验证表单中的字符串大小

Question

While setting up a doctrine entity to be used alongside a Symfony form, I want to validate that the given string size is not going to exceed the column size of the database. Notice I use the word size and not length.

Symfony ships with a number of validation constraints, in particular the Length Constraint. However, looking at it's documentation

The charset to be used when computing value's length. The grapheme_strlen PHP function is used if available. If not, the mb_strlen PHP function is used if available. If neither are available, the strlen PHP function is used.

It uses grapheme_strlen or mb_strlen which return the visual length of the string and NOT the actual size. When dealing with non ASCII strings, the actual size is a factor. For example most Asian languages use 3 bytes for each character.

The doctrine documentation states nothing about the @Column(length) annotation which leads me to believe it's a byte count. So, If I declare a column of length 64 and a constraint of max-size 64, there is going to be a problem.

Now, I could use a Callback Constraint or even create a custom constraint. But, is there a better way? How should strings received from form fields have their size validated before being persisted to the database?

Answer 1

Yes, the documentation does mention the order of function that will be chosen between.

However, that got me thinking and I went to see it for myself in a source code. There's no trace of such thing. I would tend to believe that they wanted to say that these functions will be used to determine the charset, however, no such thing exists in the source code either. I think it's some kind of typo, copy/paste error.

Here, take a look:

$stringValue = (string) $value;
if ('UTF8' === $charset = strtoupper($constraint->charset)) {
    $charset = 'UTF-8'; // iconv on Windows requires "UTF-8" instead of "UTF8"
}

$length = @iconv_strlen($stringValue, $charset);
$invalidCharset = false === $length;

In fact, they use iconv_strlen to determine the right length. I think it's safe to assume your validation will do just fine.

As for the @Column length parameter, that one is not intended for validation, but to schema creation/migration processes. As such, it should not be regarded as a safeguard for a validation processes.

Hope this helps a bit.