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  • NFS or GFS for LVS 10 Server Setup

    - by Michael Robinson
    Currently we have a 10 servers LVS hosting setup. The people we hired to set it up did not anything about GFS which was our preferred Central Storage File System Solution. As we have tight time constraint, we just told them to use whatever they were familiar with which is NFS. I have since done some research and it seems that NFS is not ideal for the type of high traffic site we are hoping to build. I couldn't find much info online about the signaficance differences between the 2. As we to setup all servers again right now, should we stick with NFS or find someone who knows how to setup GFS amd go with that. We need a setup that is highly reliable and scalable as we intend. As after initial setup is done, we expect high increases in traffic and load.

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  • Squeeze/Lenny compilation : Library Link error

    - by PEZ
    I've got a problem here : I have a C++ Library ("DataTsBroad") and a C++ Test app ("DataTsBroadTest"), to test it. Actually, the Lib and the Test app are both compiled an a Debian Lenny. Now, i want to continue to compile my Test app on a Debian Lenny (customer constraint), but i would compile my lib on a Squeeze or a Wheezy to work on the last Debian releases. So, i successfully compiled my Lib on a Squeeze, But, after, when i try to compile my Test app with this Lib on the Lenny, it fails ! There is a Link Error : Linking CXX executable DataTsBroadTest /home/nis/pezierg/test/ProductMak/Export/DataTsBroad/L64/Release/libDataTsBroad64.so: undefined reference to `std::ctype::_M_widen_init() const@GLIBCXX_3.4.11' collect2: ld returned 1 exit status make[2]: *** [DataTsBroadTest] Error 1 make[1]: *** [CMakeFiles/DataTsBroadTest.dir/all] Error 2 make: * [all] Error 2 The problem is certainly due to ostream C++ Lib, I tried to comment all it's uses in my Lib and it works. But how can i really fix the problem ?

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  • Way to update / refresh / reschedule project plan after adding a vacation / changing calendar

    - by CodeCanvas
    I had created a project plan using MS-Project 2010 (not server). I had set the task schedule mode to "Auto Scheduled" and entered the necessary tasks. Since it is a single person project I also added one person to the Resource of the file and assigned that resource to all the tasks and leveled the project. After the plan was put in and tasks were leveled I figured the calendar was not correctly set (in UAE the weekend is Friday and Saturday instead of Saturday and Sunday). So, I updated the default calendar (Standard) of the project by going to Project-Change Working Time-Work Weeks and changed them as needed. But after doing this, the tasks are still scheduled over Friday and Saturday even though I have marked them as nonworking days in the standard calendar. I tried the following for the tasks to refresh, but I was not successful: Updated all tasks to use the "Standard" calendar in the project Selected option so that tasks do not ignore resource calendars Added a constraint "As Soon As Possible" Executed "Level All" Any help on solving this issue would be much appreciated, thanks in advance.

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  • Virtual Network Printer

    - by user113720
    I'm pretty new to Microsoft Servers so don't blame me if the question isn't that smart [I'm a Unix guy]. I need to install a Virtual Printer of a Microsoft Server 2008 r2. The requirements are: The printer must print on a file {whatever file... txt or pdf } The printer must run on a server The printer must accept plaintext from a specific IP:port The connection between the device that prints and the server is a local network I've tried to install a virtual printer, but I cannot specify the constraint about the socket from which receive data to print. Thank you so much

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  • Abbreviations override in comments and quoted text

    - by dotancohen
    I have the following handy abbreviation in VIM: iab for for<Space>(<Space>{{<Esc>kA<Left><Left><Left><Left><C-R>=Eatchar('\s')<CR> This nicely replaces for with the following text: for ( ) { } However, I would like this abbreviation to work only in code, not in comments or in single- or double- quoted strings. How might this constraint be accomplished? Note that I usually code in PHP, but often enough I find myself in other C-style languages (C, Java, occasional C#, etc.). Preventing the abbreviation from working in Python would be a nice bonus though I don't mind manually turning it off in Python if that is not an option. Thanks!

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  • SQL-Server 2008 : Table Insert and Range Check ?

    - by LB .
    I'm using the Table Value constructor to insert a bunch of rows at a time. However if i'm using sql replication, I run into a range check constraint on the publisher on my id column managed automatically. The reason is the fact that the id range doesn't seem to be increased during an insert of several values, meaning that the max id is reached before the actual range expansion could occur (or the id threshold). It looks like this problem for which the solution is either running the merge agent or run the sp_adjustpublisheridentityrange stored procedure. I'm litteraly doing something like : INSERT INTO dbo.MyProducts (Name, ListPrice) VALUES ('Helmet', 25.50), ('Wheel', 30.00), ((SELECT Name FROM Production.Product WHERE ProductID = 720), (SELECT ListPrice FROM Production.Product WHERE ProductID = 720)); GO What are my options (if I don't want or can't adopt any of the proposed solution) ? Expand the range ? Decrease the threshold ? Can I programmatically modify my request to circumvent this problem ? thanks.

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  • Postgres backup

    - by Abbass
    Hello, I have a Bacula script that does an automatic backup of a Postgres Database. The script makes two backups using (pg_dump) of the data base : The schema only and the data only. /usr/bin/pg_dump --format=c -s $dbname --file=$DUMPDIR/$dbname.schema.dump /usr/bin/pg_dump --format=c -a $dbname --file=$DUMPDIR/$dbname.data.dump The problem is that I can't figure out how to restore it with pg_restore. Do I need to create the database and the users before then restore the schema and finally the data. I did the following : pg_restore --format=c -s -C -d template1 xxx.schema.dump pg_restore --format=c -a -d xxx xxx.data.dump This first restore creates the database with emtpy tables but the second gives many error like this one : pg_restore: [archiver (db)] COPY failed: ERROR: insert or update on table "Table1" violates foreign key constraint "fkf6977a478dd41734" DETAIL: Key (contentid)=(1474566) is not present in table "Table23". Any ideas?

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  • PostgreSQL, update existing rows with pg_restore

    - by woky
    Hello. I need to sync two PostgreSQL databases (some tables from development db to production db) sometimes. So I came up with this script: [...] pg_dump -a -F tar -t table1 -t table2 -U user1 dbname1 | \ pg_restore -a -U user2 -d dbname2 [...] The problem is that this works just for newly added rows. When I edit non-PK column I get constraint error and row isn't updated. For each dumped row I need to check if it exists in destination database (by PK) and if so delete it before INSERT/COPY. Thanks for your advice. (Previously posted on stackoverflow.com, but IMHO this is better place for this question).

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  • How to use filegroups for DB split?

    - by Robin Jain
    In my project I have one DB used for everything. I want it to break into two databases. Static tables having look up values are to be stored in one DB and another DB would be having tables with dynamic data. My problem is that how would I use foreign key constraint in between those two DBs. Can someone help me out and suggest a way to proceed, better if I'm provided an example for the same. I thought of using synonyms for tables and then constraints on synonyms. but later I came to know that synonyms couldn't be used for constraints. I need to maintain relationships among the tables from both DB as the issue is with update, with a new release I just want to update look up tables and for the same I want to split my DB. I want to know how FileGroups could be used for this.

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  • Why does windows XP minimize my swing full screen window on my second screen ?

    - by Laurent K
    Hello dear fellows, In the application I'm developping (in Java/swing), I have to show a full screen window on the second screen of the user. I did this using a code similar to the one you'll find below... Be, as soon as I click in a window opened by windows explorer, or as soon as I open windows explorer (i'm using windows XP), the full screen window is minimized... Do you know any way or workaround to fix this problem, or is there something important I did not understand with full screen windows? Thanks for the help, import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.JWindow; import java.awt.BorderLayout; import java.awt.Dimension; import java.awt.GraphicsDevice; import java.awt.GraphicsEnvironment; import java.awt.Window; import javax.swing.JButton; import javax.swing.JToggleButton; import java.awt.Rectangle; import java.awt.GridBagLayout; import javax.swing.JLabel; public class FullScreenTest { private JFrame jFrame = null; // @jve:decl-index=0:visual-constraint="94,35" private JPanel jContentPane = null; private JToggleButton jToggleButton = null; private JPanel jFSPanel = null; // @jve:decl-index=0:visual-constraint="392,37" private JLabel jLabel = null; private Window window; /** * This method initializes jFrame * * @return javax.swing.JFrame */ private JFrame getJFrame() { if (jFrame == null) { jFrame = new JFrame(); jFrame.setSize(new Dimension(474, 105)); jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); jFrame.setContentPane(getJContentPane()); } return jFrame; } /** * This method initializes jContentPane * * @return javax.swing.JPanel */ private JPanel getJContentPane() { if (jContentPane == null) { jContentPane = new JPanel(); jContentPane.setLayout(null); jContentPane.add(getJToggleButton(), null); } return jContentPane; } /** * This method initializes jToggleButton * * @return javax.swing.JToggleButton */ private JToggleButton getJToggleButton() { if (jToggleButton == null) { jToggleButton = new JToggleButton(); jToggleButton.setBounds(new Rectangle(50, 23, 360, 28)); jToggleButton.setText("Show Full Screen Window on 2nd screen"); jToggleButton.addActionListener(new java.awt.event.ActionListener() { public void actionPerformed(java.awt.event.ActionEvent e) { showFullScreenWindow(jToggleButton.isSelected()); } }); } return jToggleButton; } protected void showFullScreenWindow(boolean b) { if(window==null){ window = initFullScreenWindow(); } window.setVisible(b); } private Window initFullScreenWindow() { GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment(); GraphicsDevice[] gds = ge.getScreenDevices(); GraphicsDevice gd = gds[1]; JWindow window = new JWindow(gd.getDefaultConfiguration()); window.setContentPane(getJFSPanel()); gd.setFullScreenWindow(window); return window; } /** * This method initializes jFSPanel * * @return javax.swing.JPanel */ private JPanel getJFSPanel() { if (jFSPanel == null) { jLabel = new JLabel(); jLabel.setBounds(new Rectangle(18, 19, 500, 66)); jLabel.setText("Hello ! Now, juste open windows explorer and see what happens..."); jFSPanel = new JPanel(); jFSPanel.setLayout(null); jFSPanel.setSize(new Dimension(500, 107)); jFSPanel.add(jLabel, null); } return jFSPanel; } /** * @param args */ public static void main(String[] args) { FullScreenTest me = new FullScreenTest(); me.getJFrame().setVisible(true); } }

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  • MySQL: Creating table with FK error (errno 150)

    - by Peter Bailey
    I've tried searching on this error and nothing I've found helps me, so I apologize in advance if this is a duplicate and I'm just too dumb to find it. I've created a model with MySQL Workbench and am now attempting to install it to a mysql server. Using File Export Forward Engineer SQL CREATE Script... it outputs a nice big file for me, with all the settings I ask for. I switch over to MySQL GUI Tools (the Query Browser specifically) and load up this script (note that I'm going form one official MySQL tool to another). However, when I try to actually execute this file, I get the same error over and over SQLSTATE[HY000]: General error: 1005 Can't create table './srs_dev/location.frm' (errno: 150) "OK", I say to myself, something is wrong with the location table. So I check out the definition in the output file. SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0; SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0; SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='TRADITIONAL'; -- ----------------------------------------------------- -- Table `state` -- ----------------------------------------------------- DROP TABLE IF EXISTS `state` ; CREATE TABLE IF NOT EXISTS `state` ( `state_id` INT NOT NULL AUTO_INCREMENT , `iso_3166_2_code` VARCHAR(2) NOT NULL , `name` VARCHAR(60) NOT NULL , PRIMARY KEY (`state_id`) ) ENGINE = InnoDB; -- ----------------------------------------------------- -- Table `brand` -- ----------------------------------------------------- DROP TABLE IF EXISTS `brand` ; CREATE TABLE IF NOT EXISTS `brand` ( `brand_id` INT UNSIGNED NOT NULL AUTO_INCREMENT , `name` VARCHAR(45) NOT NULL , `domain` VARCHAR(45) NOT NULL , `manager_name` VARCHAR(100) NULL , `manager_email` VARCHAR(255) NULL , PRIMARY KEY (`brand_id`) ) ENGINE = InnoDB; -- ----------------------------------------------------- -- Table `location` -- ----------------------------------------------------- DROP TABLE IF EXISTS `location` ; CREATE TABLE IF NOT EXISTS `location` ( `location_id` INT UNSIGNED NOT NULL AUTO_INCREMENT , `name` VARCHAR(255) NOT NULL , `address_line_1` VARCHAR(255) NULL , `address_line_2` VARCHAR(255) NULL , `city` VARCHAR(100) NULL , `state_id` TINYINT UNSIGNED NULL DEFAULT NULL , `postal_code` VARCHAR(10) NULL , `phone_number` VARCHAR(20) NULL , `fax_number` VARCHAR(20) NULL , `lat` DECIMAL(9,6) NOT NULL , `lng` DECIMAL(9,6) NOT NULL , `contact_url` VARCHAR(255) NULL , `brand_id` TINYINT UNSIGNED NOT NULL , `summer_hours` VARCHAR(255) NULL , `winter_hours` VARCHAR(255) NULL , `after_hours_emergency` VARCHAR(255) NULL , `image_file_name` VARCHAR(100) NULL , `manager_name` VARCHAR(100) NULL , `manager_email` VARCHAR(255) NULL , `created_date` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP , PRIMARY KEY (`location_id`) , CONSTRAINT `fk_location_state` FOREIGN KEY (`state_id` ) REFERENCES `state` (`state_id` ) ON DELETE NO ACTION ON UPDATE NO ACTION, CONSTRAINT `fk_location_brand` FOREIGN KEY (`brand_id` ) REFERENCES `brand` (`brand_id` ) ON DELETE NO ACTION ON UPDATE NO ACTION) ENGINE = InnoDB; CREATE INDEX `fk_location_state` ON `location` (`state_id` ASC) ; CREATE INDEX `fk_location_brand` ON `location` (`brand_id` ASC) ; CREATE INDEX `idx_lat` ON `location` (`lat` ASC) ; CREATE INDEX `idx_lng` ON `location` (`lng` ASC) ; Looks ok to me. I surmise that maybe something is wrong with the Query Browser, so I put this file on the server and try to load it this way ] mysql -u admin -p -D dbname < path/to/create_file.sql And I get the same error. So I start to Google this issue and find all kinds of accounts that talk about an error with InnoDB style tables that fail with foreign keys, and the fix is to add "SET FOREIGN_KEY_CHECKS=0;" to the SQL script. Well, as you can see, that's already part of the file that MySQL Workbench spat out. So, my question is then, why is this not working when I'm doing what I think I'm supposed to be doing? Version Info: # MySQL: 5.0.45 GUI Tools: 1.2.17 Workbench: 5.0.30

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  • How do I get a delete trigger working using fluent API in CTP5?

    - by user668472
    I am having trouble getting referential integrity dialled down enough to allow my delete trigger to fire. I have a dependent entity with three FKs. I want it to be deleted when any of the principal entities is deleted. For principal entities Role and OrgUnit (see below) I can rely on conventions to create the required one-many relationship and cascade delete does what I want, ie: Association is removed when either principal is deleted. For Member, however, I have multiple cascade delete paths (not shown here) which SQL Server doesn't like, so I need to use fluent API to disable cascade deletes. Here is my (simplified) model: public class Association { public int id { get; set; } public int roleid { get; set; } public virtual Role role { get; set; } public int? memberid { get; set; } public virtual Member member { get; set; } public int orgunitid { get; set; } public int OrgUnit orgunit { get; set; } } public class Role { public int id { get; set; } public virtual ICollection<Association> associations { get; set; } } public class Member { public int id { get; set; } public virtual ICollection<Association> associations { get; set; } } public class Organization { public int id { get; set; } public virtual ICollection<Association> associations { get; set; } } My first run at fluent API code looks like this: protected override void OnModelCreating(System.Data.Entity.ModelConfiguration.ModelBuilder modelBuilder) { DbDatabase.SetInitializer<ConfDB_Model>(new ConfDBInitializer()); modelBuilder.Entity<Member>() .HasMany(m=>m.assocations) .WithOptional(a=>a.member) .HasForeignKey(a=>a.memberId) .WillCascadeOnDelete(false); } My seed function creates the delete trigger: protected override void Seed(ConfDB_Model context) { context.Database.SqlCommand("CREATE TRIGGER MemberAssocTrigger ON dbo.Members FOR DELETE AS DELETE Assocations FROM Associations, deleted WHERE Associations.memberId = deleted.id"); } PROBLEM: When I run this, create a Role, a Member, an OrgUnit, and an Association tying the three together all is fine. When I delete the Role, the Association gets cascade deleted as I expect. HOWEVER when I delete the Member I get an exception with a referential integrity error. I have tried setting ON CASCADE SET NULL because my memberid FK is nullable but SQL complains again about multiple cascade paths, so apparently I can cascade nothing in the Member-Association relationship. To get this to work I must add the following code to Seed(): context.Database.SqlCommand("ALTER TABLE dbo.ACLEntries DROP CONSTRAINT member_aclentries"); As you can see, this drops the constraint created by the model builder. QUESTION: this feels like a complete hack. Is there a way using fluent API for me to say that referential integrity should NOT be checked, or otherwise to get it to relax enough for the Member delete to work and allow the trigger to be fired? Thanks in advance for any help you can offer. Although fluent APIs may be "fluent" I find them far from intuitive.

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  • Handling EJB/JPA exceptions in a “beautiful” way

    - by Rodrigues, Raphael
    In order to handle JPA exceptions, there are some ways already detailed in lots of blogs. Here, I intend to show one of them, which I consider kind of “beauty”. My use case has a unique constraint, when the User try to create a duplicate value in database. The JPA throws a java.sql.SQLIntegrityConstraintViolationException, and I have to catch it and replace the message. In fact, ADF Business Components framework already has a beautiful solution for this very well documented here . However, for EJB/JPA there's no similar approach. In my case, what I had to do was: 1. Create a custom Error Handler Class in DataBindings file; a. Here is how you accomplish it. 2. Override the reportException method and check if the type of exception exists on property file a. If yes, I change the message and rethrows the exception b. If not, go on the execution The main goal of this approach is whether a new or unhandled Exception was raised, the job is, only create a single entry in bundle property file. Here are pictures step by step: 1. CustomExceptionHandler.java 2. Databindings.cpx 3. Bundle file 4. jspx: 5. Stacktrace: Give your opinion, what did you think about that?

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  • Java Spotlight Episode 150: James Gosling on Java

    - by Roger Brinkley
    Interview with James Gosling, father of Java and Java Champion, on the history of Java, his work at Liquid Robotics, Netbeans, the future of Java and what he sees as the next revolutionary trend in the computer industry. Right-click or Control-click to download this MP3 file. You can also subscribe to the Java Spotlight Podcast Feed to get the latest podcast automatically. If you use iTunes you can open iTunes and subscribe with this link: Java Spotlight Podcast in iTunes. Show Notes Feature Interview James Gosling received a BSc in Computer Science from the University of Calgary, Canada in 1977. He received a PhD in Computer Science from Carnegie-Mellon University in 1983. The title of his thesis was "The Algebraic Manipulation of Constraints". He spent many years as a VP & Fellow at Sun Microsystems. He has built satellite data acquisition systems, a multiprocessor version of Unix, several compilers, mail systems and window managers. He has also built a WYSIWYG text editor, a constraint based drawing editor and a text editor called `Emacs' for Unix systems. At Sun his early activity was as lead engineer of the NeWS window system. He did the original design of the Java programming language and implemented its original compiler and virtual machine. He has been a contributor to the Real-Time Specification for Java, and a researcher at Sun labs where his primary interest was software development tools.     He then was the Chief Technology Officer of Sun's Developer Products Group and the CTO of Sun's Client Software Group. He briefly worked for Oracle after the acquisition of Sun. After a year off, he spent some time at Google and is now the chief software architect at Liquid Robotics where he spends his time writing software for the Waveglider, an autonomous ocean-going robot.

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  • So…is it a Seek or a Scan?

    - by Paul White
    You’re probably most familiar with the terms ‘Seek’ and ‘Scan’ from the graphical plans produced by SQL Server Management Studio (SSMS).  The image to the left shows the most common ones, with the three types of scan at the top, followed by four types of seek.  You might look to the SSMS tool-tip descriptions to explain the differences between them: Not hugely helpful are they?  Both mention scans and ranges (nothing about seeks) and the Index Seek description implies that it will not scan the index entirely (which isn’t necessarily true). Recall also yesterday’s post where we saw two Clustered Index Seek operations doing very different things.  The first Seek performed 63 single-row seeking operations; and the second performed a ‘Range Scan’ (more on those later in this post).  I hope you agree that those were two very different operations, and perhaps you are wondering why there aren’t different graphical plan icons for Range Scans and Seeks?  I have often wondered about that, and the first person to mention it after yesterday’s post was Erin Stellato (twitter | blog): Before we go on to make sense of all this, let’s look at another example of how SQL Server confusingly mixes the terms ‘Scan’ and ‘Seek’ in different contexts.  The diagram below shows a very simple heap table with two columns, one of which is the non-clustered Primary Key, and the other has a non-unique non-clustered index defined on it.  The right hand side of the diagram shows a simple query, it’s associated query plan, and a couple of extracts from the SSMS tool-tip and Properties windows. Notice the ‘scan direction’ entry in the Properties window snippet.  Is this a seek or a scan?  The different references to Scans and Seeks are even more pronounced in the XML plan output that the graphical plan is based on.  This fragment is what lies behind the single Index Seek icon shown above: You’ll find the same confusing references to Seeks and Scans throughout the product and its documentation. Making Sense of Seeks Let’s forget all about scans for a moment, and think purely about seeks.  Loosely speaking, a seek is the process of navigating an index B-tree to find a particular index record, most often at the leaf level.  A seek starts at the root and navigates down through the levels of the index to find the point of interest: Singleton Lookups The simplest sort of seek predicate performs this traversal to find (at most) a single record.  This is the case when we search for a single value using a unique index and an equality predicate.  It should be readily apparent that this type of search will either find one record, or none at all.  This operation is known as a singleton lookup.  Given the example table from before, the following query is an example of a singleton lookup seek: Sadly, there’s nothing in the graphical plan or XML output to show that this is a singleton lookup – you have to infer it from the fact that this is a single-value equality seek on a unique index.  The other common examples of a singleton lookup are bookmark lookups – both the RID and Key Lookup forms are singleton lookups (an RID lookup finds a single record in a heap from the unique row locator, and a Key Lookup does much the same thing on a clustered table).  If you happen to run your query with STATISTICS IO ON, you will notice that ‘Scan Count’ is always zero for a singleton lookup. Range Scans The other type of seek predicate is a ‘seek plus range scan’, which I will refer to simply as a range scan.  The seek operation makes an initial descent into the index structure to find the first leaf row that qualifies, and then performs a range scan (either backwards or forwards in the index) until it reaches the end of the scan range. The ability of a range scan to proceed in either direction comes about because index pages at the same level are connected by a doubly-linked list – each page has a pointer to the previous page (in logical key order) as well as a pointer to the following page.  The doubly-linked list is represented by the green and red dotted arrows in the index diagram presented earlier.  One subtle (but important) point is that the notion of a ‘forward’ or ‘backward’ scan applies to the logical key order defined when the index was built.  In the present case, the non-clustered primary key index was created as follows: CREATE TABLE dbo.Example ( key_col INTEGER NOT NULL, data INTEGER NOT NULL, CONSTRAINT [PK dbo.Example key_col] PRIMARY KEY NONCLUSTERED (key_col ASC) ) ; Notice that the primary key index specifies an ascending sort order for the single key column.  This means that a forward scan of the index will retrieve keys in ascending order, while a backward scan would retrieve keys in descending key order.  If the index had been created instead on key_col DESC, a forward scan would retrieve keys in descending order, and a backward scan would return keys in ascending order. A range scan seek predicate may have a Start condition, an End condition, or both.  Where one is missing, the scan starts (or ends) at one extreme end of the index, depending on the scan direction.  Some examples might help clarify that: the following diagram shows four queries, each of which performs a single seek against a column holding every integer from 1 to 100 inclusive.  The results from each query are shown in the blue columns, and relevant attributes from the Properties window appear on the right: Query 1 specifies that all key_col values less than 5 should be returned in ascending order.  The query plan achieves this by seeking to the start of the index leaf (there is no explicit starting value) and scanning forward until the End condition (key_col < 5) is no longer satisfied (SQL Server knows it can stop looking as soon as it finds a key_col value that isn’t less than 5 because all later index entries are guaranteed to sort higher). Query 2 asks for key_col values greater than 95, in descending order.  SQL Server returns these results by seeking to the end of the index, and scanning backwards (in descending key order) until it comes across a row that isn’t greater than 95.  Sharp-eyed readers may notice that the end-of-scan condition is shown as a Start range value.  This is a bug in the XML show plan which bubbles up to the Properties window – when a backward scan is performed, the roles of the Start and End values are reversed, but the plan does not reflect that.  Oh well. Query 3 looks for key_col values that are greater than or equal to 10, and less than 15, in ascending order.  This time, SQL Server seeks to the first index record that matches the Start condition (key_col >= 10) and then scans forward through the leaf pages until the End condition (key_col < 15) is no longer met. Query 4 performs much the same sort of operation as Query 3, but requests the output in descending order.  Again, we have to mentally reverse the Start and End conditions because of the bug, but otherwise the process is the same as always: SQL Server finds the highest-sorting record that meets the condition ‘key_col < 25’ and scans backward until ‘key_col >= 20’ is no longer true. One final point to note: seek operations always have the Ordered: True attribute.  This means that the operator always produces rows in a sorted order, either ascending or descending depending on how the index was defined, and whether the scan part of the operation is forward or backward.  You cannot rely on this sort order in your queries of course (you must always specify an ORDER BY clause if order is important) but SQL Server can make use of the sort order internally.  In the four queries above, the query optimizer was able to avoid an explicit Sort operator to honour the ORDER BY clause, for example. Multiple Seek Predicates As we saw yesterday, a single index seek plan operator can contain one or more seek predicates.  These seek predicates can either be all singleton seeks or all range scans – SQL Server does not mix them.  For example, you might expect the following query to contain two seek predicates, a singleton seek to find the single record in the unique index where key_col = 10, and a range scan to find the key_col values between 15 and 20: SELECT key_col FROM dbo.Example WHERE key_col = 10 OR key_col BETWEEN 15 AND 20 ORDER BY key_col ASC ; In fact, SQL Server transforms the singleton seek (key_col = 10) to the equivalent range scan, Start:[key_col >= 10], End:[key_col <= 10].  This allows both range scans to be evaluated by a single seek operator.  To be clear, this query results in two range scans: one from 10 to 10, and one from 15 to 20. Final Thoughts That’s it for today – tomorrow we’ll look at monitoring singleton lookups and range scans, and I’ll show you a seek on a heap table. Yes, a seek.  On a heap.  Not an index! If you would like to run the queries in this post for yourself, there’s a script below.  Thanks for reading! IF OBJECT_ID(N'dbo.Example', N'U') IS NOT NULL BEGIN DROP TABLE dbo.Example; END ; -- Test table is a heap -- Non-clustered primary key on 'key_col' CREATE TABLE dbo.Example ( key_col INTEGER NOT NULL, data INTEGER NOT NULL, CONSTRAINT [PK dbo.Example key_col] PRIMARY KEY NONCLUSTERED (key_col) ) ; -- Non-unique non-clustered index on the 'data' column CREATE NONCLUSTERED INDEX [IX dbo.Example data] ON dbo.Example (data) ; -- Add 100 rows INSERT dbo.Example WITH (TABLOCKX) ( key_col, data ) SELECT key_col = V.number, data = V.number FROM master.dbo.spt_values AS V WHERE V.[type] = N'P' AND V.number BETWEEN 1 AND 100 ; -- ================ -- Singleton lookup -- ================ ; -- Single value equality seek in a unique index -- Scan count = 0 when STATISTIS IO is ON -- Check the XML SHOWPLAN SELECT E.key_col FROM dbo.Example AS E WHERE E.key_col = 32 ; -- =========== -- Range Scans -- =========== ; -- Query 1 SELECT E.key_col FROM dbo.Example AS E WHERE E.key_col <= 5 ORDER BY E.key_col ASC ; -- Query 2 SELECT E.key_col FROM dbo.Example AS E WHERE E.key_col > 95 ORDER BY E.key_col DESC ; -- Query 3 SELECT E.key_col FROM dbo.Example AS E WHERE E.key_col >= 10 AND E.key_col < 15 ORDER BY E.key_col ASC ; -- Query 4 SELECT E.key_col FROM dbo.Example AS E WHERE E.key_col >= 20 AND E.key_col < 25 ORDER BY E.key_col DESC ; -- Final query (singleton + range = 2 range scans) SELECT E.key_col FROM dbo.Example AS E WHERE E.key_col = 10 OR E.key_col BETWEEN 15 AND 20 ORDER BY E.key_col ASC ; -- === TIDY UP === DROP TABLE dbo.Example; © 2011 Paul White email: [email protected] twitter: @SQL_Kiwi

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  • SQL SERVER – Import CSV into Database – Transferring File Content into a Database Table using CSVexpress

    - by pinaldave
    One of the most common data integration tasks I run into is a desire to move data from a file into a database table.  Generally the user is familiar with his data, the structure of the file, and the database table, but is unfamiliar with data integration tools and therefore views this task as something that is difficult.  What these users really need is a point and click approach that minimizes the learning curve for the data integration tool.  This is what CSVexpress (www.CSVexpress.com) is all about!  It is based on expressor Studio, a data integration tool I’ve been reviewing over the last several months. With CSVexpress, moving data between data sources can be as simple as providing the database connection details, describing the structure of the incoming and outgoing data and then connecting two pre-programmed operators.   There’s no need to learn the intricacies of the data integration tool or to write code.  Let’s look at an example. Suppose I have a comma separated value data file with data similar to the following, which is a listing of terminated employees that includes their hiring and termination date, department, job description, and final salary. EMP_ID,STRT_DATE,END_DATE,JOB_ID,DEPT_ID,SALARY 102,13-JAN-93,24-JUL-98 17:00,Programmer,60,"$85,000" 101,21-SEP-89,27-OCT-93 17:00,Account Representative,110,"$65,000" 103,28-OCT-93,15-MAR-97 17:00,Account Manager,110,"$75,000" 304,17-FEB-96,19-DEC-99 17:00,Marketing,20,"$45,000" 333,24-MAR-98,31-DEC-99 17:00,Data Entry Clerk,50,"$35,000" 100,17-SEP-87,17-JUN-93 17:00,Administrative Assistant,90,"$40,000" 334,24-MAR-98,31-DEC-98 17:00,Sales Representative,80,"$40,000" 400,01-JAN-99,31-DEC-99 17:00,Sales Manager,80,"$55,000" Notice the concise format used for the date values, the fact that the termination date includes both date and time information, and that the salary is clearly identified as money by the dollar sign and digit grouping.  In moving this data to a database table I want to express the dates using a format that includes the century since it’s obvious that this listing could include employees who left the company in both the 20th and 21st centuries, and I want the salary to be stored as a decimal value without the currency symbol and grouping character.  Most data integration tools would require coding within a transformation operation to effect these changes, but not expressor Studio.  Directives for these modifications are included in the description of the incoming data. Besides starting the expressor Studio tool and opening a project, the first step is to create connection artifacts, which describe to expressor where data is stored.  For this example, two connection artifacts are required: a file connection, which encapsulates the file system location of my file; and a database connection, which encapsulates the database connection information.  With expressor Studio, I use wizards to create these artifacts. First click New Connection > File Connection in the Home tab of expressor Studio’s ribbon bar, which starts the File Connection wizard.  In the first window, I enter the path to the directory that contains the input file.  Note that the file connection artifact only specifies the file system location, not the name of the file. Then I click Next and enter a meaningful name for this connection artifact; clicking Finish closes the wizard and saves the artifact. To create the Database Connection artifact, I must know the location of, or instance name, of the target database and have the credentials of an account with sufficient privileges to write to the target table.  To use expressor Studio’s features to the fullest, this account should also have the authority to create a table. I click the New Connection > Database Connection in the Home tab of expressor Studio’s ribbon bar, which starts the Database Connection wizard.  expressor Studio includes high-performance drivers for many relational database management systems, so I can simply make a selection from the “Supplied database drivers” drop down control.  If my desired RDBMS isn’t listed, I can optionally use an existing ODBC DSN by selecting the “Existing DSN” radio button. In the following window, I enter the connection details.  With Microsoft SQL Server, I may choose to use Windows Authentication rather than rather than account credentials.  After clicking Next, I enter a meaningful name for this connection artifact and clicking Finish closes the wizard and saves the artifact. Now I create a schema artifact, which describes the structure of the file data.  When expressor reads a file, all data fields are typed as strings.  In some use cases this may be exactly what is needed and there is no need to edit the schema artifact.  But in this example, editing the schema artifact will be used to specify how the data should be transformed; that is, reformat the dates to include century designations, change the employee and job ID’s to integers, and convert the salary to a decimal value. Again a wizard is used to create the schema artifact.  I click New Schema > Delimited Schema in the Home tab of expressor Studio’s ribbon bar, which starts the Database Connection wizard.  In the first window, I click Get Data from File, which then displays a listing of the file connections in the project.  When I click on the file connection I previously created, a browse window opens to this file system location; I then select the file and click Open, which imports 10 lines from the file into the wizard. I now view the file’s content and confirm that the appropriate delimiter characters are selected in the “Field Delimiter” and “Record Delimiter” drop down controls; then I click Next. Since the input file includes a header row, I can easily indicate that fields in the file should be identified through the corresponding header value by clicking “Set All Names from Selected Row. “ Alternatively, I could enter a different identifier into the Field Details > Name text box.  I click Next and enter a meaningful name for this schema artifact; clicking Finish closes the wizard and saves the artifact. Now I open the schema artifact in the schema editor.  When I first view the schema’s content, I note that the types of all attributes in the Semantic Type (the right-hand panel) are strings and that the attribute names are the same as the field names in the data file.  To change an attribute’s name and type, I highlight the attribute and click Edit in the Attributes grouping on the Schema > Edit tab of the editor’s ribbon bar.  This opens the Edit Attribute window; I can change the attribute name and select the desired type from the “Data type” drop down control.  In this example, I change the name of each attribute to the name of the corresponding database table column (EmployeeID, StartingDate, TerminationDate, JobDescription, DepartmentID, and FinalSalary).  Then for the EmployeeID and DepartmentID attributes, I select Integer as the data type, for the StartingDate and TerminationDate attributes, I select Datetime as the data type, and for the FinalSalary attribute, I select the Decimal type. But I can do much more in the schema editor.  For the datetime attributes, I can set a constraint that ensures that the data adheres to some predetermined specifications; a starting date must be later than January 1, 1980 (the date on which the company began operations) and a termination date must be earlier than 11:59 PM on December 31, 1999.  I simply select the appropriate constraint and enter the value (1980-01-01 00:00 as the starting date and 1999-12-31 11:59 as the termination date). As a last step in setting up these datetime conversions, I edit the mapping, describing the format of each datetime type in the source file. I highlight the mapping line for the StartingDate attribute and click Edit Mapping in the Mappings grouping on the Schema > Edit tab of the editor’s ribbon bar.  This opens the Edit Mapping window in which I either enter, or select, a format that describes how the datetime values are represented in the file.  Note the use of Y01 as the syntax for the year.  This syntax is the indicator to expressor Studio to derive the century by setting any year later than 01 to the 20th century and any year before 01 to the 21st century.  As each datetime value is read from the file, the year values are transformed into century and year values. For the TerminationDate attribute, my format also indicates that the datetime value includes hours and minutes. And now to the Salary attribute. I open its mapping and in the Edit Mapping window select the Currency tab and the “Use currency” check box.  This indicates that the file data will include the dollar sign (or in Europe the Pound or Euro sign), which should be removed. And on the Grouping tab, I select the “Use grouping” checkbox and enter 3 into the “Group size” text box, a comma into the “Grouping character” text box, and a decimal point into the “Decimal separator” character text box. These entries allow the string to be properly converted into a decimal value. By making these entries into the schema that describes my input file, I’ve specified how I want the data transformed prior to writing to the database table and completely removed the requirement for coding within the data integration application itself. Assembling the data integration application is simple.  Onto the canvas I drag the Read File and Write Table operators, connecting the output of the Read File operator to the input of the Write Table operator. Next, I select the Read File operator and its Properties panel opens on the right-hand side of expressor Studio.  For each property, I can select an appropriate entry from the corresponding drop down control.  Clicking on the button to the right of the “File name” text box opens the file system location specified in the file connection artifact, allowing me to select the appropriate input file.  I indicate also that the first row in the file, the header row, should be skipped, and that any record that fails one of the datetime constraints should be skipped. I then select the Write Table operator and in its Properties panel specify the database connection, normal for the “Mode,” and the “Truncate” and “Create Missing Table” options.  If my target table does not yet exist, expressor will create the table using the information encapsulated in the schema artifact assigned to the operator. The last task needed to complete the application is to create the schema artifact used by the Write Table operator.  This is extremely easy as another wizard is capable of using the schema artifact assigned to the Read Table operator to create a schema artifact for the Write Table operator.  In the Write Table Properties panel, I click the drop down control to the right of the “Schema” property and select “New Table Schema from Upstream Output…” from the drop down menu. The wizard first displays the table description and in its second screen asks me to select the database connection artifact that specifies the RDBMS in which the target table will exist.  The wizard then connects to the RDBMS and retrieves a list of database schemas from which I make a selection.  The fourth screen gives me the opportunity to fine tune the table’s description.  In this example, I set the width of the JobDescription column to a maximum of 40 characters and select money as the type of the LastSalary column.  I also provide the name for the table. This completes development of the application.  The entire application was created through the use of wizards and the required data transformations specified through simple constraints and specifications rather than through coding.  To develop this application, I only needed a basic understanding of expressor Studio, a level of expertise that can be gained by working through a few introductory tutorials.  expressor Studio is as close to a point and click data integration tool as one could want and I urge you to try this product if you have a need to move data between files or from files to database tables. Check out CSVexpress in more detail.  It offers a few basic video tutorials and a preview of expressor Studio 3.5, which will support the reading and writing of data into Salesforce.com. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Documentation, SQL Download, SQL Query, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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  • Scheduling of jobs in the presence of constraints in Java

    - by Asgard
    I want to know how to implement a solution to this problem: A task is performed by running, by more people, some basic jobs with known duration in time units (days, months, etc..). The execution of the jobs could lead to the existence of time constraints: a job, for example, can not start if it is not over another (or others) and so on. I want to design and build an application to check the correctness of jobs activities and to propose a schedule of jobs, if any, which is respectful of the constraints. Input must provide the jobs and associated constraints. The expected output is the scheduling of jobs. The specification of an elementary job consists of the pair <jobs-id, duration> A constraint is expressed by means of a quintuple of the type <S/E, id-job1, B/A, S/E, id-job2> the beginning (S) or the end (E) of a jobs Id-job1, must take place before (B) / after (A) of the beginning (S) / end (E) of the Id-job2. If there are no dependencies between some jobs, then jobs can be done before, in parallel. As a simple example, consider the input: jobs jobs(0, 3) jobs(1, 4) jobs(2, 5) jobs(3, 3) jobs(4, 3) constraints constraints(S, 1, A, E, 0) constraints(S, 4, A, E, 2) Possible output: t 0 1 2 3 4 0 * - * * - 1 * - * * - 2 * - * * - 3 * - * * - 4 - * * - - 5 - * * - - 6 - * - - * 7 - * - - * 8 - * - - * 9 - - - - * How to code an efficient java scheduler(avoiding the intense backtracking if is possible) to manage the jobs with these constraints, as described??? I have seen a discussion on a thread in a forum where an user seems has solved the problem easily, but He haven't given enough details to the users to compile a working project(I'm noob), and I'm interested to know an effective implementation of the solution (without using external libraries). If someone help me, I'll give to him a very good feedback ;)

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  • What, if anything, to do about bow-shaped burndowns?

    - by Karl Bielefeldt
    I've started to notice a recurring pattern to our team's burndown charts, which I call a "bowstring" pattern. The ideal line is the "string" and the actual line starts out relatively flat, then curves down to meet the target like a bow. My theory on why they look like this is that toward the beginning of the story, we are doing a lot of debugging or exploratory work that is difficult to estimate remaining work for. Sometimes it even goes up a little as we discover a task is more difficult once we get into it. Then we get into implementation and test which is more predictable, hence the curving down graph. Note I'm not talking about a big scale like BDUF, just the natural short-term constraint that you have to find the bug before you can fix it, coupled with the fact that stories are most likely to start toward the beginning of a two-week iteration. Is this a common occurrence among scrum teams? Do people see it as a problem? If so, what is the root cause and some techniques to deal with it?

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  • Recommended Approach to Secure your ADFdi Spreadsheets

    - by juan.ruiz
    ADF desktop integration leverages ADF security to provide access to published spreadsheets within your application. In this article I discussed a good security practice for your existing as well as any new spreadsheets that you create. ADF Desktop integration uses the adfdiRemoteServlet to process and send request back and fort from and to the ADFmodel which is allocated in the Java EE container where our application is deployed. In other words this is one of the entry points to the application server. Having said that, we need to make sure that container-based security is provided to avoid vulnerabilities. So what is needed? For existing an new ADFdi applications you need to create a Security Constraint for the ADFdi servlet on the Web.xml file of our application. Fortunately JDeveloper 11g provides a nice visual editor to do this. Open the web.xml file and go to the security category Add a new Web Resource Collection give it a meaningful name and on the URL Pattern add /adfdiRemoteServlet click on the Authorization tab and make sure the valid-users  role is selected for authorization and Voila! your application now is more secured.

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  • Is it possible for beginner to learn and develop an application in rails in 4 months?

    - by Parth
    I want to develop a web application or a website using rails. My current knowledge includes 1. HTML 2. CSS 3. C 4. Java And I am currently going through 5th chapter of the well grounded rubyist book by David A. Thomas. I came to know that learning ruby is beneficial for good knowledge of rails. So currently I am going through the basics of ruby. And learning rails in parallel. I want to know if in this scenario is it practically feasible to understand rails and develop an application/website in it within the time frame of 4 months. I need to develop an application which have atleast 3 complexity (complex functionality). Any ideas of good application for rails beginners is welcomed. But the application should be large or if it is small than it should have some complexity. Time is a constraint for me. I would have to develop application for college work but rails technology is my choice as I want to learn it.

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  • Which ecommerce framework is fast and easy to customize?

    - by Diego
    I'm working on a project where I have to put online an ecommerce system which will require some good amount of custom features. I'm therefore looking for a framework which makes customization easy enough (from an experienced developer's perspective, I mean). Language shoul be PHP and time is a constraint, I don't have months to learn. Additionally, the ecommerce will have to handle around 200.000 products from day one, which will increase over time, hence performance is also important. So far I examined the following: Magento - Complicated and, as far as I could read, slow when database contains many products. It's also resource intensive, and we can't afford a dedicated VPS from the beginning. OpenCart - Rough at best, documentation is extremely poor. Also, it's "free" to start, but each feature is implemented via 3rd party commercial modules. OSCommerce - Buggy, inefficient, outdated. ZenCart - Derived from OSCommerce, doesn't seem much better. Prestashop - It looks like it has many incompatibilities. Also, most of its modules are commercial, which increases the cost. In short, I'm still quite undecided, as none of the above seems to satisfy the requirements. I'm open to evaluate closed source frameworks too, if they are any better, but my knowledge about them is limited, therefore I'll welcome any suggestion. Thanks for all replies.

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  • Duck checker in Python: does one exist?

    - by elliot42
    Python uses duck-typing, rather than static type checking. But many of the same concerns ultimately apply: does an object have the desired methods and attributes? Do those attributes have valid, in-range values? Whether you're writing constraints in code, or writing test cases, or validating user input, or just debugging, inevitably somewhere you'll need to verify that an object is still in a proper state--that it still "looks like a duck" and "quacks like a duck." In statically typed languages you can simply declare "int x", and anytime you create or mutate x, it will always be a valid int. It seems feasible to decorate a Python object to ensure that it is valid under certain constraints, and that every time that object is mutated it is still valid under those constraints. Ideally there would be a simple declarative syntax to express "hasattr length and length is non-negative" (not in those words. Not unlike Rails validators, but less human-language and more programming-language). You could think of this as ad-hoc interface/type system, or you could think of it as an ever-present object-level unit test. Does such a library exist to declare and validate constraint/duck-checking on Python-objects? Is this an unreasonable tool to want? :) (Thanks!) Contrived example: rectangle = {'length': 5, 'width': 10} # We live in a fictional universe where multiplication is super expensive. # Therefore any time we multiply, we need to cache the results. def area(rect): if 'area' in rect: return rect['area'] rect['area'] = rect['length'] * rect['width'] return rect['area'] print area(rectangle) rectangle['length'] = 15 print area(rectangle) # compare expected vs. actual output! # imagine the same thing with object attributes rather than dictionary keys.

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  • Organizing Business and Presentation entities

    - by simoneL
    Background I am developing a WPF project. This is the basic structure: User Interface (WPF Project); Interfaces (class library, contains all the interfaces and the entities used by the application; Modules (every module contains the logic of a specific argument, e.g. File Management, and can eventually contains Wpf User Controls). In the WPF Controls, to facilitate the binding operations I have created a BaseViewModel class which contains a Raise method that automates the binding mechanism (for further details, I used a technique similar to that one described in this article). The problem Understand which is the best way to separate Presentation form from the Business form in the entities classes. The case In the Interfaces project I have, for instance, the class User public class User { public virtual string Name { get; set; } // Other properties } In one of the modules I need to use the User class and to bind its properties to the User Interface controls. To do so I have to use a custom implementation of the get and set keywords. At first point, I thought to create a class in the Module called, for instance, ClientUser and override the properties that I need: public class ClientUser : User { private string name; public override string Name { get { return name; } set { Raise(out name, value); } } // Other properties } The problem is the Raise method, which is declared in the BaseViewModel class, but due to C# single inheritance constraint, I can't inherit from both classes. Which is the right way to implement this architecture?

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  • Materialized View does not import properly when importing a db for a second time in another schema [closed]

    - by marinus
    When I import a database with materialized view mv_mt in just one schema there are no errors. create materialized view mv_mt refresh complete next trunc( sysdate ) + 1 as SELECT sysdate, media_type.* from media_type; But when I try to import the same database to a copy in another schema in the same tablespace I get the following errors: IMP-00017: following statement failed with ORACLE error 1: "BEGIN DBMS_JOB.ISUBMIT(JOB=>438,WHAT=>'dbms_refresh.refresh(''"ALEXANDRA"" "."MV_MT"'');',NEXT_DATE=>TO_DATE('2012-07-02:14:22:36','YYYY-MM-DD:HH24:MI:" "SS'),INTERVAL=>'sysdate + 1 / 24 / 60 / 6 ',NO_PARSE=>TRUE); END;" IMP-00003: ORACLE error 1 encountered ORA-00001: unique constraint (SYS.I_JOB_JOB) violated ORA-06512: at "SYS.DBMS_JOB", line 100 ORA-06512: at line 1 IMP-00017: following statement failed with ORACLE error 23421: "BEGIN dbms_refresh.make('"ALEXANDRA"."MV_MT"',list=>null,next_date=>null," "interval=>null,implicit_destroy=>TRUE,lax=>FALSE,job=>438,rollback_seg=>NUL" "L,push_deferred_rpc=>TRUE,refresh_after_errors=>FALSE,purge_option => 1,par" "allelism => 0,heap_size => 0); END;" IMP-00003: ORACLE error 23421 encountered ORA-23421: job number 438 is not a job in the job queue ORA-06512: at "SYS.DBMS_SYS_ERROR", line 86 ORA-06512: at "SYS.DBMS_IJOB", line 793 ORA-06512: at "SYS.DBMS_REFRESH", line 86 ORA-06512: at "SYS.DBMS_REFRESH", line 62 ORA-06512: at line 1 IMP-00017: following statement failed with ORACLE error 23410: "BEGIN dbms_refresh.add(name=>'"ALEXANDRA"."MV_MT"',list=>'"ALEXANDRA"."MV" "_MT"',siteid=>0,export_db=>'ORCL01'); END;" IMP-00003: ORACLE error 23410 encountered ORA-23410: materialized view "ALEXANDRA"."MV_MT" is already in a refresh group ORA-06512: at "SYS.DBMS_SYS_ERROR", line 95 ORA-06512: at "SYS.DBMS_IREFRESH", line 484 ORA-06512: at "SYS.DBMS_REFRESH", line 140 ORA-06512: at "SYS.DBMS_REFRESH", line 125 ORA-06512: at line 1 Anyone any ideas?

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  • Where'd My Data Go? (and/or...How Do I Get Rid of It?)

    - by David Paquette
    Want to get a better idea of how cascade deletes work in Entity Framework Code First scenarios? Want to see it in action? Stick with us as we quickly demystify what happens when you tell your data context to nuke a parent entity. This post is authored by Calgary .NET User Group Leader David Paquette with help from Microsoft MVP in Asp.Net James Chambers. We got to spend a great week back in March at Prairie Dev Con West, chalk full of sessions, presentations, workshops, conversations and, of course, questions.  One of the questions that came up during my session: "How does Entity Framework Code First deal with cascading deletes?". James and I had different thoughts on what the default was, if it was different from SQL server, if it was the same as EF proper and if there was a way to override whatever the default was.  So we built a set of examples and figured out that the answer is simple: it depends.  (Download Samples) Consider the example of a hockey league. You have several different entities in the league including games, teams that play the games and players that make up the teams. Each team also has a mascot.  If you delete a team, we need a couple of things to happen: The team, games and mascot will be deleted, and The players for that team will remain in the league (and therefore the database) but they should no longer be assigned to a team. So, let's make this start to come together with a look at the default behaviour in SQL when using an EDMX-driven project. The Reference – Understanding EF's Behaviour with an EDMX/DB First Approach First up let’s take a look at the DB first approach.  In the database, we defined 4 tables: Teams, Players, Mascots, and Games.  We also defined 4 foreign keys as follows: Players.Team_Id (NULL) –> Teams.Id Mascots.Id (NOT NULL) –> Teams.Id (ON DELETE CASCADE) Games.HomeTeam_Id (NOT NULL) –> Teams.Id Games.AwayTeam_Id (NOT NULL) –> Teams.Id Note that by specifying ON DELETE CASCADE for the Mascots –> Teams foreign key, the database will automatically delete the team’s mascot when the team is deleted.  While we want the same behaviour for the Games –> Teams foreign keys, it is not possible to accomplish this using ON DELETE CASCADE in SQL Server.  Specifying a ON DELETE CASCADE on these foreign keys would cause a circular reference error: The series of cascading referential actions triggered by a single DELETE or UPDATE must form a tree that contains no circular references. No table can appear more than one time in the list of all cascading referential actions that result from the DELETE or UPDATE – MSDN When we create an entity data model from the above database, we get the following:   In order to get the Games to be deleted when the Team is deleted, we need to specify End1 OnDelete action of Cascade for the HomeGames and AwayGames associations.   Now, we have an Entity Data Model that accomplishes what we set out to do.  One caveat here is that Entity Framework will only properly handle the cascading delete when the the players and games for the team have been loaded into memory.  For a more detailed look at Cascade Delete in EF Database First, take a look at this blog post by Alex James.   Building The Same Sample with EF Code First Next, we're going to build up the model with the code first approach.  EF Code First is defined on the Ado.Net team blog as such: Code First allows you to define your model using C# or VB.Net classes, optionally additional configuration can be performed using attributes on your classes and properties or by using a Fluent API. Your model can be used to generate a database schema or to map to an existing database. Entity Framework Code First follows some conventions to determine when to cascade delete on a relationship.  More details can be found on MSDN: If a foreign key on the dependent entity is not nullable, then Code First sets cascade delete on the relationship. If a foreign key on the dependent entity is nullable, Code First does not set cascade delete on the relationship, and when the principal is deleted the foreign key will be set to null. The multiplicity and cascade delete behavior detected by convention can be overridden by using the fluent API. For more information, see Configuring Relationships with Fluent API (Code First). Our DbContext consists of 4 DbSets: public DbSet<Team> Teams { get; set; } public DbSet<Player> Players { get; set; } public DbSet<Mascot> Mascots { get; set; } public DbSet<Game> Games { get; set; } When we set the Mascot –> Team relationship to required, Entity Framework will automatically delete the Mascot when the Team is deleted.  This can be done either using the [Required] data annotation attribute, or by overriding the OnModelCreating method of your DbContext and using the fluent API. Data Annotations: public class Mascot { public int Id { get; set; } public string Name { get; set; } [Required] public virtual Team Team { get; set; } } Fluent API: protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Entity<Mascot>().HasRequired(m => m.Team); } The Player –> Team relationship is automatically handled by the Code First conventions. When a Team is deleted, the Team property for all the players on that team will be set to null.  No additional configuration is required, however all the Player entities must be loaded into memory for the cascading to work properly. The Game –> Team relationship causes some grief in our Code First example.  If we try setting the HomeTeam and AwayTeam relationships to required, Entity Framework will attempt to set On Cascade Delete for the HomeTeam and AwayTeam foreign keys when creating the database tables.  As we saw in the database first example, this causes a circular reference error and throws the following SqlException: Introducing FOREIGN KEY constraint 'FK_Games_Teams_AwayTeam_Id' on table 'Games' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints. Could not create constraint. To solve this problem, we need to disable the default cascade delete behaviour using the fluent API: protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Entity<Mascot>().HasRequired(m => m.Team); modelBuilder.Entity<Team>() .HasMany(t => t.HomeGames) .WithRequired(g => g.HomeTeam) .WillCascadeOnDelete(false); modelBuilder.Entity<Team>() .HasMany(t => t.AwayGames) .WithRequired(g => g.AwayTeam) .WillCascadeOnDelete(false); base.OnModelCreating(modelBuilder); } Unfortunately, this means we need to manually manage the cascade delete behaviour.  When a Team is deleted, we need to manually delete all the home and away Games for that Team. foreach (Game awayGame in jets.AwayGames.ToArray()) { entities.Games.Remove(awayGame); } foreach (Game homeGame in homeGames) { entities.Games.Remove(homeGame); } entities.Teams.Remove(jets); entities.SaveChanges();   Overriding the Defaults – When and How To As you have seen, the default behaviour of Entity Framework Code First can be overridden using the fluent API.  This can be done by overriding the OnModelCreating method of your DbContext, or by creating separate model override files for each entity.  More information is available on MSDN.   Going Further These were simple examples but they helped us illustrate a couple of points. First of all, we were able to demonstrate the default behaviour of Entity Framework when dealing with cascading deletes, specifically how entity relationships affect the outcome. Secondly, we showed you how to modify the code and control the behaviour to get the outcome you're looking for. Finally, we showed you how easy it is to explore this kind of thing, and we're hoping that you get a chance to experiment even further. For example, did you know that: Entity Framework Code First also works seamlessly with SQL Azure (MSDN) Database creation defaults can be overridden using a variety of IDatabaseInitializers  (Understanding Database Initializers) You can use Code Based migrations to manage database upgrades as your model continues to evolve (MSDN) Next Steps There's no time like the present to start the learning, so here's what you need to do: Get up-to-date in Visual Studio 2010 (VS2010 | SP1) or Visual Studio 2012 (VS2012) Build yourself a project to try these concepts out (or download the sample project) Get into the community and ask questions! There are a ton of great resources out there and community members willing to help you out (like these two guys!). Good luck! About the Authors David Paquette works as a lead developer at P2 Energy Solutions in Calgary, Alberta where he builds commercial software products for the energy industry.  Outside of work, David enjoys outdoor camping, fishing, and skiing. David is also active in the software community giving presentations both locally and at conferences. David also serves as the President of Calgary .Net User Group. James Chambers crafts software awesomeness with an incredible team at LogiSense Corp, based in Cambridge, Ontario. A husband, father and humanitarian, he is currently residing in the province of Manitoba where he resists the urge to cheer for the Jets and maintains he allegiance to the Calgary Flames. When he's not active with the family, outdoors or volunteering, you can find James speaking at conferences and user groups across the country about web development and related technologies.

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