通过此ef将在数据库中执行多少sql查询

iyr7buue 于 2021-07-29 发布在 Java

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我有以下内容，想知道有多少查询将在数据库中通过这个ef执行？

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(); }
}

}

sql Database c#linq entity-framework

来源：https://stackoverflow.com/questions/63111944/how-many-sql-queries-will-be-executed-in-the-database-through-this-ef

1条答案

按热度按时间

tcomlyy61#

在解决编译器错误后，它将是一个查询：

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

如果您想获取带有子项的项目，例如学校和学生、客户和他们的订单，或者配置文件和他们的购买，请考虑使用groupjoin而不是 Join 接着是一个 GroupBy . 好的一点是，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(),
    });

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通过此ef将在数据库中执行多少sql查询

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