Neo4j Graph Database Fundamentals · Lesson

Stored Procedures and UDFs

Learn to write and deploy custom stored procedures and user-defined functions to encapsulate complex logic and extend Cypher.

Stored Procedures and UDFs is a free Neo4j Graph Database Fundamentals lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Neo4j Graph Database Fundamentals learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Extending Neo4j's Capabilities

Welcome to extending Neo4j! Sometimes, Cypher isn't enough for complex logic or specific integrations. That's where custom code comes in.

Neo4j allows you to extend its functionality using Stored Procedures and User-Defined Functions (UDFs), typically written in Java.

Stored Procedures perform actions, like creating nodes or running complex algorithms.
User-Defined Functions (UDFs) return values, just like built-in Cypher functions.

They encapsulate complex logic, improve query readability, and boost performance for repetitive tasks.

Procedures vs. User-Defined Functions

It's crucial to understand the difference between procedures and UDFs:

Stored Procedures:
- Called with CALL package.procedure()
- Can perform side effects (create, update, delete data)
- Return tabular results (rows and columns)
- Can access the graph database directly
User-Defined Functions (UDFs):
- Called within Cypher expressions (e.g., RETURN my.udf(n.property))
- Must be pure functions (no side effects)
- Return a single scalar value (e.g., string, number, boolean, list)
- Cannot modify the graph or access it directly

Stored Procedure Anatomy (Java)

Stored procedures are Java classes compiled into a JAR file. They use specific Neo4j annotations.

Here's the basic structure for a simple procedure that doesn't take any parameters and returns a string:

package com.coddykit;

import org.neo4j.procedure.Procedure;
import org.neo4j.procedure.Name;
import org.neo4j.procedure.Description;
import org.neo4j.graphdb.Result;
import java.util.stream.Stream;

public class MyProcedures {

    // Define the output record structure
    public static class StringOutput {
        public String value;

        public StringOutput(String value) {
            this.value = value;
        }
    }

    @Procedure(value = "my.hello")
    @Description("Returns a simple greeting.")
    public Stream<StringOutput> hello() {
        return Stream.of(new StringOutput("Hello from CoddyKit!"));
    }
}

Key Elements of a Procedure

Let's break down the previous code:

@Procedure(value = "my.hello"): This annotation declares a method as a stored procedure and defines its full name (my.hello).
@Description: Provides a description visible in Neo4j Browser.
Output Class (StringOutput): Procedures return a Stream of custom objects. Each object represents a row in the result, and its public fields become the column names.
Stream<StringOutput>: The return type for procedures.

This Java code is ready to be compiled into a JAR and deployed.

Deploying Your Custom Procedure

To make your Java procedure available in Neo4j, you need to compile it and place the resulting JAR file into the database's plugins directory.

Steps:

Compile your Java code into a JAR file (e.g., my-procedures.jar).
Copy the JAR file into your Neo4j installation's plugins folder.
Restart your Neo4j database instance.

After restarting, Neo4j will discover and register your new procedures and functions.

Calling a Stored Procedure

Once deployed, you can call your procedure using the CALL keyword in Cypher. Let's try calling our my.hello procedure:

CALL my.hello();

User-Defined Function (UDF) Anatomy

UDFs are similar to procedures but have different annotations and return types. They are designed to be used inline within Cypher expressions.

Here's the basic structure for a UDF that takes a string and returns a modified string:

package com.coddykit;

import org.neo4j.procedure.UserFunction;
import org.neo4j.procedure.Name;
import org.neo4j.procedure.Description;

public class MyFunctions {

    @UserFunction("my.capitalize")
    @Description("Capitalizes the first letter of an input string.")
    public String capitalize(@Name("input") String input) {
        if (input == null || input.isEmpty()) {
            return input;
        }
        return Character.toUpperCase(input.charAt(0)) + input.substring(1);
    }
}

Key Elements of a UDF

Let's look at the UDF's components:

@UserFunction("my.capitalize"): This annotation declares a method as a UDF and defines its full name (my.capitalize).
@Name("input"): Specifies the name for the parameter when used in Cypher.
Return Type: UDFs return a single scalar value (e.g., String, Long, Boolean, List<String>). They do not return a Stream or custom output objects.

Like procedures, this Java code must be compiled into a JAR and deployed to the plugins folder.

Calling a User-Defined Function

After deploying your UDF, you can use it directly within Cypher queries as part of an expression. It behaves just like built-in functions.

Let's use our my.capitalize UDF:

RETURN my.capitalize("hello world");

// Or with graph data:
MATCH (p:Person)
RETURN p.name, my.capitalize(p.name) AS CapitalizedName;

Quick Check: Procedures & UDFs

Which of the following statements is TRUE regarding Neo4j Stored Procedures and User-Defined Functions (UDFs)?

Recap & Next Steps

You've learned how to extend Neo4j with custom Java code!

Stored Procedures execute complex actions, return tabular results, and are called with CALL.
User-Defined Functions (UDFs) return single scalar values, are pure functions (no side effects), and are used inline in Cypher expressions.
Both require Java code, specific Neo4j annotations, compilation into a JAR, and deployment to the Neo4j plugins directory.

These powerful extensions allow you to integrate custom logic, algorithms, and external services directly into your Neo4j environment, significantly expanding its capabilities.

Frequently asked questions

Is the “Stored Procedures and UDFs” lesson free?

Yes — the full text of “Stored Procedures and UDFs” is free to read here on the web, and the Neo4j Graph Database Fundamentals course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Neo4j Graph Database Fundamentals course, upgrade to CoddyKit PRO.

What will I learn in “Stored Procedures and UDFs”?

Learn to write and deploy custom stored procedures and user-defined functions to encapsulate complex logic and extend Cypher. You practise Neo4j Graph Database Fundamentals with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Neo4j Graph Database Fundamentals?

No prior experience is required. Neo4j Graph Database Fundamentals on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Stored Procedures and UDFs” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Neo4j Graph Database Fundamentals lesson?

Yes. Every Neo4j Graph Database Fundamentals lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

Stored Procedures and UDFs
Integrating with BI and Visualization Tools
Advanced Data Ingestion Pipelines
Full-Text and Vector Search in Neo4j

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