cUpdate Custom attribut with reflection

6 Dec 2006 6:01 AM

Marc Robitaille

Hello,

I have this Field attribut class and a Client class that uses this Attribut
Class

<AttributeUsage(AttributeTargets.Property)> _
Public Class Field
    Inherits Attribute
    Private _FieldName As String
    Private _Changed As Boolean

    Public Sub New(ByVal changed As Boolean, ByVal fieldName As String)
        _Changed = changed
        _FieldName = fieldName
    End Sub

    Public Property FieldName() As String
        Get
            Return _FieldName
        End Get
        Set(ByVal value As String)
            _FieldName = value
        End Set
    End Property
    Public Property Changed() As Boolean
        Get
            Return _Changed
        End Get
        Set(ByVal value As Boolean)
            _Changed = value
        End Set
    End Property
End Class

Public Class Client
    Private _name As String
    <Field(False, "name")> _
    Public Property Name() As String
        Get
            Return _name
        End Get
        Set(ByVal value As String)
            If value <> _name Then
                Dim oType As Type = Me.GetType
                Dim oPropertyInfo As PropertyInfo =
oType.GetProperty("Name")
                Dim oAllAttributes As Field()
                oAllAttributes =
oPropertyInfo.GetCustomAttributes(GetType(Field), False)
                For Each oAttribute As Field In oAllAttributes
                    oAttribute.Changed = True
                    Exit For

                Next
                _name = value
            End If
        End Set
    End Property
End Class

In the click event of a button I have this

Dim x as new Client

x.Name = "My name"
x.Name = "Your name"

What I want to do is to use the Changed property of my Field attribut class
to tell me that the Name property has changed or not. With this, I want to
build the SQL update string with only the fields that the Changed attribut
is set to True. It doesn't work :-( The changed property is allways false.
What I do wrong? Is it possible to update the value of a property of an
attribut? if yes, how can I do this?

Thank you and hope that I am clear
Marc R.

6 Dec 2006 8:46 AM

Tom Shelton

On 2006-12-06, Marc Robitaille <marc.marie> wrote:
Show quoteHide quote

> Hello,
>
> I have this Field attribut class and a Client class that uses this Attribut
> Class
>
><AttributeUsage(AttributeTargets.Property)> _
> Public Class Field
>     Inherits Attribute
>     Private _FieldName As String
>     Private _Changed As Boolean
>
>     Public Sub New(ByVal changed As Boolean, ByVal fieldName As String)
>         _Changed = changed
>         _FieldName = fieldName
>     End Sub
>
>     Public Property FieldName() As String
>         Get
>             Return _FieldName
>         End Get
>         Set(ByVal value As String)
>             _FieldName = value
>         End Set
>     End Property
>     Public Property Changed() As Boolean
>         Get
>             Return _Changed
>         End Get
>         Set(ByVal value As Boolean)
>             _Changed = value
>         End Set
>     End Property
> End Class
>
> Public Class Client
>     Private _name As String
>     <Field(False, "name")> _
>     Public Property Name() As String
>         Get
>             Return _name
>         End Get
>         Set(ByVal value As String)
>             If value <> _name Then
>                 Dim oType As Type = Me.GetType
>                 Dim oPropertyInfo As PropertyInfo =
> oType.GetProperty("Name")
>                 Dim oAllAttributes As Field()
>                 oAllAttributes =
> oPropertyInfo.GetCustomAttributes(GetType(Field), False)
>                 For Each oAttribute As Field In oAllAttributes
>                     oAttribute.Changed = True
>                     Exit For
>
>                 Next
>                 _name = value
>             End If
>         End Set
>     End Property
> End Class
>
> In the click event of a button I have this
>
> Dim x as new Client
>
> x.Name = "My name"
> x.Name = "Your name"
>
> What I want to do is to use the Changed property of my Field attribut class
> to tell me that the Name property has changed or not. With this, I want to
> build the SQL update string with only the fields that the Changed attribut
> is set to True. It doesn't work :-( The changed property is allways false.
> What I do wrong? Is it possible to update the value of a property of an
> attribut? if yes, how can I do this?
>
> Thank you and hope that I am clear
> Marc R.
>
>

Marc - I don't really think it is possible to change the value of an attribute
at runtime. I'm pretty sure that attributes are compile time thing and are
embeded in the metadata of the assembly. If someone knows differently, please
jump in and correct me.

Anyway, you most likely will have to implement an internal method of tracking
changes. Maybe an array of flags. You know when a property gets changed,
just hook it in the set method.

By the way - why don't you just use one of the O/R mapper's that are already
out there? NHibernate? WilsonO/R Mapper? LLBGen Pro? Really, you would be
saving your self a heck of a lot of work :)

--
Tom Shelton

7 Dec 2006 12:53 AM

Marc Robitaille

I do this because I want to learn :-) What I have done so far, I have
something that work great to
create code but, I want to use every possible things that exist in .NET just
to learn. You can tell that I am creazy but I love to learn.

Thank you for your sugestion.

:-)

"Tom Shelton" <tom_shel***@comcastXXXXXXX.net> a écrit dans le message de

news: efqdnecRrPnQHuvYnZ2dnUVZ_r6dn***@comcast.com...
Show quoteHide quote

> On 2006-12-06, Marc Robitaille <marc.marie> wrote:
>> Hello,
>>
>> I have this Field attribut class and a Client class that uses this
>> Attribut
>> Class
>>
>><AttributeUsage(AttributeTargets.Property)> _
>> Public Class Field
>>     Inherits Attribute
>>     Private _FieldName As String
>>     Private _Changed As Boolean
>>
>>     Public Sub New(ByVal changed As Boolean, ByVal fieldName As String)
>>         _Changed = changed
>>         _FieldName = fieldName
>>     End Sub
>>
>>     Public Property FieldName() As String
>>         Get
>>             Return _FieldName
>>         End Get
>>         Set(ByVal value As String)
>>             _FieldName = value
>>         End Set
>>     End Property
>>     Public Property Changed() As Boolean
>>         Get
>>             Return _Changed
>>         End Get
>>         Set(ByVal value As Boolean)
>>             _Changed = value
>>         End Set
>>     End Property
>> End Class
>>
>> Public Class Client
>>     Private _name As String
>>     <Field(False, "name")> _
>>     Public Property Name() As String
>>         Get
>>             Return _name
>>         End Get
>>         Set(ByVal value As String)
>>             If value <> _name Then
>>                 Dim oType As Type = Me.GetType
>>                 Dim oPropertyInfo As PropertyInfo =
>> oType.GetProperty("Name")
>>                 Dim oAllAttributes As Field()
>>                 oAllAttributes =
>> oPropertyInfo.GetCustomAttributes(GetType(Field), False)
>>                 For Each oAttribute As Field In oAllAttributes
>>                     oAttribute.Changed = True
>>                     Exit For
>>
>>                 Next
>>                 _name = value
>>             End If
>>         End Set
>>     End Property
>> End Class
>>
>> In the click event of a button I have this
>>
>> Dim x as new Client
>>
>> x.Name = "My name"
>> x.Name = "Your name"
>>
>> What I want to do is to use the Changed property of my Field attribut
>> class
>> to tell me that the Name property has changed or not. With this, I want
>> to
>> build the SQL update string with only the fields that the Changed
>> attribut
>> is set to True. It doesn't work :-( The changed property is allways
>> false.
>> What I do wrong? Is it possible to update the value of a property of an
>> attribut? if yes, how can I do this?
>>
>> Thank you and hope that I am clear
>> Marc R.
>>
>>
>
> Marc - I don't really think it is possible to change the value of an
> attribute
> at runtime. I'm pretty sure that attributes are compile time thing and
> are
> embeded in the metadata of the assembly. If someone knows differently,
> please
> jump in and correct me.
>
> Anyway, you most likely will have to implement an internal method of
> tracking
> changes. Maybe an array of flags. You know when a property gets changed,
> just hook it in the set method.
>
> By the way - why don't you just use one of the O/R mapper's that are
> already
> out there? NHibernate? WilsonO/R Mapper? LLBGen Pro? Really, you would
> be
> saving your self a heck of a lot of work :)
>
> --
> Tom Shelton

7 Dec 2006 6:21 AM

Tom Shelton

On 2006-12-07, Marc Robitaille <marc.marie> wrote:

> I do this because I want to learn :-) What I have done so far, I have
> something that work great to
> create code but, I want to use every possible things that exist in .NET just
> to learn. You can tell that I am creazy but I love to learn.
>
> Thank you for your sugestion.
>:-)
>

Ok, nothing wrong with wanting to learn. Done that many times myself.
Anyway, good luck.

--
Tom Shelton