How can I set value for the property ?

Hi Jiarui,

Glad you like MetaEdit+! The generators are intended for read-only access to the models, so there aren't commands to set properties, add objects to a graph, etc. Instead you can use the API, which gives you full create, read, update and delete access to models and their representations. You can either have your API program running all the time with its own UI, from which you run the operations on MetaEdit+, or then invoke your API program with "external...execute" from a MetaEdit+ generator.

Since it sounds like you want to set a property value based on information already available elsewhere in the model, there may also be an alternative strategy. Since that property doesn't add any information that can't already be calculated from elsewhere, you may not need it: remember DRY. If it's something you want to be visible in the diagrams, then rather than storing a calculated value, you can simply calculate the value as needed when displaying. You can do this in a text element in a symbol, setting its source to a generator. Top-most on the generator stack is the object, and below that is the graph, so you can access not only the properties of this object, but also navigate in the graph - and with "do graphs", also to any other graph.

Hi sinnom,

You've unknowingly made an infinite recursion: your graph is trying to find its name, which is calling its id generator, which is executing "do graphs", which tries to sort the graphs by type then name, which asks the name of your graph...

You could change the sorting of do graphs to something explicit that doesn't ask its id, e.g. "do graphs orderby type". You might also want to avoid searching unnecessary graphs by restricting on type, "do graphs where type='MyGraphType' orderby type". [Edit: these don't help in 5.0, since "graphs" is already sorted, and only then are its results passed to "do...where...orderby"]

However, I think you ought to consider giving the graph a name. Think of it like a function: your top-level object is a call to a function, and the definition of the function is the graph. I'd say that the definition is primary. If the top-level objects should always have a subgraph, you can make their id generator show the name of that graph. If not, you can use property sharing to make the name of the subgraph be the same as the name of the top-level object. Or you can let the top-level object have an independent name: e.g. you could have a graph "Alarm", which is the subgraph of two top-level objects "Alarm1" and "Alarm2".

Edited by stevek - 31.May.2013 at 12:57

Perhaps you have something inside the loop body that's causing the infinite recursion, e.g. id? If the loop body is completely empty, do you still get the timeout message?

To create a shared property, open the pop-up menu in its field in the property dialog and choose Share Property. It will offer you a list of all instances of that property type, showing how many times each is already reused. For more detail you can go to www.metacase.com/support/50/manuals/ and search for Share Property - the first two hits should tell you everything you need to know.

Correction: adding "where" or "orderby" to "do graphs" in a graph type's identifier generator won't help avoid infinite recursion, since "graphs" is already sorted by id, and only then are its results passed to "do...where...orderby" for possible further filtering and sorting. You should also note that in the event of two elements comparing the same on all orderby clauses, the default MetaEdit+ sorting (type, id, oid) will be used as a tiebreaker, to guarantee consistent ordering in generator output.

We'll see if we can work some magic in a future version so that "graphs" notices it's being called by a "do...orderby", and avoids doing its own default sorting. But in any case, using "do graphs" in an identifier generator is never going to be best practice - MERL may be fast, but nothing can save you from an algorithmic complexity of O((n^2)*(log n)). An identifier should be based on something the object itself knows, not having to ask every other graph in the system.

Edited by stevek - 31.May.2013 at 17:50

Thank you very much for your answer. I have a question about the generator: the idea of the generator is to navigate and extract information from models, and I want to know that when navigating, wo often use foreach.() coupled with ~From~To etc, I want to navigate according to a rule, foe example, Depth-first traverse, so I need to have a flag which can control if the element is visited, if visited, the flag is true, else is false, now I cannot set vaule to the flag in the generator, and I want to know is there any other way todo so ? Yhank you very much!