C# LINQ 提示 sequence contains no elements

作者:陈格日期:2010-02-22

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C# LINQ 提示 "sequence contains no elements"错误

System.InvalidOperationException: Sequence contains no elements

While using LINQ, let’s say you decide to do something similar to the following…

    NorthWindDataContext dc = new NorthWindDataContext();
    Product p = dc.Products.First(p1 => p1.ProductName.StartsWith("My New Product"));
    if (p == null)
        return;

    dc.Products.DeleteOnSubmit(p);
    dc.SubmitChanges();
    ShowProducts();

Everything would be fine if you do have a product whose name starts with “My New Product”, but what do you think would happen if that’s not the case? Well surprisingly... you would get an un-handled runtime exception!!!

Exception Details: System.InvalidOperationException: Sequence contains no elements
Source Error:

Line 69:         NorthWindDataContext dc = new NorthWindDataContext();
Line 70:
Line 71:         Product p = dc.Products.First(p1 => p1.ProductName.StartsWith("My New Product"));
Line 72:         if (p == null)
Line 73:             return;

To get rid of this error, instead of using dc.Products.First, use dc.Products.FirstOrDefault and you should be good!

Happy Coding.
Rahul

别以为后面用 p==null 可以判断出是否包含，应该用 FirstOrDefault  作为方法来获取