While creating an entity object with the Entity Object Wizard or editing an entity object with the Entity Object Editor, you can add an attribute in the Attributes page:
In the Attributes page, click New from Table.
In the Create New Entity Attributes from Columns dialog, the Available list contains the columns of the database object that have not yet been mapped to attributes in the entity object; columns that have already been mapped will not be shown in this list.
To create one or more attributes:
Select an attribute from the Available list and click > to add it to the Selected list.
To select multiple attributes, control-click to select more than one column, or shift-click to select a contiguous group of cells, and then click >.
To move all of the items in the list, click the double right-arrow (>>).
The Selected list contains the list of columns that will be added to the entity object when you select OK. To remove an item from the list, select one or more attributes, and then click the left-arrow; to remove all attributes, click >>.
Click OK.
The new attribute appears in the Entity Attributes list. The attributes added to the entity object will have properties that correspond to the properties of the underlying database column.