Rule Summary

This table briefly summarizes the rules.

Defining Rules

Rules are declared with function calls - see logic#declare_logic(), which looks like this:

Rule.constraint(validate=Customer,
                as_condition=lambda row: row.Balance <= row.CreditLimit,
                error_msg="balance ({row.Balance}) exceeds credit ({row.CreditLimit})")
Rule.sum(derive=Customer.Balance, as_sum_of=Order.AmountTotal,
         where=lambda row: row.ShippedDate is None)

Rule.sum(derive=Order.AmountTotal, as_sum_of=OrderDetail.Amount)

Rule.formula(derive=OrderDetail.Amount, as_expression=lambda row: row.UnitPrice * row.Quantity)
Rule.copy(derive=OrderDetail.UnitPrice, from_parent=Product.UnitPrice)

Rule.formula(derive=OrderDetail.ShippedDate, as_expression=lambda row: row.OrderHeader.ShippedDate)

Activating Rules

To activate the rules (declare_logic is the function shown above):

LogicBank.activate(session=session, activator=`declare_logic`)

Rules Summary

The table shows excerpts only; see the nw sample for full syntax.

Rule	Summary	Example	Notes
Constraint	Boolean function must be True else transaction rolled back	row.Balance <= row.CreditLimit row.Salary >= Decimal('1.20') * old_row.Salary	Multi-field old_row
Formula	Function computes column value	row.UnitPrice * row.Quantity row.OrderHeader.ShippedDate	lambda, or function Parent (OrderHeader) references
Sum	Derive parent-attribute as sum of designated child attribute; optional child qualification	Rule.sum(derive=Customer.Balance, as_sum_of=Order.AmountTotal,where=lambda row: row.ShippedDate is None)	Parent attribute can be hybrid (virtual) scalable: pruning, adjustment
Count	Derive parent-attribute as count of child rows; optional child qualification	Rule.sum(derive=Customer.Balance, as_sum_of=Order.AmountTotal,where=lambda row: row.ShippedDate is None)	Parent attribute can be hybrid (virtual) scalable: pruning, adjustment
Copy	Child value set from Parent	OrderDetail.ProductPrice = copy(Product.Price)	Unlike formula references, parent changes are not propagated e.g, Order totals for Monday are not affected by a Tuesday price increase
Event	Python Function	on insert, call congratulate_sales_rep	See Extensibility for a information on early, row and commit events
Parent Check	Ensure Parent row exists	Orders must have a Customer	See Referential Integrity
Allocation	Allocate a provider amount to recipients	allocate a payment to outstanding orders	See Allocation for an example
Copy Row	Create child row by copying parent	audit Employee Salary changes to EmployeeAudit	See Rule Extensibility

Rule Patterns

Pattern	Notes	Example
Chain Up	parent sums and counts mean that child row changes can adjust parents	Derive Balance
Chain Down	child copy and parent references mean that parent row changes can cascade to children	Ship Order
Constrain a Derived Result	constraints may require derived values	Balance < creditLimit
Auditing	Note the Copy Row rule	Salary Audit
old_row	useful for state transition logic	Meaningful Raise