Firestore CRUD Operations

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import 'package:cloud_firestore/cloud_firestore.dart';
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class FirestoreRepository<T> {
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  final CollectionReference collection;
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  final T Function(Map<String, dynamic> data, String id) fromFirestore;
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  final Map<String, dynamic> Function(T item) toFirestore;
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  FirestoreRepository({
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    required String collectionPath,
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    required this.fromFirestore,
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    required this.toFirestore,
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  }) : collection = FirebaseFirestore.instance.collection(collectionPath);
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  // Create
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  Future<String> add(T item) async {
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    final ref = await collection.add(toFirestore(item));
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    return ref.id;
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  }
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  Future<void> set(String id, T item) async {
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    await collection.doc(id).set(toFirestore(item));
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  }
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  // Read
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  Future<T?> get(String id) async {
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    final doc = await collection.doc(id).get();
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    if (!doc.exists) return null;
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    return fromFirestore(doc.data() as Map<String, dynamic>, doc.id);
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  }
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  Future<List<T>> getAll({int limit = 20}) async {
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    final snapshot = await collection.limit(limit).get();
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    return snapshot.docs
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        .map((d) => fromFirestore(d.data() as Map<String, dynamic>, d.id))
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        .toList();
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  }
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  // Stream (real-time)
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  Stream<List<T>> stream({Query Function(Query q)? query}) {
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    final q = query?.call(collection) ?? collection;
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    return q.snapshots().map(
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      (snapshot) => snapshot.docs
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          .map((d) => fromFirestore(d.data() as Map<String, dynamic>, d.id))
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          .toList(),
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    );
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  }
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  // Update
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  Future<void> update(String id, Map<String, dynamic> data) async {
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    await collection.doc(id).update(data);
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  }
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  // Delete
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  Future<void> delete(String id) async {
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    await collection.doc(id).delete();
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  }
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}
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// Usage example
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final postsRepo = FirestoreRepository<Post>(
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  collectionPath: 'posts',
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  fromFirestore: (data, id) => Post.fromFirestore(data, id),
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  toFirestore: (post) => post.toFirestore(),
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);
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// Real-time stream in widget
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StreamBuilder<List<Post>>(
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  stream: postsRepo.stream(
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    query: (q) => q.where('published', isEqualTo: true).orderBy('createdAt', descending: true),
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  ),
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  builder: (context, snapshot) {
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    if (snapshot.hasError) return Text('Error: ${snapshot.error}');
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    if (!snapshot.hasData) return const CircularProgressIndicator();
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    return ListView.builder(
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      itemCount: snapshot.data!.length,
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      itemBuilder: (_, i) => PostCard(post: snapshot.data![i]),
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    );
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  },
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)