question

In the attached model, the racks are placed on a fixed resource list. One of the expression fields on an FR list is "distance". This is the distance from the item on the list to the object that is doing the pulling. After acquiring the forklift we identify it as the puller (by default it would be the token):

This only solves one problem. You don't know if the closest rack has capacity. So an expression field called "Capacity" was added to the Racks list. This field reflects the max capacity (which is set to 100) minus the current contents to give current capacity. It is marked as a dynamic field because it needs to be evaluated and updated every time a pull is made on the list.

The SQL query for the list pull is :

WHERE Capacity > 0 ORDER BY distance ASC, Capacity DESC

So we want to select a rack that has capacity greater than zero, and we want to order the racks based on the distance field ascending and the Capacity field descending. We also want to leave the racks on the list (not pull them off) so the "Leave Entries On List" box is checked.

As a "party trick" move the racks as the model is running. The rack selected will still follow the "rules".

Select rack based on proximity and contents.fsm

N.B: the following code will also work in the "Capacity" expression field:

int maxcontents = getvarnum(value,"maxcontent"); //getvarnum function to get max contents setting

int contents = value.subnodes.length; //value.subnodes.length to get current contents

This eliminates the need to cast the variant value as an object.