Can't create a condition for null values in an array? - entity-framework

Question

I am using linq expression trees to build a query.
My array:
string[] { null, null }
condition I want to implement:
x == null ? null : x.ToLower()
My linq expression looks like this:
{Param_0 => value(System.String[]).Any(Param_1 => (Param_0.FirstName.ToLower() == IIF((Param_1 == null), null, Param_1.ToLower())))}
This is my first attempt and I can't seem to find the correct way to do it
Constant = Expression.Condition(Expression.Equal(Constant, Expression.Constant(null, typeof(string))), Expression.Constant(null, typeof(string)), Expression.Call(Constant, "ToLower", null));
The expected result is to be able to call .ToLower() on elements that are not null

Answer 1

It seems to me that you want an expression that represents a function call with input a string, and output a string.
Expression<Func<string, string>>
How about a Lambda expression?
Expression<Func<string, string>> myExpression = (x) => (x==null) ? null : x.ToLower();
This expression can be used in a Queryable Select statement, like below:
IQueryable<string> myItems = new List<sring>()
{
"Abc",
null,
"DEF",
null,
"gHI",
}
.AsQueryable();
IQueryable<string> myLowerCaseItems = myItems.Select(myExpression);
foreach (string item in myLowerCaseItems)
{
if (item == null)
Console.WriteLine("<null>");
else
Console.WriteLine(item);
}
This yields the following output:
abc
def
ghi