使用实体框架获取大表的行数

Question

我正在使用实体框架来获取包含数百万条记录的表的简单行数，并且我不需要任何 where 子句。 我尝试使用 Count 方法，但获取计数需要很长时间。有没有什么有效的方法可以在等待这么长时间的情况下获取计数？

Answer 1

我认为您首先检索所有记录，然后计算它们。你应该直接统计你的记录。

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 将是您扩展 DbContext 类的类

Answer 2

您可以尝试如下所示。该查询将返回IQueryable结果。这意味着count操作发生在数据库中。

基于查询：

var countVal = (from a in context.yourTable
                select a).Count();

基于方法：

var countVal = context.yourTable.Count()