Package ac.simons.neo4j.migrations.annotations.catalog

Annotation Type Unique

@Retention(CLASS) @Target({TYPE,FIELD}) @Documented @Repeatable(UniqueProperties.class) public @interface Unique
Annotation to mark one or more fields of a class as unique properties for a given node or relationship. You will want to use it on a type for building composite constraints (constraints spanning more than one field) and on single fields for single property constraints.

When is this annotation useful?

  • You have a plain Java application with some models but no object mapper on the classpath but you still want to derive content
  • You are a Spring Data Neo4j (SDN6+) user and want to enrich your models with unique or existential constraints
  • You are an Neo4j-OGM user but are looking for an object mapper agnostic way of enriching your model

Determining labels or types: Depending on your approach and combination with other annotations (such as SDN6+ or OGM annotations), the process is as following

  • Explicitly use label()
  • On a plain class: The simple class name is used as label (we default to targeting nodes)
  • If combined any of the following SDN6+ annotations org.springframework.data.neo4j.core.schema.Node or org.springframework.data.neo4j.core.schema.RelationshipProperties, we default to the SDN6 approach
  • If combined with an Neo4j-OGM annotation, we default to the Neo4j-OGM approach
Note: We follow the above algorithm strictly, and we don't try to resolve conflicts. If in doubt, the processor will fail hard

Unique constraints are only supported for Nodes / Labels, not for Relationships / Types.

This annotation can also be repeated on a class. If you decide to put contradicting information on a class, for example targeting labels with one annotation and relationships with another, we won't stop you as long as we can resolve both error free: You might end up with a catalog that defines several constraints coming from one type and aiming for both nodes and relationship constraints.

Since:
1.15.0
Author:
Michael J. Simons
Soundtrack
Juse Ju - Shibuya Crossing

  • Optional Element Summary

    Optional Elements
    Modifier and Type
    Optional Element
    Description
    String
    label
    If this is not null it has precedence over an implicit label (either no class annotations or one without a dedicated label) but not over OGM or SDN6 annotations specifying the label or type explicitly.
    String[]
    properties
    Use this if you want to define composite, unique constraint when using Unique on the class level.

  • Element Details

    • label

      String label
      If this is not null it has precedence over an implicit label (either no class annotations or one without a dedicated label) but not over OGM or SDN6 annotations specifying the label or type explicitly. Its use must be consistent throughout the class.
      Returns:
      The target label
      Default:
      ""

    • properties

      String[] properties
      Use this if you want to define composite, unique constraint when using Unique on the class level. Leave it empty when using on field level, otherwise an exception will be thrown.
      Returns:
      The list of properties to include in the composite.
      Default:
      {}