELECT * FROM Customer WHERE FirstName LIKE '[a-m]%z' g. SELECT * FROM Customer WHERE FirstName LIKE '[a-m]z%' Contest Leave a valid answer before June 18, 2013 in the comment section. 5 winners will be selected from all the valid answers and will receive Joes 2 Pros Book #1. 1 Lucky person will get a surprise gift from Joes 2 Pros. The contest is open for all the countries where Amazon ships the book (USA, UK, Canada, India and many others). Special Note: Read all the options before you provide valid answer as there is a small trick hidden in answers. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Joes 2 Pros, PostADay, SQL, SQL Authority, SQL Puzzle, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Crime Scene Investigation: SQL Server

  - by Rodney Landrum

  “The packages are running slower in Prod than they are in Dev” My week began with this simple declaration from one of our lead BI developers, quickly followed by an emailed spreadsheet demonstrating that, over 5 executions, an extensive ETL process was running average 630 seconds faster on Dev than on Prod. The situation needed some scientific investigation to determine why the same code, the same data, the same schema would yield consistently slower results on a more powerful server. Prod had yet to be officially christened with a “Go Live” date so I had the time, and having recently been binge watching CSI: New York, I also had the inclination. An inspection of the two systems, Prod and Dev, revealed the first surprise: although Prod was indeed a “bigger” system, with double the amount of RAM of Dev, the latter actually had twice as many processor cores. On neither system did I see much sign of resources being heavily taxed, while the ETL process was running. Without any real supporting evidence, I jumped to a conclusion that my years of performance tuning should have helped me avoid, and that was that the hardware differences explained the better performance on Dev. We spent time setting up a Test system, similarly scoped to Prod except with 4 times the cores, and ported everything across. The results of our careful benchmarks left us truly bemused; the ETL process on the new server was slower than on both other systems. We burned more time tweaking server configurations, monitoring IO and network latency, several times believing we’d uncovered the smoking gun, until the results of subsequent test runs pitched us back into confusion. Finally, I decided, enough was enough. Hadn’t I learned very early in my DBA career that almost all bottlenecks were caused by code and database design, not hardware? It was time to get back to basics. With over 100 SSIS packages and hundreds of queries, each handling specific tasks such as file loads, bulk inserts, transforms, logging, and so on, the task seemed formidable. And yet, after barely an hour spent with Profiler, Extended Events, and wait statistics DMVs, I had a lead in the shape of a query that joined three tables, containing millions of rows, returned 3279 results, but performed 239K logical reads. As soon as I looked at the execution plans for the query in Dev and Test I saw the culprit, an implicit conversion warning on a join predicate field that was numeric in one table and a varchar(50) in another! I turned this information over to the BI developers who quickly resolved the data type mismatches and found and fixed “several” others as well. After the schema changes the same query with the same databases ran in under 1 second on all systems and reduced the logical reads down to fewer than 300. The analysis also revealed that on Dev, the ETL task was pulling data across a LAN, whereas Prod and Test were connected across slower WAN, in large part explaining why the same process ran slower on the latter two systems. Loading the data locally on Prod delivered a further 20% gain in performance. As we progress through our DBA careers we learn valuable lessons. Sometimes, with a project deadline looming and pressure mounting, we choose to forget them. I was close to giving into the temptation to throw more hardware at the problem. I’m pleased at least that I resisted, though I still kick myself for not looking at the code on day one. It can seem a daunting prospect to return to the fundamentals of the code so close to roll out, but with the right tools, and surprisingly little time, you can collect the evidence that reveals the true problem. It is a lesson I trust I will remember for my next 20 years as a DBA, if I’m ever again tempted to bypass the evidence.

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• Problem with creating a deterministic finite automata (DFA) - Mercury

  - by Jabba The hut

  I would like to have a deterministic finite automata (DFA) simulated in Mercury. But I’m s(t)uck at several places. Formally, a DFA is described with the following characteristics: a setOfStates S, an inputAlphabet E <-- summation symbol, a transitionFunction : S × E -- S, a startState s € S, a setOfAcceptableFinalStates F =C S. A DFA will always starts in the start state. Then the DFA will read all the characters on the input, one by one. Based on the current input character and the current state, there will be made to a new state. These transitions are defined in the transitions function. when the DFA is in one of his acceptable final states, after reading the last character, then will the DFA accept the input, If not, then the input will be is rejected. The figure shows a DFA the accepting strings where the amount of zeros, is a plurality of three. Condition 1 is the initial state, and also the only acceptable state. for each input character is the corresponding arc followed to the next state. Link to Figure What must be done A type “mystate” which represents a state. Each state has a number which is used for identification. A type “transition” that represents a possible transition between states. Each transition has a source_state, an input_character, and a final_state. A type “statemachine” that represents the entire DFA. In the solution, the DFA must have the following properties: The set of all states, the input alphabet, a transition function, represented as a set of possible transitions, a set of accepting final states, a current state of the DFA A predicate “init_machine (state machine :: out)” which unifies his arguments with the DFA, as shown as in the Figure. The current state for the DFA is set to his initial state, namely, 1. The input alphabet of the DFA is composed of the characters '0'and '1'. A user can enter a text, which will be controlled by the DFA. the program will continues until the user types Ctrl-D and simulates an EOF. If the user use characters that are not allowed into the input alphabet of the DFA, then there will be an error message end the program will close. (pred require) Example Enter a sentence: 0110 String is not ok! Enter a sentence: 011101 String is not ok! Enter a sentence: 110100 String is ok! Enter a sentence: 000110010 String is ok! Enter a sentence: 011102 Uncaught exception Mercury: Software Error: Character does not belong to the input alphabet! the thing wat I have. :- module dfa. :- interface. :- import_module io. :- pred main(io.state::di, io.state::uo) is det. :- implementation. :- import_module int,string,list,bool. 1 :- type mystate ---> state(int). 2 :- type transition ---> trans(source_state::mystate, input_character::bool, final_state::mystate). 3 (error, finale_state and current_state and input_character) :- type statemachine ---> dfa(list(mystate),list(input_character),list(transition),list(final_state),current_state(mystate)) 4 missing a lot :- pred init_machine(statemachine :: out) is det. %init_machine(statemachine(L_Mystate,0,L_transition,L_final_state,1)) :- <-probably fault 5 not perfect main(!IO) :- io.write_string("\nEnter a sentence: ", !IO), io.read_line_as_string(Input, !IO), ( Invoer = ok(StringVar), S1 = string.strip(StringVar), (if S1 = "mustbeabool" then io.write_string("Sentenceis Ok! ", !IO) else io.write_string("Sentence is not Ok!.", !IO)), main(!IO) ; Invoer = eof ; Invoer = error(ErrorCode), io.format("%s\n", [s(io.error_message(ErrorCode))], !IO) ). Hope you can help me kind regards

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• Manual (Dynamic) LINQ subquery using IN clause

  - by immortalali-msn-com

  Hi Everyone, I want to query the DB through LINQ writing manual SQL, my linq method is: var q = db.TableView.Where(sqlAfterWhere); returnValue = q.Count(); this method queries well if the value passed to variable "sqlAfterWhere" is: (this variable is String type) it.Name = 'xyz' but what if i want to use IN clause, using a sub query. (i need to use 'it' before every column name in the above query to work), i cant use 'it' before the sub query columns as its a separate query, so what should i do, if i dont use any thing, and use column names directly it gives error saying " could not be resolved" where is my column names with out 'it' at the begining. So the query not working is: (this is a string passed to the variable above): it.Name IN (SELECT Name FROM TableName WHERE Address LIKE '%SomeAddress%') the errors come out as: Name could not be resolved Address could not be resolved The exact error is: "'Name' could not be resolved in the current scope or context. Make sure that all referenced variables are in scope, that required schemas are loaded, and that namespaces are referenced correctly., near simple identifier, line 6, column 25." Same error for "Address as well if i use 'it.' before these columns it gives error as: "The element type 'Edm.Int32' and the CollectionType 'Transient.collection[Transient.rowtype(GroupID,Edm.Int32(Nullable=True,DefaultValue=))]' are not compatible. The IN expression only supports entity, primitive, and reference types. , near WHERE predicate, line 6, column 14." Thanks for the help

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• Prolog: How to make three lists the same lenght (by adding leading zeros)

  - by sixtyfootersdude

  I am writing a prolog program to solve a problem. The problem takes three lists as input: solve( [L|Lr] , [R|Rr] , [S|Sr] ) :- Unfortunately the lists all need to be equal length for the program to work. So these work: ?- solve( [A, B, C, D] , [1, 3, 5, 6], [E, F, G, H]). ?- solve( [1] , [2], [3]). But these do not: ?- solve( [A, B, C, D], [1], [B, I, T] ). ?- solve( [A], [1, 2], [4, 5]). What I would like to do is write a predicate(?) to pad the smaller lists with leading zeros. So: solve( [A, B, C, D], [1], [B, I, T] ) would become: solve( [A, B, C, D], [0, 0, 0, 1], [0, B, I, T] ) Any points on how to accomplish this would be awesome. I am from a functional background so I am struggling. Is there a way tell the length of a list? I think I could do that recursively, but it seems like a pain. Thanks

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• objc_exception_throw When Returning NSManagedObject

  - by spamguy

  I have a method dedicated to finding an NSManagedObject ('company') using a supplied NSString and, if it's not found, creating a new one and returning it. As far as I know it's fully inited and the method works perfectly. That is, until the line after the return statement, when the app crashes with an objc_exception_throw. I googled this and couldn't find what causes it, only how to use it in breakpoint debugging. What's wrong with this method, and why is it throwing specifically this exception? - (NSManagedObject*) getCompanyObject:(NSString*)theCompany { NSError *error = nil; NSManagedObjectContext *moc = [[self delegate] managedObjectContext]; NSFetchRequest *fetch = [[[NSFetchRequest alloc] init] autorelease]; NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Company" inManagedObjectContext:moc]; [fetch setEntity:entityDescription]; // object to be returned NSManagedObject *companyObject = [[NSManagedObject alloc] initWithEntity:entityDescription insertIntoManagedObjectContext:moc]; // set predicate (company name) NSPredicate *pred = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"name = \"%@\"", theCompany]]; [fetch setPredicate:pred]; NSArray *response = [moc executeFetchRequest:fetch error:&error]; if ([response count] == 0) // empty resultset --> no companies with this name { [companyObject setValue:theCompany forKey:@"name"]; NSLog(@"%@ not found. Adding.", theCompany); } else [companyObject setValue:[[response objectAtIndex:0] valueForKey:@"name"]]; return companyObject; }

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• Filtering documents against a dictionary key in MongoDB

  - by Thomas

  I have a collection of articles in MongoDB that has the following structure: { 'category': 'Legislature', 'updated': datetime.datetime(2010, 3, 19, 15, 32, 22, 107000), 'byline': None, 'tags': { 'party': ['Peter Hoekstra', 'Virg Bernero', 'Alma Smith', 'Mike Bouchard', 'Tom George', 'Rick Snyder'], 'geography': ['Michigan', 'United States', 'North America'] }, 'headline': '2 Mich. gubernatorial candidates speak to students', 'text': [ 'BEVERLY HILLS, Mich. (AP) \u2014 Two Democratic and Republican gubernatorial candidates found common ground while speaking to private school students in suburban Detroit', "Democratic House Speaker state Rep. Andy Dillon and Republican U.S. Rep. Pete Hoekstra said Friday a more business-friendly government can help reduce Michigan's nation-leading unemployment rate.", "The candidates were invited to Detroit Country Day Upper School in Beverly Hills to offer ideas for Michigan's future.", 'Besides Dillon, the Democratic field includes Lansing Mayor Virg Bernero and state Rep. Alma Wheeler Smith. Other Republicans running are Oakland County Sheriff Mike Bouchard, Attorney General Mike Cox, state Sen. Tom George and Ann Arbor business leader Rick Snyder.', 'Former Republican U.S. Rep. Joe Schwarz is considering running as an independent.' ], 'dateline': 'BEVERLY HILLS, Mich.', 'published': datetime.datetime(2010, 3, 19, 8, 0, 31), 'keywords': "Governor's Race", '_id': ObjectId('4ba39721e0e16cb25fadbb40'), 'article_id': 'urn:publicid:ap.org:0611e36fb084458aa620c0187999db7e', 'slug': "BC-MI--Governor's Race,2nd Ld-Writethr" } If I wanted to write a query that looked for all articles that had at least 1 geography tag, how would I do that? I have tried writing db.articles.find( {'tags': 'geography'} ), but that doesn't appear to work. I've also thought about changing the search parameter to 'tags.geography', but am having a devil of a time figuring out what the search predicate would be.

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• [Haskell] Problem when mixing type classes and type families

  - by Giuseppe Maggiore

  Hi! This code compiles fine: {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances, UndecidableInstances, FlexibleContexts, EmptyDataDecls, ScopedTypeVariables, TypeOperators, TypeSynonymInstances, TypeFamilies #-} class Sel a s b where type Res a s b :: * instance Sel a s b where type Res a s b = (s -> (b,s)) instance Sel a s (b->(c,a)) where type Res a s (b->(c,a)) = (b -> s -> (c,s)) but as soon as I add the R predicate ghc fails: {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances, UndecidableInstances, FlexibleContexts, EmptyDataDecls, ScopedTypeVariables, TypeOperators, TypeSynonymInstances, TypeFamilies #-} class Sel a s b where type Res a s b :: * instance Sel a s b where type Res a s b = (s -> (b,s)) class R a where type Rec a :: * cons :: a -> Rec a elim :: Rec a -> a instance Sel a s (b->(c,Rec a)) where type Res a s (b->(c,Rec a)) = (b -> s -> (c,s)) complaining that: Illegal type synonym family application in instance: b -> (c, Rec a) In the instance declaration for `Sel a s (b -> (c, Rec a))' what does it mean and (most importantly) how do I fix it? Thanks

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• Dynamic Linq Property Converting to Sql

  - by Matthew Hood

  I am trying to understand dynamic linq and expression trees. Very basically trying to do an equals supplying the column and value as strings. Here is what I have so far private IQueryable<tblTest> filterTest(string column, string value) { TestDataContext db = new TestDataContext(); // The IQueryable data to query. IQueryable<tblTest> queryableData = db.tblTests.AsQueryable(); // Compose the expression tree that represents the parameter to the predicate. ParameterExpression pe = Expression.Parameter(typeof(tblTest), "item"); Expression left = Expression.Property(pe, column); Expression right = Expression.Constant(value); Expression e1 = Expression.Equal(left, right); MethodCallExpression whereCallExpression = Expression.Call( typeof(Queryable), "Where", new Type[] { queryableData.ElementType }, queryableData.Expression, Expression.Lambda<Func<tblTest, bool>>(e1, new ParameterExpression[] { pe })); // Create an executable query from the expression tree. IQueryable<tblTest> results = queryableData.Provider.CreateQuery<tblTest>(whereCallExpression); return results; } That works fine for columns in the DB. But fails for properties in my code eg public partial class tblTest { public string name_test { get { return name; } } } Giving an error cannot be that it cannot be converted into SQL. I have tried rewriting the property as a Expression<Func but with no luck, how can I convert simple properties so they can be used with linq in this dynamic way? Many Thanks

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• Programatic re-evalutation of MVVM command's "can execute" state

  - by dzs

  Hello! I'm writing a WPF application using the MVVM pattern, based on the following article: WPF Apps With The Model-View-ViewModel Design Pattern I have two buttons on my View with the buttons' "Command" property bound (with data binding) to a given instance of the RelayCommand class (see "Figure 3 The RelayCommand Class" from the article above). The RelayCommand class has support for checking whether the given command can be executed. WPF automatically disables buttons whose command cannot be executed. Each of my commands (in the ViewModel class) start a background operation, and the command cannot be executed again until the background operation is finished. The RelayCommand instances have information whether the background operation is still working or it is finished. My problem is the following: after pressing the any of the buttons, the buttons automaticaly go disabled (which is OK) because the background operation started and the command cannot be executed until it is finished, but after the operation had finished, the buttons don't go enabled automatically because their command's "can be executed" predicate is not automatically reevaluated. The reevaluation can be manually triggered by having the application loose and regain focus (by pressing ALT+TAB). After doing this trick, the buttons get enabled once again. How can I programatically reevaluate the buttons' command's "can execute" state?

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• Simple CalendarStore query puts application into infinite loop!?

  - by Frank R.

  Hi, I've been looking at adding iCal support to my new application and everything seemed just fine and worked on my Mac OS X 10.6 Snow Leopard development machine without a hitch. Now it looks like depending on what is in your calendar the very simple query below: - (NSArray*) fetchCalendarEventsForNext50Minutes { NSLog(@"fetchCalendarEventsForNext50Minutes"); NSTimeInterval start = [NSDate timeIntervalSinceReferenceDate]; NSDate* startDate = [[NSDate alloc] init]; NSDate* endDate = [startDate addTimeInterval: 50.0 * 60.0]; NSPredicate *eventsForTheNext50Minutes = [CalCalendarStore eventPredicateWithStartDate:startDate endDate:endDate calendars:[[CalCalendarStore defaultCalendarStore] calendars]]; // Fetch all events for this year NSArray *events = [[CalCalendarStore defaultCalendarStore] eventsWithPredicate: eventsForTheNext50Minutes]; NSLog( @"fetch took: %f seconds", [NSDate timeIntervalSinceReferenceDate] - start ); return events; } produces a beachball thrash even with quite limited events in the calendar store. Am I missing something crucial here? The code snippet is pretty much exactly from the documentation at: // Create a predicate to fetch all events for this year NSInteger year = [[NSCalendarDate date] yearOfCommonEra]; NSDate *startDate = [[NSCalendarDate dateWithYear:year month:1 day:1 hour:0 minute:0 second:0 timeZone:nil] retain]; NSDate *endDate = [[NSCalendarDate dateWithYear:year month:12 day:31 hour:23 minute:59 second:59 timeZone:nil] retain]; NSPredicate *eventsForThisYear = [CalCalendarStore eventPredicateWithStartDate:startDate endDate:endDate calendars:[[CalCalendarStore defaultCalendarStore] calendars]]; // Fetch all events for this year NSArray *events = [[CalCalendarStore defaultCalendarStore] eventsWithPredicate:eventsForThisYear]; It looks like it has something to do with the recurrence rules, but as far as I can see there are no other ways of fetching events from the calendar store anyway. Has anybody else come across this? Best regards, Frank

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• Prolog adding and removing list element if non present in second list

  - by logically

  I don't know what I'm missing here. I wan't to add an element if it is in arg1 but not in arg2 and want to remove an element if it is in arg1 but not in arg2. I'm using an if condition with includes function that return true if the element is in the arg2 list, false otherwise. Then use built it predicates append and select to add or remove. I'm getting false to all my objectives searches. I comment and uncomment depending on what predicate I want, add or remove. includes([],_). includes([P|Z],S) :- memberchk(P,S), includes(Z,S). addop([],list,res). addop([P|R],list,res) :- includes(P,s0) - addop(R,list,res) ; append(P,list,res), addop(R,list,res). rem([],list,res). rem([P|R],list,res) :- includes(P,list) - rem(R,list,res) ; select(P,list,res),rem(R,list,res). Thanks for help.

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• LINQ query code for complex merging of data.

  - by Stacey

  I've posted this before, but I worded it poorly. I'm trying again with a more well thought out structure. Re-writing this a bit to make it more clear. I have the following code and I am trying to figure out the shorter linq expression to do it 'inline'. Please examine the "Run()" method near the bottom. I am attempting to understand how to join two dictionaries together based on a matching identifier in one of the objects - so that I can use the query in this sort of syntax. var selected = from a in items.List() // etc. etc. select a; This is my class structure. The Run() method is what I am trying to simplify. I basically need to do this conversion inline in a couple of places, and I wanted to simplify it a great deal so that I can define it more 'cleanly'. class TModel { public Guid Id { get; set; } } class TModels : List<TModel> { } class TValue { } class TStorage { public Dictionary<Guid, TValue> Items { get; set; } } class TArranged { public Dictionary<TModel, TValue> Items { get; set; } } static class Repository { static public TItem Single<TItem, TCollection>(Predicate<TItem> expression) { return default(TItem); // access logic. } } class Sample { public void Run() { TStorage tStorage = new TStorage(); // access tStorage logic here. Dictionary<TModel, TValue> d = new Dictionary<TModel, TValue>(); foreach (KeyValuePair<Guid, TValue> kv in tStorage.Items) { d.Add(Repository.Single<TModel, TModels>(m => m.Id == kv.Key),kv.Value); } } }

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• UICollectionView with one static cell and N dynamic ones from a fetchresultscontroller exception

  - by nflacco

  I'm trying to make a UITableView that shows a blog post and comments for that post. My setup is a tableview in storyboard with two dynamic prototype cells. The first cell is for the post and should never change. The second cell represents the 0 to N comments. My cellForRowAtIndexPath method shows the post cell properly, but fails to get the comment at the given index path (though if I comment out the fetch I get the appropriate number of comment cells with a green background that I set as a visual debug thing). let comment = fetchedResultController.objectAtIndexPath(indexPath) as Comment I get the following exception on this line: 2014-08-24 15:06:40.712 MessagePosting[21767:3266409] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 1 beyond bounds [0 .. 0]' *** First throw call stack: ( 0 CoreFoundation 0x0000000101aa43e5 __exceptionPreprocess + 165 1 libobjc.A.dylib 0x00000001037f9967 objc_exception_throw + 45 2 CoreFoundation 0x000000010198f4c3 -[__NSArrayM objectAtIndex:] + 227 3 CoreData 0x00000001016e4792 -[NSFetchedResultsController objectAtIndexPath:] + 162 Section and cell setup: override func tableView(tableView: UITableView!, numberOfRowsInSection section: Int) -> Int { // #warning Incomplete method implementation. // Return the number of rows in the section. switch section { case 0: return 1 default: if let realPost:Post = post { return fetchedResultController.sections[0].numberOfObjects } else { return 0 } } } override func tableView(tableView: UITableView!, cellForRowAtIndexPath indexPath: NSIndexPath!) -> UITableViewCell! { switch indexPath.section { case 0: let cell = tableView.dequeueReusableCellWithIdentifier(postViewCellIdentifier, forIndexPath: indexPath) as UITableViewCell cell.backgroundColor = lightGrey if let realPost:Post = self.post { cell.textLabel.text = realPost.text } return cell default: let cell = tableView.dequeueReusableCellWithIdentifier(commentCellIdentifier, forIndexPath: indexPath) as UITableViewCell cell.backgroundColor = UIColor.greenColor() let comment = fetchedResultController.objectAtIndexPath(indexPath) as Comment // <---------------------------- :( cell.textLabel.text = comment.text return cell } } FRC: func controllerDidChangeContent(controller: NSFetchedResultsController!) { tableView.reloadData() } func getFetchedResultController() -> NSFetchedResultsController { fetchedResultController = NSFetchedResultsController(fetchRequest: taskFetchRequest(), managedObjectContext: managedObjectContext, sectionNameKeyPath: nil, cacheName: nil) return fetchedResultController } func taskFetchRequest() -> NSFetchRequest { if let realPost:Post = self.post { let fetchRequest = NSFetchRequest(entityName: "Comment") let sortDescriptor = NSSortDescriptor(key: "date", ascending: false) fetchRequest.predicate = NSPredicate(format: "post = %@", realPost) fetchRequest.sortDescriptors = [sortDescriptor] return fetchRequest } else { return NSFetchRequest(entityName: "") } }

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• Recursion Problems in Prolog

  - by Humble_Student

  I'm having some difficulties in prolog, I'm trying to write a predicate that will return all paths between two cities, although at the moment it returns the first path it finds on an infinite loop. Not sure where I'm going wrong but I've been trying to figure this out all day and I'm getting nowhere. Any help that could be offered would be appreciated. go:- repeat, f([],0,lon,spa,OP,OD), write(OP), write(OD), fail. city(lon). city(ath). city(spa). city(kol). path(lon,1,ath). path(ath,3,spa). path(spa,2,kol). path(lon,1,kol). joined(X,Y,D):- path(X,D,Y);path(Y,D,X). f(Ci_Vi,Di,De,De,PaO,Di):- append([De],Ci_Vi,PaO), !. f(Cities_Visited,Distance,Start,Destination,Output_Path,Output_Distance):- repeat, city(X), joined(Start,X,D), not_member(X,Cities_Visited), New_Distance is Distance + D, f([Start|Cities_Visited],New_Distance,X,Destination,Output_Path,Output_Distance). not_member(X,List):- member(X,List), !, fail. not_member(X,List). The output I'm expecting here is [spa,ath,lon]4 [spa,kol,lon]3. Once again, any help would be appreciated. Many thanks in advance.

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• SQL Server search filter and order by performance issues

  - by John Leidegren

  We have a table value function that returns a list of people you may access, and we have a relation between a search and a person called search result. What we want to do is that wan't to select all people from the search and present them. The query looks like this SELECT qm.PersonID, p.FullName FROM QueryMembership qm INNER JOIN dbo.GetPersonAccess(1) ON GetPersonAccess.PersonID = qm.PersonID INNER JOIN Person p ON p.PersonID = qm.PersonID WHERE qm.QueryID = 1234 There are only 25 rows with QueryID=1234 but there are almost 5 million rows total in the QueryMembership table. The person table has about 40K people in it. QueryID is not a PK, but it is an index. The query plan tells me 97% of the total cost is spent doing "Key Lookup" witht the seek predicate. QueryMembershipID = Scalar Operator (QueryMembership.QueryMembershipID as QM.QueryMembershipID) Why is the PK in there when it's not used in the query at all? and why is it taking so long time? The number of people total 25, with the index, this should be a table scan for all the QueryMembership rows that have QueryID=1234 and then a JOIN on the 25 people that exists in the table value function. Which btw only have to be evaluated once and completes in less than 1 second.

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• Core Data - 'calculated' attributes

  - by nephilim

  I have two entities: A and B A has two properties from and to, both pointing to the B entity. B as a fetched property to A with predicate from == $FETCH_SOURCE or to = $FETCH_SOURCE -- (from) -> A -- (to) -> B <- (As) -- In my application I select a certain B instance, and then show all of its A instances. Now, in my table the columns are bound to an array controller containing the selected A instances. I want to 'merge' the from and to columns. I already know one of the columns will be equal to the selected B instance, so now I'm only interested in the second value. The options I see: create a custom class for the B entity and create a method that returns either value. It should somehow be able to retrieve which B instance is currently selected. create a custom DataSource. Most columns are still using bindings, so then we'd have to access the NSArrayController's array so we're sure we have the right object. create a custom DataSource, remove the NSArrayController and do all the Core Data stuff ourselves. Is there any 'right' way to solve this?

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• How do you filter a view of a DataTable in .Net 3.5 sp1 using WPF c# and xaml?

  - by Tony

  I found the MSDN example code for getting the default view of a collection and adding a filter to the view, but most of it is for .Net 4.0. I'm on a team that is not currently switching to 4.0, so I don't have that option. None of the examples I found used a DataTable as the source, so I had to adapt it a little. I'm using a DataTable because the data is comming from a DB ans it's easy to populate. After trying to implement the MSDN examples, I get a "NotSupportedException" when I try to set the Filter. This is the c# code I have: protected DataTable _data = new DataTable(); protected BindingListCollectionView _filteredDataView; ... private void On_Loaded(Object sender, RoutedEventArgs e) { _filteredDataView = (BindingListCollectionView)CollectionViewSource.GetDefaultView(_data); _filteredDataView.Filter = new Predicate(MatchesCurrentSelections); // throws NotSupportedException } ... public bool MatchesCurrentSelections(object o){...} It seems that either BindingListCollectionView does not support filtering in .Net 3.5, or it just doesn't work for a DataTable. I looked at setting it up in XAML instead of the C# code, but the XAML examples use collections in resources instead of a collection that is a memberof the class, so I have no idea how to set that up. Does any one know how to filter a view to a DataTable?

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• Conversion failed when converting the varchar value to int

  - by onedaywhen

  Microsoft SQL Server 2008 (SP1), getting an unexpected 'Conversion failed' error. Not quite sure how to describe this problem, so below is a simple example. The CTE extracts the numeric portion of certain IDs using a search condition to ensure a numeric portion actually exists. The CTE is then used to find the lowest unused sequence number (kind of): CREATE TABLE IDs (ID CHAR(3) NOT NULL UNIQUE); INSERT INTO IDs (ID) VALUES ('A01'), ('A02'), ('A04'), ('ERR'); WITH ValidIDs (ID, seq) AS ( SELECT ID, CAST(RIGHT(ID, 2) AS INTEGER) FROM IDs WHERE ID LIKE 'A[0-9][0-9]' ) SELECT MIN(V1.seq) + 1 AS next_seq FROM ValidIDs AS V1 WHERE NOT EXISTS ( SELECT * FROM ValidIDs AS V2 WHERE V2.seq = V1.seq + 1 ); The error is, 'Conversion failed when converting the varchar value 'RR' to data type int.' I can't understand why the value ID = 'ERR' should be being considered for conversion because the predicate ID LIKE 'A[0-9][0-9]' should have removed the invalid row from the resultset. When the base table is substituted with an equivalent CTE the problem goes away i.e. WITH IDs (ID) AS ( SELECT 'A01' UNION ALL SELECT 'A02' UNION ALL SELECT 'A04' UNION ALL SELECT 'ERR' ), ValidIDs (ID, seq) AS ( SELECT ID, CAST(RIGHT(ID, 2) AS INTEGER) FROM IDs WHERE ID LIKE 'A[0-9][0-9]' ) SELECT MIN(V1.seq) + 1 AS next_seq FROM ValidIDs AS V1 WHERE NOT EXISTS ( SELECT * FROM ValidIDs AS V2 WHERE V2.seq = V1.seq + 1 ); Why would a base table cause this error? Is this a known issue? UPDATE @sgmoore: no, doing the filtering in one CTE and the casting in another CTE still results in the same error e.g. WITH FilteredIDs (ID) AS ( SELECT ID FROM IDs WHERE ID LIKE 'A[0-9][0-9]' ), ValidIDs (ID, seq) AS ( SELECT ID, CAST(RIGHT(ID, 2) AS INTEGER) FROM FilteredIDs ) SELECT MIN(V1.seq) + 1 AS next_seq FROM ValidIDs AS V1 WHERE NOT EXISTS ( SELECT * FROM ValidIDs AS V2 WHERE V2.seq = V1.seq + 1 );

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• Total row count for pagination using JPA Criteria API

  - by ThinkFloyd

  I am implementing "Advanced Search" kind of functionality for an Entity in my system such that user can search that entity using multiple conditions(eq,ne,gt,lt,like etc) on attributes of this entity. I am using JPA's Criteria API to dynamically generate the Criteria query and then using setFirstResult() & setMaxResults() to support pagination. All was fine till this point but now I want to show total number of results on results grid but I did not see a straight forward way to get total count of Criteria query. This is how my code looks like: CriteriaBuilder builder = em.getCriteriaBuilder(); CriteriaQuery<Brand> cQuery = builder.createQuery(Brand.class); Root<Brand> from = cQuery.from(Brand.class); CriteriaQuery<Brand> select = cQuery.select(from); . . //Created many predicates and added to **Predicate[] pArray** . . select.where(pArray); // Added orderBy clause TypedQuery typedQuery = em.createQuery(select); typedQuery.setFirstResult(startIndex); typedQuery.setMaxResults(pageSize); List resultList = typedQuery.getResultList(); My result set could be big so I don't want to load my entities for count query, so tell me efficient way to get total count like rowCount() method on Criteria (I think its there in Hibernate's Criteria).

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• LINQ thinks I need an extra INNER JOIN, but why?

  - by Saurabh Kumar

  I have a LINQ query, which for some reason is generating an extra/duplicatre INNER JOIN. This is causing the query to not return the expected output. If I manually comment that extra JOIN from the generated SQL, then I get seemingly correct output. Can you detect what I might have done i nthis LINQ to have cuased this extra JOIN? Thanks. Here is my approx LINQ var ids = context.Code.Where(predicate); var rs = from r in ids group r by new { r.phonenumbers.person.PersonID} into g let matchcount=g.Select(p => p.phonenumbers.PhoneNum).Distinct().Count() where matchcount ==2 select new { personid = g.Key }; and here is the generated SQL (the duplicate join is [t7]) Declare @p1 VarChar(10)='Home' Declare @p2 VarChar(10)='111' Declare @p3 VarChar(10)='Office' Declare @p4 VarChar(10)='222' Declare @p5 int=2 SELECT [t9].[PersonID] AS [pid] FROM ( SELECT [t3].[PersonID], ( SELECT COUNT(*) FROM ( SELECT DISTINCT [t7].[PhoneValue] FROM [dbo].[Person] AS [t4] INNER JOIN [dbo].[PersonPhoneNumber] AS [t5] ON [t5].[PersonID] = [t4].[PersonID] INNER JOIN [dbo].[CodeMaster] AS [t6] ON [t6].[Code] = [t5].[PhoneType] INNER JOIN [dbo].[PersonPhoneNumber] AS [t7] ON [t7].[PersonID] = [t4].[PersonID] WHERE ([t3].[PersonID] = [t4].[PersonID]) AND ([t6].[Enumeration] = @p0) AND ((([t6].[CodeDescription] = @p1) AND ([t5].[PhoneValue] = @p2)) OR (([t6].[CodeDescription] = @p3) AND ([t5].[PhoneValue] = @p4))) ) AS [t8] ) AS [value] FROM ( SELECT [t0].[PersonID] FROM [dbo].[Person] AS [t0] INNER JOIN [dbo].[PersonPhoneNumber] AS [t1] ON [t1].[PersonID] = [t0].[PersonID] INNER JOIN [dbo].[CodeMaster] AS [t2] ON [t2].[Code] = [t1].[PhoneType] WHERE ([t2].[Enumeration] = @p0) AND ((([t2].[CodeDescription] = @p1) AND ([t1].[PhoneValue] = @p2)) OR (([t2].[CodeDescription] = @p3) AND ([t1].[PhoneValue] = @p4))) GROUP BY [t0].[PersonID] ) AS [t3] ) AS [t9] WHERE [t9].[value] = @p5

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• How do I create Variables in XSLT that are not document fragments?

  - by chiborg

  Consider the following XSLT template <xsl:template match="/"> <xsl:variable name="var1"> <elem>1</elem> <elem>2</elem> <elem>3</elem> </xsl:variable> <xsl:text>var1 has </xsl:text> <xsl:value-of select="count($var1)"/> <xsl:text>elements. </xsl:text> <xsl:variable name="var2" select="$var1/elem[. != '2']"/> <xsl:text>var2 has </xsl:text> <xsl:value-of select="count($var2)"/> <xsl:text>elements. </xsl:text> </xsl:template> The output of this template is var1 has 1 elements var2 has 2 elements The first line outputs 1 (and not, as I first expected 3) because var1 is a document fragment that contains the <elem> elements as childen. Now for my questions: How can I create a variable that does not contain a document fragment? I could do it like I did with var2, only leaving out the predicate. But maybe there is a way without using a second variable. Or, as an alternative: How can I preserve the document fragment in a variable while filtering out some elements?

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• How to check if something is stored in CoreData

  - by Terrel Gibson

  Hi I want to be able to tore some information in core data and but i am unsure of how to check if the file was saved properly. I tried using NSLog but it returns null when its called. I have a dictionary which has a uniqueID and a title which I want to save. I pass this in along with the context of the database. I then sort the database to check if it has any duplicates or not, if not then I add the file. +(VacationPhoto*) photoWithFlickrInfo: (NSDictionary*) flickrInfo inManagedObjectContext: (NSManagedObjectContext*) context{ //returns the dictionary NSLog(@"Photo To Store =%@", flickrInfo); VacationPhoto * photo = nil; NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"VacationPhoto"]; request.predicate = [NSPredicate predicateWithFormat:@"uniqueID = %@", [flickrInfo objectForKey:FLICKR_PHOTO_ID]]; NSSortDescriptor * descriptor = [NSSortDescriptor sortDescriptorWithKey:@"title" ascending:YES]; request.sortDescriptors = [NSArray arrayWithObject:descriptor]; NSError *error = nil; NSArray *matches = [context executeFetchRequest:request error:&error]; if (!matches || [matches count] > 1) { // handle error } else if ( [matches count] == 0){ photo.title = [flickrInfo objectForKey:FLICKR_PHOTO_TITLE]; //Returns NULL when called NSLog(@"title = %@", photo.title); photo.uniqueID = [flickrInfo objectForKey:FLICKR_PHOTO_ID]; //Returns NULL when called NSLog(@"ID = %@", photo.uniqueID); } else { //If photo already exists this is called photo = [matches lastObject]; } return photo; }

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• Best way to create a SPARQL endpoint for a RDBMS (MySQL database)

  - by Ankur

  I am doing (want to do) some experiments with Linked Open Datasets particularly those put out by governments. I have a RDBMS (more specifically MySQL). I designed it with semantic web ideas in mind i.e. I have a information stored as objects, predicates and classes which define objects. In turn all objects are related to each other though statements of the form subject -- predicate -- object (where the subjects are from the objects table). I want to be able to query other RDF triple stores from my application and let other triple stores query my data. Is it possible to "set something up" so that this is possible? I have looked at Jena. Using Jena seems to mean I have to it as a storage application rather than MySQL - the only problem with this is that I include a new concept called a category (which I don't think is part of the semantic web languages). I will use categories to help with displaying information (they don't have any other meaning) but using Jena seems to mean that I can't organise predicates under categories for more convenient viewing. I am using Java so a JAVA API is preferred. It's also possible I misunderstood the purpose of Jena, and maybe that can be of use, but I am not sure how. I am sure four days from now this question will seem rather silly, but at the moment I am somewhat confused about how to proceed.

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