How to convert a string into a class reference and send that to a generic class

Question

I have realized that there are questions that sounds similar to mine but they do not solve my problem. So I want to change a string into a class reference but I cannot change into a variable of type Type, dynamic or anything because then it doesn't work with my generic class.

Please note that the code works when I use a valid class reference. But I have many tables in the DB and it would help a lot if it can be more generic.

Generic class and all works fine here

private class GenericController<T>
        {
            private CoreGradingDBEntities db = new CoreGradingDBEntities();

            public dynamic Get(string Table, string Field, string id)
            {
                dynamic str = db.Database.SqlQuery<T>("SELECT * FROM " + Table + " WHERE " + Field + " = '" + id + "';").ToList();
                return  str;
            }
        }

The method where I am calling the generic class from. When I use a valid class reference it works. So the below code does work.

    [Route("api/Values/Table/Field/id")]
        public dynamic Get(string Table, string Field, string id)
        {
            GenericController<Account> generic = new GenericController<Account>();
            dynamic d = generic.Get(Table, Field, id);
            return d;
        }

What I want to do is replace the Account reference. I have tried this but it changes it into a "variable". The Table parameter is the class reference I want in string form. The below code is wrong but you get the idea of what I want to do.

        [Route("api/Values/Table/Field/id")]
        public dynamic Get(string Table, string Field, string id)
        {
            Type type = Type.GetType(Table); 
            GenericController<type> generic = new GenericController<type>(); //Compiler complaining 
            dynamic d = generic.Get(Table, Field, id);
            return d;
        }

Any help would be much appreciated. Thanks!

score 0 · Answer 1 · answered Aug 07 '19 at 21:15

0

I believe generic type arguments have to be specified at compile time. See this question

If you really want to do this, you will have to resort to reflection

answered Aug 07 '19 at 21:15

Mike Marshall

7,788
4
39
63

score 0 · Answer 2 · answered Aug 07 '19 at 22:04

I think you cannot use generic in this case. Instead of try this:

private class GenericController
    {
        private CoreGradingDBEntities db = new CoreGradingDBEntities();

        public dynamic Get(string Table, string Field, string id)
        {
            var task = db.Database.SqlQuery(Type.GetType(Table), "SELECT * FROM " + Table + " WHERE " + Field + " = '" + id + "';").ToListAsync();
            dynamic str = task.Result;
            return  str;
        }
    }

then your code may look like this:

        [Route("api/Values/Table/Field/id")]
    public dynamic Get(string Table, string Field, string id)
    {
        GenericController generic = new GenericController();
        dynamic d = generic.Get(Table, Field, id);
        return d;
    }

notice, then d is type of List<object> but since you use dynamic you can call:

dynamic item = d.FirstOrDefault();
var name = item.AccountName;

similiar way as generic

Thanks for the reply. I however receive a null with Type.GetType(Table). If I just return Table I get the correct value passed in by the api request. So I guess the compiler has to know the value at compile time? If nothing else works then I guess I have to check the value of Table string and create an object based on that... — Proff_D, Aug 07 '19 at 22:40
Type.GetType(Table) returns null if you put incorrect string. Try namespace and class name, divided by dot. see: https://learn.microsoft.com/pl-pl/dotnet/api/system.type.gettype?view=netframework-4.8#System_Type_GetType_System_String_ . — robert, Aug 08 '19 at 07:28

How to convert a string into a class reference and send that to a generic class

2 Answers2