I created my database in "SCHEMA-Editor" from structr.org. I have two nodes "Project" and "ProjectManager" and relationship between these is "MEMBER".
I made a cypher query to create the graph like this:
MATCH (a:Project),(b:ProjectManager)
WHERE a.name = 'X' AND b.name = 'Y'
CREATE (a)-[r:MEMBER]->(b)
RETURN r,a,b;
And i expected to display the graph, but i got this message: "MEMBER.id must_not_be_empty"
Nodes and relationships created with Cypher are not immediately usable in Structr, because Cypher bypasses the Structr layer and acts directly on the database level. There are some extra steps that need to be done to make an object known to Structr: it needs an id attribute that contains a random UUID (universally unique identifier).
See "Tools" -> "Admin" -> "Relationships" -> "Add UUIDs" in the Schema Editor.
Additional tip: in Cypher, you should use MERGE instead of CREATE to avoid creating duplicate relationships between the two nodes (depending on your use-case).
Related
I am a beginner with Neo4j/Cypher and I'm having trouble modeling my data correctly.
The Data has following relationship:
MANUFACTURER_A (unique) -> PRODUCT_A (unique just withing MANUFACTURER_A) -> CUSTOMER_A (globally unique)
MANUFACTURER_A (unique) -> PRODUCT_A (unique just withing MANUFACTURER_A) -> CUSTOMER_B (globally unique)
MANUFACTURER_B (unique) -> PRODUCT_A (unique just withing MANUFACTURER_B) -> CUSTOMER_A (globally unique)
I am not able to make Product_A unique within a Manufacturer. I always get one line from Manufacturer_A to Product_A and another one from Manufacturer_B but I actually want two Product_A nodes (one from each Manufacturer), but just one Product_A node per Manufacturer.
I tried the following:
CREATE CONSTRAINT ON (c:MANUFACTURER) ASSERT c.MANUFACTURER IS UNIQUE;
CREATE CONSTRAINT ON (c:CUSTOMER) ASSERT c.CUSTOMER IS UNIQUE;
LOAD CSV WITH HEADERS FROM
'file:///small.csv' AS line
WITH line LIMIT 20
MERGE (CUSTOMER:Customer {Name: line.CUSTOMER})
MERGE (MANUFACTURER:Manufacturer {Name:line.MANUFACTURER})
MERGE (PRODUCT:Product {Name: line.PRODUCT})
MERGE (MANUFACTURER)<-[:PRODUCES]-(PRODUCT)
MERGE (CUSTOMER)<-[:CONSUMES]-(PRODUCT)
;
How would I model that correctly?
In this case, you don't want to MERGE the :PRODUCT node alone, but as part of a pattern connected to your merged manufacturer variable, that provides the context that the pattern you are looking for must be connected, and if no such pattern exists, the non-bound parts will be created.
...
MERGE (MANUFACTURER:Manufacturer {Name:line.MANUFACTURER})
MERGE (MANUFACTURER)<-[:PRODUCES]-(PRODUCT:Product {Name: line.PRODUCT})
...
So it won't matter if a product of that name exists elsewhere in the graph, as long as one isn't found connected to that manufacturer, it will be created as part of the MERGE.
This knowledge base article may be helpful as well, as it covers this application and more:
https://neo4j.com/developer/kb/understanding-how-merge-works/
When I try to add new nodes with labels (Phone, Name) that don't exist yet with a relationship to an existing node the nodes and relationships are not being created.
This is the before and after state with one existing relationship:
MATCH (n:Identity)-[a:ATTR]->(attr) RETURN *
And this is the mutation query:
MATCH (n:Identity {id:'4a028061-8dde-4f64-80c9-ae048e3f81fc'})
MERGE (n)-[na:ATTR]->(name:Name {val: 'John Smith'})
MERGE (n)-[pa:ATTR]->(p:Phone {val:2326410083})
RETURN *
I know this question is similar to Neo4J - Merge statement not creating new nodes with a relationship but, in my case, I am using filters on the nodes. What's am I missing?
Looks like the :Identity node you're trying to match to doesn't exist in the graph.
From your query, you're looking for an identity node with id:'4a028061-8dde-4f64-80c9-ae048e3f81fc', but in the graph image you supplied, if we assume the cut off caption is the id of the identity node, we can tell it starts with:'44b7'
Now it could be that the node you're trying to match on does exist, but doesn't have any outgoing :ATTR relationship (that would explain why it wouldn't be returned by your query), but that's unconfirmed. Does a node with id:'4a028061-8dde-4f64-80c9-ae048e3f81fc' exist in your graph? You haven't shown us that, and if no such node exists then the match would fail, and then there are no rows left for the remaining MERGEs to execute upon.
I have database with entities person (name,age) and project (name).
can I query the database in cypher that specifies me it is person or project?
for example consider I have these two instances for each :
Node (name = Alice, age= 20)
Node (name = Bob, age = 31)
Node (name = project1)
Node (name = project2)
-I want to know, is there any way that I just say project1 and it tells me that this is a project.
-or I query Alice and it says me this is a person?
Thanks
So your use case is to search things by name, and those things can be of several types instead of a single type.
Just to note, in general, this is not what Neo4j is built for. Typically in Neo4j queries you know the type of the thing you're searching for, and you're exploring relationships between that thing (or things) to figure out associations or data derived from that.
That said, there are ways to do this, though it's worth going through the rest of your use cases and seeing if Neo4j is really the best tool for what you're trying to do
Whenever you're querying by a property, you either want a unique constraint on the label/property, or an index on the label/property. Note that you need a combination of a label and a property for this; you cannot blindly ask for a node with a property without specifying a label and get good performance, as it will have to do a scan of all nodes in your database (there are some older manual indexes in Neo4j, but I'm not sure if these will continue to be supported; the schema indexes are recommended by the developers).
There is a workaround to this, as Neo4j allows multiple labels on the same node. If you only expect to query certain types by name (for example, only projects and people), you might create a :Named label, and set that label on all :Project and :Person nodes (and any other labels where it should apply). You can then create an index on :Named.name. That way your query would be something like:
MATCH (n:Named)
WHERE n.name = 'blah'
WITH LABELS(n) as types
WITH FILTER(type in types WHERE type <> 'Named') as labels
RETURN labels
Keep in mind that you haven't specified if a name should be unique among node types, so it could be possible for a :Person or a :Project or multiple :Persons to have the same name, unsure how that affects what should happen on your end. If every named thing ought to have a unique name, you should create a unique constraint on :Named.name (though again, it's on you to ensure that every node you create that ought to be :Named has the :Named label applied on creation).
You should use node labels (like Person and Project) to represent node "types".
For example, to create a person and a project:
CREATE (:Person {name: 'Alice', age: 20})
CREATE (:Project {name: 'project1'})
To find the project(s) named 'Fred':
MATCH (p:Project {name: 'Fred'})
RETURN p;
To get a collection of the labels of node n, you can invoke the LABELS(n) function. You can then look in that collection to see if the label you are looking for is in there. For example, if your Cypher query somehow obtains a node n, then this snippet would return n if and only if it has the Person label:
.
.
.
WHERE 'Person' IN LABELS(n)
RETURN n;
[UPDATED]
If you want to find all nodes with the name property value of "Fred":
MATCH (n {name: 'Fred'})
...
If you want to find all relationships with the name property value of "Fred":
MATCH ()-[r {name: 'Fred'})-()
...
If you want to match both in a single query, you have many ways to do that, depending on your exact use case. For example, if you want a cartesian product of the matching nodes and relationships:
OPTIONAL MATCH (n {name: 'Fred'})
OPTIONAL MATCH ()-[r {name: 'Fred'})-()
...
I want to add a relationship between two nodes, but only if the relationship does not exist. For example:
The Relationship between node1 and node2 currently exists with these properties: time:41221323,link:www.google.com
I am trying to add a relationship with different properties for example:
time:5344241,link:www.google.com
In this case i want to keep the original properties on the relationship.
You can use the below CQL query:
MATCH(a: startNodeLabel {attributes to match start node})
MATCH(m:endNodeLabel {attributes to match end node})
MERGE(a)-[:relationshipName]->(m)
The above merge statement creates relation between nodes a and m if there is no existing relationship between a and m.
You want either the MERGE or CREATE UNIQUE clause:
http://neo4j.com/docs/stable/query-merge.html
http://neo4j.com/docs/stable/query-create-unique.html
Also note that MERGE comes with additional ON CREATE SET and ON MATCH SET so you can control when properties get set.
I believe if you give either specific properties as part of the match syntax it will not create only if all of the properties match exactly.
Create Unique clause does serve this purpose. Neo4j Documet says
CREATE UNIQUE is in the middle of MATCH and CREATE — it will match
what it can, and create what is missing. CREATE UNIQUE will always
make the least change possible to the graph — if it can use parts of
the existing graph, it will.
START a=node(...), b=node(...)
CREATE UNIQUE (a)-[r:LIKES]-(b)
return a,b;
I am not sure what I am doing wrong here, so here is how I create nodes
CREATE (urlnode_1:UrlNode {url:'url1', nodenumber:1})
CREATE (urlnode_2:UrlNode {url:'url2', nodenumber:2})
I create relations as follows
CREATE
(urlnode_1)-[:OutLink {anchor_text:['MY']}]->(urlnode_2)
Two nodes are created successfully first, now on running the code to create the relation, I would have liked the relation to exist between the two created nodes but it creates two new nodes say 3 and 4 and shows a relation between them. What am i doing wrong here?
To guide you the best way I can, let's sum up some Neo4j basics concerning node and relationships creation :
A node can have one or more labels, labels are meaned to group the nodes by domain (User, Speaker, Company, etc..see a label as a table name for e.g. ). A node can also have properties.
A relationship can have only ONE type, relationships are organizing the graph. Relationships can also have properties.
To create a node, you can use the CREATE writing clause :
CREATE (n:Person {firstname: 'John'})
The CREATE statement will not check if other nodes with same label and properties already exists, it will just create a new node
Relationships can also be created with the same clause :
MATCH (n:Person {firstname: 'John'}), (p:Person {firstname: 'Pierre'})
CREATE (n)-[:KNOWS]->(p)
A complete pattern can also be created in one go :
CREATE (n:Person {name:'Chris'})-[:KNOWS]->(p:Person {name:'Oliver'})
REMINDER : CREATE will not check for existing nodes.
--- AND NOW MERGE ---
MERGE will lazily check for existing nodes, see him as a MATCH OR CREATE clause :
MERGE (n:Person {firstname:'Fred'})
If the node with label Person and firstname Fred does not exist, the node will be created, otherwise nothing will happen. This is where come the handy ON MATCH and ON CREATE mentionned by #joslinm .
If you run this query multiple times after the node creation, your graph will not change, if you know the http protocol, you can say that MERGE is an indempotent request.
Be aware that, MERGE will ensure that an entire pattern exist in the database, by creating it if it does not already exist, meaning that if you do MERGE with a complete pattern, the entire pattern will be looked up for existence, not a single node :
Say a node with label Person and name property with value 'John' already exist in the db :
MERGE (n:Person {name:'John'})
will not affect the graph
However :
MERGE (n:Person {name:'John'})-[:KNOWS]->(:Person {name:'Nathalia'})
A new John node will be created, because the entire pattern does not exist.
It is recommended to use MERGE incrementally :
MERGE (n:Person {name:'John'})
MERGE (p:Person {name:'Nathalia'})
MERGE (n)-[:KNOWS]->(p)
If you want to know more about the MERGE clause, I can highly recommend you this wonderful article from Luanne on GraphAware : http://graphaware.com/neo4j/2014/07/31/cypher-merge-explained.html
Chris
If you create a relationship, a new one will get created every single time. They are not inherently unique. It sounds like you'd rather be merging the relationship; i.e., if they relationship is there, match it, if not, create it.
The merge syntax for it is as follows:
MERGE (a:Node)-[:LIKES]->(b:Node)
ON
MATCH SET a.msg = 'I matched!'
ON
CREATE SET a.msg = 'I created!'
RETURN a
You can try it out here: http://console.neo4j.org/
You'll notice that first the msg will be "I created!" then after it matches, it will be "I matched!"