CODEWITHSUNDEEP
neo4jcypherspring-data-neo4j-4neo4j-ogm
alexanoid
alexanoid

Reputation: 25842

Neo4j SDN 4 emulate sequence object(not UUID)

Is it possible in Neo4j or SDN4 to create/emulate something similar to a PostgreSQL sequence database object?

I need this thread safe functionality in order to be able to ask it for next, unique Long value. I'm going to use this value as a surrogate key for my entities.

UPDATED

I don't want to go with UUID because I have to expose these IDs within my web application url parameters and in case of UUID my urls look awful. I want to go with a plain Long values for IDs like StackOverflow does, for example:

stackoverflow.com/questions/42228501/neo4j-sdn-4-emulate-sequence-objectnot-uuid

Upvotes: 4

Views: 419

Answers (4)

alexanoid
alexanoid

Reputation: 25842

The most simplest way in Neo4j is to disable ids reuse and use node Graph ID like sequencer.

https://neo4j.com/docs/operations-manual/current/reference/configuration-settings/

Table A.83. dbms.ids.reuse.types.override

Description: Specified names of id types (comma separated) that should be reused. Currently only 'node' and 'relationship' types are supported.

Valid values: dbms.ids.reuse.types.override is a list separated by "," where items are one of NODE, RELATIONSHIP

Default value: [RELATIONSHIP, NODE]

Upvotes: 0

cybersam
cybersam

Reputation: 67019

If your main interest is in having a way to generate unique IDs, and you do not care if the unique IDs are strings, then you should consider using the APOC facilities for generating UUIDs.

There is an APOC function that generates a UUID, apoc.create.uuid. In older versions of APOC, this is a procedure that must be invoked using the CALL syntax. For example, to create and return a single Foo node with a new UUID:

CREATE (f:Foo {uuid: apoc.create.uuid()})
RETURN f;

There is also an APOC procedure, apoc.create.uuids(count), that generates a specified number of UUIDs. For example, to create and return 5 Foo nodes with new UUIDs:

CALL apoc.create.uuids(5) YIELD uuid
CREATE (f:Foo {uuid: uuid})
RETURN f;

Upvotes: 1

stdob--
stdob--

Reputation: 29147

This can be done with user procedures and functions. As an example:

package sequence;

import org.neo4j.procedure.*;
import java.util.concurrent.atomic.AtomicInteger;

public class Next {
    private static AtomicInteger sequence = new AtomicInteger(0);

    @UserFunction
    public synchronized Number next() {
        return sequence.incrementAndGet();
    }
}

The problem of this example is that when the server is restarted the counter will be set to zero.

So it is necessary to keep the last value of the counter. This can be done using these examples:

https://maxdemarzi.com/2015/03/25/triggers-in-neo4j/

https://github.com/neo4j-contrib/neo4j-apoc-procedures/blob/master/src/main/java/apoc/trigger/Trigger.java

Upvotes: 2

digx1
digx1

Reputation: 1088

No. As far as I'm aware there isn't any similar functionality to sequences or auto increment identifiers in Neo4j. This question has also been asked a few times in the past.

The APOC project might be worth checking out for this though. There seems to be a request to add it.

Upvotes: 1

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