access and query DbSet of DbContext by name - entity-framework

Question

how to access and query a DbSet of DbContext by name (passing a string with the entity name or the fullname)
something like (but this doesn't work)
string myTypeName= "mycustomtype"; //or "mynamespace1.mynamespace2.mycustomtype"
Type myType = Type.GetType(myTypeName);
var dbset = db.Set(myType);
// i can't query dbset
//i should do something like this (but i don't know how to do it)
var result = ((IEnumerable<myType>)db.Set(myType)).toList();

Answer 1

#alex,
I've spent a lot of time on this. I could not find a way as simple as your metacode in the question. I am welcome to improvements on the below.
My need may not be the same as yours, so let me explain:
It is easy to create a class instance by a string. There are lots of examples here on SO.
What is NOT easy (I'm pretty sure) is how to create an instance of a class that you can simply add with your context:
ctx.SomeModels.Add(myClass);
...that will work with:
ctx.SaveChanges();
I found that the class in play had to come from the DbContext in order for it to accept it back, or even to use in a Delete()...
If this matches your scenario, this might help.
Notes:
-I have removed all my logging (with NLog), which adds a lot of debugging, but makes this harder to read.
-If you make a few Breakpoints and look at the values & choices, you will see some things I had to correct for.
-There are 2 parts to the problem:
1. Finding the assembly's version of the name of the class from a simple one.
2. Using that computer-friendly name to make a class that would make DbContext not complain:
/****************************************************************
*
* CreateInstanceOf
* DbTableName = SOMETHINGS <--- note pluralization
* BaseAssembly = Assembly for your calling project-NOT this DLL
* (if this is in a dll)...
*
* This method is given a table name (plural), and returns an instance
* of that Model' class (singular)... Failing that, returns null.
*/
public object CreateInstanceOf(string DbTableName, Assembly BaseAssembly)
{
string className = String.Empty;
string baseClassName = String.Empty;
string trimmedClassName = String.Empty;
string qualifiedAssemblyName = String.Empty;
try
{
/**********************
*
* Part 1 - just get the details on a matching class...
*
*/
foreach (var t in BaseAssembly.GetTypes())
{
if (((String)t.Namespace == null) || (!t.Namespace.Contains("Models"))) // adjust to suit (I'm in MVC here)
{
// Type is not in Models namespace... skipping
continue; // just looking for classes in the Models namespace (MVC)
}
foreach (var cat in t.CustomAttributes)
{
foreach (var car in cat.ConstructorArguments)
{
if (car != null)
{
t.Name, cat.ToString(), car.ToString());
char[] charsToTrim = { '"', ' ' }; // weird how there are actual quotes in the string...
string trimmedCar = car.ToString().Trim(charsToTrim);
if (trimmedCar == DbTableName)
{
// we have a winner!
qualifiedAssemblyName = t.AssemblyQualifiedName;
baseClassName = trimmedCar;
trimmedClassName = (t.Namespace + "." + trimmedCar).Trim(charsToTrim);
break;
} else
{
// nothing to see here, move along...
}
}
}
}
}
/**********************
*
* Part 2 - create the class with this info...
*
*/
if ((trimmedClassName != null) && (trimmedClassName.Length > 0))
{
Type tipe = Type.GetType(qualifiedAssemblyName);
AssemblyName an = BaseAssembly.GetName();
char[] charsToTrim = { '"', ' ' };
string trimmedManModName = BaseAssembly.ManifestModule.Name.ToString().Trim(charsToTrim);
var result = Activator.CreateInstance(
tipe
);
return result;
} else
{
throw new ArgumentNullException();
}
}
catch (Exception ex)
{
return null;
}
}