Spring Hibernate create if not exists for child Objects

Question

I've got an issue regarding saving child objects with Spring Hibernate and hope you can give me a hint. Already searched on Stackoverflow, but I couldn't find anything for my use case.

I have two classes:

Class File {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
  @JoinColumn(name = "format_id")
  private Format format;
}

Class Format {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  @Column(name = "puid")
  private String puid;
}

When I read a given XML file..

<files>
    <file>
        <name>abc</name>
        <format>pdf</format>
    </file>
    <file>
        <name>xyz</name>
        <format>pdf</format>
    </file>
</files>

.. I create objects of class file and format accordingly. At the end I'll call fileRepository.savaAll();

My problem is, that now I have two formats in my mySQL database, although there are the same. Is there a way (perhaps through annotations) to only create new database elements for child elements, if not exists (puid should be unique).

I want to avoid to iterate manually through all files, getting the format and check if it already exists.

Thanks

Jens Schauder · Accepted Answer · 2020-06-09 07:03:46Z

1

I want to avoid to iterate manually through all files, getting the format and check if it already exists.

With your current model this is exactly what you need to do: instead of creating a new Format load it and only when that fails create a new instance. I honestly don't see why it seems so important to you to not do that since it seems like a rather trivial line of code or two.

An alternative would be to map Format as an embedded. Here is a little tutorial about that concept if you need it.

answered Jun 9, 2020 at 7:03

Jens Schauder

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