AdventureWorksEntities entities = new AdventureWorksEntities();
   entities.Contacts.Where(x => x.FirstName == "A" 
                               || x.FirstName == "B" 
                               || x.FirstName == "C")
                     .ToList();

将被翻译成这个sql,它是最好的：

//ommited for brevity
FROM [Person].[Contact] AS [Extent1]
WHERE [Extent1].[FirstName] IN (N'A',N'B',N'C')

但是,当我发出此查询时：

entities.Employee.Where(x => x.Contact.FirstName == "A" 
                             || x.Contact.FirstName == "B" 
                             || x.Contact.FirstName == "C")
                .ToList();

我得到这个sql：

//ommited for brevity
FROM   [HumanResources].[Employee] AS [Extent1]
INNER JOIN [Person].[Contact] AS [Extent2] ON [Extent1].[ContactID] = [Extent2].[ContactID]
LEFT OUTER JOIN [Person].[Contact] AS [Extent3] ON [Extent1].[ContactID] = [Extent3].[ContactID]
WHERE [Extent2].[FirstName] = N'A' OR [Extent3].[FirstName] IN (N'B',N'C')

为什么我会得到一个内部和外部联接,并且EF将两者分开？

注意使用包含创建相同的sql：

var names = new List<string>{"A","B","C"};
entities.Employee.Where(x => names.Contains(x.Contact.FirstName)).ToList();

编辑：所以它似乎是一个EF错误,我已经接受了提供解决方案的答案

编辑：打开连接问题,它位于here