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  • What are the Options for Storing Hierarchical Data in a Relational Database?

    - by orangepips
    Good Overviews One more Nested Intervals vs. Adjacency List comparison: the best comparison of Adjacency List, Materialized Path, Nested Set and Nested Interval I've found. Models for hierarchical data: slides with good explanations of tradeoffs and example usage Representing hierarchies in MySQL: very good overview of Nested Set in particular Hierarchical data in RDBMSs: most comprehensive and well organized set of links I've seen, but not much in the way on explanation Options Ones I am aware of and general features: Adjacency List: Columns: ID, ParentID Easy to implement. Cheap node moves, inserts, and deletes. Expensive to find level (can store as a computed column), ancestry & descendants (Bridge Hierarchy combined with level column can solve), path (Lineage Column can solve). Use Common Table Expressions in those databases that support them to traverse. Nested Set (a.k.a Modified Preorder Tree Traversal) First described by Joe Celko - covered in depth in his book Trees and Hierarchies in SQL for Smarties Columns: Left, Right Cheap level, ancestry, descendants Compared to Adjacency List, moves, inserts, deletes more expensive. Requires a specific sort order (e.g. created). So sorting all descendants in a different order requires additional work. Nested Intervals Combination of Nested Sets and Materialized Path where left/right columns are floating point decimals instead of integers and encode the path information. Bridge Table (a.k.a. Closure Table: some good ideas about how to use triggers for maintaining this approach) Columns: ancestor, descendant Stands apart from table it describes. Can include some nodes in more than one hierarchy. Cheap ancestry and descendants (albeit not in what order) For complete knowledge of a hierarchy needs to be combined with another option. Flat Table A modification of the Adjacency List that adds a Level and Rank (e.g. ordering) column to each record. Expensive move and delete Cheap ancestry and descendants Good Use: threaded discussion - forums / blog comments Lineage Column (a.k.a. Materialized Path, Path Enumeration) Column: lineage (e.g. /parent/child/grandchild/etc...) Limit to how deep the hierarchy can be. Descendants cheap (e.g. LEFT(lineage, #) = '/enumerated/path') Ancestry tricky (database specific queries) Database Specific Notes MySQL Use session variables for Adjacency List Oracle Use CONNECT BY to traverse Adjacency Lists PostgreSQL ltree datatype for Materialized Path SQL Server General summary 2008 offers HierarchyId data type appears to help with Lineage Column approach and expand the depth that can be represented.

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  • Suggestions: Anti-Pattern counter-examples

    - by Tom W
    It doesn't seem that this exact question has been asked before, so I'll fire away: Most of us are familiar with the concept of an anti-pattern. However, avoiding implementation of anti-patterns can in principle swing too far the other way and cause problems itself. As an example, "Design by Committee" has a counter-example that I'd call "Design by Maverick" - wherein the design of an important feature is handed off to an individual to do what they think best, with the intention of reviewing their work later and deciding whether it should be finalised or go through another iteration. This takes much longer in practice as the rest of the team are occupied by other things, and can end up with a feature that's useful to nobody, particularly if the Maverick is not themselves an experienced end-user. Does anyone have any more examples of anti-pattern counter-examples?

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  • Overload the equals method in java

    - by fastcodejava
    Does anyone overload the equals method in java? The overloaded method will be public boolean equals(final MyClass myClass) This will have the benefit of having the relevant comparison part (guts of the method) in another method. Details are in this blog.

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  • Can I embed video on external sites while still using tokens to protect the content?

    - by JKS
    On our own website, it's easy to protect against direct links to our video content by grabbing a token through AJAX and verifying the token through PHP before the file download is started. However I'm also researching how I could provide an embed feature, like YouTube or vimeo etc., without compromising this security feature. The problem is that the embed code I want to provide should look something like <object>...<embed>...</embed></object> -- but I don't know how to grab and append the token to the filename. I mean, I guess I could attach a script that did some gnarly JNOP business, but that's too dirty. I'm using JW Player for the actual video container. Huge thanks to anyone who can help...

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  • Django/Python: Save an HTML table to Excel

    - by kchau
    I have an HTML table that I'd like to be able to export to an Excel file. I already have an option to export the table into an IQY file, but I'd prefer something that didn't allow the user to refresh the data via Excel. I just want a feature that takes a snapshot of the table at the time the user clicks the link/button. I'd prefer it if the feature was a link/button on the HTML page that allows the user to save the query results displayed in the table. Is there a way to do this at all? Or, something I can modify with the IQY? I can try to provide more details if needed. Thanks in advance.

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  • Determine if string is newline in C#

    - by paradox
    I am somehow unable to determine whether a string is newline or not. The string which I use is read from a file written by Ultraedit using DOS Terminators CR/LF. I assume this would equate to "\r\n" or Environment.NewLine in C#. However , when I perform a comparison like this it always seem to return false : if(str==Environment.NewLine) Anyone with a clue on what's going on here?

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  • SQL Server Merge statement issue

    - by George2
    Hello everyone, I am learning and using SQL Server 2008 new Merge statement, merge statement will compare/operate source table and destination table row by row ("operate" I mean operations performed for when matched or not-matched conditions). My question is whether the whole merge process will be one transaction or each row comparison/operation will be one transaction? Appreciate if any document to prove it. thanks in advance, George

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  • How does one advance in programming?

    - by Joe Barr
    I really have the felling as if I'm stuck in my own craft. I've been developing and learning for a while now and keep having the feeling that I should advance more, or even be more knowledgeable. I've started projects I didn't finish because I thought I lacked the knowledge and the skill to make that feature work just right, or to make that code magically appear on my screen. I've read books I didn't finish, thinking I wasn't advanced enough for the subjects they covered. I've been around long enough to know that everything comes with experience, hard work and dedication. Having said this, I just want to be able to work without getting stuck on a particular problem that involves my cluelessness of a language or a tool feature. My question to you would be, how does one advance in programming? What are the secrets (if any) to advance to the point of fluency in a particular language or a task. Thank you!

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  • Drawbacks of Dynamic Query in Sqlserver 2005 ?

    - by KuldipMCA
    I have using the many dynamic Query in my database for the procedures because my filter is not fix so i have taken @filter as parameter and pass in the procedure. Declare @query as varchar(8000) Declare @Filter as varchar(1000) set @query = 'Select * from Person.Address where 1=1 and ' + @Filter exec(@query) Like that my filter contain any Field from the table for comparison. It will affect my performance or not ? is there any alternate way to achieve this type of things

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  • Release management with a distributed version control system

    - by See Sharp Cheddar
    We're considering a switch from SVN to a distributed VCS at my workplace. I'm familiar with all the reasons for wanting to using a DVCS for day-to-day development: local version control, easier branching and merging, etc., but I haven't seen that much that's compelling in terms of managing software releases. Here's our release process: Discover what changes are available for merging. Run a query to find the defects/tickets associated with these changes. Filter out changes associated with "open" tickets. In our environment, tickets must be in a closed state in order to merged with a release branch. Filter out changes we don't want in the release branch. We are very conservative when it comes to merging changes. If a change isn't absolutely necessary, it doesn't get merged. Merge available changes, preferably in chronological order. We group changes together if they're associated with the same ticket. Block unwanted changes from the release branch (svnmerge block) so we don't have to deal with them again. Sometimes we can be juggling 3-5 different milestones at a time. Some milestones have very different constraints, and the block list can get quite long. I've been messing around with git, mercurial and plastic, and as far as I can tell none of them address this model very well. It seems like they would work very well when you have only one product you're releasing, but I can't imagine using them for juggling multiple, very different products from the same codebase. For example, cherry-picking seems to be an afterthought in mercurial. (You have to use the 'transplant' command). After you cherry-pick a change into a branch it still shows up as an available integration. Cherry-picking breaks the mercurial way of working. DVCS seems to be better suited for feature branches. There's no need for cherry-picking if you merge directly from a feature branch to trunk and the release branch. But who wants to do all that merging all the time? And how do you query for what's available to merge? And how do you make sure all the changes in a feature branch belong together? It sounds like total chaos. I'm torn because the coder in me wants DVCS for day-to-day work. I really want it. But I fear the day when I have to put the release manager hat and sort out what needs to be merged and what doesn't. I want to write code, I don't want to be a merge monkey.

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  • How do I write a powershell script that gets the file with the most recent last write time from a fo

    - by Shoko
    The subject line says it all. I'd also like to do this using pipes. I figured that I could use Get-ChildItem, Measure-Object and Where-Object, but Measure-Object doesn't like dates. Should I have a script block which loops through each item returned from Get-ChildItem and does a comparison to see if it's the most recent? I thought that there should be a handy PS cmdlet for that.

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  • Scheduling with gearman vs. cron?

    - by Industrial
    Hi everybody, I have noticed a lot of people discussing Gearman and it's scheduling features making it enable to distribute work onto other servers. However, I have not yet seen a comparison to native cronjobs. What are the differences between cron and Gearman?

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  • Is there an Eclipse plugin to run system shell in the Console?

    - by Fernando
    Do you know of any Eclipse plugin to run a system shell in the included console? It would be awesome. Dolphin, KDE's file navigator, has this feature, you can press F4 and a console shows located on the directory you are standing. It would be awesome to have a similar feature on Eclipse, with the shell located on the directory of the project/file you are working on. Does this plugin exist? If not, would it be too complicated to code such a plugin? I have no idea about eclipse plugin development (yet).

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  • cpu floating operations cost

    - by wiso
    I'm interesting in the time cost on a modern desktop cpu of some floating point operations in order to optimize a mathematical evaluation. In particular I'm interested on the comparison between complex operations like exp, log and simple operation like +, *, /. I tried to search for these information, but I can't find a source.

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