HashSet(Of T) - how can I get elements by position number ?
-
Hello ! I'm using entity framework. I have a situation when I use the function CallByName like this :
For k=0 to I
CallByName(MyObject, "Child1", CallType.Get).ElementAt(k)
......
NextBut I get an error
Public member 'ElementAt' on type 'HashSet(Of Child1) not found. '
But when I use the standart expression
MyObject.Child1.ElementAt(k)
Everything is ok. Why CallByName return a HashSet(Of Child1) ? And what can I do in my expression in order to get the expected result ? Thank you !
-
Hello ! I'm using entity framework. I have a situation when I use the function CallByName like this :
For k=0 to I
CallByName(MyObject, "Child1", CallType.Get).ElementAt(k)
......
NextBut I get an error
Public member 'ElementAt' on type 'HashSet(Of Child1) not found. '
But when I use the standart expression
MyObject.Child1.ElementAt(k)
Everything is ok. Why CallByName return a HashSet(Of Child1) ? And what can I do in my expression in order to get the expected result ? Thank you !
A HashSet has no order. It's a set.
-
Hello ! I'm using entity framework. I have a situation when I use the function CallByName like this :
For k=0 to I
CallByName(MyObject, "Child1", CallType.Get).ElementAt(k)
......
NextBut I get an error
Public member 'ElementAt' on type 'HashSet(Of Child1) not found. '
But when I use the standart expression
MyObject.Child1.ElementAt(k)
Everything is ok. Why CallByName return a HashSet(Of Child1) ? And what can I do in my expression in order to get the expected result ? Thank you !
ElementAt(..) is an extension-method and these aren't supported for dynamic typing (which is what you're doing because the return type of CallByName(..) is Object). However, you can either cast the returned object to the actual type and then call the extension method on it:
CType(CallByName(MyObject, "Child1", CallType.Get), HashSet(Of Child1)).ElementAt(k)
..or you can pass the object to Enumerable.ElementAt(..) as a parameter:
Enumerable.ElementAt(CallByName(MyObject, "Child1", CallType.Get), k)
-
ElementAt(..) is an extension-method and these aren't supported for dynamic typing (which is what you're doing because the return type of CallByName(..) is Object). However, you can either cast the returned object to the actual type and then call the extension method on it:
CType(CallByName(MyObject, "Child1", CallType.Get), HashSet(Of Child1)).ElementAt(k)
..or you can pass the object to Enumerable.ElementAt(..) as a parameter:
Enumerable.ElementAt(CallByName(MyObject, "Child1", CallType.Get), k)
Thank you ! sorry , but if you can understand , I want to use an expression where all are variables. So Myobject is a variable , the navigation property's name is a variable ( a list of strings like "child1" that is filled on runtime ). But if I include a know type like Hashset(of Child1) then I can't realize my goal. so my final scope is to have a scenario like this : Dim varobject ------------ ( this will hold an object from Entity ). Dim l as list(of String)----- ( This will hold childs Navigation properties name as string ). And I want an expression like this : CallByname(Varobject,l(0),CallType.Get).ElementAt(k) ( of course when this expression will be used , the varobject will be an object from entity , and the list will hold navigation;s properties name that exist on varobject.( I have realized this scenario with count like this : CallByname(Varobject,l(0),CallType.Get).Count , but I don't know hot to realize for the problem I have described ) So for this reason I can't use your solution. is there any other way I can use ? Thank you !
-
Thank you ! sorry , but if you can understand , I want to use an expression where all are variables. So Myobject is a variable , the navigation property's name is a variable ( a list of strings like "child1" that is filled on runtime ). But if I include a know type like Hashset(of Child1) then I can't realize my goal. so my final scope is to have a scenario like this : Dim varobject ------------ ( this will hold an object from Entity ). Dim l as list(of String)----- ( This will hold childs Navigation properties name as string ). And I want an expression like this : CallByname(Varobject,l(0),CallType.Get).ElementAt(k) ( of course when this expression will be used , the varobject will be an object from entity , and the list will hold navigation;s properties name that exist on varobject.( I have realized this scenario with count like this : CallByname(Varobject,l(0),CallType.Get).Count , but I don't know hot to realize for the problem I have described ) So for this reason I can't use your solution. is there any other way I can use ? Thank you !
I edited my previous answer, please take a look. The second option should be what you need.
-
I edited my previous answer, please take a look. The second option should be what you need.
Thank you ! I don't know if you last solution works correctly, but after I get the element with your code :
Dim element = Enumerable.ElementAt(CallByName(MyObject, "Child1", CallType.Get), k)
I have a code like this :
Public Function CopyEntity(Of T As {Class, New})(ctx As MyEntities, entity As T, Optional copyKeys As Boolean = False) As T
Dim clone As New T()
Dim en = ctx.Entry(clone)
en.State = System.Data.Entity.EntityState.Added
ctx.Entry(clone).CurrentValues.SetValues(entity)
en.State = System.Data.Entity.EntityState.Detached
Return clone
End Functionand I pass the element I get with your code like this :
fhitm = CopyEntity(context, element,False)
I get an error on the line Dim en = ctx.Entry(clone) :
An unhandled exception of type 'System.InvalidOperationException' occurred in EntityFramework.dll
Additional information: The entity type Object is not part of the model for the current context.
I thought to using CTypeDynamic in order to cast the element to correct type, but as I wrote , I have only a string "Child1" and I have used :
CTypeDynamic(Element,System.Type.Gettype("Child1"))
, but the expression
System.Type.Gettype("Child1")
always return Nothing.
-
Thank you ! I don't know if you last solution works correctly, but after I get the element with your code :
Dim element = Enumerable.ElementAt(CallByName(MyObject, "Child1", CallType.Get), k)
I have a code like this :
Public Function CopyEntity(Of T As {Class, New})(ctx As MyEntities, entity As T, Optional copyKeys As Boolean = False) As T
Dim clone As New T()
Dim en = ctx.Entry(clone)
en.State = System.Data.Entity.EntityState.Added
ctx.Entry(clone).CurrentValues.SetValues(entity)
en.State = System.Data.Entity.EntityState.Detached
Return clone
End Functionand I pass the element I get with your code like this :
fhitm = CopyEntity(context, element,False)
I get an error on the line Dim en = ctx.Entry(clone) :
An unhandled exception of type 'System.InvalidOperationException' occurred in EntityFramework.dll
Additional information: The entity type Object is not part of the model for the current context.
I thought to using CTypeDynamic in order to cast the element to correct type, but as I wrote , I have only a string "Child1" and I have used :
CTypeDynamic(Element,System.Type.Gettype("Child1"))
, but the expression
System.Type.Gettype("Child1")
always return Nothing.
This is a bit speculation because I don't have a lot of experience with dynamic typing. But I'm almost sure about it:
Dim element = Enumerable.ElementAt(CallByName(MyObject, "Child1", CallType.Get), k)
REM "element" actually is of the type the elements of Child1 have
REM but at this point it's treated as type ObjectREM so this generic function is called for the generic type Object
Public Function CopyEntity(Of T As {Class, New})(ctx As MyEntities, entity As T, ...) As T
REM so "clone" actually is created as just an Object and not of the same type as "element" / "entity"
Dim clone As New T()
REM and the type Object of course isn't a valid entity-type in your context
Dim en = ctx.Entry(clone)Your options: 1) An ugly if-else-cascade for all potential types of entities where you test for the actual type of the entity and call CopyEntity(..) with an according cast. 2) Reflection. C#-sample here (last time you said you could read it - otherwise please ask):
// CEClass : class that contains the function CopyEntity
// CEInstance : an instance of CEClassMethodInfo mi = typeof(CEClass).GetMethod("CopyEntity");
mi = mi.MakeGenericMethod(typeof(MyEntities), element.GetType(), typeof(bool));
// you could cache "mi"object clone = mi.Invoke(CEInstance, new object[] {context, element, false});
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
-
This is a bit speculation because I don't have a lot of experience with dynamic typing. But I'm almost sure about it:
Dim element = Enumerable.ElementAt(CallByName(MyObject, "Child1", CallType.Get), k)
REM "element" actually is of the type the elements of Child1 have
REM but at this point it's treated as type ObjectREM so this generic function is called for the generic type Object
Public Function CopyEntity(Of T As {Class, New})(ctx As MyEntities, entity As T, ...) As T
REM so "clone" actually is created as just an Object and not of the same type as "element" / "entity"
Dim clone As New T()
REM and the type Object of course isn't a valid entity-type in your context
Dim en = ctx.Entry(clone)Your options: 1) An ugly if-else-cascade for all potential types of entities where you test for the actual type of the entity and call CopyEntity(..) with an according cast. 2) Reflection. C#-sample here (last time you said you could read it - otherwise please ask):
// CEClass : class that contains the function CopyEntity
// CEInstance : an instance of CEClassMethodInfo mi = typeof(CEClass).GetMethod("CopyEntity");
mi = mi.MakeGenericMethod(typeof(MyEntities), element.GetType(), typeof(bool));
// you could cache "mi"object clone = mi.Invoke(CEInstance, new object[] {context, element, false});
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
"REM so "clone" actually is created as just an Object and not of the same type as "element" / "entity"
This is not true because I try to use this instruction :
Ctype(element,Child1)
--- and after that everything works correctly But as I have explained , I can't use this kind of cast because I don't have the type Child1. I have only the string "Child1". For that I try to use CTypeDynamic. So I want to know why this line :
System.Type.Gettype("Child1")
produce Nothing ? Because with default types like "Integer" is working.
-
"REM so "clone" actually is created as just an Object and not of the same type as "element" / "entity"
This is not true because I try to use this instruction :
Ctype(element,Child1)
--- and after that everything works correctly But as I have explained , I can't use this kind of cast because I don't have the type Child1. I have only the string "Child1". For that I try to use CTypeDynamic. So I want to know why this line :
System.Type.Gettype("Child1")
produce Nothing ? Because with default types like "Integer" is working.
dilkonika wrote:
This is not true because I try to use this instruction : --- and after that everything works correctly
If we don't misunderstand each other here, this is what I would expect because you're casting element to its actual type, so CopyEntity(..) will be called for the actual type, so
Dim clone As New T()will not create clone as Object but as the same type as element. So this is essentially what I presented as your first option. The reason why Type.Gettype("Child1") doesn't work is because you have to specify more than just the name of the class, please refer to MSDN[^]. But CTypeDynamic(..) won't help you because it requires the requested target-type as a static type argument, which you don't have and won't get with Type.Gettype(..). So it's still option 1 or 2 :)If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
-
dilkonika wrote:
This is not true because I try to use this instruction : --- and after that everything works correctly
If we don't misunderstand each other here, this is what I would expect because you're casting element to its actual type, so CopyEntity(..) will be called for the actual type, so
Dim clone As New T()will not create clone as Object but as the same type as element. So this is essentially what I presented as your first option. The reason why Type.Gettype("Child1") doesn't work is because you have to specify more than just the name of the class, please refer to MSDN[^]. But CTypeDynamic(..) won't help you because it requires the requested target-type as a static type argument, which you don't have and won't get with Type.Gettype(..). So it's still option 1 or 2 :)If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
as I have read ion this link https://msdn.microsoft.com/en-us/library/ee835926(v=vs.110).aspx[^] , the type specified as parameter inside CtypeDynamic , may be a variable. Inside this link there;s an example that use Gettype inside the CTypeDynamic. and for the type.Gettype , I read that I have to use the namespace together with my string;s name type. But where can I find the namespace for my entity object ?
-
as I have read ion this link https://msdn.microsoft.com/en-us/library/ee835926(v=vs.110).aspx[^] , the type specified as parameter inside CtypeDynamic , may be a variable. Inside this link there;s an example that use Gettype inside the CTypeDynamic. and for the type.Gettype , I read that I have to use the namespace together with my string;s name type. But where can I find the namespace for my entity object ?
dilkonika wrote:
the type specified as parameter inside CtypeDynamic
That version of CTypeDynamic(..) won't help you either because it returns Object.
dilkonika wrote:
But where can I find the namespace for my entity object ?
In the source file where it's declared? :confused: Alternatively by looking at entity.GetType().FullName[^] Why don't you try my suggested Reflection-approach?
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
-
dilkonika wrote:
the type specified as parameter inside CtypeDynamic
That version of CTypeDynamic(..) won't help you either because it returns Object.
dilkonika wrote:
But where can I find the namespace for my entity object ?
In the source file where it's declared? :confused: Alternatively by looking at entity.GetType().FullName[^] Why don't you try my suggested Reflection-approach?
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
-
For namespace I'm asking because I try to use the name where it was declared but doesn't work. In the link for Type.Gettype , I found that I need the AssemblyQualifiedName. Is this the namespace + the name of class ?? for this I'm confused.
On the page for Type.GetType are links to Type.AssemblyQualifiedName[^] where this is documented.
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
-
On the page for Type.GetType are links to Type.AssemblyQualifiedName[^] where this is documented.
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
Yes , now I'm using this code :
Dim t a type
Dim s as string = "MyProg1.Child1,MyProg1,Version=1.0.0, Culture=neutral,PublicKeyToken=null"
t=System.Type.GetType(s)But the problem is that the t get this value : "MyProg1.Child1" , I'm expecting to have just "Child1" What's the problem ?
-
Yes , now I'm using this code :
Dim t a type
Dim s as string = "MyProg1.Child1,MyProg1,Version=1.0.0, Culture=neutral,PublicKeyToken=null"
t=System.Type.GetType(s)But the problem is that the t get this value : "MyProg1.Child1" , I'm expecting to have just "Child1" What's the problem ?
It's one and the same; unless you have multiple classes named "Child1" in your solution, then "Child1" may or may not be the same as "MyProg1.Child1".
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
-
It's one and the same; unless you have multiple classes named "Child1" in your solution, then "Child1" may or may not be the same as "MyProg1.Child1".
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
Ok , but then why when I use :
CTypeDynamic(Element,Child1)
everything is ok with my CopyEntity function. Whe I use :
Dim t a type
Dim s as string = "MyProg1.Child1,MyProg1,Version=1.0.0, Culture=neutral,PublicKeyToken=null"
t=System.Type.GetType(s)
CtypeDynamic(Element,t)I'm still getting the error :
An unhandled exception of type 'System.InvalidOperationException' occurred in EntityFramework.dll
Additional information: The entity type Object is not part of the model for the current context.
-
Ok , but then why when I use :
CTypeDynamic(Element,Child1)
everything is ok with my CopyEntity function. Whe I use :
Dim t a type
Dim s as string = "MyProg1.Child1,MyProg1,Version=1.0.0, Culture=neutral,PublicKeyToken=null"
t=System.Type.GetType(s)
CtypeDynamic(Element,t)I'm still getting the error :
An unhandled exception of type 'System.InvalidOperationException' occurred in EntityFramework.dll
Additional information: The entity type Object is not part of the model for the current context.
I'm trying to replicate it.. it's not actually CTypeDynamic(Element,Child1) how your working code looks like, is it? Is it CTypeDynamic(Element, GetType(Child1)) or CTypeDynamic<Child1>(Element) ?
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
-
I'm trying to replicate it.. it's not actually CTypeDynamic(Element,Child1) how your working code looks like, is it? Is it CTypeDynamic(Element, GetType(Child1)) or CTypeDynamic<Child1>(Element) ?
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
Sorry Friend. It's my mistake. Now it's confirmed : The CloneEntity Function is working correctly when I pass the element that I get from the expression :
Dim element = CType(Enumerable.ElementAt(CallByName(MyObj1, "Child1", CallType.Get), k), Child1)
But is not working correctly when I pass the element that I get from this expression :
Dim element = CTypeDynamic(Enumerable.ElementAt(CallByName(MyObj1, "Child1", CallType.Get), k), Type.GetType("MyProg1.Child1,MyProg1,Version=1.0.0, Culture=neutral,PublicKeyToken=null"))
-
Sorry Friend. It's my mistake. Now it's confirmed : The CloneEntity Function is working correctly when I pass the element that I get from the expression :
Dim element = CType(Enumerable.ElementAt(CallByName(MyObj1, "Child1", CallType.Get), k), Child1)
But is not working correctly when I pass the element that I get from this expression :
Dim element = CTypeDynamic(Enumerable.ElementAt(CallByName(MyObj1, "Child1", CallType.Get), k), Type.GetType("MyProg1.Child1,MyProg1,Version=1.0.0, Culture=neutral,PublicKeyToken=null"))
Yes, in the meantime I replicated it - both versions, simplified here:
Dim el = Enumerable.ElementAt(CallByName(MyClass, "Children", CallType.Get), 1)
REM 1
Dim el1 = CType(el, ChildClass)
Dim el1copy = CopyEntity(el1) REM works. (el1copy is of type ChildClass)REM 2
Dim el2 = CTypeDynamic(Of ChildClass)(el)
Dim el2copy = CopyEntity(el2) REM works. (el2copy is of type ChildClass)REM 3
Dim el3 = CTypeDynamic(el, GetType(ChildClass))
Dim el3copy = CopyEntity(el3) REM doesn't work. (el3copy is of type Object)That's basically the same as your code above. And it's still the same as what I'm talking about for the last messages ;P I know you can't use 1 and 2. The reason they work is because the return type of CType(el, ChildClass) and CTypeDynamic(Of ChildClass)(el) is ChildClass. The reason 3 doesn't work is because the return type of CTypeDynamic(el, GetType(ChildClass)) is Object (so it doesn't have anything to do with Type.GetType(..)). So, for 1 and 2 CopyEntity(..) is called for the correct generic type, for 3 it's called with Object as generic type. I don't know if there's a way to make 3 work. I tested the same thing (as 3) in C# and it actually works. Either VB differs there from C# or I just don't know how to do it in VB. I can assure you though that the reflection-approach that I suggested would work. If you want to find out if there is a way to make 3 work I would suggest you post a new question so that someone who knows VB better than me will be more likely to notice.
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
-
Yes, in the meantime I replicated it - both versions, simplified here:
Dim el = Enumerable.ElementAt(CallByName(MyClass, "Children", CallType.Get), 1)
REM 1
Dim el1 = CType(el, ChildClass)
Dim el1copy = CopyEntity(el1) REM works. (el1copy is of type ChildClass)REM 2
Dim el2 = CTypeDynamic(Of ChildClass)(el)
Dim el2copy = CopyEntity(el2) REM works. (el2copy is of type ChildClass)REM 3
Dim el3 = CTypeDynamic(el, GetType(ChildClass))
Dim el3copy = CopyEntity(el3) REM doesn't work. (el3copy is of type Object)That's basically the same as your code above. And it's still the same as what I'm talking about for the last messages ;P I know you can't use 1 and 2. The reason they work is because the return type of CType(el, ChildClass) and CTypeDynamic(Of ChildClass)(el) is ChildClass. The reason 3 doesn't work is because the return type of CTypeDynamic(el, GetType(ChildClass)) is Object (so it doesn't have anything to do with Type.GetType(..)). So, for 1 and 2 CopyEntity(..) is called for the correct generic type, for 3 it's called with Object as generic type. I don't know if there's a way to make 3 work. I tested the same thing (as 3) in C# and it actually works. Either VB differs there from C# or I just don't know how to do it in VB. I can assure you though that the reflection-approach that I suggested would work. If you want to find out if there is a way to make 3 work I would suggest you post a new question so that someone who knows VB better than me will be more likely to notice.
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson