There are several methods to build such a model. I have build a model wherein the items have three labels to set different attributes to them. The random Order Picklist chooses randomly 3 values to compare these values with the labels on the item in a rack. If there isn't an item to send to the next object, then another combination is compared a few seconds later.
The names of the labels are "Label_A", "Label_B" and "Label_C". Each label gets a random value from a different range Label_A: 1..3, Label_B: 4..6 and Label_C: 7..9. I store the items in the rack and set the Sendto-function in the rack to "Do Not Release Items". I have to release them on my own by a source code script.
In the Basic Fixed Resource I manage the random Pick Order by sending messages. On reset I send a message to the Basic FR to the object itself. Because the message parameter 1 is set to "0", I begin to choose the numbers randomly fitting to the 3 ranges defined above. Then I send a message to the Basic FR itself again now containing these numbers. The receiving message contains a value greater than "0" for the first parameter. Another part of the source code evaluates in the OnMessageTriggers the parameters of the message. The source code tests all stored items in the rack if their 3 label's values match with the 3 message parameter's values. If there is an item in the rack that has got the right combination the source code releases this matching item over the output port 1. If there isn't an item stored in the rack, then a delayed message is sent again with the first parameter set to "0". And the OnMessage code starts over again to choose another combination of the three labels. This happens, too, when an item is released.
