Sum Rule Type
Sum Rule Type
Sum rules are derivation rules that declare a parent attribute to be maintained as the sum of a designated child role's summed attribute, with an optional qualification to filter child objects. Parent reference names are derived from foreign key relationships.
For example, to derive the balance as the sum of the unpaid order totals:
Derive balance assum(purchaseorderList.amount_total where paid=false)
The qualification is in SQL Where syntax.
Use sum rules instead of events. The impact on performance is small. Adjustment is by way of one-row updates instead of expensive aggregate SQLs, like
Layer7 Live API Creatorupdates the value of the attribute to reflect the sum of the specified attribute in the child objects whenever necessary. This includes adding and removing child objects from the parent object, as well as modifications to the children objects that change their qualification in the sum or the summed value. Sum processing is triggered by changes to the child. For example, when you add a new (qualifying) child to the parent,
Layer7 Live API Creatorincrements the sum attribute by the child's amount.
You can view the changes in the log.
Best Practice:To maintain high performance,
Layer7 Live API Creatorassumes that sum values are correct on disk. For proper operation, if you define new sums on existing data, initialize them using SQL tools.
For more information about how to synchronize data with logic using a SQL tool, see Database Connectivity.
For more information:
Create a Sum Rule
Prerequisite:Your API is connected to an active database that contains at least one entity or view.
Follow these steps:
- In API Creator, in the Create section, clickRules.If your API does not have existing rules, the Welcome to Rules page appears. If your API has existing rules, they are listed on the By entity tab by default.
- ClickCreate a Rule.
- Select theSumrule type, the entity to which it applies, and then clickCreate Rule.
- Use logical operators such as && for "and", || for "or".
- Specify equals as "=" or "==".
- Specify not equals as !=.
- Use the attrName, not row.<attrName>.
- ClickActivate and Closeto return to the list of rules.
The sum rule is created.