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• Rails find_or_create by more than one attribute?

  - by tybro0103

  There is a handy dynamic attribute in active-record called find_or_create_by: Model.find_or_create_by_<attribute>(:<attribute> => "") But what if I need to find_or_create by more than one attribute? Say I have a model to handle a M:M relationship between Group and Member called GroupMember. I could have many instances where member_id = 4, but I don't ever want more than once instance where member_id = 4 and group_id = 7. I'm trying to figure out if it's possible to do something like this: GroupMember.find_or_create(:member_id => 4, :group_id => 7) I realize there may be better ways to handle this, but I like the convenience of the idea of find_or_create.

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• Core Data: Deleting causes 'NSObjectInaccessibleException' from NSOperation with a reference to a deleted object

  - by Bryan Irace

  My application has NSOperation subclasses that fetch and operate on managed objects. My application also periodically purges rows from the database, which can result in the following race condition: An background operation fetches a bunch of objects (from a thread-specific context). It will iterate over these objects and do something with their properties. A bunch of rows are deleted in the main managed object context. The background operation accesses a property on an object that was deleted from the main context. This results in an 'NSObjectInaccessibleException', reason: 'CoreData could not fulfill a fault' Ideally, the objects that are fetched by the NSOperation can be operated on even if one is deleted in the main context. The best way I can think to achieve this is either to: Call [request setReturnsObjectsAsFaults:NO] to ensure that Core Data won't try to fulfill a fault for an object that no longer exists in the main context. The problem here is I may need to access the object's relationships, which (to my understanding) will still be faulted. Iterate through the managed objects up front and copy the properties I will need into separate non-managed objects. The problem here is that (I think) I will need to synchronize/lock this part, in case an object is deleted in the main context before I can finish copying. Am I missing something obvious? It doesn't seem like what I'm trying to accomplish is too out of the ordinary. Thanks for your help.

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• MySQL: Calculate depth in a parent-child model?

  - by Ivarska

  As title says: How do I calculate a node's depth in a parent-child model? I'll need the depth to, among other things, create the indent in my list (coded with PHP). Thank you in advance.

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• Joining Tables Based on Foreign Keys

  - by maestrojed

  I have a table that has a lot of fields that are foreign keys referencing a related table. I am writing a script in PHP that will do the db queries. When I query this table for its data I need to know the values associated with these keys not the key. How do most people go about this? A 101 way to do this would be to query this table for its data including the foreign keys and then query the related tables to get each key's value. This could be a lot of queries (~10). Question 1: I think I could write 1 query with a bunch of joins. Would that be better? This approach also requires the querying script to know which table fields are foreign keys. Since I have many tables like this but all with different fields, this means writing nice generic functions is hard. MySQL InnoDB tables allow for foreign constraints. I know the database has these set up correctly. Question 2: What about the idea of querying the table and identifying what the constraints are and then matching them up using whatever process I decide on from Question 1. I like this idea but never see it being used in code. Makes me think its not a good idea for some reason. I would use something like SHOW CREATE TABLE tbl_name; to find what constraints/relationships exist for that table. Thank you for any suggestions or advice.

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• .NET: What is the object header used for?

  - by Jonathan Allen

  In .NET there are 8 bytes of overheard for each object. 4 bytes are a pointer to the object's type. What are the other 4 bytes, known as the object header, used for?

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• Model a Zero or One to Many Relationship

  - by John

  How should I model a zero or one to a many relationship in the database? For example, a user record may or may not have a parent. So should my user table have a t_user.parent_id or should I have an associative table called t_user_hierarchy with the columns t_user_hierarchy.parent_id and t_user_hierarchy.user_id?

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• How to isolate data per customer, Django powered website

  - by Sawwy

  I have recently started learning python and django and working on a project that includes building a website for collecting information from customers. I am currently trying to figure out best way to isolate the customer data (collected information is sensitive and should only be accessible by customer and the service provider). I found this post Postgresql - one database for everyone, or one-database per customer and my question is that can I automate the model inheritance with customer creation via admin? To be specific, when save() is called for adding customer via django admin, this should create the customer specific tables (create a new set of tables with 'company_name' -prefix). For more information of the environment, I have extended the basic user registration with custom UserProfile adding 'company' and 'role' fields for each user. Upon login, the 'company' of the user will be checked to filter out tables without the 'company_name' prefix. 'Role' will further filter the which company-specific tables and set rights (view, edit). will appreciate any suggestions if more elegant methods could be used to solve the data isolation problem than model inheritance.

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• What is Erlang's concurrency model actually ?

  - by arun_suresh

  I was reading a paper recently Why Events are Bad. The paper is a comparative study of Event based and thread based highly concurrent servers and finally concludes stating that Threads are better than events in that scenario. I find that I am not able to classify what sort of concurrency model erlang exposes. Erlang provides Light Weight Processes, but those processes are suspended most of the time until it has received some event/message of some sort. /Arun

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• Dictionary object syntax?

  - by posfan12

  I'm having trouble figuring out the syntax for a JScript .NET dictionary object. I have tried private var myDictionary: Dictionary<string><string>; but the compiler complains that it's missing a semicolon and that the Dictionary object is not declared. I know JScript does have a native dictionary-like object format, but I'm not sure if there are disadvantages to using it instead of the .NET-specific construct. I.e., what if someone wants to extend my script using another .NET language?

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• How to set up precision attribute used by @Collumn annotation ???

  - by Arthur Ronald F D Garcia

  I often use java.lang.Integer as primary key. Here you can see some piece of code @Entity private class Person { private Integer id; @Id @Column(precision=8, nullable=false) public Integer getId() { } } I need to set up its precision attribute value equal to 8. But, when exporting The schema (Oracle), it does not work as expected. AnnotationConfiguration configuration = new AnnotationConfiguration(); configuration .addAnnotatedClass(Person.class) .setProperty(Environment.DIALECT, "org.hibernate.dialect.OracleDialect") .setProperty(Environment.DRIVER, "oracle.jdbc.driver.OracleDriver"); SchemaExport schema = new SchemaExport(configuration); schema.setOutputFile("schema.sql"); schema.create(true, false); schema.sql outputs create table Person (id number(10,0) not null) Always i get 10. Is There some workaround to get 8 instead of 10 ?

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• What are the reasons *not* to use a GUID for a primary key?

  - by Yarin

  Whenever I design a database I automatically start with an auto-generating GUID primary key for each of my tables (excepting look-up tables) I know I'll never lose sleep over duplicate keys, merging tables, etc. To me it just makes sense philosophically that any given record should be unique across all domains, and that that uniqueness should be represented in a consistent way from table to table. I realize it will never be the most performant option, but putting performance aside, I'd like to know if there are philosophical arguments against this practice?

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• Value Object and View Model Property

  - by William

  I am working on a solution that used DDD for architecture. I have a property in my ViewModel which points to a ValueObject, the view model also implements INotifyPropertyChanged interface. The value of the ValueObject will change as a user enters data on the front end. The problem I am running into is the value object is suppose to be immutable. How can I work around this issue? Thank you in advance.

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• Where to start .NET Entity Framework and ORM?

  - by Freshblood

  Hello I haven't used any database system enough but i believe i know logic of databases and i have learnt little sql so i shouldn't start to learn ORM before learn them well? Where can i start to learn .NET Entity Framework and which version of framework i have to start 3.5 or 4.0 because i heard that 4.0 has strong support for Entity Framework.I am looking sources web pages,e-books or other else.

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• Zend Framework modular app, can't load models for each module, autoloading models?

  - by EricP

  Is there a way to have models for each module? I have 3 modules, one is a "contacts" module. I created a model for it in modules/contacts/models/Codes.php Codes Controller class Contacts_CodesController extends Zend_Controller_Action { public function init() { /* Initialize action controller here */ $this->view->messages = $this->_helper->flashMessenger->getMessages(); } public function indexAction() { $codesTable = new Contacts_Model_Codes(); } Codes Model: class Contacts_Model_Codes extends Zend_Db_Table { protected $_name = 'codes'; } The error I get: Fatal error: Class 'Contacts_Model_Codes' not found in /Applications/MAMP/htdocs/zf_site/application/modules/contacts/controllers/CodesController.php on line 26 thanks

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• How to Validate with ASP.NET MVC - Model State is Invalid When Form Submitted

  - by DaveDev

  I am trying to validate a form in MVC. I add custom errors to model state and get it as invalid when form is submitted. When the view is displayed it doesn’t show validation messages nor validation summary. Can anyone please let me know what am I doing wrong or point me in the right direction if there is any other way of validating? Thanks

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• Why my json_encode get corrupted

  - by Cullen SUN

  $model = new XUploadForm; $model->file = CUploadedFile::getInstance( $model, 'file' ); //We check that the file was successfully uploaded if( $model->file !== null ) { //Grab some data $model->mime_type = $model->file->getType( ); $model->size = $model->file->getSize( ); $model->name = $model->file->getName( ); $file_extention = $model->file->getExtensionName( ); //(optional) Generate a random name for our file $file_tem_name = md5(Yii::app( )->user->id.microtime( ).$model->name); $file_thumb_name = $file_tem_name.'_thumb.'.$file_extention; $file_image_name = $file_tem_name.".".$file_extention; if( $model->validate( ) ) { //Move our file to our temporary dir $model->file->saveAs( $path.$file_image_name ); if(chmod($path.$file_image_name, 0777 )){ // Yii::import("ext.EPhpThumb.EPhpThumb"); // $thumb_=new EPhpThumb(); // $thumb_->init(); // $thumb_->create($path.$file_image_name) // ->resize(110,80) // ->save($path.$file_thumb_name); } //here you can also generate the image versions you need //using something like PHPThumb //Now we need to save this path to the user's session if( Yii::app( )->user->hasState( 'images' ) ) { $userImages = Yii::app( )->user->getState( 'images' ); } else { $userImages = array(); } $userImages[] = array( "filename" => $file_image_name, 'size' => $model->size, 'mime' => $model->mime_type, "path" => $path.$file_image_name, // "thumb" => $path.$file_thumb_name, ); Yii::app( )->user->setState('images', $userImages); //Now we need to tell our widget that the upload was succesfull //We do so, using the json structure defined in // https://github.com/blueimp/jQuery-File-Upload/wiki/Setup echo json_encode( array( array( "type" => $model->mime_type, "size" => $model->size, "url" => $publicPath.$file_image_name, //"thumbnail_url" => $publicPath.$file_thumb_name, //"thumbnail_url" => $publicPath."thumbs/$filename", "delete_url" => $this->createUrl( "upload", array( "_method" => "delete", "file" => $file_image_name ) ), "delete_type" => "POST" ) ) ); Above code give me correct response, [{"type":"image/jpeg","size":2266,"url":"/uploads/tmp/0b00cbaee07c6410241428c74aae1dca.jpeg","delete_url":"/api/imageUpload/upload?_method=delete&file=0b00cbaee07c6410241428c74aae1dca.jpeg","delete_type":"POST"}] but if I uncomment the following // Yii::import("ext.EPhpThumb.EPhpThumb"); // $thumb_=new EPhpThumb(); // $thumb_->init(); // $thumb_->create($path.$file_image_name) // ->resize(110,80) // ->save($path.$file_thumb_name); it gave me corrupted response: Mac OS X 2??ATTR?dA??Y?Ycom.apple.quarantine0001;50655994;Google\x20Chrome.app;2599ECF9-69C5-4386-B3D9-9F5CC7E0EE1D|com.google.ChromeThis resource fork intentionally left blank ??[{"type":"image/jpeg","size":1941,"url":"/uploads/tmp/409c5921c6d20944e1a81f32b12fc380.jpeg","delete_url":"/api/imageUpload/upload?_method=delete&file=409c5921c6d20944e1a81f32b12fc380.jpeg","delete_type":"POST"}]

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• validate linqtosql mapping to a model

  - by Coppermill

  I have generated a LinqtoSQL mapping xml file, which I have a valid XSD schema that I check to make sure the XML is correct. Now I want to check that the field type match the Model/Interface for example: checking that the nullable fields are nullable that int are int etc anyone got any ideas if I can do this?

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• Deploying and hosting scala in the cloud?

  - by TiansHUo

  I am starting a web app considering scalability as one of the top priorities. What would be the benefits of this: cassandra scala lift vs the traditional LAMP on the cloud? Since from what I've read, please correct me, the cloud itself is scalable I have never seen anyone deploy scala on the cloud before. Is it worth the effort to learn the platform? Is it ready for production use?

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• ActiveRecord field normalization

  - by Bill

  I feel bad asking this question, as I thought I knew enough about Activerecord to answer this myslef. But such is the way of having SO available ... I'm trying to remove the commas from a field in a model of mine, I want the user to be able to type a number , ie 10,000 and that number be stored in the database as 10000. I was hoping that I could do some model-side normalization to remove the comma. I don't want to depend on the view or controller to properly format my data. I tried ; before_validation :normalize def normalize self['thenumber'] = self['thenumber'].to_s.gsub(',','') end no worky :(

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• c# - Object reference not set to an instance of an object.

  - by tom

  Line 30: sUsername.Trim(); Line 31: sPassword.Trim(); Line 32: string ConnectionString = WebConfigurationManager.ConnectionStrings["dbnameConnectionString"].ConnectionString; Line 33: SqlConnection myConnection = new SqlConnection(ConnectionString); Line 34: try Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.NullReferenceException: Object reference not set to an instance of an object. Any ideas? I don't understand the error.

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• De-normalization for the sake of reports - Good or Bad?

  - by Travis

  What are the pros/cons of de-normalizing an enterprise application database because it will make writing reports easier? Pro - designing reports in SSRS will probably be "easier" since no joins will be necessary. Con - developing/maintaining the app to handle de-normalized data will become more difficult due to duplication of data and synchronization. Others?

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• What is the corrrect way to increment a field making up part of a composit key

  - by Tr1stan

  I have a bunch of tables whose primary key is made up of the foreign keys of other tables (Composite key). Therefore for example the attributes (as a very cut down version) might look like this: A[aPK, SomeFields] 1:M B[bPK, aFK, SomeFields] 1:M C[cPK, bFK, aFK, SomeFields] as data this could look like: A[aPK, SomeFields]: 1, Foo 2, Bar B[bPK, aFK, SomeFields]: 1, 1, FooData1 2, 1, FooData2 1, 2, BarData1 2, 2, BarData2 C[cPK, bFK, aFK, SomeFields]: 1, 1, 1, FooData1More 2, 1, 1, FooData1More 1, 2, 1, FooData2More 2, 2, 1, FooData2More 1, 1, 2, BarData1More 2, 1, 2, BarData1More 1, 2, 2, BarData2More 2, 2, 2, BarData2More I've got this running in a MSSQL DBMS and I'm looking for the best way to increment the left most column, in each table when a new tuple is added to it. I can't use the Auto Increment Identity Specification option as that has no idea that it is part of a composite key. I also don't want to use any aggregate function such as: MAX(field)+1 as this will have adverse affects with multiple users inputting data, rolling back etc. There might however be a nice trigger based option here, but I'm not sure. This must be a common issue so I'm hoping that someone has a lovely solution. As a side which may or may not affect the answer, I'm using Entity Framework 1.0 as my ORM, within a c# MVC application.

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• vs2003 : assign datarow object

  - by dotnet-practitioner

  currently I am doing this... object s = new object(); ... s = mydatarow["mycolumn"]; What I would like to do is... DataRow r = null; ... r = mydatarow["mycolumn"]; and I get an error saying that can not covert from object to DataRow.. is there a better way of doing this?

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• How can I pass methods in javascript?

  - by peterjwest

  I often need to pass methods from objects into other objects. However I usually want the method to be attached to the original object (by attached I mean 'this' should refer to the original object). I know a few ways to do this: a) In the object constructor: ObjectA = function() { var that = this; var method = function(a,b,c) { that.abc = a+b+c }} b) In objectA which has been passed objectB: objectB.assign(function(a,b,c) { that.method(a,b,c) }) c) Outside both objects: objectB.assign(function(a,b,c) { objectA.method(a,b,c) }) I want to know if there is a simpler way to pass methods attached to their original objects.

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• processing json objects in jsp

  - by user98534

  i have a JSON object sent from the browser to the jsp page. how do i receive that object and process it in jsp. do i need any specific parsers? i have used the following piece of code. but it wouldnt work. essentially i should read the contents of the object and print them in the jsp. <%@page language="java" import="jso.JSONObject"%> <% JSONObject inp=request.getParameter("param1"); %> <% for(int i=0;i<inp.size();i++) {%> <%=inp.getString(i)%> <% } %>

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