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  • Sed: regular expression match lines without <!--

    - by sixtyfootersdude
    I have a sed command to comment out xml commands sed 's/^\([ \t]*\)\(.*[0-9a-zA-Z<].*\)$/\1<!-- Security: \2 -->/' web.xml Takes: <a> <!-- Comment --> <b> bla </b> </a> Produces: <!-- Security: <a> --> <!-- Security: <!-- Comment --> --> // NOTE: there are two end comments. <!-- Security: <b> --> <!-- Security: bla --> <!-- Security: </b> --> <!-- Security: </a> --> Ideally I would like to not use my sed script to comment things that are already commented. Ie: <!-- Security: <a> --> <!-- Comment --> <!-- Security: <b> --> <!-- Security: bla --> <!-- Security: </b> --> <!-- Security: </a> --> I could do something like this: sed 's/^\([ \t]*\)\(.*[0-9a-zA-Z<].*\)$/\1<!-- Security: \2 -->/' web.xml sed 's/^[ \t]*<!-- Security: \(<!--.*-->\) -->/\1/' web.xml but I think a one liner is cleaner (?) This is pretty similar: http://stackoverflow.com/questions/436850/matching-a-line-that-doesnt-contain-specific-text-with-regular-expressions

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  • How can I improve this regular expression?

    - by Michael Haren
    I want a regular expression to match valid input into a Tags input field with the following properties: 1-5 tags Each tag is 1-30 characters long Valid tag characters are [a-zA-Z0-9-] input and tags can be separated by any amount of whitespace Here's what I have so far--it seems to work but I'm interested how it could be simplified or if it has any major flaws: \s*[a-zA-Z0-9-]{1,30}(\s+[a-zA-Z0-9-]{1,30}){0,4}\s* // that is: \s* // match all beginning whitespace [a-zA-Z0-9-]{1,30} // match the first tag (\s+[a-zA-Z0-9-]{1,30}){0,4} // match all subsequent tags \s* // match all ending whitespace Preprocessing the input to make the whitespace issue easier isn't an option (e.g. trimming or adding a space). If it matters, this will be used in javascript. Any suggestions would be appreciated, thanks!

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  • Determine an object's class returned by a factory method (Error: function does not take 1 arguments

    - by tzippy
    I have a factorymethod that either returns an object of baseclass or one that is of derivedclass (a derived class of baseclass). The derived class has a method virtual void foo(int x) that takes one argument. baseclass however has virtual void foo() without an argument. In my code, a factory method returns a pointer of type bar that definetly points to an object of class derivedclass. However since this is only known at runtime I get a compiler error saying that foo() does not take an argument. Can I cast this pointer to a pointer of type derivedclass? std::auto_ptr<baseclass> bar = classfactory::CreateBar(); //returns object of class derivedclass bar->foo(5); class baseclass { public: virtual void foo(); } class derivedclass : public baseclass { public: virtual void foo(int x); }

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  • How to match a variable list of items separated by commas

    - by user261915
    I want to turn something like this CS 240, CS 246, ECE 222, ... (more or less); Software Engineering students only into ('CS 240', 'CS 246', 'ECE 222', 'ECE 220') in Python, code that matches a single course looks like >>> re.search('([A-Z]{2,5} \d{3})', 'SE 112').groups() ('SE 112',) I prefer a regular expression only method because I have a bunch of other alternate reg exps using '|' to combine them. However, a method with split is acceptable.

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  • Generic factory of generic containers

    - by Feuermurmel
    I have a generic abstract class Factory<T> with a method createBoxedInstance() which returns instances of T created by implementations of createInstance() wrapped in the generic container Box<T>. abstract class Factory<T> { abstract T createInstance(); public final Box<T> createBoxedInstance() { return new Box<T>(createInstance()); } public final class Box<T> { public final T content; public Box(T content) { this.content = content; } } } At some points I need a container of type Box<S> where S is an ancestor of T. Is it possible to make createBoxedInstance() itself generic so that it will return instances of Box<S> where S is chosen by the caller? Sadly, defining the function as follows does not work as a type parameter cannot be declared using the super keyword, only used. public final <S super T> Box<S> createBoxedInstance() { return new Box<S>(createInstance()); } The only alternative I see, is to make all places that need an instance of Box<S> accept Box<? extends S> which makes the container's content member assignable to S. Is there some way around this without re-boxing the instances of T into containers of type Box<S>? (I know I could just cast the Box<T> to a Box<S> but I would feel very, very guilty.)

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  • How to prevent regex from stopping at the first match of alternatives ?

    - by miket2e
    If I have the string hello world , how can I modify the regex world|wo|w so that it will match all of "world", "wo" and "w" rather than just the single first match of "world" that it comes to ? If this is not possible directly, is there a good workaround ? I'm using C# if it makes a difference: Regex testRegex = new Regex("world|wo|w"); MatchCollection theMatches = testRegex.Matches("hello world"); foreach (Match thisMatch in theMatches) { ... }

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  • How can I detect common substrings in a list of strings

    - by danio
    Given a set of strings, for example: EFgreen EFgrey EntireS1 EntireS2 J27RedP1 J27GreenP1 J27RedP2 J27GreenP2 JournalP1Black JournalP1Blue JournalP1Green JournalP1Red JournalP2Black JournalP2Blue JournalP2Green I want to be able to detect that these are three sets of files: EntireS[1,2] J27[Red,Green]P[1,2] JournalP[1,2][Red,Green,Blue] Are there any known ways of approaching this problem - any published papers I can read on this? The approach I am considering is for each string look at all other strings and find the common characters and where differing characters are, trying to find sets of strings that have the most in common, but I fear that this is not very efficient and may give false positives. Note that this is not the same as 'How do I detect groups of common strings in filenames' because that assumes that a string will always have a series of digits following it. [Edited 15/09/09 to add more sample strings]

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  • stop and split generated sequence at repeats - clojure

    - by fitzsnaggle
    I am trying to make a sequence that will only generate values until it finds the following conditions and return the listed results: case head = 0 - return {:origin [all generated except 0] :pattern 0} 1 - return {:origin nil :pattern [all-generated-values] } repeated-value - {:origin [values-before-repeat] :pattern [values-after-repeat] { ; n = int ; x = int ; hist - all generated values ; Keeps the head below x (defn trim-head [head x] (loop [head head] (if (> head x) (recur (- head x)) head))) ; Generates the next head (defn next-head [head x n] (trim-head (* head n) x)) (defn row [x n] (iterate #(next-head % x n) n)) ; Generates a whole row - ; Rows are a max of x - 1. (take (- x 1) (row 11 3)) Examples of cases to stop before reaching end of row: [9 8 4 5 6 7 4] - '4' is repeated so STOP. Return preceding as origin and rest as pattern. {:origin [9 8] :pattern [4 5 6 7]} [4 5 6 1] - found a '1' so STOP, so return everything as pattern {:origin nil :pattern [4 5 6 1]} [3 0] - found a '0' so STOP {:origin [3] :pattern [0]} :else if the sequences reaches a length of x - 1: {:origin [all values generated] :pattern nil} The Problem I have used partition-by with some success to split the groups at the point where a repeated value is found, but would like to do this lazily. Is there some way I can use take-while, or condp, or the :while clause of the for loop to make a condition that partitions when it finds repeats? Some Attempts (take 2 (partition-by #(= 1 %) (row 11 4))) (for [p (partition-by #(stop-match? %) head) (iterate #(next-head % x n) n) :while (or (not= (last p) (or 1 0 n) (nil? (rest p))] {:origin (first p) :pattern (concat (second p) (last p))})) # Updates What I really want to be able to do is find out if a value has repeated and partition the seq without using the index. Is that possible? Something like this - { (defn row [x n] (loop [hist [n] head (gen-next-head (first hist) x n) steps 1] (if (>= (- x 1) steps) (case head 0 {:origin [hist] :pattern [0]} 1 {:origin nil :pattern (conj hist head)} ; Speculative from here on out (let [p (partition-by #(apply distinct? %) (conj hist head))] (if-not (nil? (next p)) ; One partition if no repeats. {:origin (first p) :pattern (concat (second p) (nth 3 p))} (recur (conj hist head) (gen-next-head head x n) (inc steps))))) {:origin hist :pattern nil}))) }

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  • How to get the users set of date format pattern strings? (3 replies)

    I would like to get the current user's set of date format pattern strings as listed in the Control Panel regional settings applet. For my UK English system I see the following patterns listed: Short Date: dd/MM/yyyy dd/MM/yy d/M/yy d.M.yy yyyy MM dd Long Date: dd MMMM yyyy d MMMM yyyy If I use GetDateTimeFormats (d and D) the results match the expected patterns above, but of course they're the for...

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  • How to get the users set of date format pattern strings? (3 replies)

    I would like to get the current user's set of date format pattern strings as listed in the Control Panel regional settings applet. For my UK English system I see the following patterns listed: Short Date: dd/MM/yyyy dd/MM/yy d/M/yy d.M.yy yyyy MM dd Long Date: dd MMMM yyyy d MMMM yyyy If I use GetDateTimeFormats (d and D) the results match the expected patterns above, but of course they're the for...

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  • Is this a pattern? Should it be?

    - by Arkadiy
    The following is more of a statement than a question - it describes something that may be a pattern. The question is: is this a known pattern? Or, if it's not, should it be? I've had a situation where I had to iterate over two dissimilar multi-layer data structures and copy information from one to the other. Depending on particular use case, I had around eight different kinds of layers, combined in about eight different combinations: A-B-C B-C A-C D-E A-D-E and so on After a few unsuccessful attempts to factor out the repetition of per-layer iteration code, I realized that the key difficulty in this refactoring was the fact that the bottom level needed access to data gathered at higher levels. To explicitly accommodate this requirement, I introduced IterationContext class with a number of get() and set() methods for accumulating the necessary information. In the end, I had the following class structure: class Iterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const = 0; }; class RecursingIterator : public Iterator { RecursingIterator(const Iterator &below); }; class IterateOverA : public RecursingIterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const { // Iterate over members in dataStructure1 // locate corresponding item in dataStructure2 (passed via context) // and set it in the context // invoke the sub-iterator }; class IterateOverB : public RecursingIterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const { // iterate over members dataStructure2 (form context) // set dataStructure2's item in the context // locate corresponding item in dataStructure2 (passed via context) // invoke the sub-iterator }; void main() { class FinalCopy : public Iterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const { // copy data from structure 1 to structure 2 in the context, // using some data from higher levels as needed } } IterationContext ctx(dateStructure2); IterateOverA(IterateOverB(FinalCopy())).iterate(dataStructure1, ctx); } It so happens that dataStructure1 is a uniform data structure, similar to XML DOM in that respect, while dataStructure2 is a legacy data structure made of various structs and arrays. This allows me to pass dataStructure1 outside of the context for convenience. In general, either side of the iteration or both sides may be passed via context, as convenient. The key situation points are: complicated code that needs to be invoked in "layers", with multiple combinations of layer types possible at the bottom layer, the information from top layers needs to be visible. The key implementation points are: use of context class to access the data from all levels of iteration complicated iteration code encapsulated in implementation of pure virtual function two interfaces - one aware of underlying iterator, one not aware of it. use of const & to simplify the usage syntax.

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  • What's the difference between these design pattern books? [on hold]

    - by BSara
    I'm currently looking for a good reference/guide for design patterns and in my search I've found the following three books highly recommended: Design Patterns: Elements of Reusable Object-Oriented Software Pattern Hatching: Design Patterns Applied Design Patterns Explained: A New Perspective on Object-Oriented Design I can't decide which book (if any) to purchase. So, my question is this: What are the fundamental differences between these books?

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  • Is this a valid implementation of the repository pattern?

    - by user1578653
    I've been reading up about the repository pattern, with a view to implementing it in my own application. Almost all examples I've found on the internet use some kind of existing framework rather than showing how to implement it 'from scratch'. Here's my first thoughts of how I might implement it - I was wondering if anyone could advise me on whether this is correct? I have two tables, named CONTAINERS and BITS. Each CONTAINER can contain any number of BITs. I represent them as two classes: class Container{ private $bits; private $id; //...and a property for each column in the table... public function __construct(){ $this->bits = array(); } public function addBit($bit){ $this->bits[] = $bit; } //...getters and setters... } class Bit{ //some properties, methods etc... } Each class will have a property for each column in its respective table. I then have a couple of 'repositories' which handle things to do with saving/retrieving these objects from the database: //repository to control saving/retrieving Containers from the database class ContainerRepository{ //inject the bit repository for use later public function __construct($bitRepo){ $this->bitRepo = $bitRepo; } public function getById($id){ //talk directly to Oracle here to all column data into the object //get all the bits in the container $bits = $this->bitRepo->getByContainerId($id); foreach($bits as $bit){ $container->addBit($bit); } //return an instance of Container } public function persist($container){ //talk directly to Oracle here to save it to the database //if its ID is NULL, create a new container in database, otherwise update the existing one //use BitRepository to save each of the Bits inside the Container $bitRepo = $this->bitRepo; foreach($container->bits as $bit){ $bitRepo->persist($bit); } } } //repository to control saving/retrieving Bits from the database class BitRepository{ public function getById($id){} public function getByContainerId($containerId){} public function persist($bit){} } Therefore, the code I would use to get an instance of Container from the database would be: $bitRepo = new BitRepository(); $containerRepo = new ContainerRepository($bitRepo); $container = $containerRepo->getById($id); Or to create a new one and save to the database: $bitRepo = new BitRepository(); $containerRepo = new ContainerRepository($bitRepo); $container = new Container(); $container->setSomeProperty(1); $bit = new Bit(); $container->addBit($bit); $containerRepo->persist($container); Can someone advise me as to whether I have implemented this pattern correctly? Thanks!

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  • How you would you describe the Observer pattern in beginner language?

    - by Sheldon
    Currently, my level of understanding is below all the coding examples on the web about the Observer Pattern. I understand it simply as being almost a subscription that updates all other events when a change is made that the delegate registers. However, I'm very unstable in my true comprehension of the benefits and uses. I've done some googling, but most are above my level of understanding. I'm trying to implement this pattern with my current homework assignment, and to truly make sense on my project need a better understanding of the pattern itself and perhaps an example to see what its use. I don't want to force this pattern into something just to submit, I need to understand the purpose and develop my methods accordingly so that it actually serves a good purpose. My text doesn't really go into it, just mentions it in one sentence. MSDN was hard for me to understand, as I'm a beginner on this, and it seems more of an advanced topic. How would you describe this Observer pattern and its uses in C# to a beginner? For an example, please keep code very simple so I can understand the purpose more than complex code snippets. I'm trying to use it effectively with some simple textbox string manipulations and using delegates for my assignment, so a pointer would help!

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  • How to define a varying length of the string in XSD pattern?

    - by infant programmer
    The input XML tag must be validated for a pattern which is like this: type : positive int / decimal, minimum length is 0, max length is 12(before decimal point), fraction digits are optional if exist then precision must be 2. This means both positive integer and Decimal numbers(2 digit precision) are allowed. so the acceptable values can be like, null, 0, 0.00, 1234567890, 123456789012, 123456789012.12, invalid values are: 0.000, 1234567890123(13 digits - invalid), The pattern I have designed is: <xs:pattern value="|([0-9]){12}|([0-9]){12}[.][0-9][0-9]"/> The problem with this pattern is, it doesn't allow the number with string-length less than 12, it says "1234567890" is an invalid value, where as it must be allowed!

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  • Service Layer Pattern - Could we avoid the service layer on a specific case?

    - by lidermin
    Hi, we are trying to implement an application using the Service Layer Pattern cause our application needs to connect to other multiple applications too, and googling on the web, we found this link of a demonstrative graphic for the "right" way of apply the pattern: martinfowler.com - Service Layer Pattern But now we have a question: what if our system needs to implement some business logic, only for our application (like some maintenance data for the system itself) that we don't need to share with other systems. Based on this graphic: As it seems, it will be unnecesary to implement a service layer just for that; it will be more practical to avoid the service layer, and just go from User Interface to the Business Layer (for example). What should be the right way in this case to implement the Service Layer Pattern? What do you suggest us for a scenario like the one I told you? Thanks in advance.

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  • Is this physical collection class that contains only static methods an Anti-Pattern?

    - by Tj Kellie
    I'm trying to figure out if I should continue on with a current pattern in an application I'm working in, or refactor this into something else. I have a set of collection classes off a generic base of List. These classes have public constructors but contain only static methods that return collections. They look like this: public class UserObjCollection : BaseCollection<UserObj> { public static UserObjCollection GetAllUserObj() { UserObjCollection obj = new UserObjCollection(); obj.MapObjects(new UserObjDataService().GetAllUserObj()); return obj; } } Is this a Pattern or Anti-Pattern and what are the merits of this over a straight factory pattern?

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  • Understanding Service Compensation part of Industrial SOA series

    - by JuergenKress
    Some of the most important SOA design patterns that we have successfully applied in projects will be described in this article. These include the Compensation pattern and the UI mediator pattern, the Common Data Format pattern and the Data Access pattern. All of these patterns are included in Thomas Erl's book, "SOA Design Patterns", and are presented here in detail, together with our practical experiences. We begin our "best of" SOA pattern collection with the Compensation pattern. Compensation is required in error situations in an SOA, as multiple atomic service operations cannot generally be linked with classic transactions this would violate the principle of loose coupling. An error situation of this sort will occur, particularly if service operations are combined into processes or new services during orchestration or by applying the Composite pattern, and the transaction bracket has to be expanded as a result. We need mechanisms to undo the effects of individual services (the status changes in the overall system) and to ensure that a consistent system state is maintained at all times, so as to preserve system integrity. For the Compensation pattern, we would like to address the following questions: Why is compensation important in relation to SOA? How is the topic of compensation linked with the topic of transactions? What are the challenges with regard to compensation... Read the full article in the Service Technology Magazine or at OTN. Share your comments and feedback on the Industrial SOA series by using the hashtag #industrialsoa. Missed an article of the Industrial SOA series visit the overview at OTN. SOA & BPM Partner Community For regular information on Oracle SOA Suite become a member in the SOA & BPM Partner Community for registration please visit www.oracle.com/goto/emea/soa (OPN account required) If you need support with your account please contact the Oracle Partner Business Center. Blog Twitter LinkedIn Facebook Wiki Mix Forum Technorati Tags: Industrial SOA,SOA,SOA Service Compensation,Community,Oracle SOA,Oracle BPM,OPN,Jürgen Kress

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  • How to compile a C++ source code written for Linux/Unix on Windows Vista (code given)

    - by HTMZ
    I have a c++ source code that was written in linux/unix environment by some other author. It gives me errors when i compile it in windows vista environment. I am using Bloodshed Dev C++ v 4.9. please help. #include <iostream.h> #include <map> #include <vector> #include <string> #include <string.h> #include <strstream> #include <unistd.h> #include <stdlib.h> using namespace std; template <class T> class PrefixSpan { private: vector < vector <T> > transaction; vector < pair <T, unsigned int> > pattern; unsigned int minsup; unsigned int minpat; unsigned int maxpat; bool all; bool where; string delimiter; bool verbose; ostream *os; void report (vector <pair <unsigned int, int> > &projected) { if (minpat > pattern.size()) return; // print where & pattern if (where) { *os << "<pattern>" << endl; // what: if (all) { *os << "<freq>" << pattern[pattern.size()-1].second << "</freq>" << endl; *os << "<what>"; for (unsigned int i = 0; i < pattern.size(); i++) *os << (i ? " " : "") << pattern[i].first; } else { *os << "<what>"; for (unsigned int i = 0; i < pattern.size(); i++) *os << (i ? " " : "") << pattern[i].first << delimiter << pattern[i].second; } *os << "</what>" << endl; // where *os << "<where>"; for (unsigned int i = 0; i < projected.size(); i++) *os << (i ? " " : "") << projected[i].first; *os << "</where>" << endl; *os << "</pattern>" << endl; } else { // print found pattern only if (all) { *os << pattern[pattern.size()-1].second; for (unsigned int i = 0; i < pattern.size(); i++) *os << " " << pattern[i].first; } else { for (unsigned int i = 0; i < pattern.size(); i++) *os << (i ? " " : "") << pattern[i].first << delimiter << pattern[i].second; } *os << endl; } } void project (vector <pair <unsigned int, int> > &projected) { if (all) report(projected); map <T, vector <pair <unsigned int, int> > > counter; for (unsigned int i = 0; i < projected.size(); i++) { int pos = projected[i].second; unsigned int id = projected[i].first; unsigned int size = transaction[id].size(); map <T, int> tmp; for (unsigned int j = pos + 1; j < size; j++) { T item = transaction[id][j]; if (tmp.find (item) == tmp.end()) tmp[item] = j ; } for (map <T, int>::iterator k = tmp.begin(); k != tmp.end(); ++k) counter[k->first].push_back (make_pair <unsigned int, int> (id, k->second)); } for (map <T, vector <pair <unsigned int, int> > >::iterator l = counter.begin (); l != counter.end (); ) { if (l->second.size() < minsup) { map <T, vector <pair <unsigned int, int> > >::iterator tmp = l; tmp = l; ++tmp; counter.erase (l); l = tmp; } else { ++l; } } if (! all && counter.size () == 0) { report (projected); return; } for (map <T, vector <pair <unsigned int, int> > >::iterator l = counter.begin (); l != counter.end(); ++l) { if (pattern.size () < maxpat) { pattern.push_back (make_pair <T, unsigned int> (l->first, l->second.size())); project (l->second); pattern.erase (pattern.end()); } } } public: PrefixSpan (unsigned int _minsup = 1, unsigned int _minpat = 1, unsigned int _maxpat = 0xffffffff, bool _all = false, bool _where = false, string _delimiter = "/", bool _verbose = false): minsup(_minsup), minpat (_minpat), maxpat (_maxpat), all(_all), where(_where), delimiter (_delimiter), verbose (_verbose) {}; ~PrefixSpan () {}; istream& read (istream &is) { string line; vector <T> tmp; T item; while (getline (is, line)) { tmp.clear (); istrstream istrs ((char *)line.c_str()); while (istrs >> item) tmp.push_back (item); transaction.push_back (tmp); } return is; } ostream& run (ostream &_os) { os = &_os; if (verbose) *os << transaction.size() << endl; vector <pair <unsigned int, int> > root; for (unsigned int i = 0; i < transaction.size(); i++) root.push_back (make_pair (i, -1)); project (root); return *os; } void clear () { transaction.clear (); pattern.clear (); } }; int main (int argc, char **argv) { extern char *optarg; unsigned int minsup = 1; unsigned int minpat = 1; unsigned int maxpat = 0xffffffff; bool all = false; bool where = false; string delimiter = "/"; bool verbose = false; string type = "string"; int opt; while ((opt = getopt(argc, argv, "awvt:M:m:L:d:")) != -1) { switch(opt) { case 'a': all = true; break; case 'w': where = true; break; case 'v': verbose = true; break; case 'm': minsup = atoi (optarg); break; case 'M': minpat = atoi (optarg); break; case 'L': maxpat = atoi (optarg); break; case 't': type = string (optarg); break; case 'd': delimiter = string (optarg); break; default: cout << "Usage: " << argv[0] << " [-m minsup] [-M minpat] [-L maxpat] [-a] [-w] [-v] [-t type] [-d delimiter] < data .." << endl; return -1; } } if (type == "int") { PrefixSpan<unsigned int> prefixspan (minsup, minpat, maxpat, all, where, delimiter, verbose); prefixspan.read (cin); prefixspan.run (cout); }else if (type == "short") { PrefixSpan<unsigned short> prefixspan (minsup, minpat, maxpat, all, where, delimiter, verbose); prefixspan.read (cin); prefixspan.run (cout); } else if (type == "char") { PrefixSpan<unsigned char> prefixspan (minsup, minpat, maxpat, all, where, delimiter, verbose); prefixspan.read (cin); prefixspan.run (cout); } else if (type == "string") { PrefixSpan<string> prefixspan (minsup, minpat, maxpat, all, where, delimiter, verbose); prefixspan.read (cin); prefixspan.run (cout); } else { cerr << "Unknown Item Type: " << type << " : choose from [string|int|short|char]" << endl; return -1; } return 0; }

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  • Azure &ndash; Part 5 &ndash; Repository Pattern for Table Service

    - by Shaun
    In my last post I created a very simple WCF service with the user registration functionality. I created an entity for the user data and a DataContext class which provides some methods for operating the entities such as add, delete, etc. And in the service method I utilized it to add a new entity into the table service. But I didn’t have any validation before registering which is not acceptable in a real project. So in this post I would firstly add some validation before perform the data creation code and show how to use the LINQ for the table service.   LINQ to Table Service Since the table service utilizes ADO.NET Data Service to expose the data and the managed library of ADO.NET Data Service supports LINQ we can use it to deal with the data of the table service. Let me explain with my current example: I would like to ensure that when register a new user the email address should be unique. So I need to check the account entities in the table service before add. If you remembered, in my last post I mentioned that there’s a method in the TableServiceContext class – CreateQuery, which will create a IQueryable instance from a given type of entity. So here I would create a method under my AccountDataContext class to return the IQueryable<Account> which named Load. 1: public class AccountDataContext : TableServiceContext 2: { 3: private CloudStorageAccount _storageAccount; 4:  5: public AccountDataContext(CloudStorageAccount storageAccount) 6: : base(storageAccount.TableEndpoint.AbsoluteUri, storageAccount.Credentials) 7: { 8: _storageAccount = storageAccount; 9:  10: var tableStorage = new CloudTableClient(_storageAccount.TableEndpoint.AbsoluteUri, 11: _storageAccount.Credentials); 12: tableStorage.CreateTableIfNotExist("Account"); 13: } 14:  15: public void Add(Account accountToAdd) 16: { 17: AddObject("Account", accountToAdd); 18: SaveChanges(); 19: } 20:  21: public IQueryable<Account> Load() 22: { 23: return CreateQuery<Account>("Account"); 24: } 25: } The method returns the IQueryable<Account> so that I can perform the LINQ operation on it. And back to my service class, I will use it to implement my validation. 1: public bool Register(string email, string password) 2: { 3: var storageAccount = CloudStorageAccount.FromConfigurationSetting("DataConnectionString"); 4: var accountToAdd = new Account(email, password) { DateCreated = DateTime.Now }; 5: var accountContext = new AccountDataContext(storageAccount); 6:  7: // validation 8: var accountNumber = accountContext.Load() 9: .Where(a => a.Email == accountToAdd.Email) 10: .Count(); 11: if (accountNumber > 0) 12: { 13: throw new ApplicationException(string.Format("Your account {0} had been used.", accountToAdd.Email)); 14: } 15:  16: // create entity 17: try 18: { 19: accountContext.Add(accountToAdd); 20: return true; 21: } 22: catch (Exception ex) 23: { 24: Trace.TraceInformation(ex.ToString()); 25: } 26: return false; 27: } I used the Load method to retrieve the IQueryable<Account> and use Where method to find the accounts those email address are the same as the one is being registered. If it has I through an exception back to the client side. Let’s run it and test from my simple client application. Oops! Looks like we encountered an unexpected exception. It said the “Count” is not support by the ADO.NET Data Service LINQ managed library. That is because the table storage managed library (aka. TableServiceContext) is based on the ADO.NET Data Service and it supports very limit LINQ operation. Although I didn’t find a full list or documentation about which LINQ methods it supports I could even refer a page on msdn here. It gives us a roughly summary of which query operation the ADO.NET Data Service managed library supports and which doesn't. As you see the Count method is not in the supported list. Not only the query operation, there inner lambda expression in the Where method are limited when using the ADO.NET Data Service managed library as well. For example if you added (a => !a.DateDeleted.HasValue) in the Where method to exclude those deleted account it will raised an exception said "Invalid Input". Based on my experience you should always use the simple comparison (such as ==, >, <=, etc.) on the simple members (such as string, integer, etc.) and do not use any shortcut methods (such as string.Compare, string.IsNullOrEmpty etc.). 1: // validation 2: var accountNumber = accountContext.Load() 3: .Where(a => a.Email == accountToAdd.Email) 4: .ToList() 5: .Count; 6: if (accountNumber > 0) 7: { 8: throw new ApplicationException(string.Format("Your account {0} had been used.", accountToAdd.Email)); 9: } We changed the a bit and try again. Since I had created an account with my mail address so this time it gave me an exception said that the email had been used, which is correct.   Repository Pattern for Table Service The AccountDataContext takes the responsibility to save and load the account entity but only for that specific entity. Is that possible to have a dynamic or generic DataContext class which can operate any kinds of entity in my system? Of course yes. Although there's no typical database in table service we can threat the entities as the records, similar with the data entities if we used OR Mapping. As we can use some patterns for ORM architecture here we should be able to adopt the one of them - Repository Pattern in this example. We know that the base class - TableServiceContext provide 4 methods for operating the table entities which are CreateQuery, AddObject, UpdateObject and DeleteObject. And we can create a relationship between the enmity class, the table container name and entity set name. So it's really simple to have a generic base class for any kinds of entities. Let's rename the AccountDataContext to DynamicDataContext and make the type of Account as a type parameter if it. 1: public class DynamicDataContext<T> : TableServiceContext where T : TableServiceEntity 2: { 3: private CloudStorageAccount _storageAccount; 4: private string _entitySetName; 5:  6: public DynamicDataContext(CloudStorageAccount storageAccount) 7: : base(storageAccount.TableEndpoint.AbsoluteUri, storageAccount.Credentials) 8: { 9: _storageAccount = storageAccount; 10: _entitySetName = typeof(T).Name; 11:  12: var tableStorage = new CloudTableClient(_storageAccount.TableEndpoint.AbsoluteUri, 13: _storageAccount.Credentials); 14: tableStorage.CreateTableIfNotExist(_entitySetName); 15: } 16:  17: public void Add(T entityToAdd) 18: { 19: AddObject(_entitySetName, entityToAdd); 20: SaveChanges(); 21: } 22:  23: public void Update(T entityToUpdate) 24: { 25: UpdateObject(entityToUpdate); 26: SaveChanges(); 27: } 28:  29: public void Delete(T entityToDelete) 30: { 31: DeleteObject(entityToDelete); 32: SaveChanges(); 33: } 34:  35: public IQueryable<T> Load() 36: { 37: return CreateQuery<T>(_entitySetName); 38: } 39: } I saved the name of the entity type when constructed for performance matter. The table name, entity set name would be the same as the name of the entity class. The Load method returned a generic IQueryable instance which supports the lazy load feature. Then in my service class I changed the AccountDataContext to DynamicDataContext and that's all. 1: var accountContext = new DynamicDataContext<Account>(storageAccount); Run it again and register another account. The DynamicDataContext now can be used for any entities. For example, I would like the account has a list of notes which contains 3 custom properties: Account Email, Title and Content. We create the note entity class. 1: public class Note : TableServiceEntity 2: { 3: public string AccountEmail { get; set; } 4: public string Title { get; set; } 5: public string Content { get; set; } 6: public DateTime DateCreated { get; set; } 7: public DateTime? DateDeleted { get; set; } 8:  9: public Note() 10: : base() 11: { 12: } 13:  14: public Note(string email) 15: : base(email, string.Format("{0}_{1}", email, Guid.NewGuid().ToString())) 16: { 17: AccountEmail = email; 18: } 19: } And no need to tweak the DynamicDataContext we can directly go to the service class to implement the logic. Notice here I utilized two DynamicDataContext instances with the different type parameters: Note and Account. 1: public class NoteService : INoteService 2: { 3: public void Create(string email, string title, string content) 4: { 5: var storageAccount = CloudStorageAccount.FromConfigurationSetting("DataConnectionString"); 6: var accountContext = new DynamicDataContext<Account>(storageAccount); 7: var noteContext = new DynamicDataContext<Note>(storageAccount); 8:  9: // validate - email must be existed 10: var accounts = accountContext.Load() 11: .Where(a => a.Email == email) 12: .ToList() 13: .Count; 14: if (accounts <= 0) 15: throw new ApplicationException(string.Format("The account {0} does not exsit in the system please register and try again.", email)); 16:  17: // save the note 18: var noteToAdd = new Note(email) { Title = title, Content = content, DateCreated = DateTime.Now }; 19: noteContext.Add(noteToAdd); 20: } 21: } And updated our client application to test the service. I didn't implement any list service to show all notes but we can have a look on the local SQL database if we ran it at local development fabric.   Summary In this post I explained a bit about the limited LINQ support for the table service. And then I demonstrated about how to use the repository pattern in the table service data access layer and make the DataContext dynamically. The DynamicDataContext I created in this post is just a prototype. In fact we should create the relevant interface to make it testable and for better structure we'd better separate the DataContext classes for each individual kind of entity. So it should have IDataContextBase<T>, DataContextBase<T> and for each entity we would have class AccountDataContext<Account> : IDataContextBase<Account>, DataContextBase<Account> { … } class NoteDataContext<Note> : IDataContextBase<Note>, DataContextBase<Note> { … }   Besides the structured data saving and loading, another common scenario would be saving and loading some binary data such as images, files. In my next post I will show how to use the Blob Service to store the bindery data - make the account be able to upload their logo in my example.   Hope this helps, Shaun   All documents and related graphics, codes are provided "AS IS" without warranty of any kind. Copyright © Shaun Ziyan Xu. This work is licensed under the Creative Commons License.

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