Validators

A validator is an optional extra format check you attach to a Text field at definition time, so a value in the wrong shape is refused the moment somebody tries to save it instead of quietly becoming bad data that surfaces months later. You pick one of 13 built-in checks from a dropdown, and seven of them need no further setting.

Why there is no pattern box

There is deliberately no free-text or regular-expression entry anywhere in the product. A pattern written by hand can be made to consume enormous amounts of processing time on a short input, which turns a data-entry form into a way of taking the system down. The set of checks is therefore fixed and curated instead, and each one carries its own short length cap and its own time limit.

How a validator runs

Four things happen in this order every time a value is saved into the field.

1. If the value is empty or nothing but spaces, it is treated as empty and no validator runs at all.
2. The global 4,000-character Text cap runs, and refuses with VALIDATION_MAX_LENGTH if the value is longer.
3. The validator's own, much shorter length cap runs — 11 characters for a SWIFT code, 15 for an IMEI, and so on — and also refuses with VALIDATION_MAX_LENGTH.
4. Only then does the validator's actual check run, refusing with its own code and message.

The check is enforced at two separate points, and it is worth knowing both exist. At definition time, an invalid validator or setting combination is refused when you save the definition. At value time, the validator runs again against every value somebody saves into the field.

The seven checks with no setting

These validate a specific external format and never take a parameter — supplying one is itself refused. Three of them verify a real check digit, which means a single mistyped digit is caught rather than only a wrong length.

IBAN

For an international bank account number. Use it wherever a wrong digit would send money to the wrong place.

The shape is checked first, then the real ISO check digits are verified. Capped at 34 characters — no live IBAN is longer. The value is matched exactly as submitted: it is not uppercased and spaces are not stripped for you.

IMEI

For a mobile device's identity number, as printed on the device or its box.

Exactly 15 digits, then the real check digit is verified. Capped at 15 characters. The 16- and 17-character display variants some devices show are not accepted.

SWIFT / BIC Code

For a bank identifier code, used alongside an account number for an international transfer.

Eight or eleven characters: six letters, then two letters or digits, then optionally three more letters or digits. Upper case only, no separators, capped at 11 characters. There is no check digit in the standard, so a well-formed code that belongs to no real bank is accepted.

Vehicle Plate Number

For a vehicle registration plate, where you want to catch obvious nonsense without committing to any one country's format.

2 to 15 characters, made up of letters, digits, spaces and hyphens in any combination. Case-insensitive. Deliberately permissive — there is no country-specific plate format anywhere in this check, because plate formats differ by country and by vehicle class within a country.

Egyptian National ID

For an Egyptian national identity number.

Fourteen digits: a century marker of 2 or 3, then a date of birth as YYMMDD that has to be calendar-plausible, then seven more digits. Structure only — Egypt has never published a check-digit algorithm, so the last digit is not verified. Shipping a guessed algorithm would reject real, valid IDs, which is worse than not checking.

Saudi National ID

For a Saudi national identity number or an Iqama (residency) number.

Ten digits, the first being 1 for a citizen or 2 for a resident, and the real check digit is verified. Capped at 10 characters.

Emirati ID (UAE)

For an Emirates ID number.

The 784-YYYY-XXXXXXX-C form, with the hyphens optional. Capped at 18 characters. Structure only — the UAE has never published a check-digit algorithm, so the final digit is not verified, for the same reason as the Egyptian check.

The six checks that need a setting

These require a Validator Parameter, and leaving it blank is refused at definition time — as is supplying one for a validator that takes none. The Validator Parameter control appears as soon as you pick one of these six.

Postal Code

For a postal code in a specific country. The country is part of the definition, not something the person filling in the record chooses.

The value is matched against the real postal-code format of the country you configured. Capped at 16 characters. Seven countries are supported and the dropdown never offers any others.

Numeric Range

For a number inside bounds you set, on a field that is Text rather than Number — a shirt number, a squad size, a jersey count.

The value must parse as a number and fall inside the range. The setting is two comma-separated bounds; leaving one side blank makes that end open, but leaving both blank is refused, because a range that accepts everything is the same as attaching no validator at all.

Length Range

For text that has to be a certain length — a two-letter code, a reference of at least eight characters.

The number of characters must fall inside the range. The setting is two comma-separated character counts, and either side may be left blank for an open end. This check produces two distinct codes rather than one, so you can tell too short from too long.

One of a List

For a closed set of answers on a Text field. If the closed set is the whole point of the field, a Select field is usually the better choice — but this exists for the case where you want a validator's behaviour on a Text field.

The value must exactly match one line of the list you configured, one value per line. Matching is case-sensitive.

Contains Text

For a value that must include a marker somewhere in it — a club prefix, a season tag, a department code.

The value must contain the literal text you configured, matched case-sensitively.

Starts With Text

For a value that must begin with a prefix — a country code, a branch code, a fixed reference stem.

The value must begin with the literal text you configured, matched case-sensitively.

The seven Postal Code countries

Postal Code ships real, cited formats for exactly seven countries, and the setting is a dropdown rather than free text, so no other country can be chosen from the form.

Rejections when attaching a validator

These all happen at definition time, before any value is ever saved. Several are only reachable from a request that bypasses the form, because the form does not offer the invalid combination in the first place.

Validator error codes

Every validator rejection is an HTTP 422, never a 500. If a validator failure ever produces a 500, that is a defect worth reporting — each one is written to refuse cleanly.

What validators do not do

• They only ever attach to a Text field. There is no way to put a format check on any of the other twenty-one types.
• They never re-check values that were already saved. Attaching a validator to a field that holds answers leaves those answers exactly as they are, including ones that would now fail, until somebody re-enters and saves them.
• They never run on an empty value. On a field that is not Required, a value of nothing but spaces is stored as cleared with no validator error at all — mark the field Required if a blank answer should be refused.
• They cannot be searched or filtered for. There is no view of every field using IBAN; the only way to see which validator a field has is to open that field.
• They have no browsable reference inside the product. To see the list of validators you open a Text field's definition form and read the dropdown.
• They cannot be written by hand. There is no regular-expression or pattern entry anywhere, by design, and the 13 built-in checks are the complete set.