Question

我有一个模型，其中包括可以具有附件的打孔，附件具有Id，Name和BinaryData的属性。

如果我这样做：

var result = context.PunchSet
   .Where(p => p.PunchType == punchType && p.Project.Id == projectId)
   .Include(c => c.Contractor)
   .Include(c => c.ClearedBy)
   .Include(c => c.CreatedBy)
   .Include(a => a.Attachments)

由于附件可能既多又大，因此查询速度很慢。在这种情况下，我需要的是附件的ID和名称。所以我试过了：

var result = context.PunchSet
    .Where(p => p.PunchType == punchType && p.Project.Id == projectId)
    .Include(c => c.Contractor)
    .Include(c => c.ClearedBy)
    .Include(c => c.CreatedBy)
    .Include(a => a.Attachments.Select(a2 => new Attachment() { Id=a2.Id, Name=a2.Name} );

但最终会出现这个错误：

Include路径表达式必须引用导航属性在类型上定义。使用虚线路径进行参考导航属性和集合导航的Select运算符属性。参数名称：路径

不知道这意味着什么，我被困了好几个小时。如何在结果中包含部分权利？即不读二进制数据。

Answer 1

您可以尝试在单个查询中选择所有需要的属性，然后将它们连接在一起。

db.PunchSet
    .Include(x => x.Contractor)
    // ... other includes of complete objects
    // then select properties for partial include
    .Select(x => new { obj = x, att = x.Attachments.Select(a => new { a.Id, a.Name }) })
    // end of database query context
    .AsEnumerable()
    // join the results in memory
    .Select(x =>
    {
        x.obj.Attachments = x.att.Select(a => new Attachment() { Id = a.Id, Name = a.Name }).ToList();
        return x.obj;
    });

Answer 2

您可以尝试如下所示。

var result =  from p in context.PunchSet 
               where (p.PunchType == punchType && p.Project.Id == projectId) 
               select new { 
                           p,  
                           Contractor=p.Contractor,
                           ClearedBy =p.ClearedBy,
                           CreatedBy=p.CreatedBy,

                           Attachments= from a in p.Attachments
                                        select new {
                                                     Id=  a.Id,
                                                     Name =a.Name, 
                                                   },

             };

var result2 = result.AsEnumerable() 
                    .Select(c => c.p);

之后你可以按照自己的意愿进行迭代：）

foreach(var r in result2 ) 
{ 
    foreach(var a in r.Attachments) 
     {
       //your code; 
     }
}

仅在EF6中包含部分实体包含

2 个答案: