I refer to the link below:
http://rogeralsing.com/2008/02/28/linq-expressions-creating-objects/
Is it possible to enhance it to create object by providing the class name?
Basically to achieve what Activator.CreateInstance could do below by using Lambda Expression
Dim typeName As String = "Testing.ClassNameth, Testing"
Dim typ As Type = Type.GetType(typeName)
Dim testObj = Activator.CreateInstance(typ)
Dim methodInfo As MethodInfo = testObj.GetType().GetMethod("TestPrintObject")
The purpose on why I am doing it is because the Activator.CreateInstance's performance is quite slow.
Thanks!
Ok. After few researches, below is the answer:
Add the functions below to any of your related class:
Public Function GetActivator(Of T)(type As Type) As ObjectActivator(Of T)
'make a NewExpression that calls the
'ctor with the args we just created
Dim newExp As NewExpression = Expression.[New](type)
'create a lambda with the New
'Expression as body
Dim lambda As LambdaExpression = Expression.Lambda(GetType(ObjectActivator(Of T)), newExp)
'compile it
Dim compiled As ObjectActivator(Of T) = DirectCast(lambda.Compile(), ObjectActivator(Of T))
Return compiled
End Function
Public Delegate Function ObjectActivator(Of T)() As T
Then we can call the function above as:
Dim typeName As String = "Testing.ClassNameth, Testing"
Dim typ As Type = Type.GetType(typeName)
Dim testObj As Object = YourHelperClassInstance.GetActivator(Of Object)(typ).Invoke()
Hope this post would help someone in the future.
Thanks!
Related
Ok, so I have been stuck on this for a while, combining various question solutions from on here.
Situation:
I instantiate an Object of Type x by using the activator.CreateInstance(x)
Type x can vary but always has the same properties and methods.
The problem is that type x has an event ReadCompleted as ReadCompleted (this is a delegate), type y has the same event, with the same delegate but it is of type ReadCompleted1, z => ReadCompleted2, etc...
Solution:
I assign a delegate at runtime using the following code:
Dim Client As Object = ServiceProvider.GetService(TypeDict(Entity))
Dim TaskCompletionSource As New TaskCompletionSource(Of Entity)()
Dim addMethod As MethodInfo = Client.GetType().GetMethod("add_ReadCompleted")
Dim removeMethod As MethodInfo = Client.GetType().GetMethod("remove_ReadCompleted")
Dim self As Object = Nothing
Dim getSelf As Func(Of Object) = Function() self
Dim eventArgType As Type = Client.GetType().GetEvent("ReadCompleted").EventHandlerType.GetMethod("Invoke").GetParameters()(1).ParameterType
Dim e As ParameterExpression = Expression.Variable(eventArgType)
Dim ExpBlock As BlockExpression = Expression.Block({Expression.Parameter(GetType(Object)), e},
Expression.Call(
Nothing,
Me.GetType().GetMethod("ProcessTask"),
Expression.Convert(e, eventArgType),
Expression.Constant(TaskCompletionSource)),
Expression.Call(
Expression.Constant(Client),
removeMethod,
Expression.Convert(
Expression.Invoke(
Expression.Constant(getSelf)),
addMethod.GetParameters()(0).ParameterType)
)
)
Dim lambda As LambdaExpression = Expression.Lambda(
addMethod.GetParameters()(0).ParameterType,
ExpBlock,
Expression.Parameter(GetType(Object)),
Expression.Parameter(eventArgType))
Dim dlg As [Delegate] = lambda.Compile()
self = dlg
addMethod.Invoke(Client, {dlg})
Client.ReadAsync(PrimaryKey)
Now my knowledge on linq and it's Expression class is limited and i did my best to research the msdn documentation but i can't figure it out:
the method ProcessTask gets called properly, for which i've worked long enough, but my parameter e is always Nothing, resulting in a NullReferenceException.
The method:
Public Shared Sub ProcessTask(ByVal e, ByRef tcs)
'Console.WriteLine(e.GetType())
If e.Error IsNot Nothing Then
tcs.TrySetException(e.Error)
ElseIf e.Cancelled Then
tcs.TrySetCanceled()
Else
tcs.TrySetResult(e.Result)
End If
End Sub
I have no idea why, according to how i see it this is the correct way to call my method, but obviously it isn't. Can someone point me in the right direction for this?
Could be I'm just plain blind and missing something very obvious....
Thanks in advance!
EDIT:
Whilst awaiting an answer i tried to do some more debugging(which is hell in this scenario) saw that if i do:
Dim s As ParameterExpression = Expression.Variable(GetType(Object), "Sender")
Dim ExpBlock As BlockExpression = Expression.Block({s, e},
Expression.Call(
Nothing,
GetType(Console).GetMethod("WriteLine", New Type() {GetType(String)}),
Expression.Call(s, GetType(Object).GetMethod("ToString"))),
Expression.Call(
Expression.Constant(Client),
removeMethod,
Expression.Convert(
Expression.Invoke(
Expression.Constant(getSelf)),
addMethod.GetParameters()(0).ParameterType)
))
The sender as object parameter is also nothing, so i'm getting the feeling that none of my arguments are getting passed through...
Hope this helps shed more light on the matter.
I figured it out, turns out i misinterpreted the whole parameter thing of Expression:
Dim Client As Object = ServiceProvider.GetService(TypeDict(Entity))
Dim TaskCompletionSource As New TaskCompletionSource(Of Entity)()
Dim addMethod As MethodInfo = Client.GetType().GetMethod("add_ReadCompleted")
Dim removeMethod As MethodInfo = Client.GetType().GetMethod("remove_ReadCompleted")
Dim self As Object = Nothing
Dim getSelf As Func(Of Object) = Function() self
Dim eventArgType As Type = Client.GetType().GetEvent("ReadCompleted").EventHandlerType.GetMethod("Invoke").GetParameters()(1).ParameterType
Dim s As ParameterExpression = Expression.Parameter(GetType(Object), "Sender")
Dim e As ParameterExpression = Expression.Variable(eventArgType, "EventArgs")
Dim ExpBlock As BlockExpression = Expression.Block(\*{Expression.Parameter('GetType(Object)), e},*\ <--- this has to go
Expression.Call(
Nothing,
Me.GetType().GetMethod("ProcessTask"),
Expression.Convert(e, eventArgType),
Expression.Constant(TaskCompletionSource)),
Expression.Call(
Expression.Constant(Client),
removeMethod,
Expression.Convert(
Expression.Invoke(
Expression.Constant(getSelf)),
addMethod.GetParameters()(0).ParameterType)
)
)
Dim lambda As LambdaExpression = Expression.Lambda(
addMethod.GetParameters()(0).ParameterType,
ExpBlock,
s,
e)
\*Expression.Parameter(GetType(Object)),
Expression.Parameter(eventArgType))*\ <-- this has to change
Dim dlg As [Delegate] = lambda.Compile()
self = dlg
addMethod.Invoke(Client, {dlg})
Client.ReadAsync(PrimaryKey)
So as i see it the parameters don't have to be defined in the expression itself, but they sould be created, and the reference should be kept to use them in the lambda in which you compile the expression.
Hope someone in the future has some use for this answer, and thanks to all for taking a look at this.
I want to run a Method using a variable name that is stored in a Module with a parameter:
Dim subName as String = "sub1"
Dim param as Integer = 123
sub1(param) <- I want to run this using the **subName** string
I don't want to use Select Case because the Methods are in many different modules and I don't want to maintain a select-case function.
I looked up CallByName but it seems this only works for Classes. I can't figure out how to set the object ObjectRef when it comes to Modules :
Public Function CallByName(ByVal ObjectRef As System.Object,ByVal ProcName As String,ByVal UseCallType As CallType, ByVal Args() As Object) As Object
Is there a way to do this in VB.Net?
Edit: To make it really simple, I need the equivalent of VBA's:
Application.Run module_name.sub_name param
You can use reflection to create a delegate to the methods in the Module. I would load the created delegates into a Dictionary(Of String, Action(Of Int32)).
Action(Of Int32) is chosen because it matches the signature you specified of a subroutine taking an integer parameter.
Assume you have a Module defined like this:
Module SomeModule
Public Sub Sub1(arg As Int32)
Console.WriteLine("Sub1: {0}", arg)
End Sub
Public Sub Sub2(arg As Int32)
Console.WriteLine("Sub2: {0}", arg)
End Sub
End Module
Now to create and store the delegates in a dictionary.
Private methods As New Dictionary(Of String, Action(Of Int32))
Sub LoadMethods()
Dim modType As Type = GetType(SomeModule)
Dim mi As Reflection.MethodInfo
mi = modType.GetMethod("Sub1", BindingFlags.Static Or BindingFlags.Public)
methods.Add(mi.Name, CType(mi.CreateDelegate(GetType(Action(Of Int32))), Action(Of Int32)))
mi = modType.GetMethod("Sub2", BindingFlags.Static Or BindingFlags.Public)
methods.Add(mi.Name, CType(mi.CreateDelegate(GetType(Action(Of Int32))), Action(Of Int32)))
End Sub
You can retrieve and invoke the delegate like this:
methods("Sub1")(123)
methods("Sub2")(456)
Edit: I sometimes makes things to complicated. The LoadMethods method can be done without reflection like this:
Sub LoadMethods()
methods.Add("Sub1", New Action(Of Int32)(AddressOf SomeModule.Sub1))
methods.Add("Sub2", New Action(Of Int32)(AddressOf SomeModule.Sub1))
End Sub
Edit 2: Based on edit to question and comment below.
Edit: To make it really simple, I need the equivalent of VBA's:
Application.Run module_name.sub_name param
You will need to first extract the Module type from its containing assembly based on the entered name. Then you can retrieve the MethodInfo as shown above. The following example assumes that the module is contained in the executing assembly and has minimal checks implemented. It will require you to provide the module name, method name and an array properly typed method arguments. In a real world scenario, it would probably need to take a string of the arguments and perform some type of dynamic type casting to build up the typedArgs array based on calling MethodInfo.GetParameters.
Private Shared Sub Exec(moduleName As String, methodName As String, typedArgs As Object())
Dim asm As Reflection.Assembly = Assembly.GetExecutingAssembly
Dim modType As Type = asm.GetType(String.Format("{0}.{1}", asm.GetName.Name, moduleName))
If modType IsNot Nothing Then
Dim mi As Reflection.MethodInfo
mi = modType.GetMethod(methodName, BindingFlags.Static Or BindingFlags.Public)
If mi IsNot Nothing Then
mi.Invoke(Nothing, typedArgs)
End If
End If
End Sub
Example usage: Exec("SomeModule", "Sub1", New Object() {123})
Lets say you want to call subroutine (or function) sub1 with parameter 123 with optionally given module name module1
Call example, If module name is not available (function name to invoke should be unique among project):
Dim FunctionName As String = "sub1"
Dim Param As Integer = 123
InvokeModuleFunction(FunctionNameToCall:=FunctionName, FunctionParameters:=Param)
Alternatively, If you know module name:
Dim FunctionName As String = "sub1"
Dim Param As Integer = 123
Dim ModuleName As String = "module1"
InvokeModuleFunction(FunctionNameToCall:=FileType, ModuleName:=ModuleName, FunctionParameters:=Param)
InvokeModuleFunction definition
Private Sub InvokeModuleFunction(FunctionNameToCall As String, FunctionParameters As Object, Optional ModuleName As String = Nothing)
Dim MyReflectionAssembly = Reflection.Assembly.GetExecutingAssembly()
Dim MyFunctionType As Type
If IsNothing(ModuleName) Then
'Gets function without ModuleName. FunctionName should be unique in the assembly/programm.
MyFunctionType = MyReflectionAssembly.DefinedTypes.Where(Function(x) x.DeclaredMethods.Where(Function(y) y.Name = FunctionNameToCall).Count > 0).FirstOrDefault
Else
'Gets function using ModuleName, if available
MyFunctionType = MyReflectionAssembly.DefinedTypes.Where(Function(x) x.Name = ModuleName AndAlso x.DeclaredMethods.Where(Function(y) y.Name = FunctionNameToCall).Count > 0).FirstOrDefault
End If
If Not IsNothing(MyFunctionType) Then MyFunctionType.GetMethod(FunctionNameToCall).Invoke(MyFunctionType, New Object() {FunctionParameters})
End Sub
Alternatively you can use more than one parameter in invoking.
You would need to modify the above function to allow to pass more than one parameter.
The invoke part would look like:
FunctionType.GetMethod(FunctionNameToCall).Invoke(FunctionType, New Object() {Par1, Par2, Par3})
I'm using Entity Framework 6.0, DbContext. I'm using this method to copy an object and some related children:
Imports System.Data.Objects
Imports System.Data.Objects.DataClasses
Imports System.Runtime.CompilerServices
Public Module Entities
<Extension()>
Public Function CloneEntity(Of T As Class)(entity As T, context As ObjectContext, Optional include As List(Of IncludeEntity) = Nothing, Optional copyKeys As Boolean = False) As T
Return CloneEntityHelper(entity, context, include, copyKeys)
End Function
Private Function CloneEntityHelper(Of T As Class)(entity As T, context As ObjectContext, Optional include As List(Of IncludeEntity) = Nothing, Optional copyKeys As Boolean = False) As T
If include Is Nothing Then include = New List(Of IncludeEntity)()
Dim myType = entity.GetType()
Dim methodInfo = context.GetType().GetMethod("CreateObject").MakeGenericMethod(myType)
Dim result = methodInfo.Invoke(context, Nothing)
Dim propertyInfo = entity.GetType().GetProperties()
For Each info In propertyInfo
Dim attributes = info.GetCustomAttributes(GetType(EdmScalarPropertyAttribute), False).ToList()
For Each attr As EdmScalarPropertyAttribute In attributes
If (Not copyKeys) AndAlso attr.EntityKeyProperty
Continue For
End If
info.SetValue(result, info.GetValue(entity, Nothing), Nothing)
Next
If info.PropertyType.Name.Equals("EntityCollection`1", StringComparison.OrdinalIgnoreCase) Then
Dim shouldInclude = include.SingleOrDefault(Function(i) i.Name.Equals(info.Name, StringComparison.OrdinalIgnoreCase))
If shouldInclude Is Nothing Then Continue For
Dim relatedChildren = info.GetValue(entity, Nothing)
Dim propertyType As Type = relatedChildren.GetType().GetGenericArguments().First()
Dim genericType As Type = GetType(EntityCollection(Of ))
Dim boundType = genericType.MakeGenericType(propertyType)
Dim children = Activator.CreateInstance(boundType)
For Each child In relatedChildren
Dim cloneChild = CloneEntityHelper(child, context, shouldInclude.Children, shouldInclude.CopyKeys)
children.Add(cloneChild)
Next
info.SetValue(result, children, Nothing)
End If
Next
Return result
End Function
Public Class IncludeEntity
Public Property Name As String
Public Property Children As New List(Of IncludeEntity)
Public Property CopyKeys As Boolean
Public Sub New(propertyName As String, ParamArray childNodes() As String)
Name = propertyName
Children = childNodes.Select(Function(n) new IncludeEntity(n)).ToList()
End Sub
End Class
End Module
Now I'm using the code like below :
Dim litm, newitm As New MyObject
Dim inc = New List(Of IncludeEntity)()
inc.Add(New IncludeEntity("Child_list"))
litm=context.MyObjects.FirstOrDefault
newitm = litm.CloneEntity(CType(context, Entity.Infrastructure.IObjectContextAdapter).ObjectContext,include:=inc)
The code is executed without errors, but nothing is copied, so newitm is empty.
I have inspected the code and found that this line on the CloneEntity function :
Dim myType = entity.GetType()
Is producing a strange type.
I'm expecting that the type will be of MyObject type, but instead this return :
MyObject_F2FFE64DA472EB2B2BDF7E143DE887D3845AD9D1731FD3107937062AC0C2E4BB
This line too :
Dim result = methodInfo.Invoke(context, Nothing)
produces the same strange type.
I don't know if this is the problem, but this is the only strange thing I have noticed.
Can you help me to find out why this code doesn't work?
Thank you!
Entity framework, like many other ORMs will build a proxy type for your entities so that it can intercept calls to:
Lazy load the contents of any collection contained as properties within your entity, when you access those collection properties.
Detect that you have made changes to the properties of an instance as part of dirty checking, so that it will know which objects are dirty and need to be saved to the database when you invoke SaveChanges.
Refer for example to EF returning proxy class instead of actual entity or Working with Proxies.
If you want to find out the underlying type of your entity that is wrapped by the proxy, i.e. the one that would match with the type you are looking for (e.g. MyObject), you can do that using a method in the object context:
var underlyingType = ObjectContext.GetObjectType(entity.GetType());
In Visual Basic.net, can I create an Object, or a List of T with the type from another object.
Here is some code:
Dim TestObjectType As Author
Dim TestObject As TestObjectType.GetType
I am getting an error:
TestObjectType.GetType is not defined
EDIT
Can I create a Type object of a certain type, and then create objects, lists or cast objects to this type from this Type object?
Dim TestObject As TestObjectType.GetType will look for a type named GetType in the namespace TestObjectType.
To create an instance of a class using System.Type, you can use Activator.CreateInstance:
Dim TestObject = Activator.CreateInstance(TestObjectType.GetType())
To create a generic list, you can use Type.MakeGenericType:
Dim listType = GetType(List(Of )).MakeGenericType(TestObjectType.GetType())
Dim list = Activator.CreateInstance(listType)
Note that both snippets above return an Object; however, you can make use of generics to achieve compile time safety:
Dim TestObject = CreateNew(TestObjectType)
Dim AuthorList = CreateNewList(TestObjectType)
...
Function CreateNew(Of T As New)(obj As T) As T
Return New T()
End Function
Function CreateNewList(Of T)(obj As T) As List(Of T)
Return New List(Of T)
End Function
In Entity Framework I usually do something like:
modelBuilder.Entity(Of Model).HasKey(Function(item As Model) New With {item.PropertyA, item.PropertyB })
to map a composite primary key
I need to write a generic function like:
modelBuilder.Entity(Of TModelo).HasKey( MakeLambda({“PropertyA”, “PropertyB” })
Private Function MakeLambda(Of TModelo)(nameProperties As String()) As Expression(Of Func(Of TModelo, Object))
Dim type = GetType(TModelo)
Dim listProperties As New List(Of Expression)
Dim parameter = Expression.Parameter(type, "item")
For Each n As String In nameProperties
Dim refProperty = type.GetProperty(n)
listProperties.Add(Expression.MakeMemberAccess(parameter, refProperty))
Next
Dim arrayInit = Expression.NewArrayInit(GetType(Object), listProperties)
In this point the system fails creating the new expression
Dim newExpression = Expression.Lambda(Of Func(Of TModelo, Object))(arrayInit)
Return newExpression
End Function
May be somebody has another solution to this problem
This will do.
dynamic newExpression = Expression.Lambda>(arrayInit, parameter);
But this still not work for me yet.
I need something like this...
HasKey(p => new { p.FAMILY, p.CACHE_FAMILY, p.CUSTOMER_CODE, p.CCC, p.OPERATION, p.EVAL_CODE, p.VDT_FLAG, p.TEST_PLATFORM, p.PCBA_VENDOR });