应对 Linq-To-Entities Entity SQL 中的 ObjectQuery 单一枚举挑战

发布于 2024-07-21 21:30:29 字数 752 浏览 7 评论 0原文

我正在修改这个示例：

Using advWorksContext As New AdventureWorksEntities
    ' Call the constructor that takes a command string and ObjectContext.
    Dim productQuery1 As New ObjectQuery(Of Product)("Product", advWorksContext)

    Dim result As Product
    For Each result In productQuery1
        Console.WriteLine("Product Name: {0}", result.Name)
    Next
End Using

可以对 ObjectQuery 进行编号只有一次。（随后的枚举尝试会抛出异常。）枚举发生在 foreach 语句中。问题是，如果查询为空，尝试 For Each 将引发异常。但如果我检查计数：

If productQuery1.Count > 0 Then . . .

那就耗尽了我一次计数的机会。我可以将 For Each 嵌套在 try/catch 块中并丢弃空查询异常，但这很丑陋。有更好的解决方案吗？

原文

I'm working on modifying this example:

Using advWorksContext As New AdventureWorksEntities
    ' Call the constructor that takes a command string and ObjectContext.
    Dim productQuery1 As New ObjectQuery(Of Product)("Product", advWorksContext)

    Dim result As Product
    For Each result In productQuery1
        Console.WriteLine("Product Name: {0}", result.Name)
    Next
End Using

An ObjectQuery can be enumberated only once. (Subsequent attempts at enumeration throw an exception.) The enumberation takes place in the for each statement. The problem is that if the query is empty attempting a For Each will throw an exception. But if I check for a count:

If productQuery1.Count > 0 Then . . .

That eats up my one chance at enumeration. I could nest the For Each in a try/catch block and throw away the empty query exceptions, but that's ugly. Is there a better solution?

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