在AQL中使用IF THEN的正确方法是什么？

Question

I'm trying to use IF THEN style AQL, but the only relevant operator I could find in the AQL documentation was the ternary operator. I tried to add IF THEN syntax to my already working AQL but it gives syntax errors no matter what I try.

LET doc = DOCUMENT('xp/a-b')
LET now = DATE_NOW()
doc == null || now - doc.last >= 45e3 ? 
  LET mult = (doc == null || now - doc.last >= 6e5 ? 1 : doc.multiplier)
  LET gained = FLOOR((RAND() * 3 + 3) * mult)
  UPSERT {_key: 'a-b'}
  INSERT {
    amount: gained,
    total: gained,
    multiplier: 1.1,
    last: now
  }
  UPDATE {
    amount: doc.amount + gained,
    total: doc.total + gained,
    multiplier: (mult < 4 ? FLOOR((mult + 0.1) * 10) / 10 : 4),
    last: now
  }
  IN xp
  RETURN NEW
 : 
  RETURN null

Gives the following error message:

stacktrace: ArangoError: AQL: syntax error, unexpected identifier near 'doc == null || now - doc.last >=...' at position 1:51 (while parsing)

Answer 1

The ternary operator can not be used like an if/else construct in the way to tried. It is for conditional (sub-)expressions like you use to calculate mult . It can not stand by itself, there is nothing it can be returned or assigned to if you write it like an if-expression.

Moreover, it would require braces, but the actual problem is that the body contains operations like LET , UPSERT and RETURN . These are language constructs which can not be used inside of expressions.

If I understand correctly, you want to:

• insert a new document if no document with key ab exists yet in collection xb
• if it does exist, then update it, but only if the last update was 45 seconds or longer ago

Does the following query work for you?

FOR id IN [ 'xp/a-b' ]
    LET doc = DOCUMENT(id)
    LET key = PARSE_IDENTIFIER(id).key
    LET now = DATE_NOW()
    FILTER doc == null || now - doc.last >= 45e3
    LET mult = (doc == null || now - doc.last >= 6e5 ? 1 : doc.multiplier)
    LET gained = FLOOR((RAND() * 3 + 3) * mult)
    UPSERT { _key: key }
    INSERT {
        _key: key,
        amount: gained,
        total: gained,
        multiplier: 1.1,
        last: now
    }
    UPDATE {
        amount: doc.amount + gained,
        total: doc.total + gained,
        multiplier: (mult < 4 ? FLOOR((mult + 0.1) * 10) / 10 : 4),
        last: now
    }
    IN xp
    RETURN NEW

I added _key to INSERT , otherwise the document will get an auto-generated key, which does not seem intended. Using a FOR loop and a FILTER acts like an IF construct (without ELSE). Because this is a data modification query, it is not necessary to explicitly RETURN anything and in your original query you RETURN null for the ELSE case anyway. While yours would result in [ null ] , mine produces [ ] (truly empty result) if you try execute the query in quick succession and nothing gets updated or inserted.

Note that it is necessary to use PARSE_IDENTIFIER() to get the key from the document ID string and do INSERT { _key: key } . With INSERT { _key: doc._key } you would run into an invalid document key error in the insert case, because if there is no document xp/ab , DOCUMENT() returns null and doc._key is therefore also null , leading to _key: null - which is invalid.