Validate a $Location in Firebase - validation

Question

I am trying to do some validation on incoming data into my firebase app. My structure is at the bottom. I have removed existing validation rules for clarity - however we can assume that reads and writes are allowed at the root rules level.
$categoryid will look something like this:
1234: {1:{...}, 2:{...}, 3:{...}}
I want to ensure that $categoryid (which is 1234 in the above example) is numerical - however the rule ".validate": "$categoryid.isNumeric()" results in an "no such method or property" error.
I could check for data.child($categoryid) in categories, however the variable doesn't exist at that level and results in an "unknown variable" error.
I'm sure I'm missing a trick here...
{
"rules": {
"categories": {
"$categoryid": {
"$itemid": {
"members": {
"$id": {
}
}
}
}
}
}
}

Answer 1

There is currently no good way to do this, but there is a hacky work around that involves storing the $categoryId in a field, then checking that that field is numeric.
Using these security rules:
{
"rules": {
"categories": {
"$categoryid": {
".validate": "'' + newData.child('meta/id') === $categoryId && newData.child('meta/id').isNumber()"
"meta": {},
"items": {
"$itemid": {
"members": {
"$id": {
}
}
}
}
}
}
}
}
We can then create a new category by running:
categoriesRef.child(1234).set({meta: {id: 1234}});
These rules will check that a) the $categoryId matches $categoryId/meta/id and that $categoryId/meta/id is a number.

Answer 2

To do this validation you can use RegEx /^[0-9]+$/
{
"rules": {
"categories": {
"$categoryid": {
.validate": "$categoryid.matches(/^[0-9]+$/)"
"$itemid": {
"members": {
"$id": {
}
}
}
}
}
}
}