A generic specification base class.

Specification.cs

using System;
using System.Linq.Expressions;

namespace Foundation.Specifications
{
    /// <summary>
    /// Defines an abstract class from which to create conditional specifications.
    /// </summary>
    /// <typeparam name="T">The type of entity used in the specification.</typeparam>
    /// <seealso href="http://ubik.com.au/article/named/implementing_the_specification_pattern_with_linq" />
    /// <seealso href="http://www.lostechies.com/blogs/chrismissal/archive/2009/09/10/using-the-specification-pattern-for-querying.aspx" />
    public abstract class Specification<T> : ISpecification<T>
    {
        #region fields

        private Func<T, bool> _func;

        #endregion

        #region properties

        /// <summary>
        /// Gets the condition expression.
        /// </summary>
        /// <value>The <see cref="Expression{TDelegate}" />.</value>
        public abstract Expression<Func<T, bool>> Condition { get; }

        /// <summary>
        /// Gets the is satisfied by.
        /// </summary>
        /// <value>The <see cref="Func{T,TResult}" />.</value>
        public virtual bool IsSatisfiedBy(T candidate)
        {
            if (_func == null)
                _func = Condition.Compile();

            return _func(candidate);
        }

        #endregion
    }
}