Laravel Validator如何验证数组长度与另一字段值匹配？

The issue here is that when you use size:numItems, Laravel treats "numItems" as a literal string instead of referencing the actual value of the numItems field in your request. It’s trying to check if the items array has exactly 7 elements (the length of the string "numItems") instead of matching the integer value from numItems.

Here are two straightforward ways to fix this validation:

Solution 1: Use the Rule facade with dynamic size #

Leverage Laravel’s Rule facade to pass the real value of numItems to the size rule. Add the bail rule to numItems to stop validation early if numItems is invalid (like a non-integer), preventing issues with non-numeric values:

use Illuminate\Validation\Rule;

public function yourValidationMethod(Request $request)
{
    $validated = $request->validate([
        'numItems' => 'required|int|max:10|bail',
        'items' => [
            'required',
            'array',
            Rule::size($request->numItems),
        ],
    ]);

    // Process your validated data here
}

Solution 2: Custom validation closure #

For full control over the error message or extra logic, use a custom validation closure. This lets you directly compare the count of items to the numItems value:

public function yourValidationMethod(Request $request)
{
    $validated = $request->validate([
        'numItems' => 'required|int|max:10',
        'items' => [
            'required',
            'array',
            function ($attribute, $value, $fail) use ($request) {
                $expectedCount = (int)$request->numItems;
                if (count($value) !== $expectedCount) {
                    $fail("The {$attribute} must contain exactly {$expectedCount} items.");
                }
            },
        ],
    ]);

    // Process your validated data here
}

A quick note on your JSON structure: The example you provided has an invalid array format for items (JSON arrays can’t include key-value pairs like "1": {...}). You likely want either an array of objects:

{ 
  "numItems": 3, 
  "items": [ 
    {"A": "Foo", "B":"bar"}, 
    {"A": "Foo", "B":"bar"}, 
    {"A": "Foo", "B":"bar"} 
  ] 
}

Or an object with numeric keys:

{ 
  "numItems": 3, 
  "items": { 
    "1": {"A": "Foo", "B":"bar"}, 
    "2": {"A": "Foo", "B":"bar"}, 
    "3": {"A": "Foo", "B":"bar"} 
  } 
}

Either structure will work correctly with the validation logic above.

内容的提问来源于stack exchange，提问作者MikeVelazco