One of the benefits of Neo4j is to be able to extend it in case there is some functionality missing. There are two ways of extending your database:
GrapheneDB allows you to manage server extensions and stored procedures right from your admin interface. The Extensions feature is available on the Developer plan or higher (Sandstone and higher on Heroku).
Writing an extension will require you to be familiar with the Java programming language and to have an environment setup for compiling Java code. Please read Neo4j Extending Neo4j documents section carefully.
Keep in mind
Before using an extension make sure you understand how it works. Additionally, if you are adding a third party unmanaged extension make sure to audit the code before you proceed.