How to dynamically create a class

Question

I have a class which looks like this   public class Field       public string FieldName      public string FieldType      And an object List lt Field gt  with values     EmployeeID   int      EmployeeName   String      Designation   String     I want to create a class that looks like this   Class DynamicClass       int EmployeeID      String EmployeeName      String Designation     Is there any way to do this    I want this to be generated at runtime  I don t want a physical CS file residing in my filesystem

User · Answer

Wow  Thank you for that answer  I added some features to it to create a  datatable to json  converter that I share with you       Public Shared Sub dt2json ByVal  dt As DataTable  ByVal  sb As StringBuilder      Dim t As System Type      Dim oList  dt Rows Count - 1  As Object     Dim jss As New JavaScriptSerializer       Dim i As Integer   0      t   CompileResultType  dt       For Each dr As DataRow In  dt Rows         Dim o As Object   Activator CreateInstance t           For Each col As DataColumn In  dt Columns             setvalue o  col ColumnName  dr Item col ColumnName           Next          oList i    o         i    1     Next      jss   New JavaScriptSerializer       jss Serialize oList   sb    End Sub   And in  compileresulttype  sub  I changed that       For Each column As DataColumn In  dt Columns         CreateProperty tb  column ColumnName  column DataType      Next   Private Shared Sub setvalue ByVal  obj As Object  ByVal  propName As String  ByVal  propValue As Object      Dim pi As PropertyInfo     pi    obj GetType GetProperty  propName      If pi IsNot Nothing AndAlso pi CanWrite Then         If  propValue IsNot DBNull Value Then             pi SetValue  obj   propValue  Nothing           Else             Select Case pi PropertyType ToString                 Case  System String                      pi SetValue  obj  String Empty  Nothing                  Case Else                      let the serialiser use javascript  null  value              End Select          End If     End If  End Sub

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You can also dynamically create a class by using DynamicExpressions   Since  Dictionary s have compact initializers and handle key collisions  you will want to do something like this     var list   new Dictionary lt string  string gt                 EmployeeID          int                  EmployeeName          String                  Birthday          DateTime               Or you might want to use a JSON converter to construct your serialized string object into something manageable   Then using System Linq Dynamic     IEnumerable lt DynamicProperty gt  props   list Select property   gt  new DynamicProperty property Key  Type GetType property Value    ToList       Type t   DynamicExpression CreateClass props     The rest is just using System Reflection     object obj   Activator CreateInstance t     t GetProperty  EmployeeID   SetValue obj  34  null     t GetProperty  EmployeeName   SetValue obj   Albert   null     t GetProperty  Birthday   SetValue obj  new DateTime 1976  3  14   null

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For those wanting to create a dynamic class just properties  i e  POCO   and create a list of this class   Using the code provided later  this will create a dynamic class and create a list of this   var properties   new List lt DynamicTypeProperty gt          new DynamicTypeProperty  doubleProperty   typeof double        new DynamicTypeProperty  stringProperty   typeof string          create the new type var dynamicType   DynamicType CreateDynamicType properties      create a list of the new type var dynamicList   DynamicType CreateDynamicList dynamicType       get an action that will add to the list var addAction   DynamicType GetAddAction dynamicList       call the action  with an object   containing parameters in exact order added addAction Invoke new object    1 1   item1     addAction Invoke new object    2 1   item2     addAction Invoke new object    3 1   item3       Here are the classes that the previous code uses   Note  You ll also need to reference the Microsoft CodeAnalysis CSharp library               lt summary gt          A property name  and type used to generate a property in the dynamic class           lt  summary gt      public class DynamicTypeProperty               public DynamicTypeProperty string name  Type type                        Name   name              Type   type                    public string Name   get  set            public Type Type   get  set              public static class DynamicType                    lt summary gt              Creates a list of the specified type              lt  summary gt               lt param name  type  gt  lt  param gt               lt returns gt  lt  returns gt          public static IEnumerable lt object gt  CreateDynamicList Type type                        var listType   typeof List lt  gt                var dynamicListType   listType MakeGenericType type               return  IEnumerable lt object gt   Activator CreateInstance dynamicListType                           lt summary gt              creates an action which can be used to add items to the list              lt  summary gt               lt param name  listType  gt  lt  param gt               lt returns gt  lt  returns gt          public static Action lt object   gt  GetAddAction IEnumerable lt object gt  list                        var listType   list GetType                var addMethod   listType GetMethod  Add                var itemType   listType GenericTypeArguments 0               var itemProperties   itemType GetProperties                 var action   new Action lt object   gt   values    gt                                var item   Activator CreateInstance itemType                    for var i   0  i  lt  values Length  i                                          itemProperties i  SetValue item  values i                                       addMethod Invoke list  new    item                                 return action                          lt summary gt              Creates a type based on the property type values specified in the properties              lt  summary gt               lt param name  properties  gt  lt  param gt               lt returns gt  lt  returns gt               lt exception cref  Exception  gt  lt  exception gt          public static Type CreateDynamicType IEnumerable lt DynamicTypeProperty gt  properties                        StringBuilder classCode   new StringBuilder                    Generate the class code             classCode AppendLine  using System                 classCode AppendLine  namespace Dexih                  classCode AppendLine  public class DynamicClass                   foreach  var property in properties                                classCode AppendLine   public  property Type Name   property Name    get  set                                  classCode AppendLine                   classCode AppendLine                    var syntaxTree   CSharpSyntaxTree ParseText classCode ToString                  var references   new MetadataReference                                 MetadataReference CreateFromFile typeof object  GetTypeInfo   Assembly Location                   MetadataReference CreateFromFile typeof DictionaryBase  GetTypeInfo   Assembly Location                              var compilation   CSharpCompilation Create  DynamicClass    Guid NewGuid       dll                   syntaxTrees  new    syntaxTree                   references  references                  options  new CSharpCompilationOptions OutputKind DynamicallyLinkedLibrary                 using  var ms   new MemoryStream                                  var result   compilation Emit ms                    if   result Success                                        var failures   result Diagnostics Where diagnostic   gt                          diagnostic IsWarningAsError                            diagnostic Severity    DiagnosticSeverity Error                        var message   new StringBuilder                         foreach  var diagnostic in failures                                                message AppendFormat   0    1    diagnostic Id  diagnostic GetMessage                                                throw new Exception   Invalid property definition   message                                        else                                        ms Seek 0  SeekOrigin Begin                       var assembly   System Runtime Loader AssemblyLoadContext Default LoadFromStream ms                       var dynamicType   assembly GetType  Dexih DynamicClass                        return dynamicType

User · Answer

Runtime Code Generation with JVM and CLR -  Peter Sestoft   Work for persons that are really interested in this type of programming    My tip for You is that if You declare something try to avoid string  so if You have class Field it is better to use class System Type to store the field type than a string   And for the sake of best solutions instead of creation new classes try to use those that has been created FiledInfo instead of creation new

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Based on  danijels s answer  dynamically create a class in VB NET   Imports System Reflection Imports System Reflection Emit  Public Class ObjectBuilder  Public Property myType As Object Public Property myObject As Object  Public Sub New fields As List Of Field       myType   CompileResultType fields      myObject   Activator CreateInstance myType  End Sub  Public Shared Function CompileResultType fields As List Of Field   As Type     Dim tb As TypeBuilder   GetTypeBuilder       Dim constructor As ConstructorBuilder   tb DefineDefaultConstructor MethodAttributes  Public  Or MethodAttributes SpecialName Or MethodAttributes RTSpecialName       For Each field In fields         CreateProperty tb  field Name  field Type      Next      Dim objectType As Type   tb CreateType       Return objectType End Function  Private Shared Function GetTypeBuilder   As TypeBuilder     Dim typeSignature    MyDynamicType      Dim an   New AssemblyName typeSignature      Dim assemblyBuilder As AssemblyBuilder   AppDomain CurrentDomain DefineDynamicAssembly an  AssemblyBuilderAccess Run      Dim moduleBuilder As ModuleBuilder   assemblyBuilder DefineDynamicModule  MainModule       Dim tb As TypeBuilder   moduleBuilder DefineType typeSignature  TypeAttributes  Public  Or TypeAttributes  Class  Or TypeAttributes AutoClass Or TypeAttributes AnsiClass Or TypeAttributes BeforeFieldInit Or TypeAttributes AutoLayout  Nothing      Return tb End Function  Private Shared Sub CreateProperty tb As TypeBuilder  propertyName As String  propertyType As Type      Dim fieldBuilder As FieldBuilder   tb DefineField      amp  propertyName  propertyType  FieldAttributes  Private        Dim propertyBuilder As PropertyBuilder   tb DefineProperty propertyName  PropertyAttributes HasDefault  propertyType  Nothing      Dim getPropMthdBldr As MethodBuilder   tb DefineMethod  get    amp  propertyName  MethodAttributes  Public  Or MethodAttributes SpecialName Or MethodAttributes HideBySig  propertyType  Type EmptyTypes      Dim getIl As ILGenerator   getPropMthdBldr GetILGenerator        getIl Emit OpCodes Ldarg 0      getIl Emit OpCodes Ldfld  fieldBuilder      getIl Emit OpCodes Ret       Dim setPropMthdBldr As MethodBuilder   tb DefineMethod  set    amp  propertyName  MethodAttributes  Public  Or MethodAttributes SpecialName Or MethodAttributes HideBySig  Nothing   propertyType        Dim setIl As ILGenerator   setPropMthdBldr GetILGenerator       Dim modifyProperty As Label   setIl DefineLabel       Dim exitSet As Label   setIl DefineLabel        setIl MarkLabel modifyProperty      setIl Emit OpCodes Ldarg 0      setIl Emit OpCodes Ldarg 1      setIl Emit OpCodes Stfld  fieldBuilder       setIl Emit OpCodes Nop      setIl MarkLabel exitSet      setIl Emit OpCodes Ret       propertyBuilder SetGetMethod getPropMthdBldr      propertyBuilder SetSetMethod setPropMthdBldr  End Sub  End Class

User · Answer

You can look at using dynamic modules and classes that can do the job  The only disadvantage is that it remains loaded in the app domain  But with the version of  NET framework being used  that could change   NET 4 0 supports collectible dynamic assemblies and hence you can recreate the classes types dynamically

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you can use CSharpProvider  var code     quot      public class Abc          public string Get     return  quot  quot abc quot  quot            quot    var options   new CompilerParameters    options GenerateExecutable   false  options GenerateInMemory   false   var provider   new CSharpCodeProvider    var compile   provider CompileAssemblyFromSource options  code    var type   compile CompiledAssembly GetType  quot Abc quot    var abc   Activator CreateInstance type    var method   type GetMethod  quot Get quot    var result   method Invoke abc  null    Console WriteLine result     output  abc

User · Answer

Yes  you can use System Reflection Emit namespace for this  It is not straight forward if you have no experience with it  but it is certainly possible   Edit  This code might be flawed  but it will give you the general idea and hopefully off to a good start towards the goal   using System  using System Reflection  using System Reflection Emit   namespace TypeBuilderNamespace       public static class MyTypeBuilder               public static void CreateNewObject                         var myType   CompileResultType                var myObject   Activator CreateInstance myType                     public static Type CompileResultType                         TypeBuilder tb   GetTypeBuilder                ConstructorBuilder constructor   tb DefineDefaultConstructor MethodAttributes Public   MethodAttributes SpecialName   MethodAttributes RTSpecialName                   NOTE  assuming your list contains Field objects with fields FieldName string  and FieldType Type              foreach  var field in yourListOfFields                  CreateProperty tb  field FieldName  field FieldType                Type objectType   tb CreateType                return objectType                     private static TypeBuilder GetTypeBuilder                         var typeSignature    MyDynamicType               var an   new AssemblyName typeSignature               AssemblyBuilder assemblyBuilder   AppDomain CurrentDomain DefineDynamicAssembly an  AssemblyBuilderAccess Run               ModuleBuilder moduleBuilder   assemblyBuilder DefineDynamicModule  MainModule                TypeBuilder tb   moduleBuilder DefineType typeSignature                      TypeAttributes Public                       TypeAttributes Class                       TypeAttributes AutoClass                       TypeAttributes AnsiClass                       TypeAttributes BeforeFieldInit                       TypeAttributes AutoLayout                      null               return tb                     private static void CreateProperty TypeBuilder tb  string propertyName  Type propertyType                        FieldBuilder fieldBuilder   tb DefineField       propertyName  propertyType  FieldAttributes Private                PropertyBuilder propertyBuilder   tb DefineProperty propertyName  PropertyAttributes HasDefault  propertyType  null               MethodBuilder getPropMthdBldr   tb DefineMethod  get     propertyName  MethodAttributes Public   MethodAttributes SpecialName   MethodAttributes HideBySig  propertyType  Type EmptyTypes               ILGenerator getIl   getPropMthdBldr GetILGenerator                 getIl Emit OpCodes Ldarg 0               getIl Emit OpCodes Ldfld  fieldBuilder               getIl Emit OpCodes Ret                MethodBuilder setPropMthdBldr                   tb DefineMethod  set     propertyName                    MethodAttributes Public                     MethodAttributes SpecialName                     MethodAttributes HideBySig                    null  new     propertyType                  ILGenerator setIl   setPropMthdBldr GetILGenerator                Label modifyProperty   setIl DefineLabel                Label exitSet   setIl DefineLabel                 setIl MarkLabel modifyProperty               setIl Emit OpCodes Ldarg 0               setIl Emit OpCodes Ldarg 1               setIl Emit OpCodes Stfld  fieldBuilder                setIl Emit OpCodes Nop               setIl MarkLabel exitSet               setIl Emit OpCodes Ret                propertyBuilder SetGetMethod getPropMthdBldr               propertyBuilder SetSetMethod setPropMthdBldr

User · Answer

I don t know the intended usage of such dynamic classes  and code generation and run time compilation can be done  but takes some effort  Maybe Anonymous Types would help you  something like   var v   new   EmployeeID   108  EmployeeName    John Doe

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You can also dynamically create a class by using DynamicObject   public class DynamicClass   DynamicObject       private Dictionary lt string  KeyValuePair lt Type  object gt  gt   fields       public DynamicClass List lt Field gt  fields                 fields   new Dictionary lt string  KeyValuePair lt Type  object gt  gt             fields ForEach x   gt   fields Add x FieldName              new KeyValuePair lt Type  object gt  x FieldType  null                public override bool TrySetMember SetMemberBinder binder  object value                if   fields ContainsKey binder Name                         var type    fields binder Name  Key              if  value GetType      type                                 fields binder Name    new KeyValuePair lt Type  object gt  type  value                   return true                            else throw new Exception  Value     value     is not of type     type Name                     return false             public override bool TryGetMember GetMemberBinder binder  out object result                result    fields binder Name  Value          return true            I store all class fields in a dictionary  fields together with their types and values  The both methods are to can get or set value to some of the properties  You must use the dynamic keyword to create an instance of this class   The usage with your example   var fields   new List lt Field gt           new Field  EmployeeID   typeof int        new Field  EmployeeName   typeof string        new Field  Designation   typeof string        dynamic obj   new DynamicClass fields      set obj EmployeeID   123456  obj EmployeeName    John   obj Designation    Tech Lead    obj Age   25                Exception  DynamicClass does not contain a definition for  Age  obj EmployeeName   666      Exception  Value 666 is not of type String    get Console WriteLine obj EmployeeID         123456 Console WriteLine obj EmployeeName       John Console WriteLine obj Designation        Tech Lead   Edit  And here is how looks my class Field   public class Field       public Field string name  Type type                this FieldName   name          this FieldType   type             public string FieldName       public Type FieldType

User · Answer

It will take some work  but is certainly not impossible   What I have done is    Create a C  source in a string  no need to write out to a file    Run it through the Microsoft CSharp CSharpCodeProvider  CompileAssemblyFromSource  Find the generated Type And create an instance of that Type  Activator CreateInstance    This way you can deal with the C  code you already know  instead of having to emit MSIL   But this works best if your class implements some interface  or is derived from some baseclass   else how is the calling code  read  compiler  to know about that class that will be generated at runtime

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Ask Hans suggested  you can use Roslyn to dynamically create classes  Full source  using Microsoft CodeAnalysis  using Microsoft CodeAnalysis CSharp  using System  using System Collections Generic  using System IO  using System Linq  using System Reflection   namespace RoslynDemo1       class Program               static void Main string   args                        var fields   new List lt Field gt                                  new Field  quot EmployeeID quot   quot int quot                    new Field  quot EmployeeName quot   quot String quot                    new Field  quot Designation quot   quot String quot                               var employeeClass   CreateClass fields   quot Employee quot                 dynamic employee1   Activator CreateInstance employeeClass               employee1 EmployeeID   4213              employee1 EmployeeName    quot Wendy Tailor quot               employee1 Designation    quot Engineering Manager quot                dynamic employee2   Activator CreateInstance employeeClass               employee2 EmployeeID   3510              employee2 EmployeeName    quot John Gibson quot               employee2 Designation    quot Software Engineer quot                Console WriteLine   quot  employee1 EmployeeName  quot                Console WriteLine   quot  employee2 EmployeeName  quot                 Console WriteLine  quot Press any key to continue    quot                Console ReadKey                       public static Type CreateClass List lt Field gt  fields  string newClassName  string newNamespace    quot Magic quot                         var fieldsCode   fields                                  Select field   gt    quot public  field FieldType   field FieldName   quot                                    ToString Environment NewLine                var classCode      quot                  using System                   namespace  newNamespace                                         public class  newClassName                                                 public  newClassName                                                                                    fieldsCode                                                         quot  Trim                 classCode   FormatUsingRoslyn classCode                 var assemblies   new                                 MetadataReference CreateFromFile typeof object  Assembly Location                                              var assemblies   AppDomain                          CurrentDomain                          GetAssemblies                            Where a   gt   string IsNullOrEmpty a Location                            Select a   gt  MetadataReference CreateFromFile a Location                            ToArray                                var syntaxTree   CSharpSyntaxTree ParseText classCode                var compilation   CSharpCompilation                                  Create newNamespace                                   AddSyntaxTrees syntaxTree                                   AddReferences assemblies                                   WithOptions new CSharpCompilationOptions OutputKind DynamicallyLinkedLibrary                 using  var ms   new MemoryStream                                  var result   compilation Emit ms                     compilation Emit   quot C   Temp   newNamespace  dll quot                     if  result Success                                        ms Seek 0  SeekOrigin Begin                       Assembly assembly   Assembly Load ms ToArray                          var newTypeFullName     quot  newNamespace   newClassName  quot                        var type   assembly GetType newTypeFullName                       return type                                    else                                       IEnumerable lt Diagnostic gt  failures   result Diagnostics Where diagnostic   gt                          diagnostic IsWarningAsError                            diagnostic Severity    DiagnosticSeverity Error                        foreach  Diagnostic diagnostic in failures                                                Console Error WriteLine  quot  0    1  quot   diagnostic Id  diagnostic GetMessage                                                return null                                                     public static string FormatUsingRoslyn string csCode                        var tree   CSharpSyntaxTree ParseText csCode               var root   tree GetRoot   NormalizeWhitespace                var result   root ToFullString                return result                       public class Field               public string FieldName          public string FieldType           public Field string fieldName  string fieldType                        FieldName   fieldName              FieldType   fieldType                       public static class Extensions               public static string ToString this IEnumerable lt string gt  list  string separator                        string result   string Join separator  list               return result

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I know i reopen this old task but with c  4 0 this task is absolutely painless   dynamic expando   new ExpandoObject    expando EmployeeID 42  expando Designation  unknown   expando EmployeeName  curt     or more dynamic AddProperty expando   Language    English      for more see https   www oreilly com learning building-c-objects-dynamically

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You can use System Runtime Remoting Proxies RealProxy   It will allow you to use  normal  code rather than low level assembly type stuff   See the RealProxy answer to this question for a good example   How do I intercept a method call in C

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You want to look at CodeDOM  It allows defining code elements and compiling them  Quoting MSDN         This object graph can be rendered as   source code using a CodeDOM code   generator for a supported programming   language  The CodeDOM can also be used   to compile source code into a binary   assembly

[c#] How to dynamically create a class?

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