改进的ExpressionItem扩展

using System;
using System.Linq.Expressions;

namespace Phoenix.Modules.Common.Infrastructure.TypeExtensions.LinqExtension
{
    public static class ExpressionExtention
    {
        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> left, ExpressionItem<T> expressionItem)
        {
            //如果左边表达式为空
            if (left == null)
            {
                left = (g => true);
                return left.And(expressionItem);
            }
            //如果右表达式为空，返回左表达式
            if (expressionItem == null)
            {
                return left;
            }

            //右边表达式变量值为空
            if (expressionItem.Value == null)
            {
                //如果变量为空值不产生表达式
                if (!expressionItem.AttachWhenValueNull) return left;

                left = left.And(Specification<T>.Eval(expressionItem.Expression).GetExpression());
                return left;

            }

            //如果右边表达式变量值不为空

            Type t = expressionItem.Value.GetType();
            //如果是字符型
            if (t.Name == "String")
            {
                //如果是空白字符
                if (string.IsNullOrWhiteSpace(expressionItem.Value))
                {
                    //如果变量为空值不产生表达式
                    if (!expressionItem.AttachWhenValueNull) return left;
                }

            }
            left = left.And(Specification<T>.Eval(expressionItem.Expression).GetExpression());
            return left;

        }

        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> left, ExpressionItem<T> expressionItem)
        {
            //如果左边表达式为空
            if (left == null)
            {
                left = (g => false);
                return left.Or(expressionItem);
            }
            //如果右表达式为空，返回左表达式
            if (expressionItem == null)
            {
                return left;
            }

            //右边表达式变量值为空
            if (expressionItem.Value == null)
            {
                //如果变量为空值不产生表达式
                if (!expressionItem.AttachWhenValueNull) return left;

                left = left.Or(Specification<T>.Eval(expressionItem.Expression).GetExpression());
                return left;

            }

            //如果右边表达式变量值不为空

            Type t = expressionItem.Value.GetType();
            //如果是字符型
            if (t.Name == "String")
            {
                //如果是空白字符
                if (string.IsNullOrWhiteSpace(expressionItem.Value))
                {
                    //如果变量为空值不产生表达式
                    if (!expressionItem.AttachWhenValueNull) return left;
                }

            }
            left = left.Or(Specification<T>.Eval(expressionItem.Expression).GetExpression());
            return left;

        }
    }

    public class ExpressionItem<T>
    {
        public ExpressionItem(Expression<Func<T, bool>> expression, dynamic value, bool attachWhenValueNull)
        {
            Expression = expression;
            Value = value;
            AttachWhenValueNull = attachWhenValueNull;
        }
        public Expression<Func<T, bool>> Expression { get; }
        public dynamic Value { get; }
        public bool AttachWhenValueNull { get; }
    }
}