创建动态的linq查询

Question

我有下面的查询:

from p in dataContext.Repository<IPerson>()
     join spp1 in dataContext.Repository<ISportsPerPerson>() on p.Id equals spp1.PersonId
     join s1 in dataContext.Repository<ISports>() on spp1.SportsId equals s1.Id
     join spp2 in dataContext.Repository<ISportsPerPerson>() on p.Id equals spp2.PersonId
     join s2 in dataContext.Repository<ISports>() on spp2.SportsId equals s2.Id
     where s1.Name == "Soccer" && s2.Name == "Tennis"
     select new { p.Id };

它选择所有打足球和网球的人。
在运行时，用户可以选择其他标签添加到查询中，比如："曲棍球"。现在我的问题是，如何动态地将“曲棍球”添加到查询中？如果将“曲棍球”添加到查询中，它将像这样:

from p in dataContext.Repository<IPerson>()
     join spp1 in dataContext.Repository<ISportsPerPerson>() on p.Id equals spp1.PersonId
     join s1 in dataContext.Repository<ISports>() on spp1.SportsId equals s1.Id
     join spp2 in dataContext.Repository<ISportsPerPerson>() on p.Id equals spp2.PersonId
     join s2 in dataContext.Repository<ISports>() on spp2.SportsId equals s2.Id  
     join spp3 in dataContext.Repository<ISportsPerPerson>() on p.Id equals spp3.PersonId
     join s3 in dataContext.Repository<ISports>() on spp3.SportsId equals s3.Id
     where s1.Name == "Soccer" && s2.Name == "Tennis" && s3.Name == "Hockey"
     select new { p.Id };

最好的情况是查询可以动态构建，例如：

private void queryTagBuilder(List<string> tags)
{
    IDataContext dataContext = new LinqToSqlContext(new L2S.DataContext());
    foreach(string tag in tags)
    {
        //Build the query?
    }
}

有没有人知道如何正确设置这个？ 提前感谢！

- Bas

---

重复的问题？http://stackoverflow.com/questions/2712337/passing-a-where-clause-for-a-linq-to-sql-query-as-a-parameter/2712795 - Steven

Answer 1

LINQ查询在实际执行之前不会被解析。因此，您可以像这样执行以下操作：

var q = from r in ctx.records 
         /* Do other stuff */
         select r;

if (!string.IsNullOrEmpty(search)) {
  q = from r in q
       where r.title == search
       select r;
}

if (orderByName) {
  q = q.OrderBy(r => r.name);
}

/* etc */

这将创建一个被执行的SQL语句。

针对您的具体问题：连接操作会使事情有些复杂，但我认为您可以与其他“动态”查询进行连接。

因此，您最终会得到类似于以下内容：

var baseQ = from p in dataContext.Repository<IPerson>()
            select p;
foreach(var tag in tags) {
   baseQ = from p in baseQ 
     join spp1 in dataContext.Repository<ISportsPerPerson>() on p.Id equals spp1.PersonId
     join s1 in dataContext.Repository<ISports>() on spp1.SportsId equals s1.Id
     where s1.name == tag
     select p;
}

/* If you have defined your relations correct, simplify to something like this.
   Does not actually work because of SportsPerPerson probably has multiple sports: */
foreach(var tag in tags) {
   baseQ = baseQ.Any(p => p.SportsPerPerson.Sports.Name == tag); 
}


var resultQ = from p in baseQ
     select new { p.Id };

- GvS

---

看起来很有前途：] 我会试一试！ - Bas

Answer 2

我和我的同事找到了解决方案，并重构了查询，使其能够正常工作。我们现在使用以下查询来检索正确的结果集：

var query = dataContext.Repository<ILead>();

        foreach (var tag in tags)
        {
            String tagName = tag;
            query = query.Where(l => dataContext.Repository<ISportsPerPerson>()
                         .Any(tpl => tpl.PersonId.Equals(l.Id) && tpl.Sports.Name.Equals(tagName)));
        }
// Do something with query resultset :]

- Bas