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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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  • 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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  • C++ return a "NULL" object if search result not found

    - by aduric
    I'm pretty new to C++ so I tend to design with a lot of Java-isms while I'm learning. Anyway, in Java, if I had class with a 'search' method that would return an object T from a Collection< T that matched a specific parameter, I would return that object and if the object was not found in the collection, I would return a NULL. Then in my calling function I would just check if(T != NULL) { ... } In C++, I'm finding out that I can't return a NULL if the object doesn't exist. I just want to return an 'indicator' of type T that notifies the calling function that no object has been found. I don't want to throw an exception because it's not really an exceptional circumstance. class Node { .... Attr& getAttribute(const string& attribute_name) const { //search collection //if found at i return attributes[i]; //if not found return NULL; } private: vector<Attr> attributes; }

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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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  • Typed DefaultListModel to avoid casting

    - by Thomas R.
    Is there a way in java to have a ListModel that only accepts a certain type? What I'm looking for is something like DefaultListModel<String> oder TypedListModel<String>, because the DefaultListModel only implements addElement(Object obj) and get(int index) which returns Object of course. That way I always have to cast from Object to e.g. String and there is no guarantee that there are only strings in my model, even though I'd like to enforce that. Is this a flaw or am I using list models the wrong way?

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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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  • 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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  • Django finding which field matched in a multiple OR query

    - by Greg Hinch
    I've got a couple models which are set up something like this: class Bar(models.Model): baz = models.CharField() class Foo(models.Model): bar1 = models.ForeignKey(Bar) bar2 = models.ForeignKey(Bar) bar3 = models.ForeignKey(Bar) And elsewhere in the code, I end up with an instance of Bar, and need to find the Foo it is attached to in some capacity. Right now I came up with doing a multiple OR query using Q, something like this: foo_inst = Foo.objects.get(Q(bar1=bar_inst) | Q(bar2=bar_inst) | Q(bar3=bar_inst)) What I need to figure out is, which of the 3 cases actually hit, at least the name of the member (bar1, bar2, or bar3). Is there a good way to do this? Is there a better way to structure the query to glean that information?

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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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  • 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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  • Problem with object serialization in Applet-Servlet communication

    - by Bruce
    Hi guys, I spent a lot of time on thinking what is wrong with the following code. I send the object from my applet to servlet and then I read the object from servlet. Everything goes fine till reading serialized object from the servlet - I got IOException. Thank you in advance! Here is the code: Applet: try { URL servletURL = new URL(this.getCodeBase().getProtocol(), this.getCodeBase().getHost(), this.getCodeBase().getPort(), "/MyApplet"); URLConnection servletConnection = servletURL.openConnection(); servletConnection.setDoInput( true ); servletConnection.setDoOutput( true ); servletConnection.setUseCaches( false ); servletConnection.setRequestProperty( "Content-Type", "application/x-java-serialized-object" ); ObjectOutputStream output; output = new ObjectOutputStream( servletConnection.getOutputStream( ) ); output.writeObject( someObject ); output.flush( ); output.close( ); ObjectInputStream input = new ObjectInputStream( servletConnection.getInputStream( ) ); // Here I got the exception myObject = ( SomeObject ) input.readObject( ); } catch (java.io.IOException ioe) { System.err.println(ioe.getStackTrace()); } catch (Exception e) { System.err.println(e.getStackTrace()); } Servlet: response.setContentType("application/x-java-serialized-object"); try { ObjectInputStream inputFromApplet = new ObjectInputStream(request.getInputStream()); SomeObject myObject = (SomeObject) inputFromApplet.readObject(); ObjectOutputStream outputToApplet = new ObjectOutputStream(response.getOutputStream()); outputToApplet.writeObject(myObject); outputToApplet.flush(); } catch(Exception e) { // ... }

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  • Comparing all properties of an object using expression trees

    - by stringargs
    Hi, I'm trying to write a simple generator that uses an expression tree to dynamically generate a method that compares all properties of an instance of a type to the properties of another instance of that type. This works fine for most properties, like int an string, but fails for DateTime? (and presumably other nullable value types). The method: static Delegate GenerateComparer(Type type) { var left = Expression.Parameter(type, "left"); var right = Expression.Parameter(type, "right"); Expression result = null; foreach (var p in type.GetProperties()) { var leftProperty = Expression.Property(left, p.Name); var rightProperty = Expression.Property(right, p.Name); var equals = p.PropertyType.GetMethod("Equals", new[] { p.PropertyType }); var callEqualsOnLeft = Expression.Call(leftProperty, equals, rightProperty); result = result != null ? (Expression)Expression.And(result, callEqualsOnLeft) : (Expression)callEqualsOnLeft; } var method = Expression.Lambda(result, left, right).Compile(); return method; } On a DateTime? property it fails with: Expression of type 'System.Nullable`1[System.DateTime]' cannot be used for parameter of type 'System.Object' of method 'Boolean Equals(System.Object)' OK, so it finds an overload of Equals that expects object. So why can't I pass a DateTime? into that, as it's convertible to object? If I look at Nullable<T>, it indeed has an override of Equals(object o). PS: I realize that this isn't a proper generator yet as it can't deal with null values, but I'll get to that :)

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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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  • 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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  • 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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  • Creating form object for variable kind of form.

    - by Bunny Rabbit
    i want to create a form for users to submit questions in django ..so far the models i have created are class Question(models.Model): statement=models.CharField(max_length=100) class Choice(models.Model): statement=models.CharField(max_length=100) value=models.IntegerField() question=models.ForeignKey(Question) Now i want to write a Form class for creating a above form but the problem is the number of choices are variable,a user can decide how many choices a question must have .How do i do that in django?

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  • PHP object class variable

    - by mck89
    I have built a class in PHP and I must declare a class variable as an object. Everytime I want to declare an empty object I use: $var=new stdClass; But if I use it to declare a class variable as class foo { var $bar=new stdClass; } a parse error occurs. Is there a way to do this or must I declare the class variable as an object in the constructor function? PS: I'm using PHP 4.

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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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  • 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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  • 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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  • PostgreSQL: Why does this simple query not use the index?

    - by David
    I have a table t with a column c, which is an int and has a btree index on it. Why does the following query not utilize this index? explain select c from t group by c; The result I get is: HashAggregate (cost=1005817.55..1005817.71 rows=16 width=4) -> Seq Scan on t (cost=0.00..946059.84 rows=23903084 width=4) My understanding of indexes is limited, but I thought such queries were the purpose of indexes.

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  • Hibernate session method to update object

    - by EugeneP
    I need this roadmap of a Hibernate managed object instance. First, I create an instance with initial properties and persist this object in a db. Then session associated with this object is closed. But still, I serialize my object and on the next step deserialize it, invoke some setters, and again, I need to update what changed in a database. What methods of Hibernate session should I use? persist() or save() on the first step and saveOrUpdate() on the second? In fact I see that saveOrUpdate() can be used on each step. What would you recommend?

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