59 lines
3.2 KiB
Plaintext
59 lines
3.2 KiB
Plaintext
= 6.1 Migration Guide
|
|
:toc:
|
|
:toclevels: 4
|
|
:docsBase: https://docs.jboss.org/hibernate/orm/6.1
|
|
:userGuideBase: {docsBase}/userguide/html_single/Hibernate_User_Guide.html
|
|
:javadocsBase: {docsBase}/javadocs
|
|
|
|
|
|
This guide discusses migration from Hibernate ORM version 6.1. For migration from
|
|
earlier versions, see any other pertinent migration guides as well.
|
|
|
|
* link:../../../6.0/migration-guide/migration-guide.html[6.0 Migration guide]
|
|
|
|
== Basic array/collection mapping
|
|
|
|
Basic arrays, other than `byte[]`/Byte[] and `char[]`/`Character[]`, and basic collections (only subtypes of `Collection`)
|
|
now map to the type code `SqlTypes.ARRAY` by default, which maps to the SQL standard `array` type if possible,
|
|
as determined via the new methods `getArrayTypeName` and `supportsStandardArrays` of `org.hibernate.dialect.Dialect`.
|
|
If SQL standard array types are not available, data will be modeled as `SqlTypes.JSON`, `SqlTypes.XML` or `SqlTypes.VARBINARY`,
|
|
depending on the database support as determined via the new method `org.hibernate.dialect.Dialect.getPreferredSqlTypeCodeForArray`.
|
|
|
|
Due to this change, schema validation errors could occur as 5.x and 6.0 used the type code `SqlTypes.VARBINARY` unconditionally
|
|
and serialized the contents with Java serialization. The migration to native array or JSON/XML types is non-trivial and requires
|
|
that the data is first read through the Java serialization mechanism and then written back through the respective JDBC method for the type.
|
|
|
|
A possible migration could involve the following steps in a migration script:
|
|
|
|
1. Execute `alter table tbl rename column array_col to array_col_old` to have the old format available
|
|
2. Execute `alter table tbl add column array_col DATATYPE array` to add the column like the new mapping expects it to be
|
|
3. Run the query `select t.primary_key, t.array_col_old from table t`
|
|
4. For every result, deserialize the old representation via e.g. `org.hibernate.internal.util.SerializationHelper.deserialize(java.io.InputStream)`
|
|
5. For every result, load the Hibernate entity by primary key and set the deserialized value
|
|
6. Finally, drop the old column `alter table tbl drop column array_col_old`
|
|
|
|
|
|
== Enum mapping changes
|
|
|
|
Enums now map to the type code `SqlType.SMALLINT` by default, whereas before it mapped to `TINYINT`.
|
|
This mapping was not quite correct as Java effectively allows up to 32K enum entries, but `TINYINT` is only a 1 byte type.
|
|
|
|
In practice, this isn't a big issue though for two reasons. A lot of databases do not support a 1 byte integer DDL type,
|
|
so Hibernate falls back to the 2+ byte integer type as DDL type. Apart from that, enums in ORM models usually do not exceed the 255 value limit.
|
|
Note that the migration is not required as schema validation is able to handle the use of `SMALLINT` when the DDL type is `TINYINT`.
|
|
|
|
The migration usually requires running only a simple alter command `alter table tbl alter column enum_col smallint`
|
|
or `alter table tbl modify column enum_col smallint`, depending on your database dialect.
|
|
|
|
The following dialects currently have DDL types registered for `TINYINT` and might produce a different schema now:
|
|
|
|
* Cachè
|
|
* Ingres
|
|
* Teradata
|
|
* TimesTen
|
|
* H2
|
|
* HSQL
|
|
* MySQL
|
|
* MariaDB
|
|
* Oracle
|