linq 多条件查询 where 拼接+分页

首先定义一个静态类

public static class QueryAssembly
    {
        /// <summary>
        /// 返回true
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <returns></returns>
        public static Expression<Func<T, bool>> True<T>()
        { 
            return f => true; 
        }

        /// <summary>
        /// false
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <returns></returns>
        public static Expression<Func<T, bool>> False<T>() 
        { 
            return f => false; 
        }

        /// <summary>
        /// or
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="expr1"></param>
        /// <param name="expr2"></param>
        /// <returns></returns>
        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);
        }

        /// <summary>
        /// and
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="expr1"></param>
        /// <param name="expr2"></param>
        /// <returns></returns>
        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);
        }  
    }

定义Page类

public class Paging<T>
    {
        /// <summary>
        /// 当前页码
        /// </summary>
        [DataMember]
        public int PageNo { get; set; }

        /// <summary>
        /// 总页数
        /// </summary>
        [DataMember]
        public int PageCount { get; set; }

        /// <summary>
        /// 每页记录数
        /// </summary>
        [DataMember]
        public int PageSize { get; set; }

        /// <summary>
        /// 总记录数
        /// </summary>
        [DataMember]
        public int RecordCount { get; set; }

        /// <summary>
        /// 当前页的数据
        /// </summary>
        [DataMember]
        public List<T> CurrentList { get; set; }
    }

查询方法

public Paging<DAML> QueryAJML(int pageNo, int pageSize,DAML data)
        {
            Paging<DAML> result = null;
            Expression<Func<DAML, bool>> ExpWhere = QueryAssembly.True<DAML>(); 
            using (IStatelessSession session = _sessionFactory.OpenStatelessSession())
            {
                var queryDAML = session.Query<DAML>();

                if (!string.IsNullOrEmpty(data.MLH))
                {
                    ExpWhere=ExpWhere.Or(x=>x.MLH.Contains(data.MLH));
                }

                if (!string.IsNullOrEmpty(data.QZH))
                {
                    ExpWhere = ExpWhere.Or(x => x.MLH.Contains(data.QZH));
                }

                //查询
                queryDAML.Where(ExpWhere);

                //排序
                queryDAML.OrderBy(x=>x.ID);

                //页数
                result.PageNo = pageNo;
                //每页记录数
                result.PageSize = pageSize;
                //总记录数
                result.RecordCount = queryDAML.Count();
                //总页数
                result.PageCount = (result.RecordCount + result.PageSize - 1) / result.PageSize;
                //返回数据
                result.CurrentList = new List<DAML>();
                result.CurrentList = queryDAML.ToList();
            }
            return result;
        }