在C＃中使用Lambda返回key => value对的数组

Question

I have the following Lambda expression that returns an array of result properties:

ViewBag.Items = db.Items.Select(m => new { m.Id, m.Column1, m.Column2 }).ToArray();

This works as expected, but I need the result to be a key=>value pair with Id being the key with Column1 & Column2 being the values. I've found examples on how to create a Dictionary, but not with isolating only specific columns in the results.

ViewBag.Items is localized for jQuery in the View using:

var _items = @Html.Raw(Json.Encode(ViewBag.Items));

How do I change the Lambda above to make an array of key=>value pairs?

Answer 1

You could do it with ToDictionary :

db.Items.Select(m => new { m.Id, m.Column1, m.Column2 })
        .ToDictionary(x=>x.Id, x=>new {x.Column1, x.Column2});

That gives you Dictionary with Id as key and {Column1, Column2} as Values, if you want have Id as Value to consider good solution of HimBromBeere

Answer 2

Where is the problem?

ViewBag.Items = db.Items.Select(m => new KeyValuePair<string, MyType>
    ( 
        m.Id, 
        new MyType { Column1 = m.Column1, Column2 = m.Column2 }
    )).ToArray();

But anyway a Dictionary is nothing but a list of KeyValuePair , so why not use it?

ViewBag.Items = db.Items.ToDictionary(
        m => m.Id, 
        m => new MyType { Column1 = m.Column1, Column2 = m.Column2 });

Of course you can also use a Dictionary<anonymous, anonymous> :

ViewBag.Items = db.Items.ToDictionary(
        m => m.Id, 
        m=> new { m.Column1, m.Column2 } );

but as you´re assigning this to a view I doubt you could use anonymous types here.

Using a Dictionary over an array of KeyValuePair has the advantage that duplicate keys are also checked. If you want to avoid this use ToLookup instead which will aloow duplicate keys.