What is a multi-value property?
A multi-value property is a property that can hold one or more values. This type of data in Neo4j is represented as a list. All values in a list must have the same type. For example:
-
["USA", "Germany", "France"]
-
[100, 55, 4]
Multi-value properties in our data model
Our current data model defines lists for these properties:
-
Movie: countries
-
Movie: languages
Because of the way that we imported the data, we have an additional multi-value property, Movie: genres. Although our data model does not contain a genres property for Movie nodes, we will transform the data for this property as it will be a means to our goal of creating the Genre nodes in the graph in a later transformation.
All of these properties were imported as strings with data that looks as follows:
Notice that for this particular set of CSV files, the "|" character is specified as the separator.
Transforming list properties
Transforming multi-value fields as lists can be done as follows where we use two Cypher built-in functions to help us:
You will execute this code in the next Challenge.
Unresolved directive in lesson.adoc - include::{repository-raw}/main/modules/3-refactoring-imported-data/lessons/3-transform-lists/transform-lists.cypher[]coalesce() returns an empty string if the entry in m.countries is null.
split() identifies each element in the multi-value field where the "|" character is the separator and create a list of each element.
So the resulting transformations will look like this:
Checking the property types
Again, you can confirm that the property types for the three Movie properties has been completed also by viewing the types again:
The three list properties have been transformed to the type StringArray.
Check your understanding
1. Storage type for lists of strings
When you transform a multi-value property to a list of strings, what type does it have in the graph?
-
❏ List
-
❏ Strings
-
❏ Array
-
✓ StringArray
Hint
You can execute CALL apoc.meta.nodeTypeProperties() to view how properties are stored in the graph.
Solution
A list of strings is stored as StringArray in the graph.
2. Transform to a list
Suppose you want to transform the data in a field to be a list of strings. What built-in Cypher functions help you to do this?
-
❏
toString() -
❏
toList() -
✓
coalesce() -
✓
split()
Hint
You use two functions, one to identify the elements separated by a character and one to create the list.
Solution
The correct answers are: coalesce() and split().
Summary
In this lesson, you learned how to transform multi-value properties to lists. In the next Challenge, you will transform multi-value properties in the graph you have been working with to list properties.