从LINQ IQueryable对象返回string []？

Question

I'm trying to work with the .NET AJAX autocompletion extension. The extension is expecting the following...

public static string[] GetCompletionList(string prefixText, int count, string contextKey)

My database queries are in a LINQ var object. I'm getting compile-time errors about not being able to convert type IQueryable to string[].

InventoryDataContext assets = new InventoryDataContext();
    var assetsInStorage = from a in assets.Assets
                          where a.Name.Contains(prefixText)
                          orderby a.Name ascending
                          select new[] { a.Manufacturer.Name, a.Name };
    return (string[])assetsInStorage;

Answer 1

In order to get an string[] at first you must select only one string property on your query, not an anonymous object:

var assetsInStorage = from a in assets.Assets
                      where a.Name.Contains(prefixText)
                      orderby a.Name ascending
                      select a.Manufacturer.Name; // or a.Name

assetsInStorage at this moment is an IEnumerable<string> , and then you should convert it to string[] by:

return assetsInStorage.ToArray();

Answer 2

Your assetsInStorage doesn't appear to be an IEnumerable<string> ... as such, you'd have to project your anonymous type into a string.

assetsInStorage.Select(a=>a[0] + a[1]) 

(Or however you want to convert that anonymouns type to a string.)

And then you can return .ToArray() :

return assetsInStorage.Select(a=>a[0]+a[1]).ToArray();

Answer 3

This should do the trick:

InventoryDataContext assets = new InventoryDataContext();
var assetsInStorage = from a in assets.Assets                          
   where a.Name.Contains(prefixText)
   orderby a.Name ascending
   select String.Concat(x.ManufacturerName, " ", x.Name);    

return assetsInStorage.ToArray();

EDITED based on comment... EF is able to interpret String.Concat(), so the additional enumeration wasn't necessary.

Answer 4

If you want a single array that contains both a.Manufacturer.Name and a.Name for each of the assets, you can do that with a slight modification of CMS's answer:

var assetsInStorage = from a in assets.Assets
                      where a.Name.Contains(prefixText)
                      orderby a.Name ascending
                      select new[] { a.Manufacturer.Name, a.Name };

At this point, assetsInStorage is an IEnumerable<string[]> which also counts as an IEnumerable<IEnumerable<string>> . We can flatten this down to a single IEnumerable<string> using SelectMany and then turn it into an array.

return assetsInStorage.SelectMany(a => a).ToArray();

In this way, you're not required to select only a single string value.

Answer 5

尝试：

return assetsInStorage.ToArray();