null

问题 Platform: Windows 7 Ultimate IDE: Visual Studio 2010 Ultimate Web Environment: ASP.NET MVC 2 Database: SQL Server 2008 R2 Express Data Access: Entity Framework 4 Form Validation: DataAnnotations Sample App: NerdDinner from Wrox Pro ASP.NET MVC 2 Book: Wrox Professional MVC 2 Problem with Chapter 1 - Section: "Integrating Validation and Business Rule Logic with Model Classes" (pages 33 to 35) ERROR Synopsis: NerdDinner form validation ERROR with DataAnnotations and db nulls. DataAnnotations in

问题 I have a function which is returning "Match" if true and nil else. I need to know the number of values in the list which "Match" (hence using nil as the other value in my function). someList = {"gdj", nil, "jdis"} print(#someList) --> 3 My origination question is here if there is something I should be returning other than nil! 回答1: # operator is defined in a rather weird way; it will count until one of non-nil elements. In your case, it's entirely possible that it could return 1 as well. This

问题 I am trying to test if a list contains an object (github source). This is.null function has worked so far except in the case where I am testing an item with a name that is a partial match to a non-nul item. x <- list(ab = 1) is.null(x$ab) [1] FALSE ## expected is.null(x$b) [1] TRUE ## expected is.null(x$c) [1] TRUE ## expected is.null(x$a) [1] FALSE ## unexpected Is this expected behavior for the is.null function? I don't see any indication in the documentation. Would it be better to use the

问题 I find this behaviour very strange and counterintuitive. (Even for SQL). set ansi_nulls off go ;with sampledata(Value, CanBeNull) as ( select 1, 1 union select 2, 2 union select 3, null union select 4, null union select 5, null union select 6, null ) select ROW_NUMBER() over(partition by CanBeNull order by value) 'RowNumber',* from sampledata Which returns 1 3 NULL 2 4 NULL 3 5 NULL 4 6 NULL 1 1 1 1 2 2 Which means that all of the nulls are being treated as part of the same group for the

问题 I have two activities - a Home fragment activity, and a normal Options activity. In my home fragment activity, I'm trying to update an EditText View using data retrieved from the Options activity. Unfortunately, for some reason, the fragment activity cannot detect my view for updating. I'm not entirely sure why. Here is my function: //update text box public void updateUserData (String[] userArray){ Log.d("User Update:", "beginning..."); //get username EditText et=(EditText)getActivity()

问题 Hello all i am trying to post a form using angular but i am getting null values in my spring controller.Also in my console i see null values for the sysout.Moreover i get an error alert even though i see bull is printed on my console. My JS Controller angular.module('ngMailChimp', ['ngAria', 'ngMessages', 'ngAnimate']) .controller('SignUpController', function ($scope, $http) { $http.defaults.headers.post["Content-Type"] = "application/x-www-form-urlencoded; charset=utf-8"; var ctrl = this,

问题 I have created a Java bean class like this class BeanDemo { private double value; //getter and setter } class myApp { BeanDemo beanDemo=new BeanDemo(); int val=7; if(val<5) { beanDemo.setValue(23.456); } double value=beanDemo.getValue(); // Always returns 0.0 if it is not set System.out.println(value); } How can I check if that value is null? I mean if it is not set I should print something else(say null ) I cannot check if its 0.0 because may be i can set the value to 0.0 also. Thanks 回答1:

问题 Thanks to an answer from Nit, I have a generic type NullValuesToOptional that generates types where each nullable value becomes optional: type NullValuesToOptional<T> = Omit<T, NullableKeys<T>> & Partial<Pick<T, NullableKeys<T>>>; type NullableKeys<T> = NonNullable<({ [K in keyof T]: T[K] extends NonNull<T[K]> ? never : K })[keyof T]>; type NonNull<T> = T extends null ? never : T; It works: interface A { a: string b: string | null } type B = NullValuesToOptional<A>; // { a: string, b?: string

问题 In a Node.JS project, let's say I have a response from an API or any other object with a structure like { data: { info: { user: { name: "Hercules", password: "Iamthegreatest!" email: "hercules@olymp.gr" } } } } Accessing the members of the object is pretty easy. However, checking the existence before accessing any value gets PITA. I can assume that data is always present. Info, user, name, password and email may be present or may not. There can be a valid info object without an user and there

问题 I'm trying to make a markdown editor like Stack Overflow has. I get this error listed in the title if I don't actually type an asterisk AND a http:// containing phrase into the textarea. If I only type an asterisk containing phrase, the error refers to this line: if(linkify.length!==0) Here's a jsfiddle to show you what I mean. Here's my HTML: <textarea></textarea> <div></div><button type="button">Markdownify</button> Here's my JS: var val=$('textarea').val(), boldify = val.match(/\*\*[A-Za