Java.Hibernate.Medium.When do i need such type conversion ?

✅ Short Answer

You need custom type conversion when you want to map Java types that don’t directly match database column types, or when you need to store complex or non-standard values — beyond what JPA handles automatically.

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🔎 Detailed Explanation

🔹 Common scenarios where you need custom conversion:
✅ Value objects in your domain:

• Example: Money, Distance, GeoCoordinate, Percentage.
• These usually wrap multiple fields or add behavior → but in the DB, you need to store them as one or more columns.

✅ Enums with custom representations:

• E.g., storing enum codes like “A”, “B” instead of enum ordinal or name.
• Mapping between a business-friendly enum and a legacy DB value.

✅ Non-standard or vendor-specific DB types:

• PostgreSQL jsonb, hstore, inet.
• Oracle SDO_GEOMETRY for GIS data.
• UUIDs stored as binary instead of text.

✅ Encrypted fields:

• If you need to encrypt/decrypt fields transparently on read/write → perfect place for a custom AttributeConverter or UserType.

✅ Custom data serialization:

• Store objects as JSON or XML in a single text column.
• Store lists or sets as comma-separated strings (e.g., tags → "tag1,tag2,tag3").

✅ Legacy schemas:

• When you don’t control the DB design but must map objects cleanly → custom type mapping can bridge the mismatch.

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🔹 Examples in real apps
🔸 E-commerce → Money value object → amount + currency mapped to two columns.
🔸 Multi-tenant SaaS → TenantId as a value object → mapped to a UUID or long.
🔸 Auditing → automatically convert entity state into a JSON snapshot for storage.

📌 Key Takeaways

✅ Reach for custom types when you need to map non-standard Java-to-SQL representations, or encapsulate domain logic in value objects that can’t be stored as a simple field.
✅ Custom conversions help you keep your domain model clean without leaking persistence concerns into business logic.