如何在 LINQ 中预加载整个 SQL 表？

发布于 2024-07-11 19:22:04 字数 313 浏览 7 评论 0原文

编写我的第一个 Linq 应用程序，我试图找到执行以下操作的最佳方法：

我想立即加载整个员工表以填充缓存（用于表单自动完成）。

我可以这样做 -

var query = from employee in db.Employees select employee;
foreach (Employee e in query)
{
    ...
}

但由于这是延迟加载，它会为每个员工生成一个查询。如何立即加载整个表？

我研究过 DataLoadOptions 但这似乎只适用于关系。

原文

Writing my first Linq application, and I'm trying to find the best way to do the following:

I want to load the entire employees table at once to populate the cache (used for form autocomplete).

I can do -

var query = from employee in db.Employees select employee;
foreach (Employee e in query)
{
    ...
}

But since this is deferred loading, it generates one query per employee. How can I eager load the entire table?

I've looked into DataLoadOptions but that seems to only work for relationships.

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可爱暴击 2024-07-18 19:22:04

var query = db.Employees.ToList();

顺便说一句，这相当于：

var query = (from employee in db.Employees select employee).ToList();

当 lambda 语法更有意义且更短时，没有理由强迫自己使用查询运算符语法。

旁注 1：query 对象的类型将为 List，但是，在生成的 IL 和性能方面没有区别如果我们明确指定它。

旁注 2：重要的是要知道问题中指定的查询不是每个员工执行一次。它仅执行一次，并从数据库中逐个获取（类似于运行 SELECT * FROMEmployees 查询的 SqlDataReader 对象）。但是，ToList() 加载列表中的所有行，从而使针对该对象的进一步查询在应用程序本身（而不是 SQL Server）上执行。

var query = db.Employees.ToList();

By the way, this is equivalent to:

var query = (from employee in db.Employees select employee).ToList();

There's no reason to force yourself to use query operators syntax when lambda syntax makes more sense and is shorter.

Side note 1: The type of query object will be List<Employee>, however, there is no difference it terms of generated IL and performance if we explicitly specified it.

Side note 2: It's important to know the query specified in the question is not executed once per employee. It's executed just once and is fetched one by one from database (similar to a SqlDataReader object running a SELECT * FROM Employees query). However, ToList() loads all rows in a list making further queries going to that object get executed at the application itself, not SQL Server.

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