py2neo.WriteBatch如何工作？

Question

Here is the example given in py2neo document :

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

How can the py2neo know the id of the created node 'Alice' and node 'Bob' is 0 and 1 so that it can create the relationship between the two nodes? When I try a similar example, I find that the 0 and 1 are not the ids of nodes, so 0 means the first created node in the batch job? I read the source code and can not make sure about that.

Answer 1

As you correctly assert, the 0 and 1 refer to the index numbers of the items within the batch job, not the absolute node IDs. This feature has been built in this way as it is a layer atop the REST batch interface which uses a similar notation:

http://docs.neo4j.org/chunked/milestone/rest-api-batch-ops.html#rest-api-refer-to-items-created-earlier-in-the-same-batch-job