通过这个 EF 会在数据库中执行多少 SQL 查询

Question

我有以下内容，想知道通过这个 EF 会在 DB 中执行多少查询？

private static dbContext dbc = new ProfileDBC();

private static IQueryable<Profile> GetProfile()
{
  return dbc.Profiles;
}


private static IQueryable<Purchase> GetPurchases()
{
  return from a in dbc.Amount
            where a.IsPurchased
            select a;
}

static void Main (string[] args)
{
   var result = (from p in GetProfile()
                  join pa in GetPurchases()
                  on p.ID equals pa.ID
                  group p.total by pa into r
                  select new { r.name, totalpurchase = r.Sum( p=> p)});.ToList(); }
}

}

Answer 1

在您解决编译器错误后，这将是一个查询：

Sum( p=> p)});.ToList();

如果您想获取带有子项目的项目，例如带有学生的学校、带有订单的客户或带有购买的个人资料，请考虑使用 GroupJoin 而不是 Join 后跟 GroupBy。好消息是您还将获得没有购买的配置文件：

var profilesWithTheirPurchases = dbContext.Profiles.GroupJoin(dbContext.Purchases,

    // parameter KeySelector: compare primary and foreign key:
    profile => profile.Id,           // from every Profile take the Id
    purchase => purchase.ProfileId,  // from every Purchase take the ProfileId

    // parameter resultSelector: take every Profile with its zero or more Purchases
    // to make one new
    (profile, purchasesOfThisProfile) => new
    {
         Name = profile.Name,
         TotalPurchases = purchasesOfThisId.Select(purchase => purchase.Amount)
                                           .Sum(),
    });