wcf ria 解决linq表达式拼接动态查询的类PredicateBuilder

解决linq表达式拼接动态查询的类PredicateBuilder

在domain service 的客户端调用时使用

public static class PredicateBuilder
    {
        /// <summary>
        /// 构造函数使用True时：单个AND有效，多个AND有效；单个OR无效，多个OR无效；混合时写在AND后的OR有效
        /// 构造函数使用False时：单个AND无效，多个AND无效；单个OR有效，多个OR有效；混合时写在OR后面的AND有效
        /// </summary>
        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.Or(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.And(expr1.Body, invokedExpr), expr1.Parameters);
        }

        public static Predicate<T> ConvertToPredicate<T>(this Func<T, bool> func)
        {
            return new Predicate<T>(func);
        }
    }

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