Specifying the ItemInstanceAttribute and overriding ItemInstance_ for…

… DatabaseObjects.Generic.DatabaseObjects* types is optional. Closes #40. ItemInstanceAttribute does not need to be specified if a DatabaseObjects.Generic.DatabaseObjects collection is utilised because the T argument is instead used. Furthermore, overriding ItemInstance_ for non-DatabaseObjects.Generic.DatabaseObjects*UsingAttributes classes is no longer necessary because the T argument is used to determine the ItemInstance type to create.
hisystems · Mar 28, 2012 · 3027a5a · 3027a5a
1 parent 8cc2ffe
commit 3027a5a
Show file tree

Hide file tree

Showing 4 changed files with 87 additions and 22 deletions.
diff --git a/Database/DatabaseObjectsItemInstance.vb b/Database/DatabaseObjectsItemInstance.vb
@@ -0,0 +1,66 @@
+
+' ___________________________________________________
+'
+'  © Hi-Integrity Systems 2012. All rights reserved.
+'  www.hisystems.com.au - Toby Wicks
+' ___________________________________________________
+'
+
+Option Strict On
+Option Explicit On 
+
+Imports System.Reflection
+
+Friend Module DatabaseObjectsItemInstance
+
+    ''' <summary>
+    ''' </summary>
+    ''' <param name="itemInstanceTypeToCreate">The type of DatabaseObjects.DatabaseObject to create.</param>
+    ''' <param name="databaseObjects">Parameter that is passed to the constructor of the DatabaseObject to create. If there is a default constructor then this argument is not used.</param>
+    Public Function CreateItemInstance(itemInstanceTypeToCreate As Type, databaseObjects As Global.DatabaseObjects.DatabaseObjects) As IDatabaseObject
+
+        Dim objObjectInstance As Object = Nothing
+
+        For Each objConstructor As ConstructorInfo In itemInstanceTypeToCreate.GetConstructors(BindingFlags.Instance Or BindingFlags.Public Or BindingFlags.NonPublic)
+            Dim objConstructorParameters As ParameterInfo() = objConstructor.GetParameters()
+            If objConstructorParameters.Length = 0 Then
+                objObjectInstance = objConstructor.Invoke(Nothing)
+                Exit For
+            ElseIf objConstructorParameters.Length = 1 AndAlso (objConstructorParameters(0).ParameterType.IsSubclassOf(GetType(DatabaseObjects)) OrElse objConstructorParameters(0).ParameterType.Equals(GetType(DatabaseObjects))) Then
+                objObjectInstance = objConstructor.Invoke({databaseObjects})
+                Exit For
+            End If
+        Next
+
+        If objObjectInstance Is Nothing Then
+            Throw New Exceptions.DatabaseObjectsException("An empty constructor or constructor with argument DatabaseObjects.DatabaseObjects (or subclass) could not be found for type '" & itemInstanceTypeToCreate.FullName & "'. This type has been specified by the ItemInstanceAttribute for the type '" & databaseObjects.GetType.FullName & "' or as the T argument.")
+        ElseIf Not TypeOf objObjectInstance Is IDatabaseObject Then
+            Throw New Exceptions.DatabaseObjectsException("'" & itemInstanceTypeToCreate.FullName & "' does not implement IDatabaseObject or inherit from DatabaseObject. Type was specified for use by the ItemInstanceAttribute on the type '" & databaseObjects.GetType.FullName & "'")
+        Else
+            Return DirectCast(objObjectInstance, IDatabaseObject)
+        End If
+
+    End Function
+
+    ''' <summary>
+    ''' Returns the first generic argument that is passed to the DatabaseObjects.Generic.DatabaseObjects class (or super class).
+    ''' This is used to determine the type of item that the collection represents and the type of class that should be returned from
+    ''' the IDatabaseObjects.ItemInstance function.
+    ''' </summary>
+    Public Function GetGenericCollectionTArgument(collectionType As Type) As Type
+
+        Dim currentCollectionType As Type = collectionType
+
+        While currentCollectionType IsNot Nothing AndAlso Not (currentCollectionType.IsGenericType AndAlso currentCollectionType.GetGenericArguments(0).IsSubclassOf(GetType(DatabaseObject)))
+            currentCollectionType = currentCollectionType.BaseType
+        End While
+
+        If currentCollectionType IsNot Nothing Then
+            Return currentCollectionType.GetGenericArguments(0)
+        Else
+            Throw New Exceptions.DatabaseObjectsException("The ItemInstance type could not be found for '" & collectionType.FullName & "' because it does not inherit from DatabaseObjects.Generic.DatabaseObjects")
+        End If
+
+    End Function
+
+End Module
diff --git a/Database/DatabaseObjectsUsingAttributesHelper.vb b/Database/DatabaseObjectsUsingAttributesHelper.vb
@@ -73,31 +73,20 @@ Friend Class DatabaseObjectsUsingAttributesHelper
 
     Public Function ItemInstance() As IDatabaseObject
 
-        If pobjItemInstance Is Nothing Then
-            Throw New Exceptions.DatabaseObjectsException("ItemInstanceAttribute has not been specified or the ItemInstance function was not overridden for type '" & pobjDatabaseObjects.GetType.FullName & "'")
-        End If
+        Dim itemInstanceType As Type
 
-        Dim objObjectInstance As Object = Nothing
-
-        For Each objConstructor As ConstructorInfo In pobjItemInstance.Type.GetConstructors(BindingFlags.Instance Or BindingFlags.Public Or BindingFlags.NonPublic)
-            Dim objConstructorParameters As ParameterInfo() = objConstructor.GetParameters()
-            If objConstructorParameters.Length = 0 Then
-                objObjectInstance = objConstructor.Invoke(Nothing)
-                Exit For
-            ElseIf objConstructorParameters.Length = 1 AndAlso (objConstructorParameters(0).ParameterType.IsSubclassOf(GetType(DatabaseObjects)) OrElse objConstructorParameters(0).ParameterType.Equals(GetType(DatabaseObjects))) Then
-                objObjectInstance = objConstructor.Invoke({pobjDatabaseObjects})
-                Exit For
-            End If
-        Next
-
-        If objObjectInstance Is Nothing Then
-            Throw New Exceptions.DatabaseObjectsException("An empty constructor or constructor with argument DatabaseObjects.DatabaseObjects (or subclass) could not be found for type '" & pobjItemInstance.Type.FullName & "'. This type has been specified by the ItemInstanceAttribute for the type '" & pobjDatabaseObjects.GetType.FullName & "'")
-        ElseIf Not TypeOf objObjectInstance Is IDatabaseObject Then
-            Throw New Exceptions.DatabaseObjectsException("'" & pobjItemInstance.Type.FullName & "' does not implement IDatabaseObject or inherit from DatabaseObject. Type was specified for use by the ItemInstanceAttribute on the type '" & pobjDatabaseObjects.GetType.FullName & "'")
+        If pobjItemInstance Is Nothing Then
+            Try
+                itemInstanceType = DatabaseObjectsItemInstance.GetGenericCollectionTArgument(pobjDatabaseObjects.GetType)
+            Catch ex As Exceptions.DatabaseObjectsException
+                Throw New Exceptions.DatabaseObjectsException("ItemInstanceAttribute has not been specified and " + ex.Message)
+            End Try
         Else
-            Return DirectCast(objObjectInstance, IDatabaseObject)
+            itemInstanceType = pobjItemInstance.Type
         End If
 
+        Return DatabaseObjectsItemInstance.CreateItemInstance(itemInstanceType, pobjDatabaseObjects)
+
     End Function
 
     Public ReadOnly Property DistinctFieldName() As String

diff --git a/DatabaseObjects.vbproj b/DatabaseObjects.vbproj
@@ -122,6 +122,7 @@
     <Compile Include="Contraints\NumberIsMaximumOrLesserConstraint.vb" />
     <Compile Include="Contraints\StringMaxLengthConstraint.vb" />
     <Compile Include="Database\ConnectionScope.vb" />
+    <Compile Include="Database\DatabaseObjectsItemInstance.vb" />
     <Compile Include="Database\RootContainer.vb" />
     <Compile Include="Database\DatabaseObjectsUsingAttributes.vb" />
     <Compile Include="Database\DatabaseObjectsUsingAttributesHelper.vb" />

diff --git a/Generic/DatabaseObjects.vb b/Generic/DatabaseObjects.vb
@@ -497,6 +497,9 @@ Namespace Generic
         ''' It is suffixed with an underscore so that it does not conflict with the underlying
         ''' non-generic equivalent ItemInstance function. It's purpose is indentical to the
         ''' non-generic version.
+        ''' If this function is not overriden an object of type T will be created. 
+        ''' The type T must have a default constructor or a constructor that accepts a type of 
+        ''' DatabaseObjects.Generic.DatabaseObjects or a subclass.
         ''' </summary>
         ''' 
         ''' <example> 
@@ -510,7 +513,13 @@ Namespace Generic
         ''' </example>    
         ''' --------------------------------------------------------------------------------
         ''' 
-        Protected MustOverride Function ItemInstance_() As T
+        Protected Overridable Function ItemInstance_() As T
+
+            Dim itemInstanceType As Type = DatabaseObjectsItemInstance.GetGenericCollectionTArgument(Me.GetType)
+
+            Return DirectCast(DatabaseObjectsItemInstance.CreateItemInstance(itemInstanceType, Me), T)
+
+        End Function
 
         ''' --------------------------------------------------------------------------------
         ''' <summary>