Py2neo - creating relationships in writebatch

Question

I use py2neo to dump data in a Neo4j database.

With this

batch = neo4j.WriteBatch(graph_db)
batch.create(node(name="Alice"))
batch.create(node(name="Bob"))
batch.create(rel(0, "KNOWS", 1))
results = batch.submit()

I can create relationships using new nodes within the same batch.

However, if i try to create a relationship with a node that has already been created before the batch like this :

n = graph_db.create({"name": "Smith"})
batch = neo4j.WriteBatch(graph_db)
batch.create(node(name="Alice"))
batch.create(rel(0, "KNOWS", n))
results = batch.submit()

It fails*. How would one proceed to create nodes with relationships within a batch to nodes previously created?

Using py2neo 1.5.1 and Neo4j 1.9.2

Thanks

• Error message :

SystemError: {u'stacktrace': [u'org.neo4j.server.rest.batch.NonStreamingBatchOperations.invoke(NonStreamingBatchOperations.java:63)', u'org.neo4j.server.rest.batch.BatchOperations.performRequest(BatchOperations.java:188)', u'org.neo4j.server.rest.batch.BatchOperations.parseAndPerform(BatchOperations.java:159)', u'org.neo4j.server.rest.batch.NonStreamingBatchOperations.performBatchJobs(NonStreamingBatchOperations.java:48)', u'org.neo4j.server.rest.web.BatchOperationService.batchProcess(BatchOperationService.java:117)', u'org.neo4j.server.rest.web.BatchOperationService.performBatchOperations(BatchOperationService.java:72)', u'java.lang.reflect.Method.invoke(Method.java:606)', u'org.neo4j.server.rest.security.SecurityFilter.doFilter(SecurityFilter.java:112)'], u'message': u'{\n "message" : "For input string: \"5078\')]}\"",\n "exception" : "BadInputException",\n "fullname" : "org.neo4j.server.rest.repr.BadInputException",\n "stacktrace" : [ "org.neo4j.server.rest.web.RestfulGraphDatabase.extractNodeId(RestfulGraphDatabase.java:171)", "org.neo4j.server.rest.web.RestfulGraphDatabase.createRelationship(RestfulGraphDatabase.java:410)", "java.lang.reflect.Method.invoke(Method.java:606)", "org.neo4j.server.rest.security.SecurityFilter.doFilter(SecurityFilter.java:112)", "org.neo4j.server.web.Jetty6WebServer.invokeDirectly(Jetty6WebServer.java:302)", "org.neo4j.server.rest.batch.NonStreamingBatchOperations.invoke(NonStreamingBatchOperations.java:55)", "org.neo4j.server.rest.batch.BatchOperations.performRequest(BatchOperations.java:188)", "org.neo4j.server.rest.batch.BatchOperations.parseAndPerform(BatchOperations.java:159)", "org.neo4j.server.rest.batch.NonStreamingBatchOperations.performBatchJobs(NonStreamingBatchOperations.java:48)", "org.neo4j.server.rest.web.BatchOperationService.batchProcess(BatchOperationService.java:117)", "org.neo4j.server.rest.web.BatchOperationService.performBatchOperations(BatchOperationService.java:72)", "java.lang.reflect.Method.invoke(Method.java:606)", "org.neo4j.server.rest.security.SecurityFilter.doFilter(SecurityFilter.java:112)" ],\n "cause" : {\n "message" : "For input string: \"5078\')]}\"",\n "exception" : "NumberFormatException",\n "stacktrace" : [ "java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)", "java.lang.Long.parseLong(Long.java:441)", "java.lang.Long.parseLong(Long.java:483)", "org.neo4j.server.rest.web.RestfulGraphDatabase.extractNodeId(RestfulGraphDatabase.java:167)", "org.neo4j.server.rest.web.RestfulGraphDatabase.createRelationship(RestfulGraphDatabase.java:410)", "java.lang.reflect.Method.invoke(Method.java:606)", "org.neo4j.server.rest.security.SecurityFilter.doFilter(SecurityFilter.java:112)", "org.neo4j.server.web.Jetty6WebServer.invokeDirectly(Jetty6WebServer.java:302)", "org.neo4j.server.rest.batch.NonStreamingBatchOperations.invoke(NonStreamingBatchOperations.java:55)", "org.neo4j.server.rest.batch.BatchOperations.performRequest(BatchOperations.java:188)", "org.neo4j.server.rest.batch.BatchOperations.parseAndPerform(BatchOperations.java:159)", "org.neo4j.server.rest.batch.NonStreamingBatchOperations.performBatchJobs(NonStreamingBatchOperations.java:48)", "org.neo4j.server.rest.web.BatchOperationService.batchProcess(BatchOperationService.java:117)", "org.neo4j.server.rest.web.BatchOperationService.performBatchOperations(BatchOperationService.java:72)", "java.lang.reflect.Method.invoke(Method.java:606)", "org.neo4j.server.rest.security.SecurityFilter.doFilter(SecurityFilter.java:112)" ],\n "fullname" : "java.lang.NumberFormatException"\n }\n}', u'fullname': u'org.neo4j.server.rest.domain.BatchOperationFailedException', u'exception': u'BatchOperationFailedException'}

Answer 1

In your code example, n will actually contain a list of nodes, not a single node (see the warning on the create method). So, instead of...

n = graph_db.create({"name": "Smith"})

...you probably want...

n, = graph_db.create({"name": "Smith"})