OneToMany relation cannot be saved in spring with liquibase - spring

Question

I am trying to build a data model in spring that cascades up to 3 levels down with one-to-many relationships, but I cannot get it to work with liquibase scripts.
I am using spring boot with Kotlin and liquibase with a PostgreSQL database.
What I did so far:
cutting down the code to only contain the part that does not work (see below)
I tried both #OneToMany with #JoinTable as well as with #JoinColumn, and I also tried the same with #ManyToMany to rule out an issue with #OneToMany
I ran the same code (below) without liquibase to have Hibernate/JPA create the tables from the models
this actually worked, so I generated liquibase scripts out of these tables, but they look exactly the same as my own (except key names)
retrieving data with these models work (if I insert data via SQL directly)
To be honest I am not sure, if the issue is in the model, in the configuration, or in the liquibase scripts, so I'll just post all of those. Am I missing a configuration? Did I configure the cascading correct? Are my model definitions/liquibase scripts wrong?
The exception I get on saving a parent is:
Hibernate: insert into parent (name) values (?)
2021-12-15 23:29:16.797 WARN 14115 --- [ Test worker] o.h.engine.jdbc.spi.SqlExceptionHelper : SQL Error: 0, SQLState: 23502
2021-12-15 23:29:16.798 ERROR 14115 --- [ Test worker] o.h.engine.jdbc.spi.SqlExceptionHelper : ERROR: null value in column "id" of relation "parent" violates not-null constraint
Detail: Failing row contains (null, Test 1).
org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint [id" of relation "parent]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement
...
Caused by: org.hibernate.exception.ConstraintViolationException: could not execute statement
...
Caused by: org.postgresql.util.PSQLException: ERROR: null value in column "id" of relation "parent" violates not-null constraint
Detail: Failing row contains (null, Test 2).
The code I am trying to run:
val parent = Parent(
id = 0,
name = "Test 2"
).apply {
children = mutableSetOf(
Child(
id = 0,
name = "Test 21",
parent = this
).apply {
grandchildren =
mutableSetOf(
Grandchild(
id = 0,
name = "Test 211",
child = this
)
)
},
Child(
id = 0,
name = "Test 22",
parent = this
)
)
}
val saveParent: Parent = parentRepository.save(parent)
models:
#Entity
class Parent(
#Id #GeneratedValue(strategy = GenerationType.IDENTITY)
var id: Long = 0,
var name: String,
#OneToMany(mappedBy = "parent", cascade = [CascadeType.ALL])
var children: MutableSet<Child> = mutableSetOf()
)
#Entity
class Child(
#Id #GeneratedValue(strategy = GenerationType.IDENTITY)
var id: Long = 0,
var name: String,
#ManyToOne #JoinColumn(name = "child_id")
var parent: Parent,
#OneToMany(mappedBy = "child", cascade = [CascadeType.ALL])
var grandchildren: MutableSet<Grandchild> = mutableSetOf()
)
#Entity
class Grandchild(
#Id #GeneratedValue(strategy = GenerationType.IDENTITY)
var id: Long = 0,
var name: String,
#ManyToOne #JoinColumn(name = "child_id")
var child: Child
)
application.yml
spring:
datasource:
platform: postgres
url: jdbc:postgresql://localhost:5432/onetomany?ssl=false
driver-class-name: org.postgresql.Driver
initialization-mode: always
jpa:
database: postgresql
database-platform: org.hibernate.dialect.PostgreSQLDialect
generate-ddl: false
hibernate:
ddl-auto: none
liquibase:
enabled: true
change-log: classpath:db/master.xml
liquibase script:
<?xml version="1.1" encoding="UTF-8" standalone="no"?>
<databaseChangeLog xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-4.1.xsd">
<changeSet author="bruce (generated)" id="data-1">
<createTable tableName="parent">
<column name="id" type="BIGINT">
<constraints nullable="false" primaryKey="true" primaryKeyName="PK_PARENT"/>
</column>
<column name="name" type="VARCHAR(255)">
<constraints nullable="false"/>
</column>
</createTable>
</changeSet>
<changeSet author="bruce (generated)" id="data-2">
<createTable tableName="child">
<column name="id" type="BIGINT">
<constraints nullable="false" primaryKey="true" primaryKeyName="PK_CHILD"/>
</column>
<column name="name" type="VARCHAR(255)">
<constraints nullable="false"/>
</column>
<column name="parent_id" type="BIGINT">
<constraints nullable="false"/>
</column>
</createTable>
</changeSet>
<changeSet author="bruce (generated)" id="data-3">
<createTable tableName="grandchild">
<column name="id" type="BIGINT">
<constraints nullable="false" primaryKey="true" primaryKeyName="PK_GRANDCHILD"/>
</column>
<column name="name" type="VARCHAR(255)">
<constraints nullable="false"/>
</column>
<column name="child_id" type="BIGINT">
<constraints nullable="false"/>
</column>
</createTable>
</changeSet>
<changeSet author="bruce (generated)" id="data-6">
<addForeignKeyConstraint baseColumnNames="parent_id" baseTableName="child" constraintName="FK_CHILD_PARENT"
deferrable="false" initiallyDeferred="false" onDelete="RESTRICT" onUpdate="RESTRICT"
referencedColumnNames="id" referencedTableName="parent" validate="true"/>
</changeSet>
<changeSet author="bruce (generated)" id="data-8">
<addForeignKeyConstraint baseColumnNames="child_id" baseTableName="grandchild" constraintName="FK_CHILD_GRANDCHILD"
deferrable="false" initiallyDeferred="false" onDelete="RESTRICT" onUpdate="RESTRICT"
referencedColumnNames="id" referencedTableName="child" validate="true"/>
</changeSet>
</databaseChangeLog>

Answer 1

#GeneratedValue(strategy = GenerationType.IDENTITY) would normally work by specifying an auto-incrementing default value at the database, such as nextval('my_entity_sequence'::regclass). Upon insert, the DB will generate the identifier.
In Postgres, there are serial/bigserial pseudo-types to specify an auto-increment column (which will internally create the sequence as well as the column default value), so the DDL could e.g. look like this:
create table my_entity ( id bigserial not null, primary key (id) )
https://www.postgresql.org/docs/current/datatype-numeric.html
In your case, liquibase missed the type/defaults for all of the ID columns (right now just a "parent"-insert fails, but inserts for the other entities will fail as well).
This is a known liquibase issue: https://github.com/liquibase/liquibase/issues/1009 - suggestions to work around it include manually specifying autoIncrement="true" in the changeset.