Linq to Entities 4.0 - 优化查询并在单个查询中多次调用数据库

发布于 2024-09-12 21:50:03 字数 579 浏览 7 评论 0原文

谁能告诉我以下查询是多次调用数据库还是只调用一次数据库？

var bizItems = new
{
    items = (
        from bl in db.rc_BusinessLocations
        orderby bl.rc_BusinessProfiles.BusinessName
        select new BusinessLocationItem
        {
            BusinessLocation = bl,
            BusinessProfile = bl.rc_BusinessProfiles,
            Products = bl.rc_InventoryProducts_Business
        })
        .Skip(pageSkip).Take(pageSize),

    Count = db.rc_BusinessLocations.Count()
};

我真的需要从查询中获取 Count() ，但我找不到其他方法来做到这一点，所以如果您有一些更好的优化代码，请随时分享！

提前致谢！

格瓦尔

原文

Can anyone tell me if the following query calls the database multiple times or just once?

var bizItems = new
{
    items = (
        from bl in db.rc_BusinessLocations
        orderby bl.rc_BusinessProfiles.BusinessName
        select new BusinessLocationItem
        {
            BusinessLocation = bl,
            BusinessProfile = bl.rc_BusinessProfiles,
            Products = bl.rc_InventoryProducts_Business
        })
        .Skip(pageSkip).Take(pageSize),

    Count = db.rc_BusinessLocations.Count()
};

I really need to get the Count() out of the query and I couldn't find another way to do it so if you have some better optimized code, feel free to share it!

Thanks in advance!

Gwar

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只是我以为 2024-09-19 21:50:03

这完全取决于您对 bizItems 变量执行的操作，因为在运行此代码后，只会运行 COUNT(*) 查询。这是因为 item 包含一个 IQueryable，它是查询的描述（运行意图），而不是操作的结果。仅当您使用 foreach 或 .Count() 等运算符开始迭代此查询时，该查询才会运行。除此之外，BusinessProfile 和 Products 属性可能还会包含 IQueryable。

那么，让我们看看你可能用这段代码做什么：

foreach (var item in bizItems.items)
{
    Console.WriteLine(item.BusinessLocation.City);

    foreach (var profile in item.BusinessProfile)
    {
        Console.WriteLine(profile.Name);
    }

    foreach (var product in item.Products)
    {
        Console.WriteLine(product.Price);
    }

    Console.WriteLine(item.Count);
    Console.WriteLine();
}

所以，如果你再问我，看看这段代码，有多少查询将发送到数据库，我的答案是：2 + 2 * 项目数在 bizItems.items 中。因此查询数量将在 2 到 (2 + 2 * pageSize) 之间。

It totally depends on what you are doing with the bizItems variable, because after you've ran just this code, only a COUNT(*) query will have ran. This is because the item contains an IQueryable which is a description of a query (an intent to run), not the result of the operation. The query will only run when you start iterating this query, by using foreach or an operator such as .Count(). Besides this, the BusinessProfile and Products properties will probably also contain IQueryables.

So, let's take a look at what you might do with this code:

foreach (var item in bizItems.items)
{
    Console.WriteLine(item.BusinessLocation.City);

    foreach (var profile in item.BusinessProfile)
    {
        Console.WriteLine(profile.Name);
    }

    foreach (var product in item.Products)
    {
        Console.WriteLine(product.Price);
    }

    Console.WriteLine(item.Count);
    Console.WriteLine();
}

So, if you ask me again, looking at this code, how many queries will be sent to the database, my answer is: 2 + 2 * the number of items in bizItems.items. So the number of queries will be between 2 and (2 + 2 * pageSize).

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