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• Data architecture for event log metrics?

  - by elliot42

  My service has a large ongoing number of user events, and we would like to do things like "count occurrence of event type T since date D." We are trying to make two basic decisions: What to store? Storing every event vs. only storing aggregates (Event log style) log every event and count them later, vs. (Time-series style) store a single aggregated "count of event E for date D" for every day Where to store the data In a relational database (particularly MySQL) In a non-relational (NoSQL) database In flat log files (collected centrally over the network via syslog-ng) What is standard practice / where can I read more about comparing the different types of systems? Additional details: The total event stream is large, potentially hundreds of thousands of entries per day But our current need is only to count certain types of events within it We don't necessarily need real-time access to the raw data or aggregation results IMHO, "log all events to files, crawl them at a later time to filter and aggregate the stream" is a pretty standard UNIX Way, but my Rails-y compatriots seem to think that nothing is real unless it's in MySQL.

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• DDD: service contains two repository

  - by tikhop

  Does it correct way to have two repository inside one service and will it be an application or domain service? Suppose I have a Passenger object that should contains Passport (government id) object. I am getting Passenger from PassengerRepository. PassengerRepository create request to server and obtain data (json) than parse received data and store inside repository. I have confused because I want to store Passport as Entity and put it to PassportRepository but all information about password contains inside json than i received above. I guess that I should create a PassengerService that will be include PassengerRepository and PassportRepository with several methods like removePassport, addPassport, getAllPassenger and etc. UPDATE: So I guess that the better way is represent Passport as VO and store all passports inside Passenger aggregate. However there is another question: Where I should put the methods (methods calls server api) for management passenger's passport. I think the better place is so within Passenger aggregate.

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• What soft can create deb repository with several versions of the same package?

  - by bessarabov

  I want to create my own deb repository to store some packages. I've tried reprepro and it works fine, except one but fundamental feature. Reprepro can't store several versions of the same package in the repository. But the ability to store several versions of the same package is essential to me, so I'm asking what soft can do such a thing. Here is a piece of reprepro FAQ that shows that it can't do it: 3.1) Can I have two versions of a package in the same distribution? ------------------------------------------------------------------- Sorry, this is not possible right now, as reprepro heavily optimizes at only having one version of a package in a suite-type-component-architecture quadruple. You can have different versions in different architectures and/or components within the same suite. (Even different versions of a architecture all package in different architectures of the same suite). But within the same architecture and the same component of a distribution it is not possible.

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• Nested Routes and Parameters for Rails URLs (Best Practice)

  - by viatropos

  Hey there, I have a decent understanding of RESTful urls and all the theory behind not nesting urls, but I'm still not quite sure how this looks in an enterprise application, like something like Amazon, StackOverflow, or Google... Google has urls like this: http://code.google.com/apis/ajax/ http://code.google.com/apis/maps/documentation/staticmaps/ https://www.google.com/calendar/render?tab=mc Amazon like this: http://www.amazon.com/books-used-books-textbooks/b/ref=sa_menu_bo0?ie=UTF8&node=283155&pf_rd_p=328655101&pf_rd_s=left-nav-1&pf_rd_t=101&pf_rd_i=507846&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=1PK4ZKN4YWJJ9B86ANC9 http://www.amazon.com/Ruby-Programming-Language-David-Flanagan/dp/0596516177/ref=sr_1_1?ie=UTF8&s=books&qid=1258755625&sr=1-1 And StackOverflow like this: http://stackoverflow.com/users/169992/viatropos http://stackoverflow.com/questions/tagged/html http://stackoverflow.com/questions/tagged?tagnames=html&sort=newest&pagesize=15 So my question is, what is best practice in terms of creating urls for systems like these? When do you start storing parameters in the url, when don't you? These big companies don't seem to be following the rules so hotly debated in the ruby community (that you should almost never nest URLs for example), so I'm wondering how you go about implementing your own urls in larger scale projects because it seems like the idea of not nesting urls breaks down at anything larger than a blog. Any tips?

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• Associating an Object with other Objects and Properties of those Objects

  - by alzoid

  I am looking for some help with designing some functionality in my application. I already have something similar designed but this problem is a little different. Background: In my application we have different Modules. Data in each module can be associated to other modules. Each Module is represented by an Object in our application. Module 1 can be associated with Module 2 and Module 3. Currently I use a factory to provide the proper DAO for getting and saving this data. It looks something like this: class Module1Factory { public static Module1BridgeDAO createModule1BridgeDAO(int moduleid) { switch (moduleId) { case Module.Module2Id: return new Module1_Module2DAO(); case Module.Module3Id: return new Module1_Module3DAO(); default: return null; } } } Module1_Module2 and Module1_Module3 implement the same BridgeModule interface. In the database I have a Table for every module (Module1, Module2, Module3). I also have a bridge table for each module (they are many to many) Module1_Module2, Module1_Module3 etc. The DAO basically handles all code needed to manage the association and retrieve its own instance data for the calling module. Now when we add new modules that associate with Module1 we simply implement the ModuleBridge interface and provide the common functionality. New Development We are adding a new module that will have the ability to be associated with other Modules as well as specific properties of that module. The module is basically providing the user the ability to add their custom forms to our other modules. That way they can collect additional information along with what we provide. I want to start associating my Form module with other modules and their properties. Ie if Module1 has a property Category, I want to associate an instance From data with that property. There are many Forms. If a users creates an instance of Module2, they may always want to also have certain form(s) attached to that Module2 instance. If they create an instance of Module2 and select Category 1, then I may want additional Form(s) created. I prototyped something like this: Form FormLayout (contains the labels and gui controls) FormModule (associates a form with all instances of a module) Form Instance (create an instance of a form to be filled out) As I thought about it I was thinking about making a new FormModule table/class/dao for each Module and Property that I add. So I might have: FormModule1 FormModule1Property1 FormModule1Property2 FormModule1Property3 FormModule1Property4 FormModule2 FormModule3 FormModule3Property1 Then as I did previously, I would use a factory to get the proper DAO for dealing with all of these. I would hand it an array of ids representing different modules and properties and it would return all of the DAOs that I need to call getForms(). Which in turn would return all of the forms for that particular bridge. Some points This will be for a new module so I dont need to expand on the factory code I provided. I just wanted to show an example of what I have done in the past. The new module can be associated with: Other Modules (ie globally for any instance of that module data), Other module properties (ie only if the Module instance has a certian value in one of its properties) I want to make it easy for developers to add associations with other modules and properties easily Can any one suggest any design patterns or strategy's for achieving this? If anything is unclear please let me know. Thank you, Al

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• Dynamically creating a Generic Type at Runtime

  - by Rick Strahl

  I learned something new today. Not uncommon, but it's a core .NET runtime feature I simply did not know although I know I've run into this issue a few times and worked around it in other ways. Today there was no working around it and a few folks on Twitter pointed me in the right direction. The question I ran into is: How do I create a type instance of a generic type when I have dynamically acquired the type at runtime? Yup it's not something that you do everyday, but when you're writing code that parses objects dynamically at runtime it comes up from time to time. In my case it's in the bowels of a custom JSON parser. After some thought triggered by a comment today I realized it would be fairly easy to implement two-way Dictionary parsing for most concrete dictionary types. I could use a custom Dictionary serialization format that serializes as an array of key/value objects. Basically I can use a custom type (that matches the JSON signature) to hold my parsed dictionary data and then add it to the actual dictionary when parsing is complete. Generic Types at Runtime One issue that came up in the process was how to figure out what type the Dictionary<K,V> generic parameters take. Reflection actually makes it fairly easy to figure out generic types at runtime with code like this: if (arrayType.GetInterface("IDictionary") != null) { if (arrayType.IsGenericType) { var keyType = arrayType.GetGenericArguments()[0]; var valueType = arrayType.GetGenericArguments()[1]; … } } The GetArrayType method gets passed a type instance that is the array or array-like object that is rendered in JSON as an array (which includes IList, IDictionary, IDataReader and a few others). In my case the type passed would be something like Dictionary<string, CustomerEntity>. So I know what the parent container class type is. Based on the the container type using it's then possible to use GetGenericTypeArguments() to retrieve all the generic types in sequential order of definition (ie. string, CustomerEntity). That's the easy part. Creating a Generic Type and Providing Generic Parameters at RunTime The next problem is how do I get a concrete type instance for the generic type? I know what the type name and I have a type instance is but it's generic, so how do I get a type reference to keyvaluepair<K,V> that is specific to the keyType and valueType above? Here are a couple of things that come to mind but that don't work (and yes I tried that unsuccessfully first): Type elementType = typeof(keyvalue<keyType, valueType>); Type elementType = typeof(keyvalue<typeof(keyType), typeof(valueType)>); The problem is that this explicit syntax expects a type literal not some dynamic runtime value, so both of the above won't even compile. I turns out the way to create a generic type at runtime is using a fancy bit of syntax that until today I was completely unaware of: Type elementType = typeof(keyvalue<,>).MakeGenericType(keyType, valueType); The key is the type(keyvalue<,>) bit which looks weird at best. It works however and produces a non-generic type reference. You can see the difference between the full generic type and the non-typed (?) generic type in the debugger: The nonGenericType doesn't show any type specialization, while the elementType type shows the string, CustomerEntity (truncated above) in the type name. Once the full type reference exists (elementType) it's then easy to create an instance. In my case the parser parses through the JSON and when it completes parsing the value/object it creates a new keyvalue<T,V> instance. Now that I know the element type that's pretty trivial with: // Objects start out null until we find the opening tag resultObject = Activator.CreateInstance(elementType); Here the result object is picked up by the JSON array parser which creates an instance of the child object (keyvalue<K,V>) and then parses and assigns values from the JSON document using the types  key/value property signature. Internally the parser then takes each individually parsed item and adds it to a list of  List<keyvalue<K,V>> items. Parsing through a Generic type when you only have Runtime Type Information When parsing of the JSON array is done, the List needs to be turned into a defacto Dictionary<K,V>. This should be easy since I know that I'm dealing with an IDictionary, and I know the generic types for the key and value. The problem is again though that this needs to happen at runtime which would mean using several Convert.ChangeType() calls in the code to dynamically cast at runtime. Yuk. In the end I decided the easier and probably only slightly slower way to do this is a to use the dynamic type to collect the items and assign them to avoid all the dynamic casting madness: else if (IsIDictionary) { IDictionary dict = Activator.CreateInstance(arrayType) as IDictionary; foreach (dynamic item in items) { dict.Add(item.key, item.value); } return dict; } This code creates an instance of the generic dictionary type first, then loops through all of my custom keyvalue<K,V> items and assigns them to the actual dictionary. By using Dynamic here I can side step all the explicit type conversions that would be required in the three highlighted areas (not to mention that this nested method doesn't have access to the dictionary item generic types here). Static <- -> Dynamic Dynamic casting in a static language like C# is a bitch to say the least. This is one of the few times when I've cursed static typing and the arcane syntax that's required to coax types into the right format. It works but it's pretty nasty code. If it weren't for dynamic that last bit of code would have been a pretty ugly as well with a bunch of Convert.ChangeType() calls to litter the code. Fortunately this type of type convulsion is rather rare and reserved for system level code. It's not every day that you create a string to object parser after all :-)© Rick Strahl, West Wind Technologies, 2005-2011Posted in .NET  CSharp   Tweet (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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• Configuring Oracle HTTP Server 12c for WebLogic Server Domain

  - by Emin Askerov

  Oracle HTTP Server (OHS) 12c 12.1.2 which was released in July 2013 as a part of Oracle Web Tier 12c is the web server component of Oracle Fusion Middleware. In essence this is Apache HTTP Server 2.2.22 (with critical bug fixes from higher versions) which includes modules developed specifically by Oracle. It provides a listener functionality for Oracle WebLogic Server and the framework for hosting static pages, dynamic pages, and applications over the Web. OHS can be easily managed by Weblogic Management Framework, a set of tools which provides administrative capabilities (start, stop, lifecycle operations, etc.) for Oracle Fusion Middleware products. In other words all tools which are familiar to us (Node Manager, WLST, Administration Console, Fusion Middleware Control etc.) presented as a part of Weblogic Management Framework and using for managing Java and System Components both for Weblogic Server and Standalone Domain types. You can familiarize yourself with these terms using related documentation: 1. Introduction to Oracle HTTP Server: http://docs.oracle.com/middleware/1212/webtier/index.html 2. Weblogic Management Framework: http://docs.oracle.com/middleware/1212/core/ASCON/terminology.htm#ASCON11260 In the given post I would like to cover rather simple use case how to configure OHS as web proxy in Weblogic Cluster environment. For example, we have existing Weblogic Domain where some managed servers have been joined to cluster and host business applications. We need to configure web proxy component which will act as entry point, load balancer for our cluster for user requests. Of course, we could install old good Apache HTTP Server and configure mod_wl plugin. However this solution not optimal from manageability perspective: we need to install Apache, install additional plugin then configure it by editing configuration file which is not really convenient for FMW Administrators and often increase time of performing of simple administrative task. Alternatively, we could use OHS as System Component within Weblogic Domain and use full power of Weblogic Management Framework in order to configure, manage and monitor it! I like this idea! What about you? I hope after reading this post you will agree with me. First of all it is necessary to download OHS binaries. You can use this link for downloading: http://www.oracle.com/technetwork/java/webtier/downloads/index2-303202.html As we will use Fusion Middleware Control for managing OHS instances it is necessary to extend your domain with Enterprise Manager and Oracle ADF and JRF templates. This is not topic for focusing in this post, but you could get more information from documentation or one of my previous posts: http://docs.oracle.com/middleware/1212/wls/WLDTR/fmw_templates.htm#sthref64 https://blogs.oracle.com/imc/entry/the_specifics_of_adf_12c Note: you should have properly configured Node Manager utility for managing OHS instances Let’s consider configuration process step by step: 1. Shut down all Weblogic instances of existing domain including Admin Server; 2. Install Oracle HTTP Server. You should use your Fusion Middleware Home Path (e.g. /u01/Oracle/FMW12) for Installation Location and select Colocated HTTP Server option as Installation Type. I will not focus on this topic in this post. All information related to OHS installation you could find here: http://docs.oracle.com/middleware/1212/webtier/WTINS/install_gui.htm#i1082009 3. Next we need to extend our existing domain with OHS component. In order to do this you should do the following: a. Run Fusion Middleware Configuration Wizard (ORACLE_HOME/oracle_common/common/bin/config.sh); b. On the step 1 select Update an existing domain option and point your Fusion Middleware Home Path; c. On the step 2 check Oracle HTTP Server, Oracle Enterprise Manager Plugin for WEBTIER templates; d. Go through other steps without any changes and finish configuration process. 4. Start Admin Server and all managed servers related to your cluster 5. Log in to Enterprise Manager FMW Control using http://<hostname>:<port>/em URL 6. Now we will create OHS instance within our Weblogic Domain Infrastructure. Navigate to Weblogic Domain -> Administration -> Create/Delete OHS menu item; 7. Enter to edit mode, clicking Changes -> Lock&Edit menu item; 8. Create new OHS instance clicking Create button; 9. Define Instance Name (e.g. DevOSH) and Machine parameters; 10. Now we need to define listen port. By default OHS will use 7777 port number for income HTTP requests. We could change it to any free port number we would like to use. In order to do it, right click on our created OHS instance (left hand panel) and navigate to Administration -> Port Configuration; 11. Click on record with port number 7777 and then click Edit button; 12. Change port number value (in our case this will be 8080) and then click OK button; 13. Now we need to edit mod_wl_ohs configuration in order to enable OHS to act as proxy for WebLogic Server Instances/Cluster; 14. In order to do it right click on our created OHS instance (left panel) and navigate to Administration -> mod_wl_ohs Configuration; a. In Weblogic Cluster you should enter cluster address (define <host:port> for all managed servers which participated in cluster), e.g: 192.168.56.2:7004,192.168.56.2:7005 b. Define Weblogic Port parameter at which the Oracle WebLogic Server host is listening for connection requests from the module (or from other servers); c. Check Dynamic Server List option. This will dynamically update cluster list for every request; d. In the Location table define list of endpoint locations which you would like to process. In order to do this click Add Row button and define Location, Weblogic Cluster, Path Trim and Path Prefix parameters (if required); e. Click Apply button in order to save changes. 15. Activate changes clicking Changes ? Activate Changes menu item; 16. Finally we will start configured OHS instance. Right click on OHS instance tree item under Web Tier folder, select Control -> Start Up menu item; 17. Ensure that OHS instance up and running and then test your environment. Run deployed application to your Weblogic Cluster accessing via OHS web proxy; Normal 0 false false false RU X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-fareast-language:EN-US;}

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• Orchestrating the Virtual Enterprise

  - by John Murphy

  During the American Industrial Revolution, the Ford Motor Company did it all. It turned raw materials into a showroom full of Model Ts. It owned a steel mill, a glass factory, and an automobile assembly line. The company was both self-sufficient and innovative and went on to become one of the largest and most profitable companies in the world. Nowadays, it's unusual for any business to follow this vertical integration model because its much harder to be best in class across such a wide a range of capabilities and services. Instead, businesses focus on their core competencies and outsource other business functions to specialized suppliers. They exchange vertical integration for collaboration. When done well, all parties benefit from this arrangement and the collaboration leads to the creation of an agile, lean and successful "virtual enterprise." Case in point: For Sun hardware, Oracle outsources most of its manufacturing and all of its logistics to third parties. These are vital activities, but ones where Oracle doesn't have a core competency, so we shift them to business partners who do. Within our enterprise, we always retain the core functions of product development, support, and most of the sales function, because that's what constitutes our core value to our customers. This is a perfect example of a virtual enterprise.  What are the implications of this? It means that we must exchange direct internal control for indirect external collaboration. This fundamentally changes the relative importance of different business processes, the boundaries of security and information sharing, and the relationship of the supply chain systems to the ERP. The challenge is that the systems required to support this virtual paradigm are still mired in "island enterprise" thinking. But help is at hand. Developments such as the Web, social networks, collaboration, and rules-based orchestration offer great potential to fundamentally re-architect supply chain systems to better support the virtual enterprise.  Supply Chain Management Systems in a Virtual Enterprise Historically enterprise software was constructed to automate the ERP - and then the supply chain systems extended the ERP. They were joined at the hip. In virtual enterprises, the supply chain system needs to be ERP agnostic, sitting above each of the ERPs that are distributed across the virtual enterprise - most of which are operating in other businesses. This is vital so that the supply chain system can manage the flow of material and the related information through the multiple enterprises. It has to have strong collaboration tools. It needs to be highly flexible. Users need to be able to see information that's coming from multiple sources and be able to react and respond to events across those sources.  Oracle Fusion Distributed Order Orchestration (DOO) is a perfect example of a supply chain system designed to operate in this virtual way. DOO embraces the idea that a company's fulfillment challenge is a distributed, multi-enterprise problem. It enables users to manage the process and the trading partners in a uniform way and deliver a consistent user experience while operating over a heterogeneous, virtual enterprise. This is a fundamental shift at the core of managing supply chains. It forces virtual enterprises to think architecturally about how best to construct their supply chain systems.  Case in point, almost everyone has ordered from Amazon.com at one time or another. Our orders are as likely to be fulfilled by third parties as they are by Amazon itself. To deliver the order promptly and efficiently, Amazon has to send it to the right fulfillment location and know the availability in that location. It needs to be able to track status of the fulfillment and deal with exceptions. As a virtual enterprise, Amazon's operations, using thousands of trading partners, requires a very different approach to fulfillment than the traditional 'take an order and ship it from your own warehouse' model. Amazon had no choice but to develop a complex, expensive and custom solution to tackle this problem as there used to be no product solution available. Now, other companies who want to follow similar models have a better off-the-shelf choice -- Oracle Distributed Order Orchestration (DOO).  Consider how another of our customers is using our distributed orchestration solution. This major airplane manufacturer has a highly complex business and interacts regularly with the U.S. Government and major airlines. It sits in the middle of an intricate supply chain and needed to improve visibility across its many different entities. Oracle Fusion DOO gives the company an orchestration mechanism so it could improve quality, speed, flexibility, and consistency without requiring an organ transplant of these highly complex legacy systems. Many retailers face the challenge of dealing with brick and mortar, Web, and reseller channels. They all need to be knitted together into a virtual enterprise experience that is consistent for their customers. When a large U.K. grocer with a strong brick and mortar retail operation added an online business, they turned to Oracle Fusion DOO to bring these entities together. Disturbing the Peace with Acquisitions Quite often a company's ERP system is disrupted when it acquires a new company. An acquisition can inject a new set of processes and systems -- or even introduce an entirely new business like Sun's hardware did at Oracle. This challenge has been a driver for some of our DOO customers. A large power management company is using Oracle Fusion DOO to provide the flexibility to rapidly integrate additional products and services into its central fulfillment operation. The Flip Side of Fulfillment Meanwhile, we haven't ignored similar challenges on the supply side of the equation. Specifically, how to manage complex supply in a flexible way when there are multiple trading parties involved? How to manage the supply to suppliers? How to manage critical components that need to merge in a tier two or tier three supply chain? By investing in supply orchestration solutions for the virtual enterprise, we plan to give users better visibility into their network of suppliers to help them drive down costs. We also think this technology and full orchestration process can be applied to the financial side of organizations. An example is transactions that flow through complex internal structures to minimize tax exposure. We can help companies manage those transactions effectively by thinking about the internal organization as a virtual enterprise and bringing the same solution set to this internal challenge.  The Clear Front Runner No other company is investing in solving the virtual enterprise supply chain issues like Oracle is. Oracle is in a unique position to become the gold standard in this market space. We have the infrastructure of Oracle technology. We already have an Oracle Fusion DOO application which embraces the best of what's required in this area. And we're absolutely committed to extending our Fusion solution to other use cases and delivering even more business value.

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• ?11.2RAC??????????????

  - by JaneZhang(???)

         ?????,???????????????,???dbca???????,???????????dbca,?????????11.2???????,???????,??dbca??????????????????,????????????????     ????11.2???????RACDB2???,?????RACDB1? ?????rac1,????rac2?     ?11.2?,?????grid?????GI,??oracle????????,????????oracle?????? 1. ??????????????????,?????,???????????:audit_file_dest, background_dump_dest, user_dump_dest ?core_dump_dest????audit_file_dest=/u01/app/oracle/admin/RACDB/adump,?????????,?????????:ORA-09925: Unable to create audit trail fileLinux-x86_64 Error: 2: No such file or directoryAdditional information: 99252. ????????????????????????????:SQL> alter system set instance_number=2 scope=spfile sid='RACDB2';SQL> alter system set thread=2 scope=spfile sid='RACDB2';SQL> alter system set undo_tablespace='UNDOTBS2' scope=spfile sid='RACDB2';SQL> alter system set local_listener='(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=192.0.2.122)(PORT=1521))))' sid='RACDB2'; <=====192.0.2.122???2?VIP 3. ???????DB?$ORACLE_HOME/dbs/init<sid>.ora ?????DB?$ORACLE_HOME/dbs/init<sid>.ora,??????????????init<sid>.ora ????,????spfile???:=======================SPFILE='+DATA/racdb/spfileracdb.ora'??:[oracle@rac1 ~]$ scp $ORACLE_HOME/dbs/initRACDB1.ora rac2:$ORACLE_HOME/dbs/initRACDB2.ora <===????????24.  ??????/etc/oratab,????????????:RACDB2:/u01/app/oracle/product/11.2.0/dbhome_1:N       5.  ???????????: DB?$ORACLE_HOME/dbs/ora<sid>.pwd ????DB?$ORACLE_HOME/dbs/ora<sid>.pwd,??????????????:[oracle@rac1 dbs]$ scp $ORACLE_HOME/dbs/orapwRACDB1 rac2:$ORACLE_HOME/dbs/orapwRACDB2 <==?????26.  ?????????????,????????UNDO TABLESPACE?(??????dbca?????,???????undo tablespace????,?????????)??:SQL>CREATE UNDO TABLESPACE "UNDOTBS2" DATAFILE '/dev/….' SIZE 4096M ;???????:SQL>CREATE UNDO TABLESPACE "UNDOTBS2" DATAFILE '+DATA' SIZE 4096M ;7.  ?????????????,????????redo thread?redo log:??:SQL> alter database add logfile thread 2      group 3 ('/dev/...', '/dev/...') size 1024M,     group 4 ('/dev/...','dev/...') size 1024M;???????:SQL> alter database add logfile thread 2     group 3 ('+DATA','+RECO') size 1024M,     group 4 ('+DATA','+RECO') size 1024M;SQL> alter database enable thread 2; <==????thread8.  ??????????,?????????????:[oracle@rac2 admin]$su - oracle[oracle@rac2 admin]$export ORACLE_HOME=/u01/app/oracle/product/11.2.0/dbhome_1[oracle@rac2 admin]$export ORACLE_SID=RACDB2[oracle@rac2 admin]$ sqlplus / as sysdbaSQL> startup <==??????,???????2????????????9. ?????OCR???GI??,?????????????:$srvctl add instance -d <database name> -i <new instance name> -n <new node name>Example of srvctl add instance command:============================[oracle@rac2 ~]$ srvctl add instance -d racdb -i RACDB2 -n rac2  <==????????,????ps -ef|grep smon???[oracle@rac2 dbs]$ ps -ef|grep smonroot      3453     1  1 Jun12 ?        04:03:05 /u01/app/11.2.0/grid/bin/osysmond.bingrid      3727     1  0 Jun12 ?        00:00:19 asm_smon_+ASM2oracle    5343  4543  0 14:06 pts/1    00:00:00 grep smonoracle   28736     1  0 Jun25 ?        00:00:03 ora_smon_RACDB2 <========??????10. ???????:$su - grid[grid@rac2 ~]$ crsctl stat res -t...ora.racdb.db      1        ONLINE  ONLINE       rac1                     Open                      2        OFFLINE OFFLINE             rac2????,??????offline,????????????sqlplus??????sqlplus??????,???srvctl??:[grid@rac2 ~]$ su  - oraclePassword: [oracle@rac2 ~]$ sqlplus / as sysdbaSQL> shutdown immediate;Database closed.Database dismounted.ORACLE instance shut down.SQL> exit[oracle@rac2 ~]$ srvctl start instance -d racdb -i RACDB2[oracle@rac2 ~]$ su - gridPassword: [grid@rac2 ~]$ crsctl stat res -tora.racdb.db      1        ONLINE  ONLINE       rac1                     Open                      2        ONLINE  ONLINE       rac2                     Open                11. ?????????:[oracle@rac2 ~]$ crsctl stat res ora.racdb.db -pNAME=ora.racdb.dbTYPE=ora.database.typeACL=owner:oracle:rwx,pgrp:oinstall:rwx,other::r--ACTION_FAILURE_TEMPLATE=ACTION_SCRIPT=ACTIVE_PLACEMENT=1AGENT_FILENAME=%CRS_HOME%/bin/oraagent%CRS_EXE_SUFFIX%AUTO_START=restoreCARDINALITY=2CHECK_INTERVAL=1CHECK_TIMEOUT=30CLUSTER_DATABASE=trueDATABASE_TYPE=RACDB_UNIQUE_NAME=RACDBDEFAULT_TEMPLATE=PROPERTY(RESOURCE_CLASS=database) PROPERTY(DB_UNIQUE_NAME= CONCAT(PARSE(%NAME%, ., 2), %USR_ORA_DOMAIN%, .)) ELEMENT(INSTANCE_NAME= %GEN_USR_ORA_INST_NAME%) ELEMENT(DATABASE_TYPE= %DATABASE_TYPE%)DEGREE=1DESCRIPTION=Oracle Database resourceENABLED=1FAILOVER_DELAY=0FAILURE_INTERVAL=60FAILURE_THRESHOLD=1GEN_AUDIT_FILE_DEST=/u01/app/oracle/admin/RACDB/adumpGEN_START_OPTIONS=GEN_START_OPTIONS@SERVERNAME(rac1)=openGEN_START_OPTIONS@SERVERNAME(rac2)=openGEN_USR_ORA_INST_NAME=GEN_USR_ORA_INST_NAME@SERVERNAME(rac1)=RACDB1HOSTING_MEMBERS=INSTANCE_FAILOVER=0LOAD=1LOGGING_LEVEL=1MANAGEMENT_POLICY=AUTOMATICNLS_LANG=NOT_RESTARTING_TEMPLATE=OFFLINE_CHECK_INTERVAL=0ONLINE_RELOCATION_TIMEOUT=0ORACLE_HOME=/u01/app/oracle/product/11.2.0/dbhome_1ORACLE_HOME_OLD=PLACEMENT=restrictedPROFILE_CHANGE_TEMPLATE=RESTART_ATTEMPTS=2ROLE=PRIMARYSCRIPT_TIMEOUT=60SERVER_POOLS=ora.RACDBSPFILE=+DATA/RACDB/spfileRACDB.oraSTART_DEPENDENCIES=hard(ora.DATA.dg,ora.RECO.dg) weak(type:ora.listener.type,global:type:ora.scan_listener.type,uniform:ora.ons,global:ora.gns) pullup(ora.DATA.dg,ora.RECO.dg)START_TIMEOUT=600STATE_CHANGE_TEMPLATE=STOP_DEPENDENCIES=hard(intermediate:ora.asm,shutdown:ora.DATA.dg,shutdown:ora.RECO.dg)STOP_TIMEOUT=600TYPE_VERSION=3.2UPTIME_THRESHOLD=1hUSR_ORA_DB_NAME=RACDBUSR_ORA_DOMAIN=USR_ORA_ENV=USR_ORA_FLAGS=USR_ORA_INST_NAME=USR_ORA_INST_NAME@SERVERNAME(rac1)=RACDB1USR_ORA_INST_NAME@SERVERNAME(rac2)=RACDB2USR_ORA_OPEN_MODE=openUSR_ORA_OPI=falseUSR_ORA_STOP_MODE=immediateVERSION=11.2.0.3.0???11.2,?OCR???database??,??????,???????????database???????database???????,??????,???????????????ASM????????????  ?:dbca ???????????:????????oracle????dbca:su - oracledbca?? RAC database?? Instance Management?? add an instance???active rac database??????? ??undo?redo??

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• Getting WCF Bindings and Behaviors from any config source

  - by cibrax

  The need of loading WCF bindings or behaviors from different sources such as files in a disk or databases is a common requirement when dealing with configuration either on the client side or the service side. The traditional way to accomplish this in WCF is loading everything from the standard configuration section (serviceModel section) or creating all the bindings and behaviors by hand in code. However, there is a solution in the middle that becomes handy when more flexibility is needed. This solution involves getting the configuration from any place, and use that configuration to automatically configure any existing binding or behavior instance created with code.  In order to configure a binding instance (System.ServiceModel.Channels.Binding) that you later inject in any endpoint on the client channel or the service host, you first need to get a binding configuration section from any configuration file (you can generate a temp file on the fly if you are using any other source for storing the configuration).  private BindingsSection GetBindingsSection(string path) { System.Configuration.Configuration config = System.Configuration.ConfigurationManager.OpenMappedExeConfiguration( new System.Configuration.ExeConfigurationFileMap() { ExeConfigFilename = path }, System.Configuration.ConfigurationUserLevel.None); var serviceModel = ServiceModelSectionGroup.GetSectionGroup(config); return serviceModel.Bindings; }   The BindingsSection contains a list of all the configured bindings in the serviceModel configuration section, so you can iterate through all the configured binding that get the one you need (You don’t need to have a complete serviceModel section, a section with the bindings only works).  public Binding ResolveBinding(string name) { BindingsSection section = GetBindingsSection(path); foreach (var bindingCollection in section.BindingCollections) { if (bindingCollection.ConfiguredBindings.Count > 0 && bindingCollection.ConfiguredBindings[0].Name == name) { var bindingElement = bindingCollection.ConfiguredBindings[0]; var binding = (Binding)Activator.CreateInstance(bindingCollection.BindingType); binding.Name = bindingElement.Name; bindingElement.ApplyConfiguration(binding); return binding; } } return null; }   The code above does just that, and also instantiates and configures the Binding object (System.ServiceModel.Channels.Binding) you are looking for. As you can see, the binding configuration element contains a method “ApplyConfiguration” that receives the binding instance that needs to be configured. A similar thing can be done for instance with the “Endpoint” behaviors. You first get the BehaviorsSection, and then, the behavior you want to use.  private BehaviorsSection GetBehaviorsSection(string path) { System.Configuration.Configuration config = System.Configuration.ConfigurationManager.OpenMappedExeConfiguration( new System.Configuration.ExeConfigurationFileMap() { ExeConfigFilename = path }, System.Configuration.ConfigurationUserLevel.None); var serviceModel = ServiceModelSectionGroup.GetSectionGroup(config); return serviceModel.Behaviors; }public List<IEndpointBehavior> ResolveEndpointBehavior(string name) { BehaviorsSection section = GetBehaviorsSection(path); List<IEndpointBehavior> endpointBehaviors = new List<IEndpointBehavior>(); if (section.EndpointBehaviors.Count > 0 && section.EndpointBehaviors[0].Name == name) { var behaviorCollectionElement = section.EndpointBehaviors[0]; foreach (BehaviorExtensionElement behaviorExtension in behaviorCollectionElement) { object extension = behaviorExtension.GetType().InvokeMember("CreateBehavior", BindingFlags.InvokeMethod | BindingFlags.NonPublic | BindingFlags.Instance, null, behaviorExtension, null); endpointBehaviors.Add((IEndpointBehavior)extension); } return endpointBehaviors; } return null; }   In this case, the code for creating the behavior instance is more tricky. First of all, a behavior in the configuration section actually represents a set of “IEndpoint” behaviors, and the behavior element you get from the configuration does not have any public method to configure an existing behavior instance. This last one only contains a protected method “CreateBehavior” that you can use for that purpose. Once you get this code implemented, a client channel can be easily configured as follows  var binding = resolver.ResolveBinding("MyBinding"); var behaviors = resolver.ResolveEndpointBehavior("MyBehavior"); SampleServiceClient client = new SampleServiceClient(binding, new EndpointAddress(new Uri("http://localhost:13749/SampleService.svc"), new DnsEndpointIdentity("localhost"))); foreach (var behavior in behaviors) { if(client.Endpoint.Behaviors.Contains(behavior.GetType())) { client.Endpoint.Behaviors.Remove(behavior.GetType()); } client.Endpoint.Behaviors.Add(behavior); }   The code above assumes that a configuration file (in any place) with a binding “MyBinding” and a behavior “MyBehavior” exists. That file can look like this,  <system.serviceModel> <bindings> <basicHttpBinding> <binding name="MyBinding"> <security mode="Transport"></security> </binding> </basicHttpBinding> </bindings> <behaviors> <endpointBehaviors> <behavior name="MyBehavior"> <clientCredentials> <windows/> </clientCredentials> </behavior> </endpointBehaviors> </behaviors> </system.serviceModel>   The same thing can be done of course in the service host if you want to manually configure the bindings and behaviors.  

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• Classes / instances in Ontology

  - by SODA

  Hi, I'm trying to comprehend ontology basics. Here's an example: car (class) 2009 VW CC (sub-class or instance?) My neighbor's 2009 VW CC (instance) My issue is understanding what is "2009 VW CC" (as a car model). If you're making product model a sub-class in the ontology - all of a sudden your ontology becomes bloated with thousands of subclasses of a "car". That's redundant. At the same time we can't say "2009 VW CC" is an instance, at least it's not material instance of a class. Does it make sense to distinguish between regular instances and material (distinct physical objects)? At the other hand, if both are instances (of different nature so to say), then how can instance inherit properties / relations of a non-class?

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• Boost C++ Singleton error LNK2001: unresolved external symbol "private: static long Nsp::HL::flag" (

  - by Soós Roland

  I try to create a multi-threaded singleton pattern class. Header: class HL{ public: static HL* getInstance(); ......... private: static HL* instance; static boost::once_flag flag; HL(); static void initOnce(); } CPP: HL* HL::instance = NULL; HL* HL::getInstance(){ if(instance == NULL){ boost::call_once(flag, initOnce); } return instance; } void HL::initOnce(){ instance = new HL(); } I get this error: error LNK2001: unresolved external symbol "private: static long Nsp::HL::flag" (?flag@HL@Nsp@@0JA) What's wrong?

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• Subterranean IL: Constructor constraints

  - by Simon Cooper

  The constructor generic constraint is a slightly wierd one. The ECMA specification simply states that it: constrains [the type] to being a concrete reference type (i.e., not abstract) that has a public constructor taking no arguments (the default constructor), or to being a value type. There seems to be no reference within the spec to how you actually create an instance of a generic type with such a constraint. In non-generic methods, the normal way of creating an instance of a class is quite different to initializing an instance of a value type. For a reference type, you use newobj: newobj instance void IncrementableClass::.ctor() and for value types, you need to use initobj: .locals init ( valuetype IncrementableStruct s1 ) ldloca 0 initobj IncrementableStruct But, for a generic method, we need a consistent method that would work equally well for reference or value types. Activator.CreateInstance<T> To solve this problem the CLR designers could have chosen to create something similar to the constrained. prefix; if T is a value type, call initobj, and if it is a reference type, call newobj instance void !!0::.ctor(). However, this solution is much more heavyweight than constrained callvirt. The newobj call is encoded in the assembly using a simple reference to a row in a metadata table. This encoding is no longer valid for a call to !!0::.ctor(), as different constructor methods occupy different rows in the metadata tables. Furthermore, constructors aren't virtual, so we would have to somehow do a dynamic lookup to the correct method at runtime without using a MethodTable, something which is completely new to the CLR. Trying to do this in IL results in the following verification error: newobj instance void !!0::.ctor() [IL]: Error: Unable to resolve token. This is where Activator.CreateInstance<T> comes in. We can call this method to return us a new T, and make the whole issue Somebody Else's Problem. CreateInstance does all the dynamic method lookup for us, and returns us a new instance of the correct reference or value type (strangely enough, Activator.CreateInstance<T> does not itself have a .ctor constraint on its generic parameter): .method private static !!0 CreateInstance<.ctor T>() { call !!0 [mscorlib]System.Activator::CreateInstance<!!0>() ret } Going further: compiler enhancements Although this method works perfectly well for solving the problem, the C# compiler goes one step further. If you decompile the C# version of the CreateInstance method above: private static T CreateInstance() where T : new() { return new T(); } what you actually get is this (edited slightly for space & clarity): .method private static !!T CreateInstance<.ctor T>() { .locals init ( [0] !!T CS$0$0000, [1] !!T CS$0$0001 ) DetectValueType: ldloca.s 0 initobj !!T ldloc.0 box !!T brfalse.s CreateInstance CreateValueType: ldloca.s 1 initobj !!T ldloc.1 ret CreateInstance: call !!0 [mscorlib]System.Activator::CreateInstance<T>() ret } What on earth is going on here? Looking closer, it's actually quite a clever performance optimization around value types. So, lets dissect this code to see what it does. The CreateValueType and CreateInstance sections should be fairly self-explanatory; using initobj for value types, and Activator.CreateInstance for reference types. How does the DetectValueType section work? First, the stack transition for value types: ldloca.s 0 // &[!!T(uninitialized)] initobj !!T // ldloc.0 // !!T box !!T // O[!!T] brfalse.s // branch not taken When the brfalse.s is hit, the top stack entry is a non-null reference to a boxed !!T, so execution continues to to the CreateValueType section. What about when !!T is a reference type? Remember, the 'default' value of an object reference (type O) is zero, or null. ldloca.s 0 // &[!!T(null)] initobj !!T // ldloc.0 // null box !!T // null brfalse.s // branch taken Because box on a reference type is a no-op, the top of the stack at the brfalse.s is null, and so the branch to CreateInstance is taken. For reference types, Activator.CreateInstance is called which does the full dynamic lookup using reflection. For value types, a simple initobj is called, which is far faster, and also eliminates the unboxing that Activator.CreateInstance has to perform for value types. However, this is strictly a performance optimization; Activator.CreateInstance<T> works for value types as well as reference types. Next... That concludes the initial premise of the Subterranean IL series; to cover the details of generic methods and generic code in IL. I've got a few other ideas about where to go next; however, if anyone has any itching questions, suggestions, or things you've always wondered about IL, do let me know.

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• Calling a method from within a django model save() override

  - by Jonathan

  I'm overriding a django model save() method. Within the override I'm calling another method of the same class and instance which calculates one of the instance's fields based on other fields of the same instance. class MyClass(models.Model): field1 = models.FloatField() field2 = models.FloatField() field3 = models.FloatField() def calculateField1(self) self.field1 = self.field2 + self.field3 def save(self, *args, **kwargs): self.calculateField1() super(MyClass, self).save(*args, **kwargs) The override method is called when I change the model in admin. Alas I've discovered that within calculateField1() field2 and field3 have the values of the instance from before I edited them in admin. If I enter the instance again in admin and save again, only then field1 receives the correct value as field2 and field3 are already updated. Is this the correct behavior on django's side? If yes, then how can I use the new values within calculateField1? I cannot implement the calculation within the save() as calculateField1() actually quite long and I need it to be called from elsewhere.

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• TFS and working with multiple solutions

  - by RandomEngy

  How do people generally deal with TFS when you've got to work with multiple solution files? If you've got one instance it's easy because you can always go to that window for the source control explorer, pending changes, check on builds or work items. But when you have 4-5 solutions, it becomes tricky to deal with. You might expand some folders or check some pending items on one VS instance but you have to remember which one you did it on. Having a separate instance dedicated just to TFS tasks is tempting, but there's only one window state for the whole program. If that instance is closed last, all instances will come up with all the TFS windows open. How do other people deal with this? Can you use separate profiles somehow and cordon off a "TFS" instance of Visual Studio?

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• Why enumerator structs are a really bad idea

  - by Simon Cooper

  If you've ever poked around the .NET class libraries in Reflector, I'm sure you would have noticed that the generic collection classes all have implementations of their IEnumerator as a struct rather than a class. As you will see, this design decision has some rather unfortunate side effects... As is generally known in the .NET world, mutable structs are a Very Bad Idea; and there are several other blogs around explaining this (Eric Lippert's blog post explains the problem quite well). In the BCL, the generic collection enumerators are all mutable structs, as they need to keep track of where they are in the collection. This bit me quite hard when I was coding a wrapper around a LinkedList<int>.Enumerator. It boils down to this code: sealed class EnumeratorWrapper : IEnumerator<int> { private readonly LinkedList<int>.Enumerator m_Enumerator; public EnumeratorWrapper(LinkedList<int> linkedList) { m_Enumerator = linkedList.GetEnumerator(); } public int Current { get { return m_Enumerator.Current; } } object System.Collections.IEnumerator.Current { get { return Current; } } public bool MoveNext() { return m_Enumerator.MoveNext(); } public void Reset() { ((System.Collections.IEnumerator)m_Enumerator).Reset(); } public void Dispose() { m_Enumerator.Dispose(); } } The key line here is the MoveNext method. When I initially coded this, I thought that the call to m_Enumerator.MoveNext() would alter the enumerator state in the m_Enumerator class variable and so the enumeration would proceed in an orderly fashion through the collection. However, when I ran this code it went into an infinite loop - the m_Enumerator.MoveNext() call wasn't actually changing the state in the m_Enumerator variable at all, and my code was looping forever on the first collection element. It was only after disassembling that method that I found out what was going on The MoveNext method above results in the following IL: .method public hidebysig newslot virtual final instance bool MoveNext() cil managed { .maxstack 1 .locals init ( [0] bool CS$1$0000, [1] valuetype [System]System.Collections.Generic.LinkedList`1/Enumerator CS$0$0001) L_0000: nop L_0001: ldarg.0 L_0002: ldfld valuetype [System]System.Collections.Generic.LinkedList`1/Enumerator EnumeratorWrapper::m_Enumerator L_0007: stloc.1 L_0008: ldloca.s CS$0$0001 L_000a: call instance bool [System]System.Collections.Generic.LinkedList`1/Enumerator::MoveNext() L_000f: stloc.0 L_0010: br.s L_0012 L_0012: ldloc.0 L_0013: ret } Here, the important line is 0002 - m_Enumerator is accessed using the ldfld operator, which does the following: Finds the value of a field in the object whose reference is currently on the evaluation stack. So, what the MoveNext method is doing is the following: public bool MoveNext() { LinkedList<int>.Enumerator CS$0$0001 = this.m_Enumerator; bool CS$1$0000 = CS$0$0001.MoveNext(); return CS$1$0000; } The enumerator instance being modified by the call to MoveNext is the one stored in the CS$0$0001 variable on the stack, and not the one in the EnumeratorWrapper class instance. Hence why the state of m_Enumerator wasn't getting updated. Hmm, ok. Well, why is it doing this? If you have a read of Eric Lippert's blog post about this issue, you'll notice he quotes a few sections of the C# spec. In particular, 7.5.4: ...if the field is readonly and the reference occurs outside an instance constructor of the class in which the field is declared, then the result is a value, namely the value of the field I in the object referenced by E. And my m_Enumerator field is readonly! Indeed, if I remove the readonly from the class variable then the problem goes away, and the code works as expected. The IL confirms this: .method public hidebysig newslot virtual final instance bool MoveNext() cil managed { .maxstack 1 .locals init ( [0] bool CS$1$0000) L_0000: nop L_0001: ldarg.0 L_0002: ldflda valuetype [System]System.Collections.Generic.LinkedList`1/Enumerator EnumeratorWrapper::m_Enumerator L_0007: call instance bool [System]System.Collections.Generic.LinkedList`1/Enumerator::MoveNext() L_000c: stloc.0 L_000d: br.s L_000f L_000f: ldloc.0 L_0010: ret } Notice on line 0002, instead of the ldfld we had before, we've got a ldflda, which does this: Finds the address of a field in the object whose reference is currently on the evaluation stack. Instead of loading the value, we're loading the address of the m_Enumerator field. So now the call to MoveNext modifies the enumerator stored in the class rather than on the stack, and everything works as expected. Previously, I had thought enumerator structs were an odd but interesting feature of the BCL that I had used in the past to do linked list slices. However, effects like this only underline how dangerous mutable structs are, and I'm at a loss to explain why the enumerators were implemented as structs in the first place. (interestingly, the SortedList<TKey, TValue> enumerator is a struct but is private, which makes it even more odd - the only way it can be accessed is as a boxed IEnumerator!). I would love to hear people's theories as to why the enumerators are implemented in such a fashion. And bonus points if you can explain why LinkedList<int>.Enumerator.Reset is an explicit implementation but Dispose is implicit... Note to self: never ever ever code a mutable struct.

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• Django: way to test what class a generic relation content_object is?

  - by bitbutter

  In my project I have a class, NewsItem. Instances of NewsItem act like a wrapper. They can be associated with either an ArtWork instance, or an Announcement instance. Here's how the NewsItem model looks: class NewsItem(models.Model): content_type = models.ForeignKey(ContentType) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey('content_type', 'object_id') date = models.DateTimeField(default=datetime.datetime.now,) class Meta: ordering = ('-date',) def __unicode__(self): return (self.title()) In a template I'm dealing with a NewsItem instance, and would like to output a certain bunch of html it it's 'wrapping' an Artwork instance, and a different bunch of html if it's wrapping an Announcement instance. Could someone explain how I can write a conditional to test for this? My first naive try looked like this: {% if news_item.content_object.type=='Artwork' %}do this{% else %}do that{% endif %}

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• SSIS process files from folder

  - by RT

  Background: I've a folder that gets pumped with files continuously. My SSIS package needs to process the files and delete them. The SSIS package is scheduled to run once every minute. I'm picking up the files in ascending order of file creation time. I'm building an array of files and then processing-deleting them one at a time. Problem: If an instance of my package takes longer than one minute to run, the next instance of the SSIS package will pick up some of the files the previous instance has in its buffer. By the time the second instance of teh package gets around to processing a file, it may already have been deleted by the first instance, creating an exception condition. I was wondering whether there was a way to avoid the exception condition. Thanks.

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• Haskell: variant of `show` that doesn't wrap String and Char in quotes

  - by Joey Adams

  I'd like a variant of show (let's call it label) that acts just like show, except that it doesn't wrap Strings in " " or Chars in ' '. Examples: > label 5 "5" > label "hello" "hello" > label 'c' "c" I tried implementing this manually, but I ran into some walls. Here is what I tried: {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE UndecidableInstances #-} module Label where class (Show a) => Label a where label :: a -> String instance Label [Char] where label str = str instance Label Char where label c = [c] -- Default case instance Show a => Label a where label x = show x However, because the default case's class overlaps instance Label [Char] and instance Label Char, those types don't work with the label function. Is there a library function that provides this functionality? If not, is there a workaround to get the above code to work?

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• How can I simulate the effects of an observable collection in this situation?

  - by MGSoto

  I am making a configuration editor for another application and am using reflection to pull editable fields from the configuration class. The following class is the base class for my various "DataTypeViewModels" and shows how I get and set the appropriate properties. public abstract class DataTypeViewModel<T> : ViewModelBase { Func<T> getFunction; Action<T> setAction; public const string ValuePropertyName = "Value"; public string Label { get; set; } public T Value { get { return getFunction.Invoke(); } set { if (getFunction.Invoke().Equals(value)) { return; } setAction.Invoke(value); // Update bindings, no broadcast RaisePropertyChanged(ValuePropertyName); } } /// <summary> /// Initializes a new instance of the StringViewModel class. /// </summary> public DataTypeViewModel(string sectionName, string label) { if (IsInDesignMode) { // Code runs in Blend --> create design time data. } else { Label = label; getFunction = new Func<T>(() => { return (T)Settings.Instance.GetType().GetProperty(sectionName).PropertyType. GetProperty(label).GetValue(Settings.Instance.GetType().GetProperty(sectionName).GetValue(Settings.Instance, null), null); }); setAction = new Action<T>(value => { Settings.Instance.GetType().GetProperty(sectionName).PropertyType.GetProperty(label). SetValue(Settings.Instance.GetType().GetProperty(sectionName).GetValue(Settings.Instance, null), value, null); }); } } } This part works the way I want it to, the next part is a sample DataTypeViewModel on a list of strings. public class StringListViewModel : DataTypeViewModel<ICollection<string>> { /// <summary> /// The <see cref="RemoveItemCommand" /> property's name. /// </summary> public const string RemoveItemCommandPropertyName = "RemoveItemCommand"; private RelayCommand<string> _removeItemCommand = null; public ObservableCollection<string> ObservableValue { get; set; } /// <summary> /// Gets the RemoveItemCommand property. /// TODO Update documentation: /// Changes to that property's value raise the PropertyChanged event. /// This property's value is broadcasted by the Messenger's default instance when it changes. /// </summary> public RelayCommand<string> RemoveItemCommand { get { return _removeItemCommand; } set { if (_removeItemCommand == value) { return; } var oldValue = _removeItemCommand; _removeItemCommand = value; // Update bindings, no broadcast RaisePropertyChanged(RemoveItemCommandPropertyName); } } /// <summary> /// The <see cref="AddItemCommand" /> property's name. /// </summary> public const string AddItemCommandPropertyName = "AddItemCommand"; private RelayCommand<string> _addItemCommand = null; /// <summary> /// Gets the AddItemCommand property. /// TODO Update documentation: /// Changes to that property's value raise the PropertyChanged event. /// This property's value is broadcasted by the Messenger's default instance when it changes. /// </summary> public RelayCommand<string> AddItemCommand { get { return _addItemCommand; } set { if (_addItemCommand == value) { return; } var oldValue = _addItemCommand; _addItemCommand = value; // Update bindings, no broadcast RaisePropertyChanged(AddItemCommandPropertyName); } } /// <summary> /// Initializes a new instance of the StringListViewModel class. /// </summary> public StringListViewModel(string sectionName, string label) : base(sectionName, label) { ObservableValue = new ObservableCollection<string>(Value); AddItemCommand = new RelayCommand<string>(param => { if (param != string.Empty) { Value.Add(param); ObservableValue.Add(param); } }); RemoveItemCommand = new RelayCommand<string>(param => { if (param != null) { Value.Remove(param); ObservableValue.Remove(param); } }); } } As you can see in the constructor, I currently have "Value" mirrored into a new ObservableCollection called "ObservableValue", which is then bound to by a ListView in the XAML. It works well this way, but cloning the List seems like such a hacky way to do this. While bound to Value, I've tried adding: RaisePropertyChanged("Value"); to the AddItemCommand and RemoveItemCommand, but this doesn't work, the ListView won't get updated. What is the proper way to do this?

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• Navigation in a #WP7 application with MVVM Light

  - by Laurent Bugnion

  In MVVM applications, it can be a bit of a challenge to send instructions to the view (for example a page) from a viewmodel. Thankfully, we have good tools at our disposal to help with that. In his excellent series “MVVM Light Toolkit soup to nuts”, Jesse Liberty proposes one approach using the MVVM Light messaging infrastructure. While this works fine, I would like to show here another approach using what I call a “view service”, i.e. an abstracted service that is invoked from the viewmodel, and implemented on the view. Multiple kinds of view services In fact, I use view services quite often, and even started standardizing them for the Windows Phone 7 applications I work on. If there is interest, I will be happy to show other such view services, for example Animation services, responsible to start/stop animations on the view. Dialog service, in charge of displaying messages to the user and gathering feedback. Navigation service, in charge of navigating to a given page directly from the viewmodel. In this article, I will concentrate on the navigation service. The INavigationService interface In most WP7 apps, the navigation service is used in quite a straightforward way. We want to: Navigate to a given URI. Go back. Be notified when a navigation is taking place, and be able to cancel. The INavigationService interface is quite simple indeed: public interface INavigationService { event NavigatingCancelEventHandler Navigating; void NavigateTo(Uri pageUri); void GoBack(); } Obviously, this interface can be extended if necessary, but in most of the apps I worked on, I found that this covers my needs. The NavigationService class It is possible to nicely pack the navigation service into its own class. To do this, we need to remember that all the PhoneApplicationPage instances use the same instance of the navigation service, exposed through their NavigationService property. In fact, in a WP7 application, it is the main frame (RootFrame, of type PhoneApplicationFrame) that is responsible for this task. So, our implementation of the NavigationService class can leverage this. First the class will grab the PhoneApplicationFrame and store a reference to it. Also, it registers a handler for the Navigating event, and forwards the event to the listening viewmodels (if any). Then, the NavigateTo and the GoBack methods are implemented. They are quite simple, because they are in fact just a gateway to the PhoneApplicationFrame. The whole class is as follows: public class NavigationService : INavigationService { private PhoneApplicationFrame _mainFrame; public event NavigatingCancelEventHandler Navigating; public void NavigateTo(Uri pageUri) { if (EnsureMainFrame()) { _mainFrame.Navigate(pageUri); } } public void GoBack() { if (EnsureMainFrame() && _mainFrame.CanGoBack) { _mainFrame.GoBack(); } } private bool EnsureMainFrame() { if (_mainFrame != null) { return true; } _mainFrame = Application.Current.RootVisual as PhoneApplicationFrame; if (_mainFrame != null) { // Could be null if the app runs inside a design tool _mainFrame.Navigating += (s, e) => { if (Navigating != null) { Navigating(s, e); } }; return true; } return false; } } Exposing URIs I find that it is a good practice to expose each page’s URI as a constant. In MVVM Light applications, a good place to do that is the ViewModelLocator, which already acts like a central point of setup for the views and their viewmodels. Note that in some cases, it is necessary to expose the URL as a string, for instance when a query string needs to be passed to the view. So for example we could have: public static readonly Uri MainPageUri = new Uri("/MainPage.xaml", UriKind.Relative); public const string AnotherPageUrl = "/AnotherPage.xaml?param1={0}&param2={1}"; Creating and using the NavigationService Normally, we only need one instance of the NavigationService class. In cases where you use an IOC container, it is easy to simply register a singleton instance. For example, I am using a modified version of a super simple IOC container, and so I can register the navigation service as follows: SimpleIoc.Register<INavigationService, NavigationService>(); Then, it can be resolved where needed with: SimpleIoc.Resolve<INavigationService>(); Or (more frequently), I simply declare a parameter on the viewmodel constructor of type INavigationService and let the IOC container do its magic and inject the instance of the NavigationService when the viewmodel is created. On supported platforms (for example Silverlight 4), it is also possible to use MEF. Or, of course, we can simply instantiate the NavigationService in the ViewModelLocator, and pass this instance as a parameter of the viewmodels’ constructor, injected as a property, etc… Once the instance has been passed to the viewmodel, it can be used, for example with: NavigationService.NavigateTo(ViewModelLocator.ComparisonPageUri); Testing Thanks to the INavigationService interface, navigation can be mocked and tested when the viewmodel is put under unit test. Simply implement and inject a mock class, and assert that the methods are called as they should by the viewmodel. Conclusion As usual, there are multiple ways to code a solution answering your needs. I find that view services are a really neat way to delegate view-specific responsibilities such as animation, dialogs and of course navigation to other classes through an abstracted interface. In some cases, such as the NavigationService class exposed here, it is even possible to standardize the implementation and pack it in a class library for reuse. I hope that this sample is useful! Happy coding. Laurent   Laurent Bugnion (GalaSoft) Subscribe | Twitter | Facebook | Flickr | LinkedIn

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• What comes first in Ruby's object model?

  - by Timothy

  I've been reading Metaprogramming Ruby and the object model like the chicken or egg dilemma. In Ruby 1.8, the Object class is an instance of Class. Module's superclass is Object and is an instance of Class. Class' superclass is Module, and it is an instance of Class (self-referential). Say class SomeClass; end is defined somewhere; SomeClass is an instance of Class, however its superclass is Object. Why does an instance of Class have Object as the superclass instead of nil? Also, if Object is to exist, then Class has to exist, but then Module has to exist, but for Module to exist Object has to exist. How are these classes created?

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• Override Django inlineformset_factory has_changed() to always return True

  - by John

  Hi, I am using the django inlineformset_factory function. a = get_object_or_404(ModelA, pk=id) FormSet = inlineformset_factory(ModelA, ModelB) if request.method == 'POST': metaform = FormSet (instance=a, data=request.POST) if metaform.is_valid(): f = metaform.save(commit=False) for instance in f: instance.updated_by = request.user instance.save() else: metaform = FormSet(instance=a) return render_to_response('nodes/form.html', {'form':metaform}) What is happening is that if I change any of the data then everything works ok and all the data gets updated. However if I don't change any of the data then the data is not updated. i.e. only entries which are changed go through the for loop to be saved. I guess this makes sense as there is no point saving data if it has not changed. However I need to go through and save every object in the form regardless of whether it has any changes on not. So my question is how do I override this so that it goes through and saves every record whether it has any changes or not? Hope this makes sense Thanks

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• how does serializable work in java?

  - by Karl Trumstedt

  If I have an instance of a class that I store in a session I need to make it serializable. This class has a static variable, will this be serialized in every instance stored? The static variable is a reference to a cache containing a lot of data in the background. Will all of this data be serialized? If so, it seems preferable to make this variable transient and re-fetch the cache instance each time the instance is restored. Maybe not store the cache instance at all in the class. Will the constructor execute when a class is restored from a serialized state? if not is there any other method I can use to re-instate a transient variable?

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• Serialization of a TChan String

  - by J Fritsch

  I have declared the following type KEY = (IPv4, Integer) type TPSQ = TVar (PSQ.PSQ KEY POSIXTime) type TMap = TVar (Map.Map KEY [String]) data Qcfg = Qcfg { qthresh :: Int, tdelay :: Rational, cwpsq :: TPSQ, cwmap :: TMap, cw chan :: TChan String } deriving (Show) and would like this to be serializable in a sense that Qcfg can either be written to disk or be sent over the network. When I compile this I get the error No instances for (Show TMap, Show TPSQ, Show (TChan String)) arising from the 'deriving' clause of a data type declaration Possible fix: add instance declarations for (Show TMap, Show TPSQ, Show (TChan String)) or use a standalone 'deriving instance' declaration, so you can specify the instance context yourself When deriving the instance for (Show Qcfg) I am now not quite sure whether there is a chance at all to serialize my TChan although all individual nodes in it are members of the show class. For TMap and TPSQ I wonder whether there are ways to show the values in the TVar directly (because it does not get changed, so there should no need to lock it) without having to declare an instance that does a readTVar ?

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