Predicate Builder
/// <summary>
/// This class adds the ability to use the Or and And extension methods on any other expression.
/// </summary>
/// <remarks>Whilst extremely recursive in nature, this is the only way to add an OR to Linq at present without writing a huge number of things
/// Source is here: http://www.albahari.com/nutshell/predicatebuilder.aspx
/// But it's easy enough to write one, it is just a boolean expression chainer with and and or operations.
/// </remarks>
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);
}
}
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