不能与空值合并； neo4j中的“无法使用空属性值合并节点" [英] Can't MERGE with null values; 'Cannot merge node using null property value' in neo4j

问题描述

我在csv中有一列如下所示:

我正在使用以下代码测试日期拆分的工作方式:

LOAD CSV WITH HEADERS FROM
'file:///..some_csv.csv' AS line
WITH
SPLIT(line.date_of_birth, '/') AS date_of_birth
return date_of_birth;

此代码块可以正常工作，并提供我期望的结果，它是每个日期的三个值的集合；如果没有日期，则可能是一个null(例如

[4, 5, 1971]  
[0, 0, 2003]  
[0, 0, 2005]  
 . . .  
null  
null  
 . . .  

我的问题是，创建的null会导致什么问题?为什么在存在null的情况下不能合并?

LOAD CSV WITH HEADERS FROM
'file:///..some_csv.csv' AS line
WITH
SPLIT(line.date_of_birth, '/') AS date_of_birth, line
MERGE (p:Person {
 date_of_birth: date_of_birth
});

上面的代码块给了我错误:

Cannot merge node using null property value for date_of_birth  

我四处搜寻，但仅发现关于此错误的另一个SO问题 ，没有答案.其他搜索无济于事.

我的印象是，如果没有值，那么Neo4j根本就不会创建该元素.

我认为也许无法生成该节点，因为毕竟，如果没有值可生成该节点，那么如何生成该节点呢?因此，由于我知道没有ID缺失，也许我可以将ID和日期合并，所以Neo4j总是看到一个值.

但是此代码并没有更好的表现(相同的错误消息):

LOAD CSV WITH HEADERS FROM
'file:///..some_csv.csv' AS line
WITH
SPLIT(line.date_of_birth, '/') AS date_of_birth, line
MERGE (p:Person {
 ID: line.ID
,date_of_birth: date_of_birth
});  

我的下一个想法是，也许此错误是因为我试图在斜杠上拆分空值?也许整个问题是由于SPLIT造成的.

但是，当简化为这个错误时，会出现相同的错误:

LOAD CSV WITH HEADERS FROM
'file:///..some_csv.csv' AS line
WITH line
MERGE (p:Person {
 subject_person_id: line.subject_person_id
,date_of_birth: line.date_of_birth
});

所以我不太了解错误的原因.感谢您的关注.

编辑

解决方案

正如@cybersam所说，合并不适用于在范围内将属性设置为null的查询.因此，您可以在创建和匹配时使用 :

LOAD CSV WITH HEADERS FROM
  'file:///..some_csv.csv' AS line
MERGE (p:Person {
  subject_person_id: line.subject_person_id
})
  ON CREATE SET p.date_of_birth = line.date_of_birth
  ON MATCH SET p.date_of_birth = line.date_of_birth

I have a column in a csv that looks like this:

I am using this code to test how the splitting of the dates is working:

LOAD CSV WITH HEADERS FROM
'file:///..some_csv.csv' AS line
WITH
SPLIT(line.date_of_birth, '/') AS date_of_birth
return date_of_birth;

This code block works fine and gives me what I'd expect, which is a collection of three values for each date, or perhaps a null if there was no date ( e.g,

[4, 5, 1971]  
[0, 0, 2003]  
[0, 0, 2005]  
 . . .  
null  
null  
 . . .  

My question is, what is this problem with the nulls that are created, and why can't I do a MERGE when there are nulls?

LOAD CSV WITH HEADERS FROM
'file:///..some_csv.csv' AS line
WITH
SPLIT(line.date_of_birth, '/') AS date_of_birth, line
MERGE (p:Person {
 date_of_birth: date_of_birth
});

This block above gives me the error:

Cannot merge node using null property value for date_of_birth  

I have searched around and have only found one other SO question about this error, which has no answer. Other searches didn't help.

I was under the impression that if there isn't a value, then Neo4j simply doesn't create the element.

I figured maybe the node can't be generated since, after all, how can a node be generated if there is no value to generate it from? So, since I know there are no ID's missing, maybe I could MERGE with ID and date, so Neo4j always sees a value.

But this code didn't fare any better (same error message):

LOAD CSV WITH HEADERS FROM
'file:///..some_csv.csv' AS line
WITH
SPLIT(line.date_of_birth, '/') AS date_of_birth, line
MERGE (p:Person {
 ID: line.ID
,date_of_birth: date_of_birth
});  

My next idea is that maybe this error is because I'm trying to split a null value on slashes? Maybe the whole issue is due to the SPLIT.

But alas, same error when simplified to this:

LOAD CSV WITH HEADERS FROM
'file:///..some_csv.csv' AS line
WITH line
MERGE (p:Person {
 subject_person_id: line.subject_person_id
,date_of_birth: line.date_of_birth
});

So I don't really understand the cause of the error. Thanks for looking at this.

EDIT

Both @stdob-- and @cybersam have both answered with equally excellent responses, if you came here via Google please consider them as if both were accepted

解决方案

As @cybersam said merge not work well with queries where the properties are set within the scope in null. So, you can use on create and on match:

LOAD CSV WITH HEADERS FROM
  'file:///..some_csv.csv' AS line
MERGE (p:Person {
  subject_person_id: line.subject_person_id
})
  ON CREATE SET p.date_of_birth = line.date_of_birth
  ON MATCH SET p.date_of_birth = line.date_of_birth

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