Order of Operations and Best Practices

What You'll Learn

This guide explains critical technical aspects of conditional rules, including field ordering requirements, rule processing sequence, and best practices for implementation. You'll discover how to avoid common pitfalls and create reliable, effective rule systems.

Order of Operations

The order in which fields appear in your table has a significant impact on how conditional rules function. This is one of the most important concepts to understand when working with conditional rules.

Field Ordering Requirements

Any field referenced in a conditional rule must be listed above (or prior to) the field that contains the rule in your table's field list. This ordering is crucial for consistent results.

For example, if a "Task Status" field has conditional rules that reference "Assigned Contact" and "Due Date" fields, both "Assigned Contact" and "Due Date" must appear above (or prior to) "Task Status" in the field list.

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Tip: You can rearrange fields in the Fields tab of the DataTable by dragging and dropping

Dependencies and Calculations

This ordering rule extends to equation fields and other calculated fields:

• If an equation field depends on fields with conditional rules, the equation field must be listed after those fields
• If a field with conditional rules depends on an equation field, the conditional rule field must be listed after the equation field

In general, Knack processes fields in the order they're listed in the table, so the proper sequence is:

1. Basic fields referenced by other fields
2. Equation fields that reference basic fields
3. Fields with conditional rules that reference the above fields
4. Equation fields that reference fields with conditional rules

Rule Processing Sequence

Understanding how rules are processed is essential for creating effective conditional rules:

1. Rules are evaluated in order from top to bottom
2. The first rule that matches its conditions is applied
3. Once a match is found, no further rules are checked
4. If no rules match, the field value remains unchanged

Setting Default Values

Because of this processing sequence, default rules (rules that should apply when no other conditions are met) should always be placed at the bottom of your rule list.

For example, if you want:

• Task Status = "Overdue" if past due date
• Task Status = "In Progress" if assigned but not past due
• Task Status = "Not Started" in all other cases

The rules should be ordered exactly as listed above, with the "Not Started" default rule at the bottom.

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Place the most generic conditional rule at the bottom

Limitations and Considerations

Form Interaction

Once a field has conditional rules:

• It cannot be included in forms for editing
• It cannot be edited inline in tables
• Its values will be determined exclusively by the rules, regardless of form submissions

However, you can include the field in form record actions, where the value will still be determined by the conditional rule.

Multiple Criteria

When setting up the "When" conditions:

• You can add multiple criteria to a single rule
• For a rule to match, all criteria must be true (treated as AND conditions)
• If you need OR logic, create separate rules for each condition

Rule Persistence

Values set by conditional rules do not automatically update when the conditions that set them change:

• If Condition A sets Field X to "Yes"
• And later Condition A is no longer true
• Field X will still be "Yes" until a different rule applies

To handle this, create opposite rules to update values when conditions change. For example:

• Rule 1: When Due Date is in the past, set Status to "Overdue"
• Rule 2: When Due Date is not in the past, set Status to "Current"

Best Practices

1. Plan your field order carefully before implementing conditional rules
2. Document your rule logic to make maintenance easier
3. Place specific rules before general rules to ensure proper execution
4. Use default rules at the bottom of your rule list
5. Test thoroughly with various data scenarios
6. Consider rule chain reactions when fields with conditional rules affect other fields
7. Create comprehensive rule sets that handle all possible conditions
8. Review performance impact for tables with many records and complex rule sets

Remember: Once you add conditional rules to a field, that field's values are controlled exclusively by those rules. Plan accordingly and ensure your rules handle all possible scenarios.