OhSnap OhSnap - 1 year ago 86
C# Question

Select properties with specific attribute value

I'm looking for a way to select properties that have specific custom attributes with particular values in a single LINQ Statement.

I got the properties that have the attribute that I want, but I have no clue how to select its particular value.

Public Class PropertyIsMailHeaderParamAttribute
Inherits System.Attribute

Public Property HeaderAttribute As String = Nothing
Public Property Type As ParamType = Nothing

Public Sub New()

End Sub

Public Sub New(ByVal headerAttribute As String, ByVal type As ParamType)
Me.HeaderAttribute = headerAttribute
Me.Type = type
End Sub

Public Enum ParamType
base = 1
End Enum
End Class

private MsgData setBaseProperties(MimeMessage mailItem, string fileName)
var msgData = new MsgData();
Type type = msgData.GetType();
var props = from p in this.GetType().GetProperties()
let attr = p.GetCustomAttributes(typeof(Business.IT._21c.AddonFW.PropertyIsMailHeaderAttribute), true)
where attr.Length == 1
select new { Property = p, Attribute = attr.FirstOrDefault() as Business.IT._21c.AddonFW.PropertyIsMailHeaderAttribute };


var baseProps = from p in this.GetType().GetProperties()
let attr = p.GetCustomAttribute<PropertyIsMailHeaderParamAttribute>()
where attr != null && attr.Type == PropertyIsMailHeaderParamAttribute.ParamType.@base
select new { Property = p, Attribute = attr as Business.IT._21c.AddonFW.PropertyIsMailHeaderParamAttribute };

Answer Source

You either have to cast the Attribute object (using a regular cast or by e.g. using the OfType<> extension) to your type, but the easiest way would be to use the generic version of GetCustomAttribute<>:

var props = from p in this.GetType().GetProperties()
            let attr = p.GetCustomAttribute<PropertyIsMailHeaderAttribute>
            where attr != null && attr.HeaderAttribute == "FooBar"
                               && attr.Type = ParamType.open
            select whatever;
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