datamodel

问题 The following table...: CREATE TABLE v ( height int, width int, depth int, volume int, PRIMARY KEY (height, width, depth); ) ... could be used to store the inputs and outputs of a function of 3 variables named volume: volume(height, width, depth) = height * width * depth . What kind of data model am I using here? Is it Entity-Attribute-Value? 回答1: You appear to be mathematically oriented. When Codd(Date) introduced the relational model, he(they) reshaped the existing mathematical language to

问题 This article Connecting to PowerPivot with C# is the closest to my question but it seems that it is out of date. I attempted the methods they showed in the answer but the example ThisWorkbook.Connections["PowerPivot Data"].OLEDBConnection.ADOConnection Does not return the connection information, rather an exception. But I was able to access the PP Data Model using: ThisAddIn.Current.Application.ActiveWorkbook.Connections[1]. ModelTables[1].ModelTableColumns[1].Name` But the object only allows

问题 I want to build a recommendation model based on Mahout. My dataset format has extra columns other than userID, itemID, rating and timestamp. Thus, I think I need to extend the FileDataModel. I looked into JesterDataModel as an example. However, I have a problem with the logic flow. In its buildModel() method, an empty map "data" is first constructed. It is then thrown into processFile. I assume that "data" is modified in this method, since later it is used to construct the GenericDataModel

问题 I'm having some thoughts about proper building my app and provide a good and consistent API for it but now I'm having some doubts about the user/accounts model. It's funny but if you consider some apps you will see that they treat you like user but when editing your details your are redirect to account. One good example of this is twitter. So I would like to know your opinion about what's the best method to build this kind of architecture? Is the account really necessary? Why should I use

问题 In JSF 1.2 One was listing Items using Java List : private List<Customer> customerItems = null; , but in JSF 2.0 JSf DataModel (ListDataModel) is the way to go. (I am using JSF 2.0) private DataModel customerItems = null; public abstract DataModel createPageDataModel(); However, I still don't get how to efficiently work with it. Rather say, I can't even implement a simple and mandatory case which is, navigation. I have a <h:datatable value="#{customerController}" var="customer"> that gets its

问题 I'm using JSF 2.0, Primefaces 3.4.2, Spring 3.1.2. I'm facing a similar problem of the guy of this link: h:commandButton works from the second click. Like him I'm not using ajax in the <p:commandButton> but I'm using a <p:fileDownload /> inside the button tag. I have two views: "list.xhtml" and "downloadView.xhtml". In myBean.java I send a DataModel from view "list.xhtml" to view "downloadView.xhtml" as a request attribute as shown in the code below: FacesUtil.getServletContext().setAttribute

问题 I understand that camel case is the usual convention, as per http://forums.laravel.io/viewtopic.php?id=8857 However, Laravel is using created_at and updated_at for timestamp fields. I'm confused as what would be the best naming convention for field-names in the database? If camel cased, can I then switch created_at to createdAt, or should I use camel case for own fields and snake case for the timestamps? It doesn't seem clear to me. Maybe Laravel wants me to use snake case all the way, like

问题 I have an issue while trying to develop a data model for my application with Qt/QML. I already used a QAbstractListModel to be able to pass customs data model from C++ to QML and it worked like a charm with simple model (such as a model based on strings and bools). But now I need to build a more difficult model and I was wondering if it was possible to use a QAbstractListModel inside another QAbstractListModel . Let me explain myself. I have a data model called model_A build like that : model

问题 newbie to Entity Framework here. Using VS 2010 and SQL Server 2008 express DB. I was having trouble refreshing an Entity Data Model after adding new tables. So, I followed a suggestion I found here to just delete and regenerate the model. I get to the "Choose Your Data Connection" section of the Entity Data Model Wizard and "Save entity connection settings in Web.config as:" is checked. However, my existing name has a 1 appended to it. For example MyDatabaseEntities is now MyDatabaseEntities1

问题 I'm using Xcode 4.2 and I'm trying to use Core Data. Upon clicking the .xcdatamodeld file I see a strange view instead of the Data Model Editor View. I have reinstalled Xcode 4.2 and have even created a starter project from scratch with Core Data Enabled but the issue persists. When I create a Data Model using new file --> Data Model. It is not being recognized as a DataModel. Ctrl+Click --> 'Open As' only displays a "Preview" option. I compared my basic project with that created on a