Understanding validation errors

When validation fails, there are two layers of information:

1. the thrown exception
2. the validator's ErrorList

The exception tells us that validation failed. The ErrorList tells us which fields failed and what message to show.

The thrown exception

Validator::validate() throws a ValidationException when one or more fields are invalid.

The message is intentionally broad:

• There is 1 invalid field
• There are 2 invalid fields

That message is useful for logging or for a general summary, but not for field-by-field display.

The ErrorList

The detailed information is available through:

$validator->getLastErrorList()

The returned object is iterable and countable.

catch(ValidationException) {
	$errorList = $validator->getLastErrorList();

	foreach($errorList as $name => $message) {
		// ...
	}
}

Keys and values of getLastErrorList()

During iteration:

• the key is the field name
• the value is the message to show for that field

Example:

foreach($validator->getLastErrorList() as $name => $message) {
	echo "$name => $message\n";
}

Possible output:

password => This field is required; This field's value must contain at least 12 characters

Multiple problems on one field

One field may fail more than one rule.

For example:

<input name="password" minlength="12" required />

If the submitted value is empty, both rules fail:

• required
• minlength

The ErrorList combines those messages into one string using ; as a separator.

That means the library gives us one display message per field, even if several rules contributed to it.

Specific exception classes

Internally, the library also tracks more specific exception classes such as:

• ValueMissingException
• PatternMismatchException
• TypeMismatchException
• RangeUnderflowException
• RangeOverflowException
• StepMismatchException
• BadInputException

If every invalid field belongs to the same category, the validator throws that specific exception class.

If the invalid fields belong to mixed categories, it throws the broader ValidityStateException.

For most applications, the field-level messages are the part we act on most often. The exception type becomes useful when a higher-level handler needs to distinguish one family of validation problems from another.

Counting invalid fields

The ErrorList count is the number of invalid fields, not the number of individual failed rules.

So if one field fails both required and minlength, it still counts as one invalid field.

A practical pattern

Use the exception to branch the control flow, and use the error list to render the response:

try {
	$validator->validate($form, $input);
}
catch(ValidationException) {
	foreach($validator->getLastErrorList() as $name => $message) {
		// Render field-level errors.
	}

	return;
}

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Now that the error data shape is clear, continue with Displaying error messages or move on to Extending custom rules.