Dynamically generate ENUMs through assembly


In C# ENUMs are storage efficient data structure acting at run-time just like primitive types. The following presents one way to generate an enumeration class within a dynamic assembly using database data.

Let’s assume we have the following table and we want to map this to an enum type:
id | description
0 | pink
1 | magenta

First will retrieve the data constructing the enum source code into a string variable. For data access we use a SQL helper class that loads a DataReader object.
One thing we have to check here is to remove not allowed characters from the enumeration names list. Also values must be integer numbers.

            string strEnumSource = "enum colors {";
            OracleDataReader rdr = Sql.ExecuteReader("SELECT id, description FROM colors");
            if (rdr.HasRows)
                while (rdr.Read())
                    int nValue;
                    string strKey;
                    strKey = Convert.ToString(rdr[1]);
                    strKey = Regex.Replace(strKey, @"[^\w\.@-]", "");
                    if (!Int32.TryParse(Convert.ToString(rdr[0]), out nValue))
                        throw new Exception("ERROR: value must be an integer!");
                    strEnumSource += strKey + "=" + nValue + ",";
            if (strEnumSource.EndsWith(","))
                strEnumSource = strEnumSource.Remove(strEnumSource.LastIndexOf(","));
            strEnumSource += "}";

Next will compile the enum using the CodeDomProvider abstract class. A CodeDomProvider implementation provides an interface for generating code and managing compilation for a single programming language.

  CodeDomProvider codeProvider = CodeDomProvider.CreateProvider("CSharp");

We don’t want to save anything to disk so will use a CompilerParameters object to specify the compiler settings.

  CompilerParameters cparam = new CompilerParameters();
  cparam.GenerateExecutable = false;
  cparam.GenerateInMemory = true;
  cparam.TreatWarningsAsErrors = false;
  CompilerResults cresult = codeProvider.CompileAssemblyFromSource(cparam, strEnumSource);

The Errors property of the CompilerResults class exposes the messages resulting from compilation, if any.

                    if (cresult.Errors.Count > 0)
                        foreach (CompilerError ce in cresult.Errors)
                            strErrors += ce.ToString() + System.Environment.NewLine;
                        throw new Exception("ERROR: " + strErrors);

If there are no compilation errors we can simply get the type compiled and ready for use.

  Type enumType = cresult.CompiledAssembly.GetType("colors");
  int[] nValues = (int[])Enum.GetValues(enumType);
  string str = "";
  foreach (int nValue in nValues)
    str += String.Format(" {0}: {1} ", Enum.GetName(enumType, nValue), nValue);

Namespace: System.CodeDom.Compiler

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