C elegant way to check if a property s property is null

Question

In C   say that you want to pull a value off of PropertyC in this example and ObjectA  PropertyA and PropertyB can all be null   ObjectA PropertyA PropertyB PropertyC  How can I get PropertyC safely with the least amount of code   Right now I would check   if ObjectA    null  amp  amp  ObjectA PropertyA   null  amp  amp  ObjectA PropertyA PropertyB    null           safely pull off the value     int value   objectA PropertyA PropertyB PropertyC      It would be nice to do something more like this  pseudo-code    int value   ObjectA PropertyA PropertyB   ObjectA PropertyA PropertyB   defaultVal    Possibly even further collapsed with a null-coalescing operator   EDIT Originally I said my second example was like js  but I changed it to psuedo-code since it was correctly pointed out that it would not work in js

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I would write your own method in the type of PropertyA  or an extension method if it s not your type  using the similar pattern to the Nullable type   class PropertyAType      public PropertyBType PropertyB  get  set        public PropertyBType GetPropertyBOrDefault               return PropertyB    null   PropertyB   defaultValue

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Refactor to observe the Law of Demeter

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You re obviously looking for the Nullable Monad   string result   new A   PropertyB PropertyC Value    becomes  string result   from a in new A                   from b in a PropertyB                 from c in b PropertyC                 select c Value    This returns null  if any of the nullable properties are null  otherwise  the value of Value   class A   public B PropertyB   get  set      class B   public C PropertyC   get  set      class C   public string Value   get  set          LINQ extension methods   public static class NullableExtensions       public static TResult SelectMany lt TOuter  TInner  TResult gt           this TOuter source          Func lt TOuter  TInner gt  innerSelector          Func lt TOuter  TInner  TResult gt  resultSelector          where TOuter   class         where TInner   class         where TResult   class               if  source    null  return null          TInner inner   innerSelector source           if  inner    null  return null          return resultSelector source  inner

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When I need to chain calls like that  I rely on a helper method I created  TryGet         public static U TryGet lt T  U gt  this T obj  Func lt T  U gt  func                return obj TryGet func  default U               public static U TryGet lt T  U gt  this T obj  Func lt T  U gt  func  U whenNull                return obj    null   whenNull   func obj           In your case  you would use it like so       int value   ObjectA          TryGet p   gt  p PropertyA           TryGet p   gt  p PropertyB           TryGet p   gt  p PropertyC  defaultVal

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Update 2014  C  6 has a new operator    various called  safe navigation  or  null propagating   parent  child   Read http   blogs msdn com b jerrynixon archive 2014 02 26 at-last-c-is-getting-sometimes-called-the-safe-navigation-operator aspx for details  This has long been a hugely popular request  https   visualstudio uservoice com forums 121579-visual-studio suggestions 3990187-add-operator-to-c- tracking code 594c10a522f8e9bc987ee4a5e2c0b38d

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var result   nullableproperty    defaultvalue    The     null-coalescing operator  means if the first argument is null  return the second one instead

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In C  6 you can use the Null Conditional Operator  So the original test will be   int  value   objectA  PropertyA  PropertyB  PropertyC

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I wrote a method that accepts a default value  here is how to use it   var teacher   new Teacher    return teacher GetProperty t   gt  t Name   return teacher GetProperty t   gt  t Name   Default name      Here is the code   public static class Helper            lt summary gt          Gets a property if the object is not null          var teacher   new Teacher            return teacher GetProperty t   gt  t Name           return teacher GetProperty t   gt  t Name   Default name             lt  summary gt      public static TSecond GetProperty lt TFirst  TSecond gt  this TFirst item1          Func lt TFirst  TSecond gt  getItem2  TSecond defaultValue   default TSecond                 if  item1    null                        return defaultValue                     return getItem2 item1

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It is not possible  ObjectA PropertyA PropertyB will fail if ObjectA is null due to null dereferencing  which is an error   if ObjectA    null  amp  amp  ObjectA PropertyA     works due to short circuiting  ie ObjectA PropertyA will never be checked if ObjectA is null   The first way you propose is the best and most clear with intent   If anything you could try to redesign without having to rely on so many nulls

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I saw something in the new C  6 0  this is by using     instead of checking   for example instead of using   if  Person    null  amp  amp  Person Contact  null  amp  amp  Person Contact Address   null  amp  amp  Person Contact Address City    null       var city   person contact address city      you simply use  var city   person  contact  address  city    I hope it helped somebody      UPDATE   You could do like this now   var city    Person    null                 Person Contact  null                    Person Contact Address   null                           Person Contact Address City  null                                     Person Contact Address City   null                           null                  null                null

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Just stumbled accross this post   Some time ago I made a suggestion on Visual Studio Connect about adding a new     operator   http   visualstudio uservoice com forums 121579-visual-studio suggestions 4104392-add-as-an-recursive-null-reference-check-opera  This would require some work from the framework team but don t need to alter the language but just do some compiler magic  The idea was that the compiler should change this code  syntax not allowed atm   string product name   Order OrderDetails 0  Product Name      no product defined     into this code  Func lt string gt   get default        gt   no product defined    string product name   Order    null         get default Invoke          Order OrderDetails 0     null             get default Invoke              Order OrderDetails 0  Product    null                 get default Invoke                  Order OrderDetails 0  Product Name     get default Invoke     For null check this could look like  bool isNull    Order OrderDetails 0  Product     null     null

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you can use the following extension and I think it is really good        lt summary gt      Simplifies null checking      lt  summary gt  public static TR Get lt TF  TR gt  TF t  Func lt TF  TR gt  f      where TF   class       return t    null   f t    default TR           lt summary gt      Simplifies null checking      lt  summary gt  public static TR Get lt T1  T2  TR gt  T1 p1  Func lt T1  T2 gt  p2  Func lt T2  TR gt  p3      where T1   class     where T2   class       return Get Get p1  p2   p3           lt summary gt      Simplifies null checking      lt  summary gt  public static TR Get lt T1  T2  T3  TR gt  T1 p1  Func lt T1  T2 gt  p2  Func lt T2  T3 gt  p3  Func lt T3  TR gt  p4      where T1   class     where T2   class     where T3   class       return Get Get Get p1  p2   p3   p4       And it is used like this   int value   Nulify Get objectA  x  gt x PropertyA  x  gt x PropertyB  x  gt x PropertyC

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This approach is fairly straight-forward once you get over the lambda gobbly-gook   public static TProperty GetPropertyOrDefault lt TObject  TProperty gt  this TObject model  Func lt TObject  TProperty gt  valueFunc                                                            where TObject   class               try                       return valueFunc Invoke model                     catch  NullReferenceException nex                        return default TProperty                     With usage that might look like   ObjectA objectA   null   Assert AreEqual 0 objectA GetPropertyOrDefault prop  gt prop ObjectB ObjectB ObjectC ID     Assert IsNull objectA GetPropertyOrDefault prop   gt  prop ObjectB

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Short Extension Method   public static TResult IfNotNull lt TInput  TResult gt  this TInput o  Func lt TInput  TResult gt  evaluator    where TResult   class where TInput   class     if  o    null  return null    return evaluator o       Using  PropertyC value   ObjectA IfNotNull x   gt  x PropertyA  IfNotNull x   gt  x PropertyB  IfNotNull x   gt  x PropertyC     This simple extension method and much more you can find on http   devtalk net csharp chained-null-checks-and-the-maybe-monad   EDIT   After using it for moment I think the proper name for this method should be IfNotNull   instead of original With

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You could do this   class ObjectAType       public int PropertyC               get                       if  PropertyA    null                  return 0              if  PropertyA PropertyB    null                  return 0              return PropertyA PropertyB PropertyC                       if  ObjectA    null        int value   ObjectA PropertyC              Or even better might be this   private static int GetPropertyC ObjectAType objectA        if  objectA    null          return 0      if  objectA PropertyA    null          return 0      if  objectA PropertyA PropertyB    null          return 0      return objectA PropertyA PropertyB PropertyC      int value   GetPropertyC ObjectA

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This code is  the least amount of code   but not the best practice   try       return ObjectA PropertyA PropertyB PropertyC    catch NullReferenceException         return null

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Assuming you have empty values of types one approach would be this   var x      objectA    A Empty  PropertyOfB    B Empty  PropertyOfC    C Empty  PropertyOfString    I m a big fan of C  but a very nice thing in new Java  1 7   is the    operator    var x   objectA  PropertyOfB  PropertyOfC  PropertyOfString

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The way you re doing it is correct   You could use a trick like the one described here  using Linq expressions    int value   ObjectA NullSafeEval x   gt  x PropertyA PropertyB PropertyC  0     But it s much slower that manually checking each property

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Can you add a method to your class  If not  have you thought about using extension methods  You could create an extension method for your object type called GetPropC     Example   public static class MyExtensions       public static int GetPropC this MyObjectType obj  int defaltValue                if  obj    null  amp  amp  obj PropertyA    null  amp  obj PropertyA PropertyB    null              return obj PropertyA PropertyB PropertyC          return defaltValue            Usage   int val   ObjectA GetPropC 0      will return PropC value  or 0  defaltValue    By the way  this assumes you are using  NET 3 or higher

[c#] C# elegant way to check if a property's property is null

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