Java.Hibernate.Medium.So we don’t need write here “on tableA.key = tableB.foreignKey” ?

✅ Short Answer

Correct: In JPQL/HQL joins, you do not write ON tableA.key = tableB.foreignKey like in SQL.
Instead, you navigate mapped entity relationships using Java object paths (e.g., o.customer) → JPA knows how to join based on the entity mappings (@ManyToOne, @OneToMany, etc.).

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🔎 Detailed Explanation

• In SQL, you manually join tables by specifying:

SELECT * FROM orders o JOIN customers c ON o.customer_id = c.id

In JPQL/HQL, the ON clause is not needed, because your JPA entity relationships already define how tables are related.

• JPA uses metadata from annotations like @ManyToOne or @OneToMany to know which columns to join on.
• You just join via object fields: javaCopyEdit

String jpql = "SELECT o FROM Order o JOIN o.customer c";

Here:

• o.customer navigates the Order.customer Java field.
• JPA automatically generates the proper SQL join using the foreign key mapping defined in your entities.

🔹 Why you don’t need ON
✅ Mappings in entities define foreign key relationships once → no need to repeat in queries.
✅ Keeps JPQL/HQL concise and object-oriented.
✅ Reduces errors: the entity model guarantees the join path is correct.

🔹 Important Exception

• If you need complex joins without mapped associations, JPQL doesn’t support manual ON clauses like raw SQL.
• For such cases, you must:
  • Use native SQL queries (createNativeQuery()), where you can write full SQL with ON.
  • Or map missing relationships in your entities.

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📌 Key Takeaways

✅ In JPQL/HQL, you never write ON key=foreignKey — JPA uses mapped relationships to determine join conditions.
✅ You join via entity fields → e.g., o.customer, not via table/column names.
✅ This makes JPQL simpler and less error-prone, leveraging your object model.