I'm trying to use the Java API for Neo4j but I seem to be stuck at IndexHits. If I query the DB with Cypher using
START n=node:types(type="Process") RETURN n;
I get all 2087 nodes of type "Process".
In my application I have the following lines
Index<Node> nodeIndex = db.index().forNodes("types");
IndexHits<Node> hits = nodeIndex.get("type", "Process");
System.out.println("Node index size: " + hits.size());
which leads my console to spit out a value of 0. Here, db is of course an instance of GraphDatabaseService.
I expected an object that included all 2087 nodes. What am I doing wrong?
The .size() question is just the prelude to my iterator
for(Node process : hits) { ... }
but that does not much when hits.size() == 0. According to http://api.neo4j.org/1.9.2/org/neo4j/graphdb/index/IndexHits.html this should be possible, provided there is something in hits.
Thanks in advance for your help.
I figured it out. Man, I feel so embarrassed...
It so happens that I had set up the DB_PATH to my default data folder, whereas the default storage folder is the default data folder plus graph.db. When I tried to run the code from that corrected DB_PATH I got an error saying that a lock file was in place because the Neo4j server was running. After shutting it down it worked perfectly.
So, if you happen to see the following error, just stop the server and run the code again:
Caused by: org.neo4j.kernel.StoreLockException: Could not create lock file
at org.neo4j.kernel.StoreLocker.checkLock(StoreLocker.java:74)
at org.neo4j.kernel.StoreLockerLifecycleAdapter.start(StoreLockerLifecycleAdapter.java:40)
at org.neo4j.kernel.lifecycle.LifeSupport$LifecycleInstance.start(LifeSupport.java:491)
I found on several forums that you cannot run the Neo4j server and use the Java API to query it at the same time.
Related
I am trying to create several .qgs project files to be served at a later time by an instance of qgis Server.
To this end I need to start a new PyQGIS application several times upon request. The application runs smoothly the first time it is called, but if I try to run it a second time I get a Segmentation Fault error.
Here is an example code that triggers the problem:
from qgis.core import QgsApplication
import os
os.environ["QT_QPA_PLATFORM"] = "offscreen"
for i in range(2):
print(f'Iteration number {i}')
print('\tSet prefix path')
QgsApplication.setPrefixPath('/usr', False)
print('\tInstantiating application')
qgs = QgsApplication([], False)
print('\tInitializing application')
qgs.initQgis()
print('\tExiting')
qgs.exitQgis()
When executed, I get this output:
Iteration number 0
Set prefix path
Instantiating application
QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-root'
Initializing application
Exiting
Iteration number 1
Set prefix path
Instantiating application
Initializing application
Segmentation fault
Something similar happens if I enclose the content of the loop inside a function and call it multiple times. In this case the segmentation fault happens upon calling qgs.exitQgis() the second time (and any vector or raster layers added before that would be invalid).
Maybe the problem is that for some reason qgs.exitQgis() is not really cleaning up before exit?
The code is running on a Python:3.9 docker container that comes with Debian Bullseye.
Qgis has been installed following the instruction from the QGIS docs:
https://qgis.org/en/site/forusers/alldownloads.html#debian-ubuntu. QGIS version is QGIS 3.22.3-Białowieża 'Białowieża'.
To prevent an import error when loading qgis.core I had to set the environment variable PYTHONPATH = /usr/lib/python3/dist-packages/.
UPDATE: Following a suggestion of one comment found on this post:
https://gis.stackexchange.com/questions/250933/using-exitqgis-in-pyqgis,
I substituted qgs.exitQgis() with qgs.exit() and now the app can be instantiated again any number of times without crashing.
It is still not clear what causes the segmentation fault, but at least I found this workaround.
It seems like the problem was fixed in QGIS ver. 3.24 Tisler. Now qgs.exitQgis() can be called in a loop without triggering a segmentation fault.
I am using Elasticsearch 6.2.4 with my RoR application using elasticsearch-rails and elasticsearch-model.
My indexation is runninng without getting any errors. but when I try to perform a search from the application I am getting this error from Elasticsearch
<Elasticsearch::Transport::Transport::Errors::BadRequest: [400] {"error":{"root_cause":[{"type":"illegal_argument_exception","reason":"text is empty (possibly HTTP/0.9)"}],"type":"illegal_argument_exception","reason":"text is empty (possibly HTTP/0.9)"},"status":400}>
Everything was working normal prior to the upgrade of Elasticsearch from 1.5 to 6.2.4
I simplified my search query to try narrowing down the problem.
q = { "query" => { "match_all" => {} } }
But I still getting the same error. Probably I am not specifying a type in the query but wouldn't be unnecessary since I have a match_all condition ?
> {"query":{"match_all":{}}}
< {"error":{"root_cause":[{"type":"illegal_argument_exception","reason":"text is empty (possibly HTTP/0.9)"}],"type":"illegal_argument_exception","reason":"text is empty (possibly HTTP/0.9)"},"status":400}
I am brand new to Elasticsearch so excuse me in advance if there are some evident stuff that I am missing
Do you have any idea what is causing this error ? If you need more specific info just ask and I'll update this question.
Thanks.
Search request from application is resulting in HTTP 400 Bad Request. Are you able to perform a search request from outside the application i.e. invoking a curl command from your local etc ?
My simple code is retrieving attributes from nodes in neo4j.
results = graph.cypher.execute("MATCH (m)-[:AB]->(a) "
"RETURN m.searchField as origin, a.searchField as destination "
"LIMIT {limit}", {"limit": 100})
nodes = []
rels = []
i = 0
for r in results:
print (r)
ent1 = {"title": r.origin, "label": "entity"}
but the server returns "NameError("global name 'searchField' is not defined",)" Certainly I missed something, but I'm puzzled that the searchField inside the Cypher query is the object of the error.
This is still with py2neo 2.0.8.
Thanks for any pointer, hj
Later editing:
Thanks for taking the time to look at this question. Two elements further puzzle me in this error:
1. The query in cypher is fine, and returns the result I expect in neo4j-shell without problem
2. This code seems to work fine when I run bottle as standalone (run(port=8080) in main), but fails when I run it as wsgi under an apache server. I am wondering if it is a problem of running user, or of context in some part of the code.
Do you have a property called searchField on the node(s)?
If not, the query will fail.
BTW, it is easier to use a string for the query like so:
query = '''
MATCH (m)-[:AB]->(a)
RETURN m.searchField as origin, a.searchField as destination
LIMIT {limit}
'''
result = graph.cypher.execute(query, limit='foo')
Got it to work! It was unrelated to code, but I did not know that any refresh of a new python code served through wsgi requires an apache reload at least.
sudo service apache2 reload
With that I obtain the same (and correct) behavior as with the direct server. The error was the result of an old version of the code... newbie mistake!
Thanks and sorry for the hassle, hj
I just created a new folder name-Test and started Neo4j server.
When i run the below script, i get the error - "Neo.ClientError.Statement.EntityNotFound"
and a message "Node with id 0"
start root=node(0)
create
(tatham {Name:'Tatham'}),
(tom {Name:'Tom'}),
(pat {Name:'Pat'}),
(chrissy {Name:'Chrissy'}),
(sailing {Name:'Sailing'}),
(mtb {Name:'MTB'}),
(rowing {Name:'Rowing'}),
(tennis {Name:'Tennis'}),
root-[:HAS_USER]->tatham,
root-[:HAS_USER]->tom,
root-[:HAS_USER]->pat,
root-[:HAS_USER]->chrissy,
tatham-[:FRIEND]->tom,
tom-[:FRIEND]->pat,
tatham-[:FRIEND]->chrissy,
tatham-[:LIKES]->sailing,
tatham-[:LIKES]->mtb,
tom-[:LIKES]->sailing,
pat-[:LIKES]->mtb,
tom-[:LIKES]->rowing,
pat-[:LIKES]->tennis,
chrissy-[:LIKES]->mtb,
chrissy-[:LIKES]->sailing
Can you kindly help me hot to fix this issue
A #WilliamLyon indicated:
A new DB has no nodes, and therefore has no node with the ID of 0.
The START clause is now deprecated.
You are apparently using a very old version of neo4j. If possible, you should install the latest version.
In addition:
Nodes now must always be specified within parentheses.
Try the following, instead, which should work with your version of neo4j as well as the latest versions:
CREATE
(tatham {Name:'Tatham'}),
(tom {Name:'Tom'}),
(pat {Name:'Pat'}),
(chrissy {Name:'Chrissy'}),
(sailing {Name:'Sailing'}),
(mtb {Name:'MTB'}),
(rowing {Name:'Rowing'}),
(tennis {Name:'Tennis'}),
(root)-[:HAS_USER]->(tatham),
(root)-[:HAS_USER]->(tom),
(root)-[:HAS_USER]->(pat),
(root)-[:HAS_USER]->(chrissy),
(tatham)-[:FRIEND]->(tom),
(tom)-[:FRIEND]->(pat),
(tatham)-[:FRIEND]->(chrissy),
(tatham)-[:LIKES]->(sailing),
(tatham)-[:LIKES]->(mtb),
(tom)-[:LIKES]->(sailing),
(pat)-[:LIKES]->(mtb),
(tom)-[:LIKES]->(rowing),
(pat)-[:LIKES]->(tennis),
(chrissy)-[:LIKES]->(mtb),
(chrissy)-[:LIKES]->(sailing);
The root node will be created automatically the first time it is encountered by the query, and then re-used.
The problem is the first line of your Cypher query: start root=node(0). That statement is saying "find a Node with id 0", however if you haven't inserted any data yet there is no Node to find, thus the error.
start has been deprecated and is no longer required so you can just remove it.
All I'm trying to do is the following:
BatchInserter ins = BatchInserters.inserter("target/batchinserter-example");
where "target/batchinserter-example" is a given store directory. It compiles fine, but I get:
Exception in thread "main" java.lang.ExceptionInInitializerError
at org.neo4j.unsafe.batchinsert.BatchInserterImpl.rejectAutoUpgrade(BatchInserterImpl.java:556)
at org.neo4j.unsafe.batchinsert.BatchInserterImpl.<init>(BatchInserterImpl.java:219)
at org.neo4j.unsafe.batchinsert.BatchInserters.inserter(BatchInserters.java:94)
at org.neo4j.unsafe.batchinsert.BatchInserters.inserter(BatchInserters.java:88)
at org.neo4j.unsafe.batchinsert.BatchInserters.inserter(BatchInserters.java:63)
at org.neo4j.unsafe.batchinsert.BatchInserters.inserter(BatchInserters.java:51)
at NeoBatchInserter.main(NeoBatchInserter.java:26)
Caused by: java.lang.ArrayIndexOutOfBoundsException: 0
at org.neo4j.graphdb.factory.GraphDatabaseSettings.<clinit>(GraphDatabaseSettings.java:69)
... 7 more
I don't understand how this isn't working. I'm literally just calling a constructor that takes a String. I'm quite frustrated at the moment. If there is a better way to do this, I am welcome to trying it. All I want to do is set up a BatchInserter (from scratch) so that I can begin my work.
EDIT:
I just attempted to point it a graph.db from a test graph, and this still didn't work...
I'm also using kernel.2.1.3
EDIT 2:
Since my server is 2.1.2, I changed my jars to the 2.1.2 version, yet I still get the same error.
What version of Neo4j was the directory created with? I'm pretty sure that you cannot use batchinserter of 2.1.3 with an earlier version.
Install 2.1.3, set allow_store_upgrade=true in neo4j.properties, start the server and shut it down. It's crucial to have a clean shutdown. Then use your batchinserter code.