1. Why do you need this attribute for properties that have Multiplicity One?
2. Please specify your ORM (e.g.: NHibernate), your template and its non-default settings. Send us
a test model for reproducing the issue.
You can add this attribute via Attributes menu of Entity Developer:
a) navigate to Model > Settings > Attributes > select the assembly with the needed attributes and make sure that the needed attributes (DataMember, etc) are checked in the window below, press OK
b) select the needed attribute in the Attributes collection of a particular class property
Or modify a predefined template: right click on it in Model Explorer > Copy to Model Folder. After this, you can edit it with an embedded T4-Editor.