Transaction-Participation for Neo4j-REST-API

This is a Neo4j Server Extension to make Neo4j REST-API participate in transactions started by the transactional Cypher endpoint.

Why do I need it?

There are a number of operations with Neo4j server that currently can’t be done with Cypher but are exposed as REST-API endpoints.

Notably working with manual indexes, traversals and graph algorithms.

As the Cypher endpoint starts it’s own transactions, all the data created during those transactions is not visible to the outside until that transaction is committed. So you can’t create a node and add it to a manual fulltext or spatial index within the same transaction.

This extension makes it possible for other REST-operations to participate in transactions started by the cypher endpoint.

Installation

You can build it with mvn package and copy target/transaction-participation-2.2.2-1.0-SNAPSHOT.jar to your server’s plugins directory.

A pre-built version is here.

And edit conf/neo4j-server.properties to contain this registration for the extension:

org.neo4j.server.thirdparty_jaxrs_classes=org.neo4j.server.extension.tx=/tx

Then restart your server.

How does it work?

The extension installs a filter that intercepts the http request to the REST API takes the transaction id from the X-TxId HTTP Header and resumes the transaction, so that the REST-API calls participates in that transaction.

After executing the request it suspends the transaction again, so that you can continue it with the Cypher endpoint and also committing it at the end.

Here is a sample session with explanations:

# open transaction, create node
curl -i -H accept:application/json -H content-type:application/json \
     -d '{"statements":[{"statement":"create (p:Person {name:\"Jack\"}) return id(p)"}]}' \
     http://localhost:7474/db/data/transaction

# response, see the transaction-id "6" and the returned node-id of "1" (nested in "data":[{"row":[1]}]}])
HTTP/1.1 201 Created
Location: http://localhost:7474/db/data/transaction/6
{"commit":"http://localhost:7474/db/data/transaction/6/commit",
 "results":[{"columns":["id(p)"],"data":[{"row":[1]}]}],
 "transaction":{"expires":"Sun, 24 May 2015 08:43:11 +0000"},
 "errors":[]}

curl -H X-TxId:6 \
     -i -H accept:application/json -H content-type:application/json \
     -d'{"key":"bio","value":"Jack was born in London in 1925","uri":"/db/data/node/1"}' \
     http://localhost:7474/db/data/index/node/people

# response, added to index

HTTP/1.1 201 Created
{  ...
   "indexed" : "http://localhost:7474/db/data/index/node/people/bio/Jack%20was%20born%20in%20London%20in%201925/1"
}

# commit transaction number 6
curl  -i -XPOST \
      http://localhost:7474/transaction/6

jexp/neo4j-tx-participation

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