CODEWITHSUNDEEP
c#lambda
Kyle
Kyle

Reputation: 1172

C# Converting Lambda Expression Function to Descriptive String

I have quite an unnecessary dilemma. I'm lazily looking for a function that would convert a lamda expression into a string. It bothers me that I'm typing in this cache key every time but I don't really want to take the time to create it.

I want to use it for a cache function I created:

Where if I wanted to get a name for a person without calling the function every time.

public static string GetPersonName(int id)
{
    return Repository.PersonProvider.Cached(x => x.GetById(id)).Name;
}

The GetExpressionDescription would return "PersonProvider.GetById(int 10)"

I figure this is possible but I wonder if anyone has already built this or has seen it somewhere.

public static R Cached<T, R>(this T obj, Expression<Func<T, R>> function, double hours = 24)
{
    var expressionDescription = GetExpressionDescription(function); 
    return Cached(function, expressionDescription, hours); 
}

public static R Cached<T, R>(this T obj, Expression<Func<T, R>> function, string cacheName, double hours = 24)
{
    var context = HttpContext.Current;
    if (context == null)
        return function.Compile().Invoke(obj);

    R results = default(R);
    try { results = (R)context.Cache[cacheName]; }
    catch { }
    if (results == null)
    {
        results = function.Compile().Invoke(obj);
        if (results != null)
        {
            context.Cache.Add(cacheName, results, null, DateTime.Now.AddHours(hours),
                              Cache.NoSlidingExpiration,
                              CacheItemPriority.Default, null);
        }
    }
    return results;
}

Upvotes: 6

Views: 11405

Answers (2)

Olivier Jacot-Descombes
Olivier Jacot-Descombes

Reputation: 112259

You can simply get a string representation of an Expression<> with .ToString():

using System;
using System.Linq.Expressions;

public class Program
{
    public static void Main()
    {
        Test(s => s.StartsWith("A"));
    }

    static void Test(Expression<Func<string,bool>> expr)
    {
        Console.WriteLine(expr.ToString());
        Console.ReadKey();
    }
}

Prints:

s => s.StartsWith("A")

See: https://dotnetfiddle.net/CJwAE5

But of course it will not yield you the caller and the values of variables, just the expression itself.

Upvotes: 7

R&#233;nald
R&#233;nald

Reputation: 1430

Maybe you should try DynamicExpresso. I used that library to develop a lightweight business-rules engine.

https://github.com/davideicardi/DynamicExpresso

Upvotes: 3

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