Question

我已经编写了2个Linq到sql查询，但是我不喜欢我必须遍历第一个查询才能运行第二个查询。

第二个表上有一个引用第一个表Id的外键。任何人都可以改进我编写的代码或者这个解决方案是理想的吗？

using (var entities = new dbEntities())
{
    var groups = (from g in entities.ObjectGroup
                    select g);

    var mappings = (AutoMapper.Mapper.Map<IEnumerable<ObjectGroupModel>>(groups));

    foreach (var map in mappings) 
    {
        var types = (from t in entities.ObjectTypeToObjectGroupMappings
                        where t.ObjectGroupId == map.Id
                        select t.ObjectTypeId);
        map.ObjectTypeIds = types;
    }

    return mappings;
}

感谢您的帮助。

Answer 1

您可以尝试这样的事情：

var mappings = (from gr in entities.ObjectGroup
                join t in entities.ObjectTypeToObjectGroupMappings
                on gr.Id equals t.ObjectGroupId into subTs
                from subT in subTs.DefaultIfEmpty()
                group new { gr, subT } by new { gr.Id /*and other gr's properties*/} into sub
                select new ObjectGroupModel 
                {
                     Id = sub.Key.Id,
                     /*other gr's properties via propN = sub.Key.propN*/
                     ObjectTypeIds = sub.Where(x => x.subT != null).Select(x => x.subT.ObjectTypeId).ToList()
                }).ToList();

如何以最有效的方式从多个表中选择数据？

1 个答案: