/// <summary>/// 構造函數使用True時：單個AND有效，多個AND有效；單個OR無效，多個OR無效；混合時寫在AND后的OR有效/// 構造函數使用False時：單個AND無效，多個AND無效；單個OR有效，多個OR有效；混合時寫在OR后面的AND有效/// </summary>public static class PRedicateExtensions{    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>> expression1, Expression<Func<T, bool>> expression2)    {        var invokedExpression = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());        return Expression.Lambda<Func<T, bool>>(Expression.Or(expression1.Body, invokedExpression), expression1.Parameters);    }    public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)    {        var invokedExpression = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());        return Expression.Lambda<Func<T, bool>>(Expression.And(expression1.Body, invokedExpression), expression1.Parameters);    }}

調用方法：

HUBDataDataContext db = new HUBDataDataContext();var predicate = PredicateExtensions.False <T_DISPATCH>();predicate = predicate.Or(c => c.ToHUBID == 1);var dispatch = db.T_DISPATCH.Where(predicate).Where(c => c.State == 3); 

轉自：http://www.cnblogs.com/ejiyuan/archive/2009/07/14/1523515.html