spring-data-jpa

Name: spring-data-jpa
Author: rrezartprebreza

174stars33forks

How to install spring-data-jpa?

rrezartprebreza/spring-boot-skills/spring-data-jpa

$npx -y skills add rrezartprebreza/spring-boot-skills --skill spring-data-jpa

Installs into the current project.

Summary

Use when generating JPA entities, repositories, queries, or anything touching the persistence layer. Covers entity conventions, N+1 prevention, projections, and query patterns.

Files · 1

View on GitHub

SKILL.md

1	# Spring Data JPA
2
3	## Entity Conventions
4
5	```java
6	@Entity
7	@Table(name = "orders")
8	@Getter
9	@NoArgsConstructor(access = AccessLevel.PROTECTED) // JPA requires no-arg, hide from callers
10	public class Order {
11
12	@Id
13	@GeneratedValue(strategy = GenerationType.UUID)
14	@Column(updatable = false, nullable = false)
15	private UUID id;
16
17	@Column(nullable = false)
18	private String customerEmail;
19
20	@Enumerated(EnumType.STRING) // always STRING, never ORDINAL
21	@Column(nullable = false)
22	private OrderStatus status;
23
24	@OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true)
25	private List<OrderItem> items = new ArrayList<>();
26
27	@CreationTimestamp
28	@Column(updatable = false)
29	private Instant createdAt;
30
31	@UpdateTimestamp
32	private Instant updatedAt;
33
34	// Static factory, not public constructor
35	public static Order create(String customerEmail) {
36	Order order = new Order();
37	order.customerEmail = customerEmail;
38	order.status = OrderStatus.PENDING;
39	return order;
40	}
41
42	// Behavior on entity, not in service
43	public void addItem(Product product, int quantity) {
44	items.add(OrderItem.create(this, product, quantity));
45	}
46	}
47	```
48
49	## Rules
50	- `@Enumerated(EnumType.STRING)` always — `ORDINAL` breaks on enum reordering
51	- `GenerationType.UUID` for IDs — never expose auto-increment integers
52	- `@NoArgsConstructor(access = PROTECTED)` — required by JPA, hidden from app code
53	- `@Getter` from Lombok — no `@Setter` on entities (use behavior methods)
54	- Collections initialized inline (`= new ArrayList<>()`) — never null
55
56	## N+1 Prevention
57
58	Identify: One query for orders + N queries for each order's items = N+1.
59
60	Fix with JOIN FETCH:
61	```java
62	@Query("SELECT o FROM Order o JOIN FETCH o.items WHERE o.id = :id")
63	Optional<Order> findByIdWithItems(@Param("id") UUID id);
64
65	// For lists — use @EntityGraph to avoid duplicates
66	@EntityGraph(attributePaths = {"items", "items.product"})
67	List<Order> findByStatus(OrderStatus status);
68	```
69
70	Fix with Projections for read-only views:
71	```java
72	// Interface projection — no entity loaded
73	public interface OrderSummary {
74	UUID getId();
75	String getCustomerEmail();
76	OrderStatus getStatus();
77	Instant getCreatedAt();
78	}
79
80	List<OrderSummary> findByStatus(OrderStatus status); // fast, no lazy loading issues
81	```
82
83	## Query Patterns
84
85	```java
86	public interface OrderRepository extends JpaRepository<Order, UUID> {
87
88	// Derived query — simple conditions
89	List<Order> findByStatusAndCustomerEmail(OrderStatus status, String email);
90
91	// JPQL — for joins and complex conditions
92	@Query("SELECT o FROM Order o JOIN FETCH o.items WHERE o.status = :status")
93	List<Order> findActiveOrdersWithItems(@Param("status") OrderStatus status);
94
95	// Native SQL — only when JPQL can't do it
96	@Query(value = "SELECT * FROM orders WHERE created_at > NOW() - INTERVAL '7 days'",
97	nativeQuery = true)
98	List<Order> findRecentOrders();
99
100	// Exists check — faster than findById + isPresent
101	boolean existsByCustomerEmailAndStatus(String email, OrderStatus status);
102
103	// Projection
104	List<OrderSummary> findByCustomerEmail(String email);
105	}
106	```
107
108	## Pagination
109
110	```java
111	// Always use Pageable for list endpoints
112	Page<Order> findByStatus(OrderStatus status, Pageable pageable);
113
114	// In service
115	Page<Order> orders = orderRepository.findByStatus(status, PageRequest.of(page, size, Sort.by("createdAt").descending()));
116	```
117
118	## Bidirectional Relationships
119
120	```java
121	// Parent side (Order)
122	@OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true)
123	private List<OrderItem> items = new ArrayList<>();
124
125	// Child side (OrderItem) — owns the FK
126	@ManyToOne(fetch = FetchType.LAZY) // LAZY always on @ManyToOne
127	@JoinColumn(name = "order_id", nullable = false)
128	private Order order;
129
130	// Helper on parent to keep both sides in sync
131	public void addItem(OrderItem item) {
132	items.add(item);
133	item.setOrder(this);
134	}
135	```
136
137	## Deep Pagination — Keyset over OFFSET
138
139	`OFFSET` pagination scans and discards every skipped row. On page 5,000 the DB reads 100,000 rows to
140	return 20. For large or infinite-scroll datasets, paginate by the last seen key (the "seek" method):
141
142	```java
143	// ❌ Slow on deep pages — OFFSET grows linearly
144	Page<Order> findByStatus(OrderStatus status, Pageable pageable);
145
146	// ✅ Keyset — constant time regardless of depth. Pass the last row's createdAt + id.
147	@Query("""
148	SELECT o FROM Order o
149	WHERE o.status = :status
150	AND (o.createdAt < :lastCreatedAt
151	OR (o.createdAt = :lastCreatedAt AND o.id < :lastId))
152	ORDER BY o.createdAt DESC, o.id DESC
153	""")
154	List<Order> findNextPage(OrderStatus status, Instant lastCreatedAt, UUID lastId, Limit limit);
155	```
156
157	The `(

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Type

spring-data-jpa

174stars33forks

View on GitHub

How to install spring-data-jpa?

rrezartprebreza/spring-boot-skills/spring-data-jpa

$npx -y skills add rrezartprebreza/spring-boot-skills --skill spring-data-jpa

Installs into the current project.

Summary

Use when generating JPA entities, repositories, queries, or anything touching the persistence layer. Covers entity conventions, N+1 prevention, projections, and query patterns.

Files · 1

View on GitHub

SKILL.md

1	# Spring Data JPA
2
3	## Entity Conventions
4
5	```java
6	@Entity
7	@Table(name = "orders")
8	@Getter
9	@NoArgsConstructor(access = AccessLevel.PROTECTED) // JPA requires no-arg, hide from callers
10	public class Order {
11
12	@Id
13	@GeneratedValue(strategy = GenerationType.UUID)
14	@Column(updatable = false, nullable = false)
15	private UUID id;
16
17	@Column(nullable = false)
18	private String customerEmail;
19
20	@Enumerated(EnumType.STRING) // always STRING, never ORDINAL
21	@Column(nullable = false)
22	private OrderStatus status;
23
24	@OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true)
25	private List<OrderItem> items = new ArrayList<>();
26
27	@CreationTimestamp
28	@Column(updatable = false)
29	private Instant createdAt;
30
31	@UpdateTimestamp
32	private Instant updatedAt;
33
34	// Static factory, not public constructor
35	public static Order create(String customerEmail) {
36	Order order = new Order();
37	order.customerEmail = customerEmail;
38	order.status = OrderStatus.PENDING;
39	return order;
40	}
41
42	// Behavior on entity, not in service
43	public void addItem(Product product, int quantity) {
44	items.add(OrderItem.create(this, product, quantity));
45	}
46	}
47	```
48
49	## Rules
50	- `@Enumerated(EnumType.STRING)` always — `ORDINAL` breaks on enum reordering
51	- `GenerationType.UUID` for IDs — never expose auto-increment integers
52	- `@NoArgsConstructor(access = PROTECTED)` — required by JPA, hidden from app code
53	- `@Getter` from Lombok — no `@Setter` on entities (use behavior methods)
54	- Collections initialized inline (`= new ArrayList<>()`) — never null
55
56	## N+1 Prevention
57
58	Identify: One query for orders + N queries for each order's items = N+1.
59
60	Fix with JOIN FETCH:
61	```java
62	@Query("SELECT o FROM Order o JOIN FETCH o.items WHERE o.id = :id")
63	Optional<Order> findByIdWithItems(@Param("id") UUID id);
64
65	// For lists — use @EntityGraph to avoid duplicates
66	@EntityGraph(attributePaths = {"items", "items.product"})
67	List<Order> findByStatus(OrderStatus status);
68	```
69
70	Fix with Projections for read-only views:
71	```java
72	// Interface projection — no entity loaded
73	public interface OrderSummary {
74	UUID getId();
75	String getCustomerEmail();
76	OrderStatus getStatus();
77	Instant getCreatedAt();
78	}
79
80	List<OrderSummary> findByStatus(OrderStatus status); // fast, no lazy loading issues
81	```
82
83	## Query Patterns
84
85	```java
86	public interface OrderRepository extends JpaRepository<Order, UUID> {
87
88	// Derived query — simple conditions
89	List<Order> findByStatusAndCustomerEmail(OrderStatus status, String email);
90
91	// JPQL — for joins and complex conditions
92	@Query("SELECT o FROM Order o JOIN FETCH o.items WHERE o.status = :status")
93	List<Order> findActiveOrdersWithItems(@Param("status") OrderStatus status);
94
95	// Native SQL — only when JPQL can't do it
96	@Query(value = "SELECT * FROM orders WHERE created_at > NOW() - INTERVAL '7 days'",
97	nativeQuery = true)
98	List<Order> findRecentOrders();
99
100	// Exists check — faster than findById + isPresent
101	boolean existsByCustomerEmailAndStatus(String email, OrderStatus status);
102
103	// Projection
104	List<OrderSummary> findByCustomerEmail(String email);
105	}
106	```
107
108	## Pagination
109
110	```java
111	// Always use Pageable for list endpoints
112	Page<Order> findByStatus(OrderStatus status, Pageable pageable);
113
114	// In service
115	Page<Order> orders = orderRepository.findByStatus(status, PageRequest.of(page, size, Sort.by("createdAt").descending()));
116	```
117
118	## Bidirectional Relationships
119
120	```java
121	// Parent side (Order)
122	@OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true)
123	private List<OrderItem> items = new ArrayList<>();
124
125	// Child side (OrderItem) — owns the FK
126	@ManyToOne(fetch = FetchType.LAZY) // LAZY always on @ManyToOne
127	@JoinColumn(name = "order_id", nullable = false)
128	private Order order;
129
130	// Helper on parent to keep both sides in sync
131	public void addItem(OrderItem item) {
132	items.add(item);
133	item.setOrder(this);
134	}
135	```
136
137	## Deep Pagination — Keyset over OFFSET
138
139	`OFFSET` pagination scans and discards every skipped row. On page 5,000 the DB reads 100,000 rows to
140	return 20. For large or infinite-scroll datasets, paginate by the last seen key (the "seek" method):
141
142	```java
143	// ❌ Slow on deep pages — OFFSET grows linearly
144	Page<Order> findByStatus(OrderStatus status, Pageable pageable);
145
146	// ✅ Keyset — constant time regardless of depth. Pass the last row's createdAt + id.
147	@Query("""
148	SELECT o FROM Order o
149	WHERE o.status = :status
150	AND (o.createdAt < :lastCreatedAt
151	OR (o.createdAt = :lastCreatedAt AND o.id < :lastId))
152	ORDER BY o.createdAt DESC, o.id DESC
153	""")
154	List<Order> findNextPage(OrderStatus status, Instant lastCreatedAt, UUID lastId, Limit limit);
155	```
156
157	The `(

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