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IHydratable - An Interesting Side-Effect

In 4.6.0 a new IHydratable interface was added to the core.

This interface could be used to delegate Hydration of a Business Object from the CBO class to the object itself.  I have discussed this in an earlier blog.  If the interface is implemented in an Info class, you need to implement the Fill method to hydrate the objects properties from the passed in DataReader.  For example, lets implement this for the Announcements module.:

        Public Sub Fill(ByVal dr As IDataReader) Implements IHydratable.Fill

            ItemId = Convert.ToInt32(Null.SetNull(dr.Item("ItemID"), ItemId))
            ModuleId = Convert.ToInt32(Null.SetNull(dr.Item("ModuleID"), ModuleId))
            Title = Convert.ToString(Null.SetNull(dr.Item("Title"), Title))
            Url = Convert.ToString(Null.SetNull(dr.Item("Url"), Url))
            ViewOrder = Convert.ToInt32(Null.SetNull(dr.Item("ViewOrder"), ViewOrder))
            Description = Convert.ToString(Null.SetNull(dr.Item("Description"), Description))
            ImageSource = Convert.ToString(Null.SetNull(dr.Item("ImageSource"), ImageSource))
            CreatedByUser = Convert.ToInt32(Null.SetNull(dr.Item("CreatedByUser"), CreatedByUser))
            CreatedDate = Convert.ToDateTime(Null.SetNull(dr.Item("CreatedDate"), CreatedDate))
            TrackClicks = Convert.ToBoolean(Null.SetNull(dr.Item("TrackClicks"), TrackClicks))
            NewWindow = Convert.ToBoolean(Null.SetNull(dr.Item("NewWindow"), NewWindow))
            PublishDate = Convert.ToDateTime(Null.SetNull(dr.Item("PublishDate"), PublishDate))
            ExpireDate = Convert.ToDateTime(Null.SetNull(dr.Item("ExpireDate"), ExpireDate))

        End Sub

So far so good, but the title of this blog refers to an interesting side-effect.  The side-effect is this: 

Using IHydratable allows the module developer to use "ReadOnly" properties and still use CBO.

Traditionally, CBO does not support the use of ReadOnly properties as the CreateObject method needs to set the property (from the value in the DataReader).  Quite often, for business reason we don't want to be allow the property to be set, BUT we still want to load the value from the Data Store.  This can now be accomplished by implementing IHydratable, as the Fill method can be used to set the underlying private member.

Lets look as an example.  The CreatedByUser and CreatedDate could be changed to ReadOnly properties, and the Fill method above would be rewritten as:

        Public Sub Fill(ByVal dr As IDataReader) Implements IHydratable.Fill

            _CreatedByUser = Convert.ToInt32(Null.SetNull(dr.Item("CreatedByUser"), _CreatedByUser))
            _CreatedDate = Convert.ToDateTime(Null.SetNull(dr.Item("CreatedDate"), _CreatedDate))
        End Sub

This would allow us to remove the setter in the properties. - other changes would be needed in code in order to set the CreatedByUser/CreatedDate for new announcments - but this ability provides more flexibility for Module Developers (and core developers) to provide better APIs.


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