LINQ查询出了什么问题

Question

I have never done anything with LINQ before, however I have experience with MySQL.

I am on page 232 of Microsoft® ASP.NET 4 Step by Step and the book has started to talk about LINQ which is cool.

The book has instructed my to type my first LINQ query which I have, however it has resulted in 19 errors from Visual Studio, because the where , orderby and select commands are not recognised.

Below is the code from the book:

Below is my code (in the form of a screenshot so you can see what Visual Studio doesn't like):

What am I doing wrong?

Thankyou

Answer 1

In your Linq query, the TechnologyDescriptor tag wih the "<>" is barfing. What you need to do is specify a named variable instance for an individual item in the technologyDescriptor list. For example:

GridView1.DataSource = from td in technologyDescriptor where td.TechnologyName.Contains(".Net") == true order by td.TechologyName.Length
select td.TechnologyName.ToUpper();

You can think of this query as similar to a foreach loop that is looping over technologyDesciptor list and "td" being the individual record for each loop

Answer 2

您可能在TechnologyDescriptor周围没有多余的尖括号（<>）。

Answer 3

You have surrounded your variable name, technologyDescriptor, with angle brackets. Please remove these brackets from your code.

Answer 4

应该说：“来自...中的technologyDescriptor ”，而不是from <TechnologyDescriptor>

Answer 5

Your variable usage is a little off. Also, is technologyDescriptor a collection?

If so, change your code to:

GridView1.DataSource = from t in technologyDescriptor
                       where t.TechnologyName.Contains(".NET")
                       orderby t.TechnologyName.Length
                       select t.TechnologyName.ToUpper();

Answer 6

In addition to the problems with your linq query, the screen shot shows that you have a variable scope problem. Specifically, you are using technologyDescriptor to refer to two different things. Does your form have a control called "technologyDescriptor", or a field of that name declared in another part of the partial class?