This document discusses importing data from Stack Exchange into Neo4j. It describes extracting data from the Stack Exchange API and data dump into JSON and CSV files. It then covers using Cypher and the LOAD CSV command to import the data into Neo4j, creating nodes for questions, answers, users and tags and relationships between them. It also provides tips for optimizing the import process such as indexing keys, using periodic commit, and cleaning the data. For very large datasets, it recommends using the Neo4j import tool to directly write to the database files.

1. Importing data quickly
and easily
Michael Hunger @mesirii
Mark Needham @markhneedham

2. The data set

3. The data set
‣ Stack Exchange API
‣ Stack Exchange Data Dump

4. Stack Exchange API
{ "items": [{
"question_id": 24620768,
"link": "http://stackoverflow.com/questions/24620768/neo4j-cypher-query-get-last-n-elements",
"title": "Neo4j cypher query: get last N elements",
"answer_count": 1,
"score": 1,
.....
"creation_date": 1404771217,
"body_markdown": "I have a graph....How can I do that?",
"tags": ["neo4j", "cypher"],
"owner": {
"reputation": 815,
"user_id": 1212067,
....
"link": "http://stackoverflow.com/users/1212067/"
},
"answers": [{
"owner": {
"reputation": 488,
"user_id": 737080,
"display_name": "Chris Leishman",
....
},
"answer_id": 24620959,
"share_link": "http://stackoverflow.com/a/24620959",
....
"body_markdown": "The simplest would be to use an ... some discussion on this here:...",
"title": "Neo4j cypher query: get last N elements"
}]
}

5. JSON to CSV
JSON ??? CSV
LOAD
CSV

6. Initial Model
{ "items": [{
"question_id": 24620768,
"link": "http://stackoverflow.com/questions/24620768/neo4j-cypher-query-get-last-n-elements",
"title": "Neo4j cypher query: get last N elements",
"answer_count": 1,
"score": 1,
.....
"creation_date": 1404771217,
"body_markdown": "I have a graph....How can I do that?",
"tags": ["neo4j", "cypher"],
"owner": {
"reputation": 815,
"user_id": 1212067,
....
"link": "http://stackoverflow.com/users/1212067/"
},
"answers": [{
"owner": {
"reputation": 488,
"user_id": 737080,
"display_name": "Chris Leishman",
....
},
"answer_id": 24620959,
"share_link": "http://stackoverflow.com/a/24620959",
....
"body_markdown": "The simplest would be to use an ... some discussion on this here:...",
"title": "Neo4j cypher query: get last N elements"
}]
}

7. jq: Converting JSON to CSV

8. jq: Converting questions to CSV
jq -r '.[] | .items[] |
[.question_id,
.title,
.up_vote_count,
.down_vote_count,
.creation_date,
.last_activity_date,
.owner.user_id,
.owner.display_name,
(.tags | join(";"))] |
@csv ' so.json

9. jq: Converting questions to CSV
$ head -n5 questions.csv
question_id,title,up_vote_count,down_vote_count,creation_date,last_activity_date,
owner_user_id,owner_display_name,tags
33023306,"How to delete multiple nodes by specific ID using Cypher",
0,0,1444328760,1444332194,260511,"rayman","jdbc;neo4j;cypher;spring-data-neo4j"
33020796,"How do a general search across string properties in my nodes?",
1,0,1444320356,1444324015,1429542,"osazuwa","ruby-on-rails;neo4j;neo4j.rb"
33018818,"Neo4j match nodes related to all nodes in collection",
0,0,1444314877,1444332779,1212463,"lmazgon","neo4j;cypher"
33018084,"Problems upgrading to Spring Data Neo4j 4.0.0",
0,0,1444312993,1444312993,1528942,"Grégoire Colbert","neo4j;spring-data-neo4j"

10. jq: Converting answers to CSV
jq -r '.[] | .items[] |
{ question_id: .question_id, answer: .answers[]? } |
[.question_id,
.answer.answer_id,
.answer.title,
.answer.owner.user_id,
.answer.owner.display_name,
(.answer.tags | join(";")),
.answer.up_vote_count,
.answer.down_vote_count] |
@csv'

11. jq: Converting answers to CSV
$ head -n5 answers.csv
question_id,answer_id,answer_title,owner_id,owner_display_name,tags,up_vote_count,
down_vote_count
33023306,33024189,"How to delete multiple nodes by specific ID using Cypher",
3248864,"FylmTM","",0,0
33020796,33021958,"How do a general search across string properties in my nodes?",
2920686,"FrobberOfBits","",0,0
33018818,33020068,"Neo4j match nodes related to all nodes in collection",158701,"
Stefan Armbruster","",0,0
33018818,33024273,"Neo4j match nodes related to all nodes in collection",974731,"
cybersam","",0,0

12. Time to import into Neo4j...

13. Introducing Cypher
‣ The Graph Query Language
‣ Declarative language (think SQL) for graphs
‣ ASCII art based

14. ‣ CREATE create a new pattern in the graph
Cypher primer
CREATE (user:User {name:"Michael Hunger"})
CREATE (question:Question {title: "..."})
CREATE (answer:Answer {text: "..."})
CREATE (user)-[:PROVIDED]->(answer)
CREATE (answer)-[:ANSWERS]->(question);

15. ‣ CREATE create a new pattern in the graph
Cypher primer
CREATE (user:User {name:"Michael Hunger"})
CREATE (question:Question {title: "..."})
CREATE (answer:Answer {text: "..."})
CREATE (user)-[:PROVIDED]->(answer)
CREATE (answer)-[:ANSWERS]->(question);
CREATE (user:User {name:"Michael Hunger"})
Label PropertyNode

16. ‣ CREATE create a new pattern in the graph
Cypher primer
CREATE (user:User {name:"Michael Hunger"})
CREATE (question:Question {title: "..."})
CREATE (answer:Answer {text: "..."})
CREATE (user)-[:PROVIDED]->(answer)
CREATE (answer)-[:ANSWERS]->(question);
CREATE (user)-[:PROVIDED]->(answer)
Relationship

17. ‣ MATCH find a pattern in the graph
Cypher primer
MATCH (answer:Answer)<-[:PROVIDED]-(user:User),
(answer)-[:ANSWERS]->(question)
WHERE user.display_name = "Michael Hunger"
RETURN question, answer;

18. ‣ MERGE find pattern if it exists,
create it if it doesn’t
MERGE (user:User {name:"Mark Needham"})
MERGE (question:Question {title: "..."})
MERGE (answer:Answer {text: "..."})
MERGE (user)-[:PROVIDED]->(answer)
MERGE (answer)-[:ANSWERS]->(question);
Cypher primer

19. Import using LOAD CSV
‣ LOAD CSV iterates CSV files applying the
provided query line by line
LOAD CSV [WITH HEADERS] FROM [URI/File path]
AS row
CREATE ...
MERGE ...
MATCH ...

20. LOAD CSV: The naive version
LOAD CSV WITH HEADERS FROM "questions.csv" AS row
MERGE (question:Question {
id:row.question_id,
title: row.title,
up_vote_count: row.up_vote_count,
creation_date: row.creation_date})
MERGE (owner:User {id:row.owner_user_id, display_name: row.owner_display_name})
MERGE (owner)-[:ASKED]->(question)
FOREACH (tagName IN split(row.tags, ";") |
MERGE (tag:Tag {name:tagName})
MERGE (question)-[:TAGGED]->(tag));

21. Tip: Start with a sample
LOAD CSV WITH HEADERS FROM "questions.csv" AS row
WITH row LIMIT 100
MERGE (question:Question {
id:row.question_id,
title: row.title,
up_vote_count: row.up_vote_count,
creation_date: row.creation_date})
MERGE (owner:User {id:row.owner_user_id, display_name: row.owner_display_name})
MERGE (owner)-[:ASKED]->(question)
FOREACH (tagName IN split(row.tags, ";") |
MERGE (tag:Tag {name:tagName})
MERGE (question)-[:TAGGED]->(tag));

22. Tip: MERGE on a key
LOAD CSV WITH HEADERS FROM "questions.csv" AS row
WITH row LIMIT 100
MERGE (question:Question {id:row.question_id})
ON CREATE SET question.title = row.title,
question.up_vote_count = row.up_vote_count,
question.creation_date = row.creation_date
MERGE (owner:User {id:row.owner_user_id})
ON CREATE SET owner.display_name = row.owner_display_name
MERGE (owner)-[:ASKED]->(question)
FOREACH (tagName IN split(row.tags, ";") |
MERGE (tag:Tag {name:tagName})
MERGE (question)-[:TAGGED]->(tag));

23. Tip: Index/Constrain those keys
CREATE INDEX ON :Label(property);
CREATE CONSTRAINT ON (n:Label) ASSERT n.property IS UNIQUE;

24. Tip: Index those keys
CREATE INDEX ON :Label(property);
CREATE CONSTRAINT ON (n:Label) ASSERT n.property IS UNIQUE;
CREATE CONSTRAINT ON (q:Question) ASSERT q.id IS UNIQUE;
CREATE CONSTRAINT ON (u:User) ASSERT u.id IS UNIQUE;
CREATE INDEX ON :Question(title);

25. LOAD CSV WITH HEADERS FROM "questions.csv" AS row
WITH row LIMIT 100
MERGE (question:Question {id:row.question_id})
ON CREATE SET question.title = row.title,
question.up_vote_count = row.up_vote_count,
question.creation_date = row.creation_date;
Tip: One MERGE per statement

26. LOAD CSV WITH HEADERS FROM "questions.csv" AS row
WITH row LIMIT 100
MERGE (owner:User {id:row.owner_user_id})
ON CREATE SET owner.display_name = row.owner_display_name;
Tip: One MERGE per statement

27. LOAD CSV WITH HEADERS FROM "questions.csv" AS row
WITH row LIMIT 100
MATCH (question:Question {id:row.question_id})
MATCH (owner:User {id:row.owner_user_id})
MERGE (owner)-[:ASKED]->(question);
Tip: One MERGE per statement

28. Tip: Use DISTINCT
LOAD CSV WITH HEADERS FROM "questions.csv" AS row
WITH row LIMIT 100
UNWIND split(row.tags, ";") AS tag
WITH distinct tag
MERGE (:Tag {name: tag});

29. Tip: Use periodic commit
USING PERIODIC COMMIT
LOAD CSV WITH HEADERS FROM "questions.csv" AS row
MERGE (question:Question {id:row.question_id})
ON CREATE SET question.title = row.title,
question.up_vote_count = row.up_vote_count,
question.creation_date = row.creation_date;

30. Periodic commit
‣ Neo4j keeps all transaction state in memory
which is problematic for large CSV files
‣ USING PERIODIC COMMIT flushes the
transaction after a certain number of rows
‣ Default is 1000 rows but it’s configurable
‣ Currently only works with LOAD CSV

31. Tip: Script your import commands

32. Tip: Use neo4j-shell to load script
$ ./neo4j-enterprise-2.3.0/bin/neo4j-shell
-file import.cql [-path so.db]

33. LOAD CSV: Summary
‣ ETL power tool
‣ Built into Neo4J since version 2.1
‣ Can load data from any URL
‣ Good for medium size data
(up to 10M rows)

34. Bulk loading an initial data set
‣ Introducing the Neo4j Import Tool
‣ Find it in the bin folder of your Neo4j
download
‣ Used to large sized initial data sets
‣ Skips the transactional layer of Neo4j and
concurrently writes store files directly

35. Importing into Neo4j
:ID(Crime) :LABEL description
export NEO=neo4j-enterprise-2.3.0
$NEO/bin/neo4j-import
--into stackoverflow.db
--id-type string
--nodes:Post extracted/Posts_header.csv,extracted/Posts.csv.gz
--nodes:User extracted/Users_header.csv,extracted/Users.csv.gz
--nodes:Tag extracted/Tags_header.csv,extracted/Tags.csv.gz
--relationships:PARENT_OF extracted/PostsRels_header.csv,extracted/PostsRels.csv.gz
--relationships:ANSWERS extracted/PostsAnswers_header.csv,extracted/PostsAnswers.csv.gz
--relationships:HAS_TAG extracted/TagsPosts_header.csv,extracted/TagsPosts.csv.gz
--relationships:POSTED extracted/UsersPosts_header.csv,extracted/UsersPosts.csv.gz

36. Expects files in a certain format
:ID(Crime) :LABEL descriptionpostId:ID(Post) title body
Nodes
userId:ID(User) displayname views
Rels
:START_ID(User) :END_ID(Post)

37. <?xml version="1.0" encoding="utf-16"?>
<posts>
...
<row Id="4" PostTypeId="1" AcceptedAnswerId="7" CreationDate="2008-07-31T21:42:52.667"
Score="358" ViewCount="24247" Body="..." OwnerUserId="8" LastEditorUserId="451518"
LastEditorDisplayName="Rich B" LastEditDate="2014-07-28T10:02:50.557" LastActivityDate="
2015-08-01T12:55:11.380" Title="When setting a form's opacity should I use a decimal or
double?" Tags="&lt;c#&gt;&lt;winforms&gt;&lt;type-conversion&gt;&lt;opacity&gt;"
AnswerCount="13" CommentCount="1" FavoriteCount="28" CommunityOwnedDate="2012-10-31T16:42:
47.213" />
...
</posts>
What do we have?

38. <posts>
...
<row Id="4" PostTypeId="1"
AcceptedAnswerId="7" CreationDate="
2008-07-31T21:42:52.667" Score="358"
ViewCount="24247" Body="..."
OwnerUserId="8" LastEditorUserId="
451518" LastEditorDisplayName="Rich
B" LastEditDate="2014-07-28T10:02:
50.557" LastActivityDate="2015-08-
01T12:55:11.380" Title="When setting
a form's opacity should I use a
decimal or double?"
XML to CSV
Java program

39. The generated files
$ cat extracted/Posts_header.csv
"postId:ID(Post)","title","postType:INT",
"createdAt","score:INT","views:INT","answers:INT",
"comments:INT","favorites:INT","updatedAt"

40. The generated files
$ gzcat extracted/Posts.csv.gz | head -n2
"4","When setting a forms opacity should I use a
decimal or double?","1","2008-07-31T21:42:52.667","
358","24247","13","1","28","2014-07-28T10:02:50.557"
"6","Why doesn’t the percentage width child in
absolutely positioned parent work?","1","2008-07-
31T22:08:08.620","156","11840","5","0","7","2015-04-
26T14:37:49.673"

41. The generated files
$ cat extracted/PostsRels_header.csv
":START_ID(Post)",":END_ID(Post)"

42. Importing into Neo4j
:ID(Crime) :LABEL description
export NEO=neo4j-enterprise-2.3.0
$NEO/bin/neo4j-import
--into stackoverflow.db
--id-type string
--nodes:Post extracted/Posts_header.csv,extracted/Posts.csv.gz
--nodes:User extracted/Users_header.csv,extracted/Users.csv.gz
--nodes:Tag extracted/Tags_header.csv,extracted/Tags.csv.gz
--relationships:PARENT_OF extracted/PostsRels_header.csv,extracted/PostsRels.csv.gz
--relationships:ANSWERS extracted/PostsAnswers_header.csv,extracted/PostsAnswers.csv.gz
--relationships:HAS_TAG extracted/TagsPosts_header.csv,extracted/TagsPosts.csv.gz
--relationships:POSTED extracted/UsersPosts_header.csv,extracted/UsersPosts.csv.gz
IMPORT DONE in 3m 10s 661ms. Imported:
31138574 nodes
77930024 relationships
218106346 properties

43. Tip: Make sure your data is clean
:ID(Crime) :LABEL description
‣ Use a consistent line break style
‣ Ensure headers are consistent with data
‣ Quote Special characters
‣ Escape stray quotes
‣ Remove non-text characters

44. Even more tips
:ID(Crime) :LABEL description
‣ Get the fastest disk you can
‣ Use separate disk for input and output
‣ Compress your CSV files
‣ The more cores the better
‣ Separate headers from data

45. The End
‣ https://github.com/mdamien/stackoverflow-neo4j
‣ http://neo4j.com/blog/import-10m-stack-overflow-questions/
‣ http://neo4j.com/blog/cypher-load-json-from-url/
Michael Hunger @mesirii
Mark Needham @markhneedham