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I have created the following LiquiGraph migration script:

<?xml version="1.0" encoding="UTF-8"?>
<changelog xmlns="http://www.liquigraph.org/schema/1.0/liquigraph.xsd">

    <changeset id="initial_indexes_and_constraints" author="alex">
        <query>CREATE INDEX ON :Action(entityId)</query>
        <query>CREATE CONSTRAINT ON ( action:Action ) ASSERT action.id IS UNIQUE</query>
    </changeset>
</changelog>

As you may see -I added 2 lines there - for INDEX and CONSTRAINT creation.

I would like to make it idempotent - this way I'd like to check that index or constraint doesn't exist and only then to create them.

Is it possible to add such kind of validation to my LiquiGraph migration script? If so, please show an example.

alexanoid
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1 Answers1

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In general, there is no need to check by index or constraint existence because no action is performed when they already exist.

For example: running the following command one time (using Neo4j Browser):

CREATE CONSTRAINT ON ( action:Action ) ASSERT action.id IS UNIQUE

will produce this output:

Added 1 constraint, completed after 285 ms.

Running the same command again will produce the following output:

(no changes, no records)
Bruno Peres
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    +1 if it was not the case, it would require a mix of APOC index-related extensions (https://neo4j-contrib.github.io/neo4j-apoc-procedures/#_index_management_2) and changeset preconditions. – fbiville Jan 09 '18 at 09:53