How To Calculate Entity Persistent Property Via Hibernate @Generated

Description: This application is an example of calculating an entity persistent property at INSERT and/or UPDATE time via Hibernate, @Generated.

Key points:

Calculate at INSERT time:

• annotate the corresponding persistent field with @Generated(value = GenerationTime.INSERT)
• annotate the corresponding persistent field with @Column(insertable = false)

Calculate at INSERT and UPDATE time:

• annotate the corresponding persistent field with @Generated(value = GenerationTime.ALWAYS)
• annotate the corresponding persistent field with @Column(insertable = false, updatable = false)

Further, apply:

Method 1:

• if the database schema is generated via JPA annotations (not recommended) then use columnDefinition element of @Column to specify as an SQL query expression the formula for calculating the persistent property

Method 2:

• if the database schema is not generated via JPA annotations (recommended way) then add the formula as part of schema in CREATE TABLE

Note: In production, you should not rely on columnDefinition. You should disable hibernate.ddl-auto (by omitting it) or set it to validate, and add the SQL query expression in CREATE TABLE (in this application, check the discount column in CREATE TABLE, file schema-sql.sql). Nevertheless, not even schema-sql.sql is ok in production. The best way is to rely on Flyway or Liquibase.

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