C# 使用实体框架获取大表的行数

我使用实体框架来获得一个包含数百万条记录的表的简单行数，我不需要任何where子句。

---

我尝试使用Count方法，但获取计数需要很长时间。等待那么久，有没有什么有效的方法来让伯爵回来

您可以按如下所示进行尝试。此查询将返回IQueryable结果。这意味着在数据库中进行计数操作

基于查询的：

基于方法的：

---

您可以按如下所示进行尝试。此查询将返回IQueryable结果。这意味着在数据库中发生计数操作

基于查询的：

基于方法的：

---

我认为您首先要检索所有记录，然后对它们进行计数。你应该直接清点你的记录

using(DatabaseContext db = new DatabaseContext())
{
    //what I think you are doing:
    int countLong = db.UserAccount.ToList().Count();
    //what you should be doing
    int countShort = db.UserAccount.Count();
    //include where clauses inside count, wrong way:
    int countLong2 = db.UserAccount.ToList().Count(x => x.Active);
    //include where clauses inside count, good way:
    int countShort2 = db.UserAccount.Count(x => x.Active);

    //or if you don't like lambda expressions.
    int countLong3 = (from x in db.UserAccount
                      //where x.Active //optional
                      select x).ToList().Count();

    int countShort3 = (from x in db.UserAccount
                      //where x.Active //optional
                      select x).Count();

}

---

DatabaseContext将是扩展DbContext类的类，我认为您首先要检索所有记录，然后对它们进行计数。你应该直接清点你的记录

using(DatabaseContext db = new DatabaseContext())
{
    //what I think you are doing:
    int countLong = db.UserAccount.ToList().Count();
    //what you should be doing
    int countShort = db.UserAccount.Count();
    //include where clauses inside count, wrong way:
    int countLong2 = db.UserAccount.ToList().Count(x => x.Active);
    //include where clauses inside count, good way:
    int countShort2 = db.UserAccount.Count(x => x.Active);

    //or if you don't like lambda expressions.
    int countLong3 = (from x in db.UserAccount
                      //where x.Active //optional
                      select x).ToList().Count();

    int countShort3 = (from x in db.UserAccount
                      //where x.Active //optional
                      select x).Count();

}

---

DatabaseContext将是扩展DbContext类的类

您有示例代码吗？如果您使用的是Count的IEnumerable版本，那么应用程序将检索所有行，然后对它们进行计数。如果您使用的是Count的IQueryable版本，则数据库服务器将进行计数，并且应该是快速的。到目前为止，您是否可以显示代码？只需对数据库执行原始SQL查询即可。这可能是实现这一目标的最快方法。你有样本代码吗？如果您使用的是Count的IEnumerable版本，那么应用程序将检索所有行，然后对它们进行计数。如果您使用的是Count的IQueryable版本，则数据库服务器将进行计数，并且应该是快速的。到目前为止，您是否可以显示代码？只需对数据库执行原始SQL查询即可。这可能是实现这一目标的最快方法。或者简单地说就是context.yourTable.count我发现这会转化为一些性能非常差的SQL，它会遍历数据库中的每一行：选择[GroupBy1]。[A1]作为[C1]从[dbo]。[Log]作为[Extent1]作为[GroupBy1]——我建议使用原始SQL，我没有找到另一种方法。或者仅仅是context.yourTable.count我发现这会转化为一些性能非常差的SQL，它会在DB中的每一行进行迭代：选择[GroupBy1]。[A1]作为[C1]从选择COUNT1作为[A1]从[dbo]。[Log]作为[Extent1]作为[GroupBy1]——我建议使用原始SQL，我还没找到别的办法。

using(DatabaseContext db = new DatabaseContext())
{
    //what I think you are doing:
    int countLong = db.UserAccount.ToList().Count();
    //what you should be doing
    int countShort = db.UserAccount.Count();
    //include where clauses inside count, wrong way:
    int countLong2 = db.UserAccount.ToList().Count(x => x.Active);
    //include where clauses inside count, good way:
    int countShort2 = db.UserAccount.Count(x => x.Active);

    //or if you don't like lambda expressions.
    int countLong3 = (from x in db.UserAccount
                      //where x.Active //optional
                      select x).ToList().Count();

    int countShort3 = (from x in db.UserAccount
                      //where x.Active //optional
                      select x).Count();

}