Users can define their own keys for documents they save. The document key will be saved along with a document in the _key attribute. Users can pick key values as required, provided that the values conform to the following restrictions:
- The key must be a string value. Numeric keys are not allowed, but any numeric value can be put into a string and can then be used as document key.
- The key must be at least 1 byte and at most 254 bytes long. Empty keys are disallowed when specified (though it may be valid to completely omit the _key attribute from a document)
- It must consist of the letters a-z (lower or upper case), the digits 0-9
or any of the following punctuation characters:
- Any other characters, especially multi-byte UTF-8 sequences, whitespace or punctuation characters cannot be used inside key values
- The key must be unique within the collection it is used
Keys are case-sensitive, i.e. myKey and MyKEY are considered to be different keys.
Specifying a document key is optional when creating new documents. If no document key is specified by the user, ArangoDB will create the document key itself as each document is required to have a key.
There are no guarantees about the format and pattern of auto-generated document keys other than the above restrictions. Clients should therefore treat auto-generated document keys as opaque values and not rely on their format.
The current format for generated keys is a string containing numeric digits.
The numeric values reflect chronological time in the sense that _key values
generated later will contain higher numbers than _key values generated earlier.
But the exact value that will be generated by the server is not predictable.
Note that if you sort on the _key attribute, string comparison will be used,
"100" is less than
When working with named graphs, their names are used as document keys in the
_graphs system collection. Therefore, the same document key restrictions apply.