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Neo4j: LOAD CSV - Handling Empty Columns

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Neo4j: LOAD CSV - Handling Empty Columns

· Java Zone
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Learn how to troubleshoot and diagnose some of the most common performance issues in Java today. Brought to you in partnership with AppDynamics.

A common problem that people encounter when trying to import CSV files into Neo4j using Cypher’s LOAD CSV command is how to handle empty or ‘null’ entries in said files.

For example let’s try and import the following file which has 3 columns, 1 populated, 2 empty:

$ cat /tmp/foo.csv
a,b,c
mark,,
load csv with headers from "file:/tmp/foo.csv" as row
MERGE (p:Person {a: row.a})
SET p.b = row.b, p.c = row.c
RETURN p

When we execute that query we’ll see that our Person node has properties ‘b’ and ‘c’ with no value:

==> +-----------------------------+
==> | p                           |
==> +-----------------------------+
==> | Node[5]{a:"mark",b:"",c:""} |
==> +-----------------------------+
==> 1 row
==> Nodes created: 1
==> Properties set: 3
==> Labels added: 1
==> 26 ms

That isn’t what we want – we don’t want those properties to be set unless they have a value.

TO achieve this we need to introduce a conditional when setting the ‘b’ and ‘c’ properties. We’ll assume that ‘a’ is always present as that’s the key for our Person nodes.

The following query will do what we want:

load csv with headers from "file:/tmp/foo.csv" as row
MERGE (p:Person {a: row.a})
FOREACH(ignoreMe IN CASE WHEN trim(row.b) <> "" THEN [1] ELSE [] END | SET p.b = row.b)
FOREACH(ignoreMe IN CASE WHEN trim(row.c) <> "" THEN [1] ELSE [] END | SET p.c = row.c)
RETURN p

Since there’s no if or else statements in cypher we create our own conditional statement by using FOREACH. If there’s a value in the CSV column then we’ll loop once and set the property and if not we won’t loop at all and therefore no property will be set.

==> +-------------------+
==> | p                 |
==> +-------------------+
==> | Node[4]{a:"mark"} |
==> +-------------------+
==> 1 row
==> Nodes created: 1
==> Properties set: 1
==> Labels added: 1

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