I've got three classes:
Users extends V
Links extends V
Edges extends E
I have 3 Users, that won't usually change.
I have potentially 10000's of Links, and each one is connected to at least one of the Users (usually only one) via an Edge.
Is it possible to join these two commands, which are always called in succession, into one?
link = "insert into Links set title='Link 1'"
"create edge Edges
from ( select from Users where user_id='"+user_id+"')
to ( select from " + link._rid + ")"
That is some kind of pseudocode, I'm checking this out with pyorient.
Take a look at SQL Batch.
Your command(s) might look like the following...
pyorient_client.batch("""begin
let link = create vertex Links set name = 'Link 1'
let user = select from Users where user_id = '{}' lock record
let edge = create edge Edges from $user to $link
commit
return $edge""".format(user_id)
)
Related
Let's say I have the following list of vertices (connected by edges) in the orient database:
[t=1] --> [t=2] --> [t=3] --> [t=4] --> [t=5] --> [t=6] --> [t=7]
Each vertex has a timestamp t. I now want to receive the last vertex before a given date. Example: give me the last vertex before t=5, which is t=4.
Currently I'am using the following query to do this:
SELECT FROM ANYVERTEX WHERE t < 5 ORDER BY t DESC LIMIT 1
This is working fine when having up to let's say 1000 elements but the performance of that query drops with the number of elements inserted in the list. I already tried using an index, which improved the overall performance, but the problem, that the performance drops with the amount of elements still persists.
When building queries, always try to use the information you have about the relationship in your query to improve performance. In this case you don't need the sort (which is an expensive operation) because you know that the vertex you need has an incoming edge to the vertex, you can simply use that information in your query.
For example, let's say I have the following setup:
CREATE CLASS T EXTENDS V
CREATE VERTEX T SET t = 1
CREATE VERTEX T SET t = 2
CREATE VERTEX T SET t = 3
CREATE VERTEX T SET t = 4
CREATE VERTEX T SET t = 5
CREATE CLASS link EXTENDS E
CREATE EDGE link FROM (SELECT * FROM T WHERE t = 1) TO (SELECT * FROM T WHERE t = 2)
CREATE EDGE link FROM (SELECT * FROM T WHERE t = 2) TO (SELECT * FROM T WHERE t = 3)
CREATE EDGE link FROM (SELECT * FROM T WHERE t = 3) TO (SELECT * FROM T WHERE t = 4)
CREATE EDGE link FROM (SELECT * FROM T WHERE t = 4) TO (SELECT * FROM T WHERE t = 5)
Then I can select the vertex before any T as such:
SELECT expand(in('link')) FROM T WHERE t = 2
This query does the following:
Select the vertex from T where t=2
From that vertex, traverse the incoming edge(s) of type link
expand() the vertex from which that edge comes from to get all of its information
The result is exactly what you want:
This should give better performance (especially if you add an index on the attribute t of the vertices) because you are using all the information you know in advance about the relationship = the node you need has an edge to the node you select.
Hope that helps you out.
I haven't been able to find an answer for the SQL for this.
Given pairs of vertices (record ids) and edge types between them, I want to check if all pairs exists.
V1 --E1--> V2
V3 --E2--> V4
... and so on. The answer I want is true / false or something equivalent. ALL connections must be present in order to evaluate to true, so at least one edge (of correct type) must exist for each pair.
Pseudo, the question would be:
Does V1 have edge <E1EdgeType> to V2?
AND
Does V3 have edge <E2EdgeType> to V4?
AND
... and so on
Does anyone know what the orientDB SQL would be to achieve this?
UPDATE
I did already have one way of checking if one single edge exists between known vertices. It's perhaps not very pretty either, but it works:
SELECT FROM (
SELECT EXPAND(out('TestEdge')) FROM #12:0
) WHERE #rid=#12:1
This will return the destination record (#12:0) if an edge of type 'TestEdge' exists from #12:0 to #12:1. However, if I have two of those, how can I query for one single result for both queries. Something like:
SELECT <something with $c> LET
$a = (SELECT FROM (SELECT EXPAND(out('TestEdge')) FROM #12:0) WHERE #rid=#12:1)
$b = (SELECT FROM (SELECT EXPAND(out('AnotherTestEdge')) FROM #12:2) WHERE #rid=#12:3)
$c = <something that checks that both a and b yield results>
That's what I aim towards doing. Please tell me if I'm solving this the wrong way. I'm not even sure what the gain is to merge queries like this compared to just repeat queries.
Given a pair of vertices, say #11:0 and #12:0, the following query will effectively check whether there is an edge of type E from #11:0
to #12:0
select from (select #this, out(E) from #11:0 unwind out) where out = #12:0
----+------+-----+-----
# |#CLASS|this |out
----+------+-----+-----
0 |null |#11:0|#12:0
----+------+-----+-----
This is highly inelegant and I would encourage you to think about formulating an enhancement request accordingly at https://github.com/orientechnologies/orientdb/issues
One way to incorporate the boolean tests you have in mind is illustrated by the following:
select from
(select $a.size() as a, $b.size() as b
let a=(select count(*) as e from (select out(E) from #11:0 unwind out)
where out = #12:0),
b=(select count(*) as e from (select out(E) from #11:1 unwind out)
where out = #12:2))
where a > 0 and b > 0
Yes, inelegance again :-(
It might be useful to you the following query
SELECT eval('sum($a.size(),$b.size())==2') as existing_edges
let $a = ( SELECT from TestEdge where out = #12:0 and in = #12:1 limit 1),
$b = ( SELECT from AnotherTestEdge where out = #12:2 and in = #12:3 limit 1)
Hope it helps.
I want to figure out where a person might be from based on who they follow and get the country together with an approximate latitude and longitude. I've got two types of nodes: Users (containing a name and possibly lat and lng) and Countries (containing a name). I've also got two types of edges: Follow and LivesIn (containing lat and lng).
At the moment both the Account as well as the LivesIn edge contain the lat and lng because I'm not completely sure where it'd be better, but at the moment I'm leaning towards putting it in the edge.
Below is an example network with five users. Three of whom I know where they're from. Now I want to make an educated guess where Alice is from:
Alice follows four users
Two of these four users are from Germany, one from Belgium and one unknown
We can assume that Alice is from Germany
The average lat and lng for the german users are (51.165691+51.115691)/2 and (10.451526+10.481526)/2
We can assume that Alice is somewhere around (51.140691; 10.466526)
.
CREATE CLASS Account EXTENDS V
CREATE PROPERTY Account.name string
CREATE PROPERTY Account.lat double
CREATE PROPERTY Account.lng double
CREATE CLASS Country EXTENDS V
CREATE PROPERTY Country.countryname string
CREATE CLASS LivesIn EXTENDS E
CREATE PROPERTY LivesIn.lat double
CREATE PROPERTY LivesIn.lng double
CREATE CLASS Follows EXTENDS E
CREATE VERTEX Account SET name='Alice'
CREATE VERTEX Account SET name='Bob', lat=50.503887, lng=4.469936 /* Belgium */
CREATE VERTEX Account SET name='Carol', lat=51.165691, lng=10.451526 /* Germany */
CREATE VERTEX Account SET name='Eve', lat=51.115691, lng=10.481526 /* Germany */
CREATE VERTEX Account SET name='Dave'
CREATE EDGE Follows FROM (SELECT FROM Account WHERE name='Alice') TO (SELECT FROM Account WHERE name='Bob')
CREATE EDGE Follows FROM (SELECT FROM Account WHERE name='Alice') TO (SELECT FROM Account WHERE name='Carol')
CREATE EDGE Follows FROM (SELECT FROM Account WHERE name='Alice') TO (SELECT FROM Account WHERE name='Eve')
CREATE EDGE Follows FROM (SELECT FROM Account WHERE name='Alice') TO (SELECT FROM Account WHERE name='Dave')
CREATE EDGE Follows FROM (SELECT FROM Account WHERE name='Bob') TO (SELECT FROM Account WHERE name='Alice')
CREATE EDGE Follows FROM (SELECT FROM Account WHERE name='Carol') TO (SELECT FROM Account WHERE name='Alice')
CREATE EDGE Follows FROM (SELECT FROM Account WHERE name='Eve') TO (SELECT FROM Account WHERE name='Alice')
CREATE EDGE Follows FROM (SELECT FROM Account WHERE name='Dave') TO (SELECT FROM Account WHERE name='Alice')
CREATE VERTEX Country SET countryname='Belgium'
CREATE VERTEX Country SET countryname='Germany'
CREATE EDGE LivesIn FROM (SELECT FROM Account WHERE name='Bob') TO (SELECT FROM Country WHERE countryname='Belgium') SET lat=50.503887, lng=4.469936
CREATE EDGE LivesIn FROM (SELECT FROM Account WHERE name='Carol') TO (SELECT FROM Country WHERE countryname='Germany') SET lat=51.165691, lng=10.451526
CREATE EDGE LivesIn FROM (SELECT FROM Account WHERE name='Eve') TO (SELECT FROM Country WHERE countryname='Germany') SET lat=51.115691, lng=10.481526
My question is if there's an effective way to achieve this using specific sql commands in OrientDB or if it needs a new function.
I got some small things figured out like getting all outgoing Follows connections:
SELECT out("Follows") FROM Account WHERE name='Alice'
But I can't really manage to get all the LivesIn edges from there.
Alternatively I can create a new function in OrientDB as they also did here. Something like:
var gdb = orient.getGraphNoTx();
var v = gdb.command("sql", "select from Account where name='" + name + "'");
neighbours = v[0].getRecord().field("out_Follows").iterator();
var result = []
print('\n');
country_dict = {}
while(neighbours.hasNext()) {
var neighbour = neighbours.next();
var temp = neighbour.field("in").field("out_LivesIn");
if(temp) {
it = temp.iterator();
print(it.next());
// Count each country and keep track of sum of lat and lng so it can be divided
// once all neighbours have been visited
}
}
But that doesn't really use any (possibly efficient?) built in methods of sql. Considering a single person can possibly follow tens of thousands of other accounts.
Would anyone have a suggestion how I can solve this?
Try this query
select countryname,eval('sum / _count') as average_lat,eval('sum2 / _count') as average_lng from
(select countryname,sum(_lat),sum(_lng),count(*) as _count from
(select outE("livesIn").lat as _lat,outE("livesIn").lng as _lng,out("livesIn").countryname as countryname from
(select expand(out("Follows")) from Account where name="Alice") unwind _lat,_lng,countryname)
group by countryname order by _count desc limit 1)
The orientdb documentation says regarding lightweight edges:
two vertices are connected by maximum 1 edge, so if you already have one edge between two vertices and you're creating a new edge between the same vertices, the second edge will be regular
Looking at the following script:
drop database plocal:../databases/test-lightweight admin admin;
create database plocal:../databases/test-lightweight admin admin;
connect plocal:../databases/test-lightweight admin admin;
alter database custom useLightweightEdges=true;
// Vertices
CREATE class Driver extends V;
CREATE PROPERTY Driver.name STRING;
// Edges
CREATE class Knows extends E;
CREATE PROPERTY Knows.in LINK Driver MANDATORY=true;
CREATE PROPERTY Knows.out LINK Driver MANDATORY=true;
// DATA
CREATE VERTEX Driver SET name = 'Jochen';
CREATE VERTEX Driver SET name = 'Ronnie';
// Jochen and Ronnie are very good friends
CREATE EDGE Knows FROM (SELECT FROM Driver WHERE name = 'Jochen') to (SELECT FROM Driver WHERE name = 'Ronnie');
CREATE EDGE Knows FROM (SELECT FROM Driver WHERE name = 'Jochen') to (SELECT FROM Driver WHERE name = 'Ronnie');
SELECT expand(out()) FROM (SELECT FROM Driver WHERE name = 'Jochen'); // 2 times Ronnie
SELECT count(*) FROM Knows; // 0
I would expect the last count to return 1, but it returns 0.
When I execute the same script but disabling the lightweight mode the result is 2 (as expected).
I read it on orientDB documentation but can't get a hold of it.
It would be great if someone could explain the use of $parent and $current in detail.
In a few examples I tried $parent.$parent.$current and $parent.$current, both give the same results which I feel should not happen. Below are my assumption:
$current gives access to the record/node currently being processed
$parent gives access to the parent of current record/node being processed
Your second assumption is wrong. It gives you access to the variables of the parent query (useful when calling traverse in a sub-query as stated here).
An example:
create class User extends V
create class Follows extends E
create vertex User set name = 'u1'
create vertex User set name = 'u2'
create vertex User set name = 'u3'
create edge Follows from (select from User where name = 'u1') to (select from User where name = 'u2')
create edge Follows from (select from User where name = 'u2') to (select from User where name = 'u3')
select $all from User
let $all = ( traverse out('Follows') from $parent.$current)