Designing Domain Exceptions for PHP Services

Designing Domain Exceptions for PHP Services shows how to apply a focused PHP technique using understandable, runnable examples and clearly defined constraints.

What Problem Does This Solve?

Model domain invariants in constructors and methods; separate expected validation failures from infrastructure errors and avoid hiding exceptions.

Core Concepts

• Identify the data entering the operation and the expected output.
• Model domain invariants in constructors and methods; separate expected validation failures from infrastructure errors and avoid hiding exceptions.
• Handle expected failures and test boundary conditions rather than assuming success.

Example 1: A Small Working Example

Start with a small input so the behavior is easy to follow.

<?php

class DomainExceptionBase extends RuntimeException {}
class InvalidOrderState extends DomainExceptionBase {}
try { throw new InvalidOrderState("Order was already shipped"); } catch (InvalidOrderState $exception) { echo $exception->getMessage(); }

The example isolates the important operation and its expected input. Adapt the values, error handling and boundaries for your application rather than assuming all input is trusted.

Example 2: A Different Case

The second example changes the task or data while using the same general technique.

<?php

function validateQuantity(int $quantity): void { if ($quantity <= 0) { throw new DomainException("Quantity must be positive"); } }
try { validateQuantity(0); } catch (DomainException $exception) { echo $exception->getMessage(); }

The example isolates the important operation and its expected input. Adapt the values, error handling and boundaries for your application rather than assuming all input is trusted.

Practical Example

This practical example is a complete standalone PHP snippet to adapt to a real application.

<?php

function validateQuantity(int $quantity): void { if ($quantity <= 0) { throw new DomainException("Quantity must be positive"); } }
try { validateQuantity(0); } catch (DomainException $exception) { echo $exception->getMessage(); }
// Inspect the next distinct state after the operation.
echo "\nSecond scenario complete";

The example isolates the important operation and its expected input. Adapt the values, error handling and boundaries for your application rather than assuming all input is trusted.

Important Behavior and Edge Cases

• Validate XML size and disable untrusted external resource loading. XMLReader is forward-only; DOM materializes a tree and can consume much more memory.
• Model domain invariants in constructors and methods; separate expected validation failures from infrastructure errors and avoid hiding exceptions.
• Test a malformed input, a missing dependency and a boundary value when those cases apply.

Comparison With Related Approaches

Common Beginner Mistakes

Key Takeaways

• Model domain invariants in constructors and methods; separate expected validation failures from infrastructure errors and avoid hiding exceptions.
• Immutable value objects protect validated state; mutable arrays are more flexible but cannot enforce invariants automatically.
• Write tests around the inputs and failure cases most likely in your application.

Use these examples as a starting point and adapt the validations and boundaries to the specific application.