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  • Non-Relational Database Design

    - by Ian Varley
    I'm interested in hearing about design strategies you have used with non-relational "nosql" databases - that is, the (mostly new) class of data stores that don't use traditional relational design or SQL (such as Hypertable, CouchDB, SimpleDB, Google App Engine datastore, Voldemort, Cassandra, SQL Data Services, etc.). They're also often referred to as "key/value stores", and at base they act like giant distributed persistent hash tables. Specifically, I want to learn about the differences in conceptual data design with these new databases. What's easier, what's harder, what can't be done at all? Have you come up with alternate designs that work much better in the non-relational world? Have you hit your head against anything that seems impossible? Have you bridged the gap with any design patterns, e.g. to translate from one to the other? Do you even do explicit data models at all now (e.g. in UML) or have you chucked them entirely in favor of semi-structured / document-oriented data blobs? Do you miss any of the major extra services that RDBMSes provide, like relational integrity, arbitrarily complex transaction support, triggers, etc? I come from a SQL relational DB background, so normalization is in my blood. That said, I get the advantages of non-relational databases for simplicity and scaling, and my gut tells me that there has to be a richer overlap of design capabilities. What have you done? FYI, there have been StackOverflow discussions on similar topics here: the next generation of databases changing schemas to work with Google App Engine choosing a document-oriented database

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  • How to prepopulate an Outlook MailItem and avoiding a com Exception from the object model guard

    - by torrente
    Hi, I work for a company that develops a CRM tool and offers integration with MS Office(2003 & 2007) from windows XP to 7. (I'm working using Win7) My task is to call an Outlook instance (using C#) from this CRM tool when the user wants to send an email and prepopulate with data of the CRM tool (email, recipient, etc..) All of this already works just fine. The problem I'm having is that Outlook's "object model guard" is throwing com Exception (Operation aborted (Exception from HRESULT: 0x80004004 (E_ABORT))) the moment I try to read a protected value from the mailItem (such as mail.bodyHTML). Example Snippet: using MSOutlook = Microsoft.Office.Interop.Outlook; //untrusted Instance _outlook = new MSOutlook.Application(); MSOutlook.MailItem mail = (MSOutlook.MailItem)_outlook.CreateItem(MSOutlook.OlItemType.olMailItem); //this where the Exception occurs string outlookStdHTMLBody = mail.HTMLBody; I've done quite a bit of reading and know that my Outlook Instance (derived by using new Application) is considered untrusted and therefore the "omg" kicks in. I do have a workaround for development: I'm running VS2010 as Administrator and if I run Outlook as Administrator as well - all is good. I suppose this is due to them having the same integrity levels(high) and the UAC(?) is not complaining. But that just ain't the way to go for deployment. Now the question is: Is there a way to obtain a trusted instance of Outlook so that I can avoid this exception? I've already read that when developing an Office Add-In using VSTO one can obtain a trusted Instance from the OnComplete event and/or using "ThisAddin" But I "merely" want to start an outlook instance and preopulate it, and do not want to develop an Add-In since this is not the requirement. And to make it clear - I have no problem with pop ups informing the user that outlook is being accessed - I just want to get rid of the exception! So how can I get around this problem using code? Any help is highly appreciated! Thomas

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  • Data in two databases, eager spool resulting in query

    - by Valkyrie
    I have two databases in SQL2k5: one that holds a large amount of static data (SQL Database 1) (never updated but frequently inserted into) and one that holds relational data (SQL Database 2) related to the static data. They're separated mainly because of corporate guidelines and business requirements: assume for the following problem that combining them is not practical. There are places in SQLDB2 that PKs in SQLDB1 are referenced; triggers control the referential integrity, since cross-database relationships are troublesome in SQL Server. BUT, because of the large amount of data in SQLDB1, I'm getting eager spools on queries that join from the Id in SQLDB2 that references the data in SQLDB1. (With me so far? Maybe an example will help:) SELECT t.Id, t.Name, t2.Company FROM SQLDB1.table t INNER JOIN SQLDB2.table t2 ON t.Id = t2.FKId This query results in a eager spool that's 84% of the load of the query; the table in SQLDB1 has 35M rows, so it's completely choking this query. I can't create a view on the table in SQLDB1 and use that as my FK/index; it doesn't want me to create a constraint based on a view. Anyone have any idea how I can fix this huge bottleneck? (Short of putting the static data in the first db: believe me, I've argued that one until I'm blue in the face to no avail.) Thanks! valkyrie Edit: also can't create an indexed view because you can't put schemabinding on a view that references a table outside the database where the view resides. Dang it.

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  • Padding is invalid and cannot be removed

    - by Ajay
    I have hosted an asp.net 2.0 site. Everyday, i am getting an error "Padding is invalid and cannot be removed" 2-3 times. Backend used is sql server 2005. the site is controlled via plesk 9.2 CP. Pooling is enabled with timeout as 120 Minutes, in IIS. Can it be the reason for this? I have not used any encryption except for the stored passwords(MD5) The error message is : " Base Exception = : Padding is invalid and cannot be removed. - Source : System.Web - TargetSite :Void ThrowError(System.Exception, System.String, System.String, Boolean)Message : Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. " & System Log (Application) says " Event code: 4009 Event message: Viewstate verification failed. Reason: The viewstate supplied failed integrity check. Event detail code: 50203 ViewStateException information: Exception message: Invalid viewstate. Port: 31235 User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1) " I have hosted it in a dedicated server and not in a web farm. Will keeping a static machine key help resolve this issue? Please guide me on this.

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  • Symfony fk issue on insertion

    - by Daniel Hertz
    Hi, I posted a similar problem but it could not be resolved. I create a relational database of users and groups but for some reason I cannot insert test data with fixtures properly. Here is a sample of the schema: User: actAs: { Timestampable: ~ } columns: name: { type: string(255), notnull: true } email: { type: string(255), notnull: true, unique: true } nickname: { type: string(255), unique: true } password: { type: string(300), notnull: true } image: { type: string(255) } Group: actAs: { Timestampable: ~ } columns: name: { type: string(500), notnull: true } image: { type: string(255) } type: { type: string(255), notnull: true } created_by_id: { type: integer } relations: User: { onDelete: SET NULL, class: User, local: created_by_id, foreign: id, foreignAlias: groups_created } FanOf: actAs: { Timestampable: ~ } columns: user_id: { type: integer, primary: true } group_id: { type: integer, primary: true } relations: User: { onDelete: CASCADE, local: user_id, foreign: id, foreignAlias: fanhood } Group: { onDelete: CASCADE, local: group_id, foreign: id, foreignAlias: fanhood } And this is the data i try to input: User: user1: name: Danny email: [email protected] nickname: danny password: f05050400c5e586fa6629ef497be Group: group1: name: Mets type: sports FanOf: fans1: user_id: user1 group_id: group1 I keep getting this error: SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`krowdd`.`fan_of`, CONSTRAINT `fan_of_user_id_user_id` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE CASCADE) The users and groups are clearly being created before the "fanhood" is so why am I getting this error?? Thanks!

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  • are there code signing certificates cheaper than US $99 per year? [closed]

    - by gerryLowry
    ksoftware discounts Commodo code signing certificates to US $99 per year. in the past, I've seen Commodo code signing certificates for US $80. I'm excluding CAcert which AFAIK are FREE but are not covered by browsers like IE AFAIK. QUESTION: What is the best price per year for a code signing certificate? Thank you ~~ gerry (lowry) Edit: **THIS SHOULD NOT HAVE BEEN CLOSED** from the FAQ: http://stackoverflow.com/faq ---------------------------- What kind of questions can I ask here? Programming questions, of course! As long as your question is: * detailed and specific <====== YES! * written clearly and simply <====== YES! * of interest to other programmers <====== YES! I've been programming for over 40 years. http://gerrylowryprogrammer.com/ I've taught computer programming at the community college level. I'm a Star level contributer to forums.asp.net. http://forums.asp.net/members/gerrylowry.aspx imo, I've a very good idea what is of interest to other programmers. MORE INFORMATION Ensuring the integrity of code and executables that one distributes is just as much about programming as is knowing how to flip bits in assembler, use delegates in c#, and use the BDD context/specification still of "test first testing".

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  • LINQDataSource and private columns

    - by fyjham
    Hey, I was trying to use a ListView bound to a LinqDataSource to insert to a table where I had a few columns private to the table class (Specifically password columns - only access I want to give outside the class is methods that generate the salt and encrypt the password to store it in 1 go). I gave this a few shots, but I didn't come up with anything I really liked... was wondering if anyone has a better way to do this. The methods I've found: Use the LinqDataSource inserting event and make the appropriate calls on e.NewObject. I don't really like this because it's so far removed from the actual input and there's no simple way to hold the password in the meantime other than a class variable set during the ListView's inserting event (Which works, but seems a little dodgy). Open up these properties and just ask everyone to use the appropriate static methods for encoding the passwords they pass in. I don't really like this cause I'd prefer that class to enforce data integrity rather than relying on all calling code doing it properly... I'm currently going with option #1, but I don't really like passing values between events using class variables like that (It just seems unstructured... even though I can guarantee the events will happen in the right order). Does anyone know a better way, or alternatively am I being too pedantic and one of the methods above is actually the right way to go? Thanks

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  • HTML to 'pretty' text conversion for printing on text only printer (dot matrix)

    - by Gala101
    Hi, I have a web-site that generates some simple tabular data as html tables, many of my users print the web-page on a laser/inkjet printer; however some like to print on legacy Dot Matrix printers (text only) and there-in lies the problem. When giving Print from web-browser onto dot-matrix printer, the printer actually perceives data as 'graphic'/image and proceeds to print it dot-by-dot. i.e If printing a character 'C', printer slices it horizontally and prints in 3-4 passes. Same printer prints a text from an ASCII file (say from notepad) as complete characters in single pass, thereby being 5 times faster and much quieter than when printing a web-page. (Even tried 'generic text-only driver' but Mozilla Firefox has a know bug that it does not print anything over this particular driver since 2.0+) So is there some clean way of formatting an already generated HTML (say method takes the entire html table as string) and generates a corresponding text file with properly aligned columns? I have tried stripping the html tags, but the major issue there is performing good 'wrapping' of a cell's data and maintaining integrity of other cells' data (from same row). eg: ( '|' and '_' not really required) Col1 | Col2 | Colum_Name3 | Col4 | _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1 | this cell | this column | smaller | | is in three| spans 2 rows | | | rows | | | - - - - - - - - - - - - - - - - - - - - - - - - 2 | smaller now| this also | but this| | | | cell's | | | | data is | | | | now | | | | bigger | _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Could you please suggest preferred approach? I've thought of using xslt and somehow outputting text (instead of more prevalent pdf), but Apache FOP's text renderer is really broken and perhaps forgotten in development path. Commercial one's are way too costly.

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  • How can I make this method more Scalalicious

    - by Neil Chambers
    I have a function that calculates the left and right node values for some collection of treeNodes given a simple node.id, node.parentId association. It's very simple and works well enough...but, well, I am wondering if there is a more idiomatic approach. Specifically is there a way to track the left/right values without using some externally tracked value but still keep the tasty recursion. /* * A tree node */ case class TreeNode(val id:String, val parentId: String){ var left: Int = 0 var right: Int = 0 } /* * a method to compute the left/right node values */ def walktree(node: TreeNode) = { /* * increment state for the inner function */ var c = 0 /* * A method to set the increment state */ def increment = { c+=1; c } // poo /* * the tasty inner method * treeNodes is a List[TreeNode] */ def walk(node: TreeNode): Unit = { node.left = increment /* * recurse on all direct descendants */ treeNodes filter( _.parentId == node.id) foreach (walk(_)) node.right = increment } walk(node) } walktree(someRootNode) Edit - The list of nodes is taken from a database. Pulling the nodes into a proper tree would take too much time. I am pulling a flat list into memory and all I have is an association via node id's as pertains to parents and children. Adding left/right node values allows me to get a snapshop of all children (and childrens children) with a single SQL query. The calculation needs to run very quickly in order to maintain data integrity should parent-child associations change (which they do very frequently). In addition to using the awesome Scala collections I've also boosted speed by using parallel processing for some pre/post filtering on the tree nodes. I wanted to find a more idiomatic way of tracking the left/right node values. After looking at the answers listed I have settled on this synthesised version: def walktree(node: TreeNode) = { def walk(node: TreeNode, counter: Int): Int = { node.left = counter node.right = treeNodes .filter( _.parentId == node.id) .foldLeft(counter+1) { (counter, curnode) => walk(curnode, counter) + 1 } node.right } walk(node,1) }

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  • Foreign key not working in MySQL: Why can I INSERT a value that's not in the foreign column?

    - by stalepretzel
    I've created a table in MySQL: CREATE TABLE actions ( A_id int NOT NULL AUTO_INCREMENT, type ENUM('rate','report','submit','edit','delete') NOT NULL, Q_id int NOT NULL, U_id int NOT NULL, date DATE NOT NULL, time TIME NOT NULL, rate tinyint(1), PRIMARY KEY (A_id), CONSTRAINT fk_Question FOREIGN KEY (Q_id) REFERENCES questions(P_id), CONSTRAINT fk_User FOREIGN KEY (U_id) REFERENCES users(P_id)); This created the table I wanted just fine (although a "DESCRIBE actions;" command showed me that the foreign keys were keys of type MUL, and I'm not sure what this means). However, when I try to enter a Q_id or a U_id that does not exist in the questions or users tables, MySQL still allows these values. What did I do wrong? How can I prevent a table with a foreign key from accepting invalid data? If I add TYPE=InnoDB to the end, I get an error: ERROR 1005 (HY000): Can't create table './quotes/actions.frm' (errno: 150) Why might that happen? I'm told that it's important to enforce data integrity with functional foreign keys, but also that InnoDB should not be used with MySQL. What do you recommend?

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  • Which Table Should be Master and Child in Database Design

    - by Jason
    I am quickly learning the ins and outs of database design (something that, as of a week ago, was new to me), but I am running across some questions that don't seem immediately obvious, so I was hoping to get some clarification. The question I have right is about foreign keys. As part of my design, I have a Company table. Originally, I had included address information directly within the table, but, as I was hoping to achieve 3NF, I broke out the address information into its own table, Address. In order to maintain data integrity, I created a row in Company called "addressId" as an INT and the Address table has a corresponding addressId as its primary key. What I'm a little bit confused about (or what I want to make sure I'm doing correctly) is determining which table should be the master (referenced) table and which should be the child (referencing) table. When I originally set this up, I made the Address table the master and the Company the child. However, I now believe this is wrong due to the fact that there should be only one address per Company and, if a Company row is deleted, I would want the corresponding Address to be removed as well (CASCADE deletion). I may be approaching this completely wrong, so I would appreciate any good rules of thumb on how to best think about the relationship between tables when using foreign keys. Thanks!

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  • ISBNs are used as primary key, now I want to add non-book things to the DB - should I migrate to EAN

    - by fish2000
    I built an inventory database where ISBN numbers are the primary keys for the items. This worked great for a while as the items were books. Now I want to add non-books. some of the non-books have EANs or ISSNs, some do not. It's in PostgreSQL with django apps for the frontend and JSON api, plus a few supporting python command-line tools for management. the items in question are mostly books and artist prints, some of which are self-published. What is nice about using ISBNs as primary keys is that in on top of relational integrity, you get lots of handy utilities for validating ISBNs, automatically looking up missing or additional information on the book items, etcetera, many of which I've taken advantage. some such tools are off-the-shelf (PyISBN, PyAWS etc) and some are hand-rolled -- I tried to keep all of these parts nice and decoupled, but you know how things can get. I couldn't find anything online about 'private ISBNs' or 'self-assigned ISBNs' but that's the sort of thing I was interested in doing. I doubt that's what I'll settle on, since there is already an apparent run on ISBN numbers. should I retool everything for EAN numbers, or migrate off ISBNs as primary keys in general? if anyone has any experience with working with these systems, I'd love to hear about it, your advice is most welcome.

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  • How to speed up an already cached pip install?

    - by Maxime R.
    I frequently have to re-create virtual environments from a requirements.txt and I am already using $PIP_DOWNLOAD_CACHE. It still takes a lot of time and I noticed the following: Pip spends a lot of time between the following two lines: Downloading/unpacking SomePackage==1.4 (from -r requirements.txt (line 2)) Using download cache from $HOME/.pip_download_cache/cached_package.tar.gz Like ~20 seconds on average to decide it's going to use the cached package, then the install is fast. This is a lot of time when you have to install dozens of packages (actually enough to write this question). What is going on in the background? Are they some sort of integrity checks against the online package? Is there a way to speed this up? edit: Looking at: time pip install -v Django==1.4 I get: real 1m16.120s user 0m4.312s sys 0m1.280s The full output is here http://pastebin.com/e4Q2B5BA. Looks like pip is spending his time looking for a valid download link while it already has a valid cache of http://pypi.python.org/packages/source/D/Django/Django-1.4.tar.gz. Is there a way to look for the cache first and stop there if versions match?

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  • Counting string length in javascript and Ruby on Rails

    - by williamjones
    I've got a text area on a web site that should be limited in length. I'm allowing users to enter 255 characters, and am enforcing that limit with a Rails validation: validates_length_of :body, :maximum => 255 At the same time, I added a javascript char counter like you see on Twitter, to give feedback to the user on how many characters he has already used, and to disable the submit button when over length, and am getting that length in Javascript with a call like this: element.length Lastly, to enforce data integrity, in my Postgres database, I have created this field as a varchar(255) as a last line of defense. Unfortunately, these methods of counting characters do not appear to be directly compatible. Javascript counts the best, in that it counts what users consider as number of characters where everything is a single character. Once the submission hits Rails, however, all of the carriage returns have been converted to \r\n, now taking up 2 characters worth of space, which makes a close call fail Rails validations. Even if I were to handcode a different length validation in Rails, it would still fail when it hits the database I think, though I haven't confirmed this yet. What's the best way for me to make all this work the way the user would want? Best Solution: an approach that would enable me to meet user expectations, where each character of any type is only one character. If this means increasing the length of the varchar database field, a user should not be able to sneakily send a hand-crafted post that creates a row with more than 255 letters. Somewhat Acceptable Solution: a javascript change that enables the user to see the real character count, such that hitting return increments the counter 2 characters at a time, while properly handling all symbols that might have these strange behaviors.

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  • how to design a schema where the columns of a table are not fixed

    - by hIpPy
    I am trying to design a schema where the columns of a table are not fixed. Ex: I have an Employee table where the columns of the table are not fixed and vary (attributes of Employee are not fixed and vary). Nullable columns in the Employee table itself i.e. no normalization Instead of adding nullable columns, separate those columns out in their individual tables ex: if Address is a column to be added then create table Address[EmployeeId, AddressValue]. Create tables ExtensionColumnName [EmployeeId, ColumnName] and ExtensionColumnValue [EmployeeId, ColumnValue]. ExtensionColumnName would have ColumnName as "Address" and ExtensionColumnValue would have ColumnValue as address value. Employee table EmployeeId Name ExtensionColumnName table ColumnNameId EmployeeId ColumnName ExtensionColumnValue table EmployeeId ColumnNameId ColumnValue There is a drawback is the first two ways as the schema changes with every new attribute. Note that adding a new attribute is frequent. I am not sure if this is the good or bad design. If someone had a similar decision to make, please give an insight on things like foreign keys / data integrity, indexing, performance, reporting etc.

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  • MSSQL: Views that use SELECT * need to be recreated if the underlying table changes

    - by cbp
    Is there a way to make views that use SELECT * stay in sync with the underlying table. What I have discovered is that if changes are made to the underlying table, from which all columns are to be selected, the view needs to be 'recreated'. This can be achieved simly by running an ALTER VIEW statement. However this can lead to some pretty dangerous situations. If you forgot to recreate the view, it will not be returning the correct data. In fact it can be returning seriously messed up data - with the names of the columns all wrong and out of order. Nothing will pick up that the view is wrong unless you happened to have it covered by a test, or a data integrity check fails. For example, Red Gate SQL Compare doesn't pick up the fact that the view needs to be recreated. To replicate the problem, try these statements: CREATE TABLE Foobar (Bar varchar(20)) CREATE VIEW v_Foobar AS SELECT * FROM Foobar INSERT INTO Foobar (Bar) VALUES ('Hi there') SELECT * FROM v_Foobar ALTER TABLE Foobar ADD Baz varchar(20) SELECT * FROM v_Foobar DROP VIEW v_Foobar DROP TABLE Foobar I am tempted to stop using SELECT * in views, which will be a PITA. Is there a setting somewhere perhaps that could fix this behaviour?

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  • How to improve multi-threaded access to Cache (custom implementation)

    - by Andy
    I have a custom Cache implementation, which allows to cache TCacheable<TKey> descendants using LRU (Least Recently Used) cache replacement algorithm. Every time an element is accessed, it is bubbled up to the top of the LRU queue using the following synchronized function: // a single instance is created to handle all TCacheable<T> elements public class Cache() { private object syncQueue = new object(); private void topQueue(TCacheable<T> el) { lock (syncQueue) if (newest != el) { if (el.elder != null) el.elder.newer = el.newer; if (el.newer != null) el.newer.elder = el.elder; if (oldest == el) oldest = el.newer; if (oldest == null) oldest = el; if (newest != null) newest.newer = el; el.newer = null; el.elder = newest; newest = el; } } } The bottleneck in this function is the lock() operator, which limits cache access to just one thread at a time. Question: Is it possible to get rid of lock(syncQueue) in this function while still preserving the queue integrity?

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  • Generic version control strategy for select table data within a heavily normalized database

    - by leppie
    Hi Sorry for the long winded title, but the requirement/problem is rather specific. With reference to the following sample (but very simplified) structure (in psuedo SQL), I hope to explain it a bit better. TABLE StructureName { Id GUID PK, Name varchar(50) NOT NULL } TABLE Structure { Id GUID PK, ParentId GUID (FK to Structure), NameId GUID (FK to StructureName) NOT NULL } TABLE Something { Id GUID PK, RootStructureId GUID (FK to Structure) NOT NULL } As one can see, Structure is a simple tree structure (not worried about ordering of children for the problem). StructureName is a simplification of a translation system. Finally 'Something' is simply something referencing the tree's root structure. This is just one of many tables that need to be versioned, but this one serves as a good example for most cases. There is a requirement to version to any changes to the name and/or the tree 'layout' of the Structure table. Previous versions should always be available. There seems to be a few possibilities to tackle this issue, like copying the entire structure, but most approaches causes one to 'loose' referential integrity. Example if one followed this approach, one would have to make a duplicate of the 'Something' record, given that the root structure will be a new record, and have a new ID. Other avenues of possible solutions are looking into how Wiki's handle this or go a lot further and look how proper version control systems work. Currently, I feel a bit clueless how to proceed on this in a generic way. Any ideas will be greatly appreciated. Thanks leppie

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  • How can I help fellow students struggling in programming classes?

    - by David Barry
    I'm a computer science student finishing up my second semester of programming classes. I've enjoyed them quite a bit, and learned a lot, but it seems other students are struggling with the concepts and assignments more than I am. When an assignment is due, the inevitable group email comes out the day or two before with people needing some help either with a specific part of the problem, or sometimes people just seem to have a hard time knowing where to start. I'd really like to be able to help out, but I have a hard time thinking of the right way to give them help without giving them the answer. When I'm having trouble understanding a concept, a code snippet can go along way to helping me, but at the same time if it makes a lot of sense, it can be difficult to think of another way to go about it. Plus the Academic Integrity section of each assignment is always looming overhead warning against sharing code with others. I've tried using pseudo code to help give others an idea on program flow, leaving them to figure out how to implement certain aspects of it, but I didn't get too much feedback and don't know how much it actually helped them out, or if it just confused them further. So I'm basically looking to see if anyone has experience with this, or good ways that I can help out other students to nudge them in the right direction or help them think about the problem in the right way.

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  • XSD: Different sub-elements depending on attribute/element value

    - by AndiDog
    Another XSD question - how can I achieve that the following XML elements are both valid: <some-element> <type>1</type> <a>...</a> </some-element> <some-element> <type>2</type> <b>...</b> </some-element> The sub-elements (either <a> or <b>) should depend on the content of <type> (could also be an attribute). It would be so simple in RelaxNG - but RelaxNG doesn't support key integrity :( Is there a way to implement this in XSD? Note: XML schema version 1.1 supports <xs:alternative>, which might be a solution, but afaik no reference implementation (e.g. libxml2) supports this yet. So I'm searching for workarounds. The only way I've come up with is: <type>1</type> <some-element type="1"> <!-- simple <xs:choice> between <a> and <b> goes here --> <a>...</a> </some-element> <!-- and now create a keyref between <type> and @type -->

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  • how can i set up a uniqueness constraint in mysql for columns that can be null?

    - by user299689
    I know that in MySQL, UNIQUE constraits don't treat NULL values as equal. So if I have a unique constraint on ColumnX, then two separate rows can have values of NULL for ColumnX and this wouldn't violate the constraint. How can I work around this? I can't just set the value to an arbitrary constant that I can flag, because ColumnX in my case is actually a foreign key to another table. What are my options here? Please note that this table also has an "id" column that is its primary key. Since I'm using Ruby on Rails, it's important to keep this id column as the primary key. Note 2: In reality, my unique key encompasses many columns, and some of them have to be null, because they are foreign keys, and only one of them should be non-null. What I'm actually trying to do is to "simulate" a polymorphic relationship in a way that keep referential integrity in the db, but using the technique outlined in the first part of the question asked here: http://stackoverflow.com/questions/922184/why-can-you-not-have-a-foreign-key-in-a-polymorphic-association

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  • How can I make Access think there is a primary key

    - by user3692757
    I have a table and I'm trying to join it with another table, but it doesn't have a distinctive primary key. The two tables do share similarities, “Acct” and “Location”. If I could concatenate “Acct&Location” it would become a primary key, but Access won’t let me make a primary key from a calculation. I provided a small sample below. Each hospital has an “Acct”, but the “Acct” will show up once for each “Location”. How can I make join these in a relationship? I connected the two in a relationships and tried to “Enforce Referential Integrity”, but it indicated “No unique index found for the referenced field of the primary key”. Also, if I run a “Find UnMatched Query” it doesn’t find anything. I think its because I can’t make it realize that in combination “Acct” and “Location” can be perceived as primary keys when used in conjunction of each other. Acct 1 2 3 1 2 3 1 2 3| Location ABI ABI ABI NHO NHO NHO NTX NTX NTX I tried to load an image to illustrate it better, but I haven't made enough post.

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  • best database design for city zip & state tables

    - by ryan a
    My application will need to reference addresses. Street info will be stored with my main objects but the rest needs to be stored seperately to reduce redundancy. How should I store/retrieve ZIPs, cities and states? Here are some of my ideas. single table solution (cant do relationships) [locations] locationID locationParent (FK for locationID - 0 for state entries) locationName (city, state) locationZIP two tables (with relationships, FK constraints, ref integrity) [state] stateID stateName [city] cityID stateID (FK for state.stateID) cityName zipCode three tables [state] stateID stateName [city] cityID stateID (FK for state.stateID) cityName [zip] zipID cityID (FK for city.cityID) zipName Then I read into ZIP codes amd how they are assigned. They aren't specifically related to cities. Some cities have more than one ZIP (ok will still work) but some ZIPs are in more than one city (oh snap) and some other ZIPs (very few) are in more than one state! Also some ZIPs are not even in the same state as the address they belong to at all. Seems ZIPs are made for carrier route identification and some remote places are best served by post offices in neighboring cities or states. Does anybody know of a good (not perfect) solution that takes this into consideration to minimize discrepencies as the database grows?

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  • Why do I get this exception? {An item with the same key has already been added."})

    - by Alan
    Aknittel NewSellerID is the result of a lookup on tblSellers. These tables (tblSellerListings and tblSellers) are not "officially" joined with a foreign key relationship, either in the model or in the database, but I want some referential integrity maintained for the future. So my issue remains. Why do I get the exception ({"An item with the same key has already been added."}) with this code, if I don't begin each iteration of the foreach loop with a new ObjectContext and end it with SaveChanges, which I think will affect performance. Also, could you tell me why ORCSolutionsDataService.tblSellerListings (An ADO.NET DataServices/WCF object is not IDisposable, like LINQ to Entities?? ============================================== // Add listings to previous seller int NewSellerID = 0; // Look up existing Seller key using SellerUniqueEBAYID var qryCurrentSeller = from s in service.tblSellers where s.SellerEBAYUserID == SellerUserID select s; foreach (var s in qryCurrentSeller) NewSellerID = s.SellerID; // Save the selected listings for this seller foreach (DataGridViewRow dgr in dgvRows) { ORCSolutionsDataService.tblSellerListings NewSellerListing = new ORCSolutionsDataService.tblSellerListings(); NewSellerListing.ItemID = dgr.Cells["txtSellerItemID"].Value.ToString(); NewSellerListing.Title = dgr.Cells["txtSellerItemTitle"].Value.ToString(); NewSellerListing.CurrentPrice = Convert.ToDecimal(dgr.Cells["txtSellerItemPrice"].Value); NewSellerListing.QuantitySold = Convert.ToInt32(dgr.Cells["txtSellerItemSold"].Value); NewSellerListing.EndTime = Convert.ToDateTime(dgr.Cells["txtSellerItemEnds"].Value); NewSellerListing.CategoryName = dgr.Cells["txtSellerItemCategory"].Value.ToString(); NewSellerListing.ExtendedPrice = Convert.ToDecimal(dgr.Cells["txtExtendedReceipts"].Value); NewSellerListing.RetrievedDtime = Convert.ToDateTime(dtSellerDataRetrieved.ToString()); NewSellerListing.SellerID = NewSellerID; service.AddTotblSellerListings(NewSellerListing); } service.SaveChanges(); } catch (Exception ex) { MessageBox.Show("Unable to add a new case. Exception: " + ex.Message); }

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  • Coldfusion 8 and HTTP PUT - is there a way to PUT an object?

    - by ciaranarcher
    Hi all We are using EHCache with CF 8 to cache stuff on a central server using a RESTful interface over HTTP. I am trying to cache a cfquery object to the cache server. I can get this to work if I call EHCache direct (i.e. store it in a local cache) but if I try to cache on a remote server over HTTP I am running into problems. The code I am using is as follows: <cfhttp url="http://localhost:8080/myCache/myKey" method="put" result="r" timeout="2" throwonerror="true" > <cfhttpparam type="body" value="#ARGUMENTS.item#" /> </cfhttp> CF doesn't like this reference to #ARGUMENTS.item# and it complains Complex object types cannot be converted to simple values. Can anyone give me an example of how to put an object over http using CF? If this is not possible with CF then a Java example would be the next best thing. Many thanks in advance! PS: I do not want to use serialization to text/JSON etc. as this approach has issues with data integrity and most importantly it's not fast enough.

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