CODEWITHSUNDEEP
c#linq
Shin
Shin

Reputation: 673

How to create a dynamic LINQ select projection function from a string[] of names?

Using C#...

Is there any way to specify property names for a projection function on a LINQ select method, from an array. 

public class Album
{
    public int Id { get; set; }
    public string Name { get; set; }
    public short Rate { get; set; }
    public string Genre { get; set; }
    public short Tracks { get; set; }
}

public class Class1
{
    private void Some<T>()
    {
        // Example of source
        var names = new[] { "Id", "Name", "Tracks" };

        var query = myDataContext.
                    GetTable<T>.
                    AsQueryable().
                    Select( /* dynamic projection from names array */ );

                    // something like
                    // Select(x => new
                    //     {
                    //         x.Id,
                    //         x.Name,
                    //         x.Tracks
                    //     }

        GoAndDoSomethingWith(query);
    }
}

Could this be done without System.Linq.Dynamic?

Upvotes: 11

Views: 2798

Answers (1)

xenolightning
xenolightning

Reputation: 4230

You could use reflection and dynamic types to generate an object with only the specified fields/properties.

Below is a simple way of doing this. You can do optimizations, like having a type cache for the reflection. But this should work for simple fields/properties.

public static object DynamicProjection(object input, IEnumerable<string> properties)
{
    var type = input.GetType();
    dynamic dObject = new ExpandoObject();
    var dDict = dObject as IDictionary<string, object>;

    foreach (var p in properties)
    {
        var field = type.GetField(p);
        if (field != null)
            dDict [p] = field.GetValue(input);

        var prop = type.GetProperty(p);
        if (prop != null && prop.GetIndexParameters().Length == 0)
            dDict[p] = prop.GetValue(input, null);
    }

    return dObject;
}

Usage:

//...
var names = new[] { "Id", "Name", "Tracks" };
var projection = collection.Select(x => DynamicProjection(x, names));
//...

Upvotes: 7

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