落实byte []的LINQ查询我自己的类型 [英] Implement Linq query on byte[] for my own type

问题描述

我有我自己的小数据库，我的工作（学习目的）。数据存储为二进制在磁盘上。 我可以做一个全表扫描和我的数据库将返回每个行作为一个byte [] ROW_BUFFER。 所述ROW_BUFFER包含每一行的字段。从逻辑上讲，它看起来像：

I have my own little database I am working on (for learning purposes). Data is stored as binary on disk. I can do a full table scan and my database will return each "row" as a byte[] row_buffer. The row_buffer contains the fields of each row. Logically, it looks like:

ROW_BUFFER = [[var_string] [INT32] [var_string]

我有一个表定义结构定义的列。点是，我知道每个数据字段的每行中的位置。

I have the column defined in a "Table Definition" structure. Point is, I know the position of each data field in each row.

现在，我想实现的LINQ能力，从我的数据库中查询数据（简单查询）：

Now, I want to implement Linq capabilities to query data from my database (simple queries):

var DemoTable = new Table<PeopleClass>();
var result = DemoTable.Where(p => p.Name == "Peter").Select(p => p).ToList();

在我的表类，我已经实现了以下逻辑：

In my Table class, I have implemented the following logic:

public IEnumerable<T> Where(Func<T, bool> predicate)
{
  foreach (var item in this.rows)
  {
    if (predicate(item)) yield return item;
  }
}

注：this.rows是包含数据库的所有记录列表

Note: this.rows is a List that contains all records of the database.

我的问题是，产生PeopleClass对象的每一行是非常低效的（由于转换字节[]字符串）。我想推迟创造尽可能多的。

My issue is that generating PeopleClass objects for each row is very inefficient (due to converting bytes[] to string). I want to defer the creation as much as possible.

目前，我正在研究的条件为byte []和比较，直接agains我行转换。但我到目前为止还没有。

Currently, I am investigating to convert the condition to byte[] and compare that directly agains my rows. But I have failed so far.

我如何实现的IEnumerable＆LT; T＆GT;凡（Func键＆LT; T，布尔＆GT; predicate）来对ROW_BUFFER，而不必产生PeopleClass对象第一个直接操作？只有全成命中应转换为PeopleClass对象

How can I implement IEnumerable<T> Where(Func<T, bool> predicate) to directly operate on the row_buffer instead of having to generate the PeopleClass objects first? Only the successfull hits should be converted to PeopleClass objects.

我没有找到一个方法来提取在predicate条件（其中字段名称，例如名称和其值的字段是必需的）。

I did not find a way to extract the condition (which field name e.g. "Name" and which value for the field is required) in the predicate.

任何帮助将是非常美联社preciated。

Any help would be highly appreciated.

推荐答案

首先，它看起来像你需要创建一个LINQ提供程序，则不需要实施其中，等，包括已经完成。我会从那里，看着在任何可能的性能问题之前。

To start with, it looks like you need to create a LINQ provider, you don't need to implement Where etc., that's already been done. I'd start there, before looking at any possible performance issues.

您需要创建一个的IQueryable 与您的自定义供应商进行解码前pression树等的特定逻辑这是相当复杂的，具有AA看 MSDN：演练：创建一个IQueryable LINQ提供或的编写自定义LINQ提供程序 ，有很多的教程左右。

You need to create an IQueryable with your custom provider to perform the specific logic of decoding the expression-tree etc. This is quite complicated, have a a look at MSDN: Walkthrough: Creating an IQueryable LINQ Provider or Writing custom LINQ provider , there's lots of tutorials around.

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