Logical Operators (and, or, not)

BGL has three logical operators for combining conditions: and, or, and not. They behave the way they read in English.

when
  order.subtotal > 100.0
  and order.shipping_address.country is "US"
then
  ...
end

Both conditions must be true for the rule to fire.

The three operators

order_line.gift_wrap and order_line.custom.is_restricted
order.status is "pending" or order.status is "processing"
not order_line.custom.is_backorder

Precedence: which goes first

When you mix operators, BGL evaluates them in this order:

1. not (highest — applies to whatever’s right next to it)
2. and
3. or (lowest)

So A or B and C means A or (B and C), not (A or B) and C.

When in doubt, use parentheses. They cost nothing and make intent obvious.

# Without parentheses — relies on precedence
when
  order.custom.is_gift or order.subtotal > 100 and order.shipping_address.country is "US"
then
  ...
end

# Same condition, parentheses make it unambiguous
when
  order.custom.is_gift or (order.subtotal > 100 and order.shipping_address.country is "US")
then
  ...
end

Real-world combinations

At least one of two countries:

when
  order.shipping_address.country is "US"
  or order.shipping_address.country is "CA"
then
  ...
end

All three must be true:

when
  order.subtotal > 500.0
  and order.shipping_address.country is "US"
  and not order.custom.is_gift
then
  ...
end

Two groups, either group qualifies:

when
  (order.subtotal > 1000.0 and order.custom.priority is "high")
  or order.custom.customer_tier is "vip"
then
  ...
end

When to split into multiple when blocks

You don’t have to cram everything into one condition. Often it reads better to split:

# One block, complex condition
when
  (order.subtotal > 500.0 or order.custom.is_priority)
  and order.shipping_address.country is "US"
then
  set order.custom.tag to "premium-us"
  set order.custom.region to "us-premium"
end

# Two blocks, simpler each
when
  order.subtotal > 500.0 or order.custom.is_priority
then
  set order.custom.tag to "premium"
end

when
  order.custom.tag is "premium" and order.shipping_address.country is "US"
then
  set order.custom.region to "us-premium"
end

The two-block version uses the fact that the first when can set up state that the second checks. (See Variables for an alternative using $variables instead of model fields.)

Tips

• Indent each and/or on its own line. Long conditions become unreadable on one line. Put the operator at the start of the line so the structure is obvious at a glance.
• and chains can be reordered for performance. BGL stops evaluating an and as soon as one side is false. Cheaper checks first means faster rules.
• not is usually clearer than the negative form of an operator. not order_line.gift_wrap reads better than checking order_line.gift_wrap = false.