Add a shape to the editor

If you have associated a shape with a field in the view definition, the shape will be automatically added when you update the corresponding field, such as adding a model or adding an association.
If you have associated a shape with a class in the view definition, the shape will not be automatically added even if you update the model. To add such a shape, you can add it using the AddNodeShape method of the IDiagram object.

public void AddNodeShape(ICommandContext c, ICommandParams p) 
{ 
//Get the currently displayed diagram 
IDiagram diagram = c.App.Workspace.CurrentEditor as IDiagram; 
if (diagram == null) 
{ 
//If no diagram is displayed, terminate the process 
c.App.Output.WriteLine("sample", "Diagram not displayed."); 
return; 
} 

//Add a model of the "Class" metaclass to the "OwnedElements" field of the diagram's parent model so that it becomes a sibling element of the diagram 
IModel package = diagram.Model.Owner; 
IModel newModel = package.AddNewModel("OwnedElements", "Class"); 

//Add a shape corresponding to the added model. 
if (!diagram.CanAddNodeShape(newModel)) 
{ 
//If unable to add, terminate processing 
c.App.Output.WriteLine("sample", $"Cannot add shape corresponding to model:{newModel.Name} to diagram:{diagram.Model.Name}."); 
return; 
} 
diagram.AddNodeShape(newModel); 
} 

See How to delete shapes here for more information.