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QueryableHelper

2018年11月15日  | 移动技术网IT编程  | 我要评论

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using system;
using system.collections.generic;
using system.linq;
using system.linq.expressions;
using system.reflection;
using system.text;

namespace oyang.tool
{
    public class queryablehelper
    {
        public static iqueryable<tsource> whereif<tsource>(iqueryable<tsource> source, bool istrue, expression<func<tsource, bool>> predicate)
        {
            if (istrue)
            {
                source = source.provider.createquery<tsource>(
                expression.call(
                    null,
                    where_tsource_2(typeof(tsource)),
                    source.expression, expression.quote(predicate)
                    ));
            }
            return source;
        }

        private static methodinfo s_where_tsource_2;

        private static methodinfo where_tsource_2(type tsource) =>
             (s_where_tsource_2 ??
             (s_where_tsource_2 = new func<iqueryable<object>, expression<func<object, bool>>, iqueryable<object>>(queryable.where).getmethodinfo().getgenericmethoddefinition()))
              .makegenericmethod(tsource);

        public static list<tsource> topagelist<tsource>(iqueryable<tsource> source, ref int pageindex, int pagesize, string sortfield, bool isasc, out int totalcount)
        {
            totalcount = source.count();
            int pagecount = totalcount % pagesize == 0 ? totalcount / pagesize : totalcount / pagesize + 1;
            if (pagecount > 0 && pageindex > pagecount)
            {
                pageindex = pagecount;
            }

            var param = expression.parameter(typeof(tsource));
            var body = expression.property(param, sortfield);
            dynamic keyselector = expression.lambda(body, param);
            source = isasc ? queryable.orderby(source, keyselector) : queryable.orderbydescending(source, keyselector);
            source = source.skip((pageindex - 1) * pagesize).take(pagesize);
            return source.tolist();
        }

        public static list<tsource> topagelist<tsource>(iqueryable<tsource> source, ipagination p)
        {
            int pageindex = p.pageindex;
            list<tsource> temp = topagelist<tsource>(source, ref pageindex, p.pagesize, p.sortfield, p.isasc, out int totalcount);
            p.totalcount = totalcount;
            p.pageindex = pageindex;
            return temp;
        }
    }
}

 

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