c# predicate builder, useful for constructing linq predicates

ExpressionWhereFinder.cs

	internal class ExpressionWhereFinder : ExpressionVisitor
	{
	private readonly IList<MethodCallExpression> _whereExpressions = new List<MethodCallExpression>();

	public IEnumerable<MethodCallExpression> GetWhere(Expression expression)
	{
	Visit(expression);
	return _whereExpressions;
	}

	protected override Expression VisitMethodCall(MethodCallExpression expression)
	{
	if (expression.Method.Name == "Where")
	{
	_whereExpressions.Add(expression);
	}

	Visit(expression.Arguments[0]);
	return expression;
	}
	}

	namespace MyApp.Linq
	{
	using System;
	using System.Linq;
	using System.Linq.Expressions;

	public static class PredicateBuilder
	{
	public static Expression<Func<T, bool>> True<T>()
	{
	return f => true;
	}

	public static Expression<Func<T, bool>> False<T>()
	{
	return f => false;
	}

	public static Expression<Func<T, bool>> Or<T>(
	this Expression<Func<T, bool>> expr1,
	Expression<Func<T, bool>> expr2
	)
	{
	var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
	return Expression.Lambda<Func<T, bool>>
	(Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters);
	}

	public static Expression<Func<T, bool>> And<T>(
	this Expression<Func<T, bool>> expr1,
	Expression<Func<T, bool>> expr2
	)
	{
	var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
	return Expression.Lambda<Func<T, bool>>
	(Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters);
	}
	}

	}