datamodel

问题 On my start page, I'd like to display the first items from several different lists that I have on other pages - somewhat like the "recent" page here on SO displays both recent posts and recent comments. In my case I want to list the two most recent posts in a guest book, and the next upcoming event. In order to do this, how can I pass several Model objects to my View? Is it even possible? If not, how should it be done? 回答1: An alternative to tvanfosson's solution is to create a strongly-typed

问题 Situation: A company has many projects A project has many tags A project belongs to only 1 company A tag can belong to multiple projects A company must have access to its own tags Example 1: In the first image, all tags for the company are available through the projects/project_tag. But if all projects are removed, then the tags for the company will not be accessible anymore, because the link between project_tag and projects is gone. The tags should be somehow always be linked to the company,

问题 Let assume 10 devices(dev01,dev02,dev03..etc). It send data with some interval time,we collect those data,so our data schema is dev01 :int signalname :string signaltime :date/time[with YY-MM-DD HHMMSS.mm] Extradata :String I want to push data into cassandra ,which way is best to store those data? My Query is Like , 1 Need to retrive device based current day data,or with some date range? 2 5 Device current day data? I am not sure the following way to store data into cassadra is best model

问题 Whenever I build my project, I'm getting the error: Command /Developer/usr/bin/momc failed with exit code 1 I've read posts here about deleting extraneous Data Model versions as a fix, and nothing works. I'm stumped because nothing changes the behavior of my Build: It always fail with the above error code, regardless of whether I actually have CoreData model files or not. What I did to cause this error: Switched to a versioning model What I tried: Removing new version of Data model Removing

问题 What is the difference between a domain model and a data model? 回答1: A datamodel is a design model that only describes data and it's relations. The model contains entities, but they are described in terms of what data they own not how they act on this data or what their responsibilities are. An domain model on the other hand, is a conceptual model used in analysis of a problem domain. It describes the domain in terms of entities that have relations, data and behaviour. It describes the

问题 I wonder how Object Oriented data modeling is different from Object Relational data modeling? Is it something like the pluses of both object oriented and relational data modeling were clubbed to achieve object relational data modeling? cheers 回答1: Object-Relational data modeling supports some object-oriented concepts, while still supporting some relational concepts: Inheritance -- one table can have an IS-A relationship with another table. Likewise custom data types support inheritance.

问题 I need to design a data model for an Amazon S3-like application. Let's simplify the problem into 3 key concepts - users, buckets and objects. There are many ways to design this model - I'll list two. Three Kinds - User, Bucket and Object. Each Object has a Bucket as its parent. Each Bucket has a User as its parent. User is the root. Dynamic Kinds - Users are stored in the User kind and buckets are stored in the Bucket kind - same as #1. However objects within a bucket are stored in a dynamic

问题 I have a question about the "Data Model" in excel. Whenever I read about this function, it is used with PowerPivot. I ask because I would like to do something like this: I have table A : ID info1 And table B : ID info2 Now if I connect these tables with with the data model function (through the ID-Column), I thought that I could then join tableB.info2 to tableA and have a table that shows ID,info1,info2 But that doesn't seem to be possible, or is it possible and I'm doing something wrong? Is

问题 I've been working with the examples in http://doc.qt.digia.com/4.7/qdeclarativemodels.html which is the Qt page on QML declarative data models. In particular, I'm working with the objectlistmodel example that comes with the Qt SDK (in examples/declarative/modelviews/objectlistmodel). It all seems to work reasonably well, until I try to combine it with the QMLPageControl example at http://www.developer.nokia.com/Community/Wiki/How_to_create_a_Page_Control_component_in_QML. When I try to

问题 while studying, im struggling to find an answer to this question: What is a generic datamodel? Are there any alternatives to a generic datamodel, if so; which one would you recommend? I've looked everywhere to find a decent answer, but i didn't find it. It might be just a very simple question, i just couldn't find these terms; 'generic datamodel'. 回答1: Perhaps by generic data model you mean an entity attribute value model: EAV on wikipedia This data model has one table and three columns. It