nullable

问题 Some of the properties in a class generated by EF are nullable, and some arent. My first instinct was that this should be driven by Nullable property returned by sp_help MyView. But that doesn't seem to be the case. Some of my types that are returned as Nullable by sp_help get generated as Nullable , while others, get generated as just bool instead of Nullable*bool* what is it driven by, and is there any way to control it by the view? as a test i created ViewA and than ViewB which selected

问题 I would like to do something like this : int? l = lc.HasValue ? (int)lc.Value : null; where lc is a nullable enumeration type, say EMyEnumeration?. So I want to test if lc has a value, so if then give its int value to l, otherwise l is null. But when I do this, C# complains that 'Error type of conditional expression cannot be determined as there is no implicit conversion between 'int' and ''. How can I make it correct? Thanks in advance!! 回答1: You have to cast null as well: int? l = lc

问题 I am using nullable doubles to store the sum of some values pulled from various sources. The sum could be any real value or null if no elements are present. Currently, I use a null check and either assign or increment: double? sum = null; ... if(sum == null) sum = someTempValue; else sum += someTempValue; I know c# has several shorthand null checks for method calls and the such. My question is if there is a shorthand notation to the addition assignment operator += when using nullables that

问题 The one feature that I cannot stand with-in the Entity framework is where the complex Result object sets some properties as Nullable. Is there a global setting to where that Nullable property is never set to yes? 回答1: It appears that even if you get the property Nullable to be False , that it will still generate a Nullable version of your object. Check out the accepted answer of Entity Framework: Set nullable to false, but type is still nullable. Also, read How to manually update your Entity

问题 I am experiencing some weird behavior when using Generic Types and null operator. Why does obj2.CurrentDate return a date value that appears to be incorrect when using the ? (short hand). If I long hand the null operator (if) in the property then it returns the correct and expected value. I thought the ? was the equivalent to the if(expression, returnIfTrue, returnIfFalse). Also, if the generic type constructor is removed, then the null operator works as expected. Why is this? Return If

问题 I am experiencing some weird behavior when using Generic Types and null operator. Why does obj2.CurrentDate return a date value that appears to be incorrect when using the ? (short hand). If I long hand the null operator (if) in the property then it returns the correct and expected value. I thought the ? was the equivalent to the if(expression, returnIfTrue, returnIfFalse). Also, if the generic type constructor is removed, then the null operator works as expected. Why is this? Return If

问题 I have a class i want to change the properties of in the editor. So i made my class System.Serializable and made the variables public that i want to be able to change. Like so: [System.Serializable] public class UIOptionsRing { public float Radius, DistanceBetweenPoints, StartOffset, GapInDegrees; public int? GapAfterElementNumer = 3; //this var doesnt show up public Vector3 CircleCenter; public GameObject CircleElementsContainer; } But the problem i am having is that the GapAfterElementNumer

问题 I'm trying to do something similar to what's described here, but with nullable types. http://www.csharp-station.com/Tutorials/Lesson23.aspx int availableUnits = unitsInStock ?? 0; In VB, it would be this: Dim availableUnits As Int32 = If(unitsInStock, 0) However I'm working with db columns, which could be DbNull, and nullable types, which can be Nothing (which is different to DbNull). If a column is DbNull, I want to return Nothing, otherwise return the value. For eg: Dim availableUnits As

问题 I'm trying to write a SQLCLR function that will return a nullable boolean value. If I declare the function like this: public static SqlBoolean? IsTimeZoneDST(SqlString timeZone) then I get an error when attempting to use the assembly saying the types for the return value do not match. Is there something I am missing or is it not possible to return a nullable boolean in this instance? 回答1: All of the .NET Sql* types have a .Null field (static property) that creates a new instance of what will

问题 I'm having trouble inserting null value from a bulk insert statement. Two columns are nullable and the Id is identity. The int nullable workd out fine, but the time doesn't. Here the bulk statement: BULK INSERT Circulation FROM '.....file.cs' WITH ( FIRSTROW = 2, MAXERRORS = 0, FIELDTERMINATOR = ',', ROWTERMINATOR = '', KEEPNULLS) Here is an extract of the csv: ID, IDStopLine, IDException, Hour, PositionHour, Day ,28, 8, 12:20, 52, 0 ,29, 163, , 1, Meaning that I'm trying to insert nulls in