为什么 EF 4.1 不支持复杂查询以及 linq-to-sql? [英] Why does EF 4.1 not support complex queries as well as linq-to-sql?

查看：26 发布时间：2022/1/7 15:47:31 entity-framework linq-to-sql entity-framework-4.1

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问题描述

我正在将我们的内部 Web 应用程序从 Linq-To-Sql 转换为现有数据库中的 EF CodeFirst.我最近越来越对 Linq-To-Sql 的限制感到恼火，并且在更新一个非常复杂的数据库表后不得不更新 edmx 终于让我感到沮丧到切换到 EF.

I am in the process of converting our internal web application from Linq-To-Sql to EF CodeFirst from an existing database. I have been getting annoyed with Linq-To-Sql's limitations more and more lately, and having to update the edmx after updating a very intertwined database table finally frustrated me enough to switch to EF.

但是，我遇到了几种情况，其中将 linq 与 Linq-To-Sql 一起使用比最新的实体框架更强大，我想知道是否有人知道其中的原因?其中大部分似乎与转换有关.例如，以下查询在 L2S 中有效，但在 EF 中无效:

However, I am encountering several situations where using linq with Linq-To-Sql is more powerful than the latest Entity Framework, and I am wondering if anyone knows the reasoning for it? Most of this seems to deal with transformations. For example, the following query works in L2S but not in EF:

        var client = (from c in _context.Clients
                      where c.id == id
                      select ClientViewModel.ConvertFromEntity(c)).First();

在 L2S 中，这会正确地从数据库中检索客户端并将其转换为 ClientViewModel 类型，但在 EF 中，此异常表示 Linq to Entities 无法识别该方法(这是有道理的，因为我写了.

In L2S, this correctly retrieves a client from the database and converts it into a ClientViewModel type, but in EF this exceptions saying that Linq to Entities does not recognize the method (which makes sense as I wrote it.

为了让它在 EF 中工作，我必须将 select 移动到 First() 调用之后.

In order to get this working in EF I have to move the select to after the First() call.

另一个例子是我检索客户列表的查询.在我的查询中，我将其转换为匿名结构以转换为 JSON:

Another example is my query to retrieve a list of clients. In my query I transform it into an anonymous structure to be converted into JSON:

        var clients = (from c in _context.Clients
                       orderby c.name ascending
                       select new
                       {
                           id = c.id,
                           name = c.name,
                           versionString = Utils.GetVersionString(c.ProdVersion),
                           versionName = c.ProdVersion.name,
                           date = c.prod_deploy_date.ToString()
                       })
                       .ToList();

不仅我的 Utils.GetVersionString() 方法导致 EF 中不受支持的方法异常，c.prod_deploy_date.ToString() 也会导致异常，而且很简单日期时间.像以前一样，为了修复它，我必须在 ToList() 之后进行选择转换.

Not only does my Utils.GetVersionString() method cause an unsupported method exception in EF, the c.prod_deploy_date.ToString() causes one too and it's a simple DateTime. Like previously, in order to fix it I had to do my select transformation after ToList().

<小时>编辑:我刚刚遇到的另一个案例是 EF 无法处理比较实体的 where 子句，因为 L2S 没有问题.例如查询

Edit: Another case I just came across is that EF cannot handle where clauses that compare entities where as L2S has no issues for with it. For example the query

context.TfsWorkItemTags.Where(x => x.TfsWorkItem == TfsWorkItemEntity).ToList()

抛出异常，而我必须这样做

throws an exception and instead I have to do

context.TfsWorkItemTags.Where(x => x.TfsWorkItem.id == tfsWorkItemEntity.id).ToList()

<小时>编辑 2:我想添加我发现的另一个问题.显然你不能在 EF Linq 查询中使用数组，这可能比任何事情都让我烦恼.例如，现在我将表示版本的实体转换为 int[4] 并尝试对其进行查询.在 Linq-to-Sql 中，我使用了以下查询:

Edit 2: I wanted to add another issue that I found. Apparently you can't use arrays in EF Linq queries, and this probably annoys me more than anything. So for example, right now I convert an entity that denotes a version into an int[4] and try to query on it. In Linq-to-Sql I used the following query:

return context.ReleaseVersions.Where(x => x.major_version == ver[0] && x.minor_version == ver[1]
                                          && x.build_version == ver[2] && x.revision_version == ver[3])
                              .Count() > 0;

此操作失败，但出现以下异常:

This fails with the following exception:

The LINQ expression node type 'ArrayIndex' is not supported in LINQ to Entities.

<小时>

编辑 3:我发现了另一个 EF 糟糕的 Linq 实现实例.以下是在 L2S 中有效但在 EF 4.1 中无效的查询:

Edit 3: I found another instance of EF's bad Linq implementation. The following is a query that works in L2S but doesn't in EF 4.1:

        DateTime curDate = DateTime.Now.Date;
        var reqs = _context.TestRequests.Where(x => DateTime.Now > (curDate + x.scheduled_time.Value)).ToList();

这将抛出一个 ArgumentException 消息 DbArithmeticExpression 参数必须具有数字公共类型.

This throws an ArgumentException with the message DbArithmeticExpression arguments must have a numeric common type.

<小时>为什么看起来他们在 EF 中比在 L2S 中降低了 Linq 查询的能力?

Why does it seem like they downgraded the ability for Linq queries in EF than in L2S?

为什么 EF 4.1 不支持复杂查询以及 linq-to-sql? [英] Why does EF 4.1 not support complex queries as well as linq-to-sql?

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为什么 EF 4.1 不支持复杂查询以及 linq-to-sql? [英] Why does EF 4.1 not support complex queries as well as linq-to-sql?

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