How to set up an on-the-fly item

If you set the OnFly local configuration directive to the name of a Sub or UserTag, then Interchange will be able to add items to the cart that are not in the DefaultTables table(s).

Interchange supplies an internal "onfly" subroutine, which will work according to the examples given below.

If you have the following your local (catalog.cfg) configuration: 

then a basic link can be generated like this:

The mv_order_fly form parameter value can contain any number of fields, separated by a pipe (|) character, which will set corresponding parameters in the item attributes.  The field(s) are expected to contain name=value pairs, and will be URI encoded by the [area] tag, in the example above.  You can use this to set parameters such as the size and colour of your on-the-fly item.

The special mv_price attribute can be used in conjunction with the "$" CommonAdjust atom to set the price for checkout and display.

The [item-description] sub-tag, when used with an [item-list] tag, will use the item's description" attribute to display the product description in the cart.  Note that [item-field description] and [item-data products description] will NOT work, as both of these sub-tags reference an actual column value for a row in the "products" table, and this is obviously not appropriate for on-the-fly items.  Similarly, an attempt to generate a flypage for an on-the-fly item ([area 000101], for example) will fail, resulting in the display of the "missing" SpecialPage.

If you want to set up a UserTag to process on-the-fly items, it should accept a call like this:

The "mv_item_code" and "mv_order_fly" parameters are required to trigger Interchange's add_item routine, along with mv_todo=refresh to set the action.

The item will always act as if SeparateItems, or mv_separate_items, is set.

Multiple items can be ordered at once by stacking the variables.  If there is only one mv_order_item instance, however, you can stack the "mv_order_fly" variable so that all are concatenated together as using "|" symbols.  The above example could be done as:

Multiple items would need multiple instances of mv_order_item, with a corresponding "mv_order_fly" for each mv_order_item.  You can order both "000101" and "000101" as follows:

The following two forms correspond to the above two examples, in order, with the slight refinement of adding a quantity: