根据Newexpression返回具有匿名类型的泛型类实例

Question

I have generic class "MSAccessQueryBuilder" with the following method

public I_QueryBuilder<T> Select(Expression<Func<T, object>> fieldNames)
    {
        NewExpression nEx = (NewExpression)fieldNames.Body;
        MsAccessQueryBuilder<"Anonymous Type Of Expression"> x = new MsAccessQueryBuilder<"Anonymous Type Of Expression">();

    }

within the method I need to create the instance of the "MSAccessQueryBuilder" with a generic type which anonymously created in lambda expression.

The method will be called like below

x.Select(s=> new {p1 = s.user_id,p2 = s.user_name})

Tried 8 hours of my own with no luck.

is this possible to get the anonymous type from NewExpression or LambdaExpression and create the instance of generic class of that anonymous type

Please help

Thank you

Answer 1

You can do like this.

var genericType = typeof(MsAccessQueryBuilder<>);
var specificType = genericType.MakeGenericType(typeof(nEx));
var x = Activator.CreateInstance(specificType);

Answer 2

have to change the method signature as Func delegate return type as generic instead of object solved the problem

public I_QueryBuilder<TResult> Select(Expression<Func<T, TResult>> fieldNames)
{

    return new MsAccessQueryBuilder<TResult>();

}