ArangoDB Indexes and arrays - arrays

Question

I am trying use document collection for fast lookup, sample document
document Person {
...
groups: ["admin", "user", "godmode"],
contacts: [
{
label: "main office",
items: [
{ type: "phone", value: '333444222' },
{ type: "phone", value: '555222555' },
{ type: "email", value: 'bob#gmail.com' }
]
}
]
...
}
Create Hash index for "groups" field
Query: For P in Person FILTER "admin" IN P.groups RETURN P
Result: Working, BUT No index used via explain query
Question: How use queries with arrays filter and indexes ? performance is main factor
Create Hash index for "contacts[].items[].value"
Query: For P in Person FILTER "333444222" == P.contacts[*].items[*].value RETURN P
Result: Double usage of wildcard not supported?? Index not used, query empty
Question: How organize fast lookup with for this structure with indexes ?
P.S. also tried MATCHES function, multi lever for-in, hash indexed for arrays never used
ArangoDB version 2.6.8

Answer 1

Indexes can be used from ArangoDB version 2.8 on.
For the first query (FILTER "admin" IN p.groups), an array hash index on field groups[*] will work:
db._create("persons");
db.persons.insert(personDateFromOriginalExample);
db.persons.ensureIndex({ type: "hash", fields: [ "groups[*]" ] });
This type of index does not exist in versions prior to 2.8.
With an array index in place, the query will produce the following execution plan (showing that the index is actually used):
Execution plan:
Id NodeType Est. Comment
1 SingletonNode 1 * ROOT
6 IndexNode 1 - FOR p IN persons /* hash index scan */
3 CalculationNode 1 - LET #1 = "admin" in p.`groups` /* simple expression */ /* collections used: p : persons */
4 FilterNode 1 - FILTER #1
5 ReturnNode 1 - RETURN p
Indexes used:
By Type Collection Unique Sparse Selectivity Fields Ranges
6 hash persons false false 100.00 % [ `groups[*]` ] "admin" in p.`groups`
The second query will not be supported by array indexes, as it contains multiple levels of nesting. The array indexes in 2.8 are restricted to one level, e.g. groups[*] or contacts[*].label will work, but not groups[*].items[*].value.

Answer 2

about 1.) this is Work-in-progress and will be included in one of the next releases (most likely 2.8).
We have not yet decided about the AQL syntax to retrieve the array, but FILTER "admin" IN P.groups is among the most likely ones.
about 2.) having implemented 1. this will work out of the box as well, the index will be able to cover several depths of nesting.
Neither of the above can be properly indexed in the current release (2.6)
The only alternative i can offer is to externalize the values and use edges instead of arrays.
In your code the data would be the following (in arangosh).
I used fixed _key values for simplicity, works without them as well:
db._create("groups"); // saves the group elements
db._create("contacts"); // saves the contact elements
db._ensureHashIndex("value") // Index on contacts.value
db._create("Person"); // You already have this
db._createEdgeCollection("isInGroup"); // Save relation group -> person
db._createEdgeCollection("hasContact"); // Save relation item -> person
db.Person.save({_key: "user"}) // The remainder of the object you posted
// Now the items
db.contacts.save({_key:"phone1", type: "phone", value: '333444222' });
db.contacts.save({_key:"phone2", type: "phone", value: '555222555' });
db.contacts.save({_key:"mail1", type: "email", value: 'bob#gmail.com'});
// And the groups
db.groups.save({_key:"admin"});
db.groups.save({_key:"user"});
db.groups.save({_key:"godmode"});
// Finally the relations
db.hasContact.save({"contacts/phone1", "Person/user", {label: "main office"});
db.hasContact.save({"contacts/phone2", "Person/user", {label: "main office"});
db.hasContact.save({"contacts/mail1", "Person/user", {label: "main office"});
db.isInGroup.save("groups/admin", "Person/user", {});
db.isInGroup.save("groups/godmode", "Person/user", {});
db.isInGroup.save("groups/user", "Person/user", {});
Now you can execute the following queries:
Fetch all admins:
RETURN NEIGHBORS(groups, isInGroup, "admin")
Get all users having a contact with value 333444222:
FOR x IN contacts FILTER x.value == "333444222" RETURN NEIGHBORS(contacts, hasContact, x)