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• Devoxx 2011: Java EE 6 Hands-on Lab Delivered

  - by arungupta

  I, along with Alexis's help, delivered a Java EE 6 hands-on lab to a packed room of about 40+ attendees at Devoxx 2011. The lab was derived from the OTN Developer Days 2012 version but added lot more content to showcase several Java EE 6 technologies. The problem statement from the lab document states: This hands-on lab builds a typical 3-tier Java EE 6 Web application that retrieves customer information from a database and displays it in a Web page. The application also allows new customers to be added to the database as well. The string-based and type-safe queries are used to query and add rows to the database. Each row in the database table is published as a RESTful resource and is then accessed programmatically. Typical design patterns required by a Web application like validation, caching, observer, partial page rendering, and cross-cutting concerns like logging are explained and implemented using different Java EE 6 technologies. The lab covered Java Persistence API 2, Servlet 3, Enterprise JavaBeans 3.1, JavaServer Faces 2, Java API for RESTful Web Services 1.1, Contexts and Dependency Injection 1.0, and Bean Validation 1.0 over 47 pages of detailed self-paced instructions. Here is the complete Table of Contents: The lab can be downloaded from here and requires only NetBeans IDE "All" or "Java EE" version, which includes GlassFish anyway. All the feedback received from the lab has been incorporated in the instructions and bugs filed (Updated 49559, 205232, 205248, 205256). 80% of the attendees could easily complete the lab and some even completed in much less than 3 hours. That indicates that either more content needs to be added to the lab or the intellectual level of the attendees at the conference was pretty high. I think the lab has enough content for 3 hours but we moved at a much more faster pace so I conclude on the latter. Truly a joy to conduct a lab to 40 Devoxxians! Another related lab that might be handy for folks is "Develop, Deploy, and Monitor your Java EE 6 applications using GlassFish 3.1 Cluster". It explains how: Create a 2-instance GlassFish cluster Front-end with a Web server and a load balancer Demonstrate session replication and fail over Monitor the application using JavaScript The complete lab instructions and source code are available and you can try them. I plan to continue evolving the contents for the Java EE 6 hands-on lab to cover more technologies and features and will announce them on this blog. Let me know on what else would you like to see in the future versions.

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• Devoxx 2011: Java EE 6 Hands-on Lab Delivered

  - by arungupta

  I, along with Alexis's help, delivered a Java EE 6 hands-on lab to a packed room of about 40+ attendees at Devoxx 2011. The lab was derived from the OTN Developer Days 2012 version but added lot more content to showcase several Java EE 6 technologies. The problem statement from the lab document states: This hands-on lab builds a typical 3-tier Java EE 6 Web application that retrieves customer information from a database and displays it in a Web page. The application also allows new customers to be added to the database as well. The string-based and type-safe queries are used to query and add rows to the database. Each row in the database table is published as a RESTful resource and is then accessed programmatically. Typical design patterns required by a Web application like validation, caching, observer, partial page rendering, and cross-cutting concerns like logging are explained and implemented using different Java EE 6 technologies. The lab covered Java Persistence API 2, Servlet 3, Enterprise JavaBeans 3.1, JavaServer Faces 2, Java API for RESTful Web Services 1.1, Contexts and Dependency Injection 1.0, and Bean Validation 1.0 over 47 pages of detailed self-paced instructions. Here is the complete Table of Contents: The lab can be downloaded from here and requires only NetBeans IDE "All" or "Java EE" version, which includes GlassFish anyway. All the feedback received from the lab has been incorporated in the instructions and bugs filed (Updated 49559, 205232, 205248, 205256). 80% of the attendees could easily complete the lab and some even completed in much less than 3 hours. That indicates that either more content needs to be added to the lab or the intellectual level of the attendees at the conference was pretty high. I think the lab has enough content for 3 hours but we moved at a much more faster pace so I conclude on the latter. Truly a joy to conduct a lab to 40 Devoxxians! Another related lab that might be handy for folks is "Develop, Deploy, and Monitor your Java EE 6 applications using GlassFish 3.1 Cluster". It explains how: Create a 2-instance GlassFish cluster Front-end with a Web server and a load balancer Demonstrate session replication and fail over Monitor the application using JavaScript The complete lab instructions and source code are available and you can try them. I plan to continue evolving the contents for the Java EE 6 hands-on lab to cover more technologies and features and will announce them on this blog. Let me know on what else would you like to see in the future versions.

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• Stairway to Transaction Log Management in SQL Server, Level 1: Transaction Log Overview

  The transaction log is used by SQL Server to maintain data consistency and integrity. If the database is not in Simple-recovery mode, it can also be used in an appropriate backup regime to restore the database to a point in time. The Future of SQL Server Monitoring "Being web-based, SQL Monitor enables you to check on your servers from almost any location" Jonathan Allen.Try SQL Monitor now.

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• Speaking at Atlanta.MDF on March 12

  - by RickHeiges

  I am fortunate enough to be speaking to a user group with a really cool name - Atlanta.MDF (Microsoft Database Forum). Although I visit Atlanta often, it usually involves running from one councourse to another and rarely do I get the chance to visit the user group. I have made it to the user group on several occassions in the past, but it has been several years. This will be my first presentation to the group. I will be speaking about Database Consolidation - something I have been doing for years....(read more)

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• "SELECT TOP", "LEFT OUTER JOIN", "ORDER BY" gives extra rows

  - by Codesleuth

  I have the following Access query I'm running through OLE DB in .NET: SELECT TOP 25 tblClient.ClientCode, tblRegion.Region FROM (tblClient LEFT OUTER JOIN tblRegion ON tblClient.RegionCode = tblRegion.RegionCode) ORDER BY tblRegion.Region There are 431 records within tblClient that have RegionCode set to NULL. For some reason, the query above returns all these 431 records instead of the first 25. If I change the query to ORDER BY tblClient.Client (the name of the client) like so: SELECT TOP 25 tblClient.ClientCode, tblRegion.Region FROM (tblClient LEFT OUTER JOIN tblRegion ON tblClient.RegionCode = tblRegion.RegionCode) ORDER BY tblClient.Client I get the expected result set of 25 records, showing a mixture of region names and NULL values. Why is it that ordering by a field retrieved through a LEFT OUTER JOIN will the TOP clause not work?

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• PHP array taking up to much memory

  - by Dylan Taylor

  I have a multidimensional array. The array itself is fine. My problem is that the script takes up monster amounts of memory, and since I'm running this on my MAMP install on my iBook G4, my computer freezes up. Below is the full script. $query = "SELECT * FROM posts ORDER BY id DESC LIMIT 10"; $result = mysql_query($query); $posts = array(); while($row = mysql_fetch_array($result)){ $posts[$row["id"]]['post_id'] = $row["id"]; $posts[$row["id"]]['post_title'] = $row["title"]; $posts[$row["id"]]['post_text'] = $row["text"]; $posts[$row["id"]]['post_tags'] = $row["tags"]; $posts[$row["id"]]['post_category'] = $row["category"]; foreach ($posts as $post) { echo $post["post_id"]; } Is there a workaround that still achieves my goal (to export the MySQL query rows to an array)? -Dylan

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• HQL(hibernate) timestamp range match

  - by Saky

  I need to write a query to get an object between a range of time, currently the query looks like this: Timestamp from = ... Timestamp to = ... getHibernateTemplate().find("from " + Person.class.getName() + " ml where ml.lastModifiedOn>="+from.toString()+" and m1.lastModifiedOn<=" + to.toString()); However, this doesnot work for obvious reasons. How can I format the timestamp to be acceptable by the query. org.springframework.orm.hibernate3.HibernateQueryException: unexpected token: 16 near line 1, column 123 [from Person ml where ml.lastModifiedOn=2010-02-12 16:00:21.292 and m1.lastModifiedOn

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• Get latest sql rows based on latest date and per user

  - by Umair

  I have the following table: RowId, UserId, Date 1, 1, 1/1/01 2, 1, 2/1/01 3, 2, 5/1/01 4, 1, 3/1/01 5, 2, 9/1/01 I want to get the latest records based on date and per UserId but as a part of the following query (due to a reason I cannot change this query as this is auto generated by a tool but I can write pass any thing starting with AND...): SELECT RowId, UserId, Date FROM MyTable WHERE 1 = 1 AND ( // everything which needs to be done goes here . . . ) I have tried similar query, but get an error: Only one expression can be specified in the select list when the subquery is not introduced with EXISTS.

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• Grails and googleJsonAPIService

  - by Calahad

  I am using the googleJsonAPIService to manipulate users (CRUD). This is how I get the Directory instance: def getBuilder() { def builder def httpTransport = googleJsonAPIService.makeTransport() def jsonFactory = googleJsonAPIService.makeJsonFactory() def requestInitialiser = googleJsonAPIService.getRequestInitialiser() builder = new Directory.Builder(httpTransport, jsonFactory, requestInitialiser); return builder } Directory getGoogleService() { Directory googleService = getBuilder().build() return googleService; } Once I have this service, I use it to get a user's details (in my own service) for example: def query = getGoogleService().users().get(id) return handleException { query.execute() } I manually populate a DTO with the result of that query, and this is where my question comes: Is there an elegant way to have this mapping (object returned to DTO) done automatically so all I have to do is pass the class of the object to be returned? This is the structure of the object returned by google : ["agreedToTerms":true,"changePasswordAtNextLogin":false, "creationTime":"2013-11-04T04:33:35.000Z", "emails":[{"address":"[email protected]","primary":true}],...]

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• Aggregate Functions on subsets of data based on current row values with SQL

  - by aasukisuki

  Hopefully that title makes sense... Let's say I have an employee table: ID | Name | Title | Salary ---------------------------- 1 | Bob | Manager | 15285 2 | Joe | Worker | 10250 3 | Al | Worker | 11050 4 | Paul | Manager | 16025 5 | John | Worker | 10450 What I'd like to do is write a query that will give me the above table, along with an averaged salary column, based on the employee title: ID | Name | Title | Salary | Pos Avg -------------------------------------- 1 | Bob | Manager | 15285 | 15655 2 | Joe | Worker | 10250 | 10583 3 | Al | Worker | 11050 | 10583 4 | Paul | Manager | 16025 | 15655 5 | John | Worker | 10450 | 10583 I've tried doing this with a sub-query along the lines of: Select *, (select Avg(e2.salary) from employee e2 where e2.title = e.title) from employee e But I've come to realize that the sub-query is executed first, and has no knowledge of the table alias'd e I'm sure I'm missing something REALLY obvious here, can anyone point me in the right diretion?

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• A strong component keeps everything together

  - by Justin Paul-Oracle

  Most of the times you implement a WebCenter Content based system, you require some sort of customization. Sometimes these customizations need a Java class or two, or libraries (for example, the JavaMail API), or Database Objects (like new tables, views, indexes, etc). I have seen that libraries and Database Objects are usually put in place using manual steps. This means that the library jar files are copied to one of the common classes directory (set in the Content CLASSPATH variable) and/or the database scripts are executed manually. I have also seen people place the custom Java classes in the common classes directory. While this may seem like an easy solution, think about a scenario where you need to disable or uninstall the component or if you have to upgrade or migrate the system. You have to keep these manual steps documented and execute them every time you encounter the above scenarios. It is very common that some of these manual steps are missed when you have multiple teams and people working on the system. Here are a few points to ponder upon: Place all your custom Java classes within your component. Create a new directory, say ${COMPONENT_DIR}/classes, and place your code there. You can choose to bundle all your classes into a jar or you can place the entire class directory structure. Add a path entry to the Build Settings so that it is bundled with the component when you build it. You also need to update the Custom Class Path and the Custom Class Path Load Order under the Advanced Build Settings. This will ensure that the system CLASSPATH is updated to add this new directory. Create a new component for any new library that you want to add. Add the appropriate path entries to the Build Settings so that it is bundled with the component when you build it. You also need to update the Custom Class Path, Custom Class Path Load Order and/or the Custom Library Path under the Advanced Build Settings. Enter a comma separated list of features that this component will provide. When you create other components that will use the features exposed by this component, make sure that you specify a dependency to this library component by specifying the comma separated list of features in the Advanced Build Settings. The component wizard allows you to create custom install/uninstall Java code. The wizard will create a install filter class when you check the “Has Install” checkbox on the “Install/Uninstall Settings” tab. Consider using this filter class to create database objects when you install the component and drop the objects when you uninstall the component. If you do a lot of custom component development, consider creating a install/uninstall Java class, which can execute queries defined within the component. To sum up, whenever you write a new custom component, make sure that you bundle everything within the component.

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• How do I write this as an expression?

  - by itchi

  I'm trying to rewrite a linq to entities query to an expression. My model is a School can have many Persons where Persons are inherited out to teachers, students, etc. The following query works for me: IQueryable<DAL.TEACHER> teacher = from p in School select p.PERSON as ESBDAL.TEACHER; How would I write this as a query expression? I thought something like: IQueryable<DAL.TEACHER> teacher = School.Select(x=>x.PERSON) as IQueryable<DAL.TEACHER>; ...but it does not. Am I misunderstanding the .Select()?

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• Insert rownumber repeatedly in records in t-sql.

  - by jeff

  Hi, I want to insert a row number in a records like counting rows in a specific number of range. example output: RowNumber ID Name 1 20 a 2 21 b 3 22 c 1 23 d 2 24 e 3 25 f 1 26 g 2 27 h 3 28 i 1 29 j 2 30 k I rather to try using the rownumber() over (partition by order by column name) but my real records are not containing columns that will count into 1-3 rownumber. I already try to loop each of record to insert a row count 1-3 but this loop affects the performance of the query. The query will use for the RDL report, that is why as much as possible the performance of the query must be good. any suggestions are welcome. Thanks

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• Double encoded url being fully decoded in ASP.NET

  - by Brad R

  I have just come across something that is quite strange and yet I haven't found any mention on the interwebs of others having the same problem. If I hit my ASP.NET application with a double encoded url then the Request["myQueryParam"] will do a double decode of the query for me. This is not desirable as I have double encoded my query string for a good reason. Can others confirm I'm not doing something obviously wrong, and why this would happen. A solution to prevent it, without doing some nasty query string parsing, would be great too! As an example if you hit the url: http://localhost/MyApp?originalUrl=http%3a%2f%2flocalhost%2fAction%2fRedirect%3fUrl%3d%252fsomeUrl%253futm_medium%253dabc%2526utm_source%253dabc%2526utm_campaign%253dabc (For reference %25 is the % symbol) Then look at the Request["originalUrl"] (page or controller) the string returned is: http://localhost/Action/Redirect?Url=/someUrl?utm_medium=abc&utm_source=abc&utm_campaign=abc I would expect: http://localhost/Action/Redirect?Url=%2fsomeUrl%3futm_medium%3dabc%26utm_source%3dabc%26utm_campaign%3dabc I have also checked in Fiddler and the URL is being passed to the server correctly (one possible culprit could have been the browser decoding the URL before sending).

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• Restlet - Access elements of the request URL

  - by DutrowLLC

  I'm unsure what the proper way is to access parts of the requested URL. In this case, I want to get the requested path without the query variables. This is the only way I found to do it: String path = getRequest().getResourceRef().getHostIdentifier() + getRequest().getResourceRef().getPath(); The result would be the bold part of this url: http://stackoverflow.com/questions/ask?query=value I also found about 6 different ways to get the server name (http://stackoverflow.com) but I'm worried that some of them would fail in certain cases that I am unaware of (why would there be 6 different ways to do one thing): getRequest().getHostRef().getHostIdentifier(); getRequest().getHostRef().getIdentifier(); getRequest().getRootRef().getHostIdentifier(); getRequest().getRootRef().getIdentifier(); getRequest().getResourceRef().getHostIdentifier(); And this seems to get the complete URL with query parameters: getRequest().getResourceRef().getIdentifier(); Any further explanation would be much appreciated.

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• SharePoint 2007 Publishing site and Audience Targeting in Web Part

  - by Robert Vukovic

  In a Publishing site I have web part that has to show news items from the list that has Audience Targeting field. I am using CAML query to retrieve small number of last news items. Is it possible to specify Target Audience in the CAML query ? If not, how should I do it ? Retrieve all results and than apply filter in a loop ? I am practically duplicating Content Query Web Part and I need Audience Targeting in my custom web part.

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• Introducing Windows Azure Mobile Services

  - by Clint Edmonson

  Today I’m excited to share that the Windows Azure Mobile Services public preview is now available. This preview provides a turnkey backend cloud solution designed to accelerate connected client app development. These services streamline the development process by enabling you to leverage the cloud for common mobile application scenarios such as structured storage, user authentication and push notifications. If you’re building a Windows 8 app and want a fast and easy path to creating backend cloud services, this preview provides the capabilities you need. You to take advantage of the cloud to build and deploy modern apps for Windows 8 devices in anticipation of general availability on October 26th. Subsequent preview releases will extend support to iOS, Android, and Windows Phone. Features The preview makes it fast and easy to create cloud services for Windows 8 applications within minutes. Here are the key benefits:  Rapid development: configure a straightforward and secure backend in less than five minutes. Create modern mobile apps: common Windows Azure plus Windows 8 scenarios that Windows Azure Mobile Services preview will support include:  Automated Service API generation providing CRUD functionality and dynamic schematization on top of Structured Storage Structured Storage with powerful query support so a Windows 8 app can seamlessly connect to a Windows Azure SQL database Integrated Authentication so developers can configure user authentication via Windows Live Push Notifications to bring your Windows 8 apps to life with up to date and relevant information Access structured data: connect to a Windows Azure SQL database for simple data management and dynamically created tables. Easy to set and manage permissions. Pricing One of the key things that we’ve consistently heard from developers about using Windows Azure with mobile applications is the need for a low cost and simple offer. The simplest way to describe the pricing for Windows Azure Mobile Services at preview is that it is the same as Windows Azure Websites during preview. What’s FREE? Run up to 10 Mobile Services for free in a multitenant environment Free with valid Windows Azure Free Trial 1GB SQL Database Unlimited ingress 165MB/day egress  What do I pay for? Scaling up to dedicated VMs Once Windows Azure Free Trial expires - SQL Database and egress     Getting Started To start using Mobile Services, you will need to sign up for a Windows Azure free trial, if you have not done so already.  If you already have a Windows Azure account, you will need to request to enroll in this preview feature. Once you’ve enrolled, this getting started tutorial will walk you through building your first Windows 8 application using the preview’s services. The developer center contains more resources to teach you how to: Validate and authorize access to data using easy scripts that execute securely, on the server Easily authenticate your users via Windows Live Send toast notifications and update live tiles in just a few lines of code Our pricing calculator has also been updated for calculate costs for these new mobile services. Questions? Ask in the Windows Azure Forums. Feedback? Send it to [email protected].

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• Interconnect nodes in a Java distributed infrastructure for tweet processing

  - by David Moreno García

  I'm working in a new version of an old project that I used to download and process user statuses from Twitter. The main problem of that project was its infrastructure. I used multiple instances of a java application (trackers) to download from Twitter given an specific task (basically terms to search for), connected with a central node (a web application) that had to process all tweets once per day and generate a new task for each trackers once each 15 minutes. The central node also had to monitor all trackers and enable/disable them under user petition. This, as I said, was too slow because I had multiple bottlenecks, so in this new version I want to improve the infrastructure and isolate all functionalities in specific nodes. I also need a good notification system to receive notifications for any node. So, in the next diagram I show the components that I'll need in this new version: As you can see, there are more nodes. Here are some notes about them: Dashboard: Controls trackers statuses and send a single task to each of them (under user request). The trackers will use this task until replaced with a new one (if done, not each 15 minutes like before). Search engine: I need to store all the tweets. They are firstly stored in a local database for each tracker but after that I'm thinking on using something like Elasticsearch to be able to do fast searches. Tweet processor: Just and isolated component with its own database (maybe something like the search engine to have fast access to info generated by the module). In the future more could be added. Application UI: A web application with a shared database with the Dashboard (mainly to store users information and preferences). Indeed, both could be merged into a single web. The main difference with the previous version of the project is that now they will be isolated and they will only show information and send requests. I will not do any heavy task in them (like process tweets as I did before). So, having this components, my main headache is how to structure all to not have to rewrite a lot of code every time I need to access any new data. Another headache is how can I interconnect nodes. I could use sockets but that is a pain in the ass. Maybe a REST layer? And finally, if all the nodes are isolated, how could I generate notifications for each user which info is only in the database used by the Application UI? I'm programming this using Java and Spring (at least I used them in the last version) but I have no problems with changing the language if I can take advantage of a tool/library/engine to make my life easier and have a better platform. Any comment will be appreciated.

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• nHibernate HQL dynamic Instantiation question

  - by Rey

  Hello all, I can't find what's going on with the following nHibernate HQL. here's my VB.Net code: Return _Session.GetNamedQuery("PersonAnthroSummary").SetInt32(0, 2).UniqueResult() My Named Query: <sql-query name="PersonAnthroSummary"> select New PersonAnthroSummary( Anthro.Height, Anthro.Weight ) from PersonAnthroContact as Anthro where Anthro.ID = ? </sql-query> and i am importing the DTO class: <import class="xxxxxxx.DataServices.PersonAnthroSummary, xxxxxxxxx.DataServices"/> PersonAnthroSummary has a constructor that will take height and weight arguments. when i test this, nHibernate throwing following exception: {"Incorrect syntax near 'Anthro'."} and generated QueryString is: "select New PersonAnthroSummary( Anthro.Height, Anthro.Weight ) from PersonAnthroContact as Anthro where Anthro.ID = @p0" Can some one tell me what i'm doing wrong here?

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• Gail Shaw's SQL Server Howlers

  For the latest in our series of SQL Server Howlers, we asked Gail Shaw which common SQL Server mistakes and misunderstandings lead to tearful DBAs and plaintive cries for help on the forums. Keep your database and application development in syncSQL Connect is a Visual Studio add-in that brings your databases into your solution. It then makes it easy to keep your database in sync, and commit to your existing source control system. Find out more.

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• JPA, scope, and autosave?

  - by arinte

  I am using JPA and lets say I do something like this public class MoRun extends Thread {... public void run() { final EntityManagerFactory emFactory = Persistence.createEntityManagerFactory("pu"); EntityManager manager = emFactory.createEntityManager(); manager.setFlushMode(FlushModeType.COMMIT); someMethod(manager); ... } public void someMethod(EntityManager manager){ Query query = manager.createNamedQuery("byStates"); List<State> list = query.getResultList(); for (State state : list) { if(someTest) state.setValue(...) } ... } So for those objects that pass "someTest" and values are updated are those changes automatically persisted to the db even though there is no transaction and I don't explicitly "manager.save(state)" the object? I ask because it seems like it is and I was wondering if the flush is doing it?

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• checkUnique function?

  - by Chris Leah

  Hey, so I have created a function to check the DB for unique entries, but when I call the function it doesn't seem to work and gives me a fatal error any ideas from the function or do you wish to see the sign up page calling it. Thanks :) //Check for unique entries function checkUnique($table, $field, $compared) { $query = $mysqli->query('SELECT '.$mysqli->real_escape_string($field).' FROM '.$mysqli->real_escape_string($table).' WHERE "'.$mysqli->real_escape_string($field).'" = "'.$mysqli->real_escape_string($compared).'"'); if(!$query){ return TRUE; } else { return FALSE; } } The page calling it..... if (!empty($_POST['username']) && !empty($_POST['password']) && $_POST['password']==$_POST['password_confirm'] && !empty($_POST['email']) && validateEmail($_POST['email']) == TRUE && checkUnqiue('users', 'email', $_POST['email']) == TRUE && checkUnique('users', 'username', $_POST['username']) == TRUE)

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• Need your feedback on our new SQL Server Connectivity portal

  - by The Official Microsoft IIS Site

  SQL Server, as a database product, has grown over the years and there are multiple ways to connect to it. Often, the different ways to connect to the database get documented and discussed in the various technology sections, and the technology choice determines which connectivity method one is going to use. For example, if one is writing a C++ application then one has to go with ODBC whereas a PHP web site developer will choose the PHP driver of course. Until now, this information was scattered all...(read more)

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• Cascading updates with business key equality: Hibernate best practices?

  - by Traphicone

  I'm new to Hibernate, and while there are literally tons of examples to look at, there seems to be so much flexibility here that it's sometimes very hard to narrow all the options down the best way of doing things. I've been working on a project for a little while now, and despite reading through a lot of books, articles, and forums, I'm still left with a bit of a head scratcher. Any veteran advice would be very appreciated. So, I have a model involving two classes with a one-to-many relationship from parent to child. Each class has a surrogate primary key and a uniquely constrained composite business key. <class name="Container"> <id name="id" type="java.lang.Long"> <generator class="identity"/> </id> <properties name="containerBusinessKey" unique="true" update="false"> <property name="name" not-null="true"/> <property name="owner" not-null="true"/> </properties> <set name="items" inverse="true" cascade="all-delete-orphan"> <key column="container" not-null="true"/> <one-to-many class="Item"/> </set> </class> <class name="Item"> <id name="id" type="java.lang.Long"> <generator class="identity"/> </id> <properties name="itemBusinessKey" unique="true" update="false"> <property name="type" not-null="true"/> <property name="color" not-null="true"/> </properties> <many-to-one name="container" not-null="true" update="false" class="Container"/> </class> The beans behind these mappings are as boring as you can possibly imagine--nothing fancy going on. With that in mind, consider the following code: Container c = new Container("Things", "Me"); c.addItem(new Item("String", "Blue")); c.addItem(new Item("Wax", "Red")); Transaction t = session.beginTransaction(); session.saveOrUpdate(c); t.commit(); Everything works fine the first time, and both the Container and its Items are persisted. If the above code block is executed again, however, Hibernate throws a ConstraintViolationException--duplicate values for the "name" and "owner" columns. Because the new Container instance has a null identifier, Hibernate assumes it is an unsaved transient instance. This is expected but not desired. Since the persistent and transient Container objects have the same business key values, what we really want is to issue an update. It is easy enough to convince Hibernate that our new Container instance is the same as our old one. With a quick query we can get the identifier of the Container we'd like to update, and set our transient object's identifier to match. Container c = new Container("Things", "Me"); c.addItem(new Item("String", "Blue")); c.addItem(new Item("Wax", "Red")); Query query = session.createSQLQuery("SELECT id FROM Container" + "WHERE name = ? AND owner = ?"); query.setString(0, c.getName()); query.setString(1, c.getOwner()); BigInteger id = (BigInteger)query.uniqueResult(); if (id != null) { c.setId(id.longValue()); } Transaction t = session.beginTransaction(); session.saveOrUpdate(c); t.commit(); This almost satisfies Hibernate, but because the one-to-many relationship from Container to Item cascades, the same ConstraintViolationException is also thrown for the child Item objects. My question is: what is the best practice in this situation? It is highly recommended to use surrogate primary keys, and it is also recommended to use business key equality. When you put these two recommendations in to practice together, however, two of the greatest conveniences of Hibernate--saveOrUpdate and cascading operations--seem to be rendered almost completely useless. As I see it, I have only two options: Manually fetch and set the identifier for each object in the mapping. This clearly works, but for even a moderately sized schema this is a lot of extra work which it seems Hibernate could easily be doing. Write a custom interceptor to fetch and set object identifiers on each operation. This looks cleaner than the first option but is rather heavy-handed, and it seems wrong to me that you should be expected to write a plug-in which overrides Hibernate's default behavior for a mapping which follows the recommended design. Is there a better way? Am I making completely the wrong assumptions? I'm hoping that I'm just missing something. Thanks.

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• What are the algorithms that are used for working with large data in popular web applications

  - by Moss Farmer

  I am looking for some well known algorithms that can be considered while handling very large amount of data.(Edit- By large amount of data I refer to records in a database excluding blobs). These algorithms if not in totality but in parts may be used in big web applications like Twitter, Last.fm , Amazon ,etc. Specifically, I'm looking for names or links to such algorithms. My primary interest lies in developing a very deep understanding on working with large database records and writing efficient code for working with the same.

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