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Expression Trees in C#

This project demonstrates the use of Expression Trees in C# to dynamically build and execute rules for filtering data. The project includes a generic Rule<T> class that evaluates conditions on a collection of User objects.

Features

  • Dynamic Expression Trees: Build and compile expressions at runtime.
  • Rule Engine: Define and execute rules dynamically using lambda expressions.
  • LINQ Integration: Filter collections using dynamically generated conditions.

Project Structure

  • Rule<T> Class: A generic class that defines a rule structure and dynamically builds expression trees.
  • User Class: Represents a user with properties like Name, Age, and Country.
  • Dummy Data: A collection of User objects is used for testing the rule engine.

How It Works

  1. Define a Rule:

    • A rule is defined using an expression tree that combines conditions (e.g., age > 25 and country == "India").

  2. Compile the Rule:

    • The expression tree is compiled into a lambda function.

  3. Filter Data:

    • The compiled lambda function is used to filter the User collection.

  4. Output Results:

    • The matching users are displayed along with the rule description.

Example Code

Here’s an example of how the rule engine works:

var parameter = Expression.Parameter(typeof(User), "u");

var ageExpr = Expression.GreaterThan(
    Expression.Property(parameter, "Age"),
    Expression.Constant(25)
);

var countryExpr = Expression.Equal(
    Expression.Property(parameter, "Country"),
    Expression.Constant("India")
);

var body = Expression.AndAlso(ageExpr, countryExpr);
var lambda = Expression.Lambda<Func<User, bool>>(body, parameter);
var isEligible = lambda.Compile();
var results = users.Where(isEligible).ToList();

Prerequisites

  • .NET 6.0 or later
  • Basic understanding of C# and LINQ

Author