langiumLangiumDocuments.getOrCreateDocument return all properties except one properties

[zrwsmd]

my requirement ast root node is Ld like below second screenshot,when i call langiumLangiumDocuments.getOrCreateDocument(URI.parse(rootUri)) method,it return all properties(coils,ldnodes,locks) like below first screenshot except 'diagram',i want to know why(note:currently ,the corresponding file is an empty file)

[msujew]

@zrwsmd Does your grammar always expect an element of VirtualDiagram to be parsed? Since you're parsing an empty file, so Langium isn't able to actually create VirtualDiagram node from the input. Arrays are always available, as Langium can easily generate a default value for them.

Langium gives no guarantee that the AST is valid in the presence of parser errors.

[zrwsmd]

there is no parse error
i guess it because document is empty, the array properties in value are initialized with empty arrays [], but the object properties, such as diagram remain undefined,but how could it not be undefined?my requirement is when i drag a node and save it ,corresponding file have text content,but when i create a node like below screenshot,at moment this.state.diagramRoot is still undefined,how could i assign it

[msujew]

In the second screenshot you've posted, the parse result clearly contains a parser error.

As for the requirement you're talking about: You could always create a synthetic diagramRoot element and put it into the state object. But I don't really see why this is necessary in the first place. If this is effectively modelling a graph wouldn't the added new node immediately become the root node in the case of an empty file? Why the need for a separate root node?

[zrwsmd]

very thanks ,my eyes are blurred and I did not see it,i always thought there is no error