qlhb/Ropin.Inspection.Repository/Base/ExpressionExtensions.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Text;
using System.Threading.Tasks;

namespace Ropin.Inspection.Repository
{
    public static class ExpressionExtensions
    {
        /// <summary>
        /// 添加And条件
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="first"></param>
        /// <param name="second"></param>
        /// <returns></returns>
        public static Expression<Func<T, bool>> And<T>(
        this Expression<Func<T, bool>> first,
        Expression<Func<T, bool>> second)
        {
            return first.AndAlso<T>(second, Expression.AndAlso);
        }
        /// <summary>
        /// 添加Or条件
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="first"></param>
        /// <param name="second"></param>
        /// <returns></returns>
        public static Expression<Func<T, bool>> Or<T>(
            this Expression<Func<T, bool>> first,
            Expression<Func<T, bool>> second)
        {
            return first.AndAlso<T>(second, Expression.OrElse);
        }
        /// <summary>
        /// 合并表达式以及参数
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="expr1"></param>
        /// <param name="expr2"></param>
        /// <param name="func"></param>
        /// <returns></returns>
        private static Expression<Func<T, bool>> AndAlso<T>(
        this Expression<Func<T, bool>> expr1,
        Expression<Func<T, bool>> expr2,
        Func<Expression, Expression, BinaryExpression> func)
        {
            var parameter = Expression.Parameter(typeof(T));

            var leftVisitor = new ReplaceExpressionVisitor(expr1.Parameters[0], parameter);
            var left = leftVisitor.Visit(expr1.Body);

            var rightVisitor = new ReplaceExpressionVisitor(expr2.Parameters[0], parameter);
            var right = rightVisitor.Visit(expr2.Body);

            return Expression.Lambda<Func<T, bool>>(
                func(left, right), parameter);



        }


        private class ReplaceExpressionVisitor
 : ExpressionVisitor
        {
            private readonly Expression _oldValue;
            private readonly Expression _newValue;

            public ReplaceExpressionVisitor(Expression oldValue, Expression newValue)
            {
                _oldValue = oldValue;
                _newValue = newValue;
            }

            public override Expression Visit(Expression node)
            {
                if (node == _oldValue)
                    return _newValue;
                return base.Visit(node);
            }
        }
    }



//    Expression<Func<IdentityUser, bool>> filter = u => true;

//            if (!string.IsNullOrEmpty(username))
//            {
//                filter = filter.And(c => c.UserName.Contains(username));
//            }
//if (!string.IsNullOrEmpty(phone))
//{
//    filter = filter.And(c => c.PhoneNumber.Contains(phone));
//}
//if (!string.IsNullOrEmpty(email))
//{
//    filter = filter.And(c => c.Email.Contains(email));
//}
}