How to Check for Nulls in a Deep Lambda Expression

How to check for nulls in a deep lambda expression?

You can't do that in a concise way. You can either make the lambda multiple lines, or use nested ternary operators:

var result = GetValue(one, x => x.Two == null ? null :
                                x.Two.Three == null ? null :
                                x.Two.Three.Four == null ? null :
                                x.Two.Three.Four.Foo;

Ugly, I know.

Clean way to check for Null in Lambda Expressions

var result = Store.FirstOrDefault(x => x.Products.Coupon != null && x.Products.Coupon.Any() && x.Products.Coupon[0] == 100);

Null value in lambda WHERE clause

Try to use Null-Conditional Operator ?. introduced in C# 6.

In your example it would be

a.InstallationDateType?.ToString().ToUpper().Equals(Constants.InstallationDateTypeDish)

Deep null checking, is there a better way?

We have considered adding a new operation "?." to the language that has the semantics you want. (And it has been added now; see below.) That is, you'd say

cake?.frosting?.berries?.loader

and the compiler would generate all the short-circuiting checks for you.

It didn't make the bar for C# 4. Perhaps for a hypothetical future version of the language.

Update (2014):
The ?. operator is now planned for the next Roslyn compiler release. Note that there is still some debate over the exact syntactic and semantic analysis of the operator.

Update (July 2015): Visual Studio 2015 has been released and ships with a C# compiler that supports the null-conditional operators ?. and ?[].

What is proper way to write this linq lambda expression and deal with nulls?

Simply

double currentPopulation = detailmetrics
    .Where(dm => dm.MetricScopeID == 2 && dm.MetricTypeID == 1 && dm.Timeframe.Equals("C"))
    .Select(a => Convert.ToDouble(a.MetricValue))
    .FirstOrDefault();

How do I check my lambda expression for null?

Firstly you can select decimal values from the objects which met the condition. And then use .DefaultIfEmpty() method before the .Sum() method:

runTime = db.Records
              .Where(c => c.MachineDesc.Contains(strMachine) && c.ProductionDate == dt && c.Shift == x)
              .Select(c => c.RunMinutes)
              .DefaultIfEmpty()
              .Sum();

DefaultIfEmpty() function inserts a single element with a default value if the sequence is empty. And as we know, defualt value for decimal type is 0.0M.
(Default Values Table)

Additionally:

You didn't tell us Linq to What? are you using. But, if you are using LinqToEntity, then you must change your code as (DefaultIfEmpty is not supported by EF):

runTime = db.Records
              .Where(c => c.MachineDesc.Contains(strMachine) && c.ProductionDate == dt && c.Shift == x)
              .Sum(c => (decimal?)c.RunMinutes) ?? 0;

How to check multiple objects for nullity?

EDIT 2018: As of Apache Commons lang 3.5, there has been ObjectUtils.allNotNull() and ObjectUtils.anyNotNull().

---

No.

None of Apache Commons Lang (3.4), Google Guava (18) and Spring (4.1.7) provide such a utility method.

You'll need to write it on your own if you really, really need it. In modern Java code, I'd probably consider need for such a construct a code smell, though.

lambda check for null and then set to 0

This expression makes no sense (and doesn't compile):

x => x.ExchangeAttempts.HasValue
   ? x.ExchangeAttempts.Value
   : 1 <= 1

That is the exact equivalent (assuming that ExchangeAttempts is an int? of:

int lambda( x MyClass )
{
  int result;

  if ( x.ExchangeAttempts.HasValue )
  {
    result = x.ExchangeAttempts.Value ;
  }
  else
  {
    result = 1 <= 1 ; 
  }
  return result;
}

It fails to compile because the expression 1 <= 1 evaluates to true.

If what you want to do is assign a default value of 1 if ExchangeAttempts is null, just say:

x => (x.ExchangeAttempts ?? 1) <= 1

It's shorter and more concise, and better expresses your intent.

Or, better yet:

x => x.ExchangeAttempts == null || x.ExchangeAttempts <= 1

Logical expressions short circuit, so the alternative is only ever tried if the first test fails, so the above returns true when either

• x.ExchangeAttempts has no value, or
• x.ExchangeAttempts has a value less than or equal to 1

And returns false when

• x.ExchangeAttempts has a value and that value is > 1.

---

Related Topics