C# How to pass a variable into a func?

Question

Simple version

var myVar = some object;

myList.Where(element => myVar != null && element.Name == myVar.Name)

What I want to write

public static (Return Value) Start<T>(this T input, Func<(IDK what goes here)> exp)
{
   var theVar = somehow get the myVar that was passed in;
   if (theVar != null)
   {
       apply exp; <= I can do this part
   }
}

myList.Start((myVar, element) => element.Name == myVar.Name));

Basically be able to write an expression without having to check for the null every single time.

Will this be used with databases (e.g. LINQ to SQL or LINQ to EF) or just LINQ to Objects? — NetMage, Jul 10 '19 at 19:30

score 0 · Answer 1 · answered Jul 09 '19 at 22:26

0

Use anonymous lambda (I think without testing) >

myList.Start((myVar, () => element) => element.Name == myVar.Name));

answered Jul 09 '19 at 22:26

RandomUs1r

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score 0 · Answer 2 · answered Jul 11 '19 at 20:13

I found a way, i wrote a class BaseExtension it doesn't have a lot in it, just a holder for some properties

public static BaseExtension<T> Start<T, TValue>(this IQueryable<T> input, TValue value, Func<TValue, Expression<Func<T, bool>>> expression) =>
        new BaseExtension<T>(input, value == null ? null : expression.Invoke(value));

this allows me to write

_context.MyEntities.Start(myVar, value => entity => entity.Id.ToString() == myVar)

and passing in myVar allows me to do c# logic behind the scenes before the query would be executed in the database.

An example would be myVar != null or I can add a custom function that would apply the expression or not

score -1 · Answer 3 · answered Jul 09 '19 at 22:02

The where method expected a Boolean type, you can use this

  private static <type> <name>(<type> arg)
        {
            return true;
        }

If this not work for you, on Visual Studio, writing something insidere where, and press ctrl + . .

See the sugested implementations

C# How to pass a variable into a func?

3 Answers3