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 - ) / result.PageSize;
                 //返回数据
                 result.CurrentList = new List<DAML>();
                 result.CurrentList = queryDAML.ToList();
             }
             return result;
         }