Plug-ins - differences between Target and Image Entity

In a plug-in there are potentially several ways to access entity data relevant to the plug-in action. For example, on the create message you can access the data on the new entity instance in one of the following ways:

1. Via the Target InputParameter
2. Via an Image Entity registered on the step
3. Via a Retrieve request in the plug-in code

These do not always work in the same way, as follows:

Availability of the data by stage

The general rules are:

1. InputParameter is available in all stages. It can be modified in the pre-stage, but changing it in the post-stage will have no effect
2. A PostImage Entity is available in the post-stage, and a PreImage Entity in the pre-stage only
3. If using a Retrieve in the plug-in, then the data returned depends on the stage. In the pre-stage, you will see the data before the modification, whereas in the post-stage you see the data after the modification
4. Some Image Entities are not relevant for some messages - e.g. there is no PreImage for a Create message, and no PostImage for a Delete message

Data in the Name attribute

If the message is updating CRM (e.g. a Create or Update message) then the InputParameter only contains the minimum information that needs to be saved to CRM. A consequence of this is that the name attribute of any of the following data types is null:

• Lookup
• Owner
• Customer
• Picklist
• Boolean

So, if your code needs to access the name, then you cannot rely on the InputParameter, and have to use either the Image Entity or a Retrieve to get the data.

My preference is to use an Image Entity, mostly as this reduces the code I have to write. The CRM SDK also suggests that this is more efficient, though I've not done any thorough performance testing on this to determine if this is relevant.