Home›Firebase in 5 Days›Day 2
Day 2 of 5
⏱ ~60 minutes
Firebase in 5 Days — Day 2

Firestore: NoSQL Database

Read and write data in Firestore with real-time listeners and one-time queries.

Firestore Data Model

Firestore uses collections (like tables) and documents (like rows). Documents are JSON objects. Collections can contain subcollections. Think of it as a nested JSON tree.

CRUD operations
import { db } from './firebase';
import {
  collection, doc, getDocs, getDoc,
  addDoc, setDoc, updateDoc, deleteDoc,
  query, where, orderBy, limit,
  onSnapshot
} from 'firebase/firestore';

// Add a document (auto-generated ID)
const docRef = await addDoc(collection(db, 'posts'), {
  title: 'My Post',
  body: 'Content',
  userId: auth.currentUser.uid,
  createdAt: new Date()
});

// Set a document (known ID)
await setDoc(doc(db, 'users', userId), { name: 'Alice', role: 'user' });

// Update specific fields
await updateDoc(doc(db, 'posts', postId), { title: 'New Title' });

// Delete
await deleteDoc(doc(db, 'posts', postId));
Queries and Real-Time Listeners
// One-time query
const q = query(
  collection(db, 'posts'),
  where('userId', '==', currentUser.uid),
  orderBy('createdAt', 'desc'),
  limit(20)
);
const snapshot = await getDocs(q);
const posts = snapshot.docs.map(doc => ({ id: doc.id, ...doc.data() }));

// Real-time listener (auto-updates when data changes)
const unsubscribe = onSnapshot(q, (snapshot) => {
  const posts = snapshot.docs.map(doc => ({ id: doc.id, ...doc.data() }));
  setPosts(posts);
});

// Cleanup: call unsubscribe() when component unmounts
📝 Day 2 Exercise
Build a Real-Time Blog
  1. C
  2. r
  3. e
  4. a
  5. t
  6. e
  8. a
  10. F
  11. i
  12. r
  13. e
  14. s
  15. t
  16. o
  17. r
  18. e
  20. c
  21. o
  22. l
  23. l
  24. e
  25. c
  26. t
  27. i
  28. o
  29. n
  31. f
  32. o
  33. r
  35. p
  36. o
  37. s
  38. t
  39. s
  40. .
  42. B
  43. u
  44. i
  45. l
  46. d
  48. a
  50. f
  51. o
  52. r
  53. m
  55. t
  56. o
  58. a
  59. d
  60. d
  62. p
  63. o
  64. s
  65. t
  66. s
  67. .
  69. D
  70. i
  71. s
  72. p
  73. l
  74. a
  75. y
  77. p
  78. o
  79. s
  80. t
  81. s
  83. i
  84. n
  86. r
  87. e
  88. a
  89. l
  90. -
  91. t
  92. i
  93. m
  94. e
  96. w
  97. i
  98. t
  99. h
  101. o
  102. n
  103. S
  104. n
  105. a
  106. p
  107. s
  108. h
  109. o
  110. t
  111. .
  113. A
  114. d
  115. d
  117. d
  118. e
  119. l
  120. e
  121. t
  122. e
  124. f
  125. u
  126. n
  127. c
  128. t
  129. i
  130. o
  131. n
  132. a
  133. l
  134. i
  135. t
  136. y
  137. .
  139. F
  140. i
  141. r
  142. e
  143. s
  144. t
  145. o
  146. r
  147. e
  149. S
  150. e
  151. c
  152. u
  153. r
  154. i
  155. t
  156. y
  158. R
  159. u
  160. l
  161. e
  162. s
  163. :
  165. o
  166. n
  167. l
  168. y
  170. a
  171. u
  172. t
  173. h
  174. e
  175. n
  176. t
  177. i
  178. c
  179. a
  180. t
  181. e
  182. d
  184. u
  185. s
  186. e
  187. r
  188. s
  190. c
  191. a
  192. n
  194. w
  195. r
  196. i
  197. t
  198. e
  199. .

Day 2 Summary

  • Firestore: collections → documents → subcollections. Documents are JSON.
  • addDoc (auto ID) vs setDoc (known ID). Both create/overwrite.
  • onSnapshot gives real-time updates. Returns an unsubscribe function — call it on cleanup.
  • Queries: where, orderBy, limit. Composite queries need an index (Firebase prompts you).
→
← Previous
Day 1: Firebase Setup and Authentication
Next →
Day 3: Firebase Storage
→
Finished this lesson?