org.neo4j.procedure

Annotation Type Procedure

@Target(value=METHOD)
 @Retention(value=RUNTIME)
public @interface Procedure

Declares a method as a Procedure, meaning the method can be called from the cypher query language.

Procedures accept input, use that input to perform work, and then return a Stream of Records. The work performed usually involves one or more resources, such as a GraphDatabaseService.

By default, procedures are read-only. If you want to perform writes to the database, you need to add the PerformsWrites annotation to your method as well.

Input declaration

A procedure can accept input arguments, which is defined in the arguments to the annotated method. Each method argument must be a valid Procedure input type, and each must be annotated with the Name annotation, declaring the input name.

Valid input types are as follows:

• String
• Long or long
• Double or double
• Number
• Boolean or boolean
• Node
• Relationship
• Path
• Map with key String and value of any type in this list, including Map
• List with element type of any type in this list, including List
• Object, meaning any valid input types

Output declaration

A procedure must always return a Stream of Records. The record is defined per procedure, as a class with only public, non-final fields. The types, order and names of the fields in this class define the format of the returned records.

Valid field types are as follows:

• String
• Long or long
• Double or double
• Number
• Boolean or boolean
• Node
• Relationship
• Path
• Map with key String and value of any type in this list, including Map
• List of elements of any valid field type, including List
• Object, meaning any of the valid field types

Resource declarations

The procedure method itself can contain arbitrary Java code - but in order to work with the underlying graph, it must have access to the graph API. This is done by declaring fields in the procedure class, and annotating them with the Context annotation. Fields declared this way are automatically injected with the requested resource. This is how procedures gain access to APIs to do work with.

All fields in the class containing the procedure declaration must either be static; or it must be public, non-final and annotated with Context.

Resources supported by default are as follows:

• GraphDatabaseService
• Log

Lifecycle and state

The class that declares your procedure method may be re-instantiated before each call. Because of this, no regular state can be stored in the fields of the procedure.

If you want to maintain state between invocations to your procedure, simply use a static field. Note that procedures may be called concurrently, meaning you need to take care to ensure the state you store in static fields can be safely accessed by multiple callers simultaneously.

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
String	value The namespace and name for the procedure, as a period-separated string.

Element Detail

value

public abstract String value

The namespace and name for the procedure, as a period-separated string. For instance myprocedures.myprocedure. If this is left empty, the name defaults to the package name of the class the procedure is declared in, combined with the method name. Notably, the class name is omitted.

Returns:

the namespace and procedure name

Default:

""