android - 您如何在 firestore android 的事务中遍历子集合中的文档？

Question

我希望能够删除子集合中的所有文档作为 android 事务的一部分。我找到了以下代码，但这是针对 Node.js 的

// First perform the query
db.collection('job_skills').where('job_id','==',post.job_id).get()
.then(function(querySnapshot) {
    // Once we get the results, begin a batch
    var batch = db.batch();

    querySnapshot.forEach(function(doc) {
        // For each doc, add a delete operation to the batch
        batch.delete(doc.ref);
    });

    // Commit the batch
    return.batch.commit();
}).then(function() {
  // Delete completed!
  // ...
}); 

如有任何帮助，我们将不胜感激!

谢谢!

Answer 1

我在你的代码中看到的不是交易，而是批处理。所以如果你想使用Android SDK删除一个集合中的所有文档，我推荐你使用以下方法:

private void deleteCollection(final CollectionReference collection, Executor executor) {
    Tasks.call(executor, new Callable<Object>() {
        @Override
        public Object call() throws Exception {
            int batchSize = 10;
            Query query = db.collection("job_skills").whereEqualTo("job_id", job_id);
            List<DocumentSnapshot> deleted = deleteQueryBatch(query);

            while (deleted.size() >= batchSize) {
                DocumentSnapshot last = deleted.get(deleted.size() - 1);
                query = collection.orderBy(FieldPath.documentId()).startAfter(last.getId()).limit(batchSize);

                deleted = deleteQueryBatch(query);
            }

            return null;
        }
    });
}

这里是 deleteQueryBatch() 方法:

@WorkerThread
private List<DocumentSnapshot> deleteQueryBatch(final Query query) throws Exception {
    QuerySnapshot querySnapshot = Tasks.await(query.get());

    WriteBatch batch = query.getFirestore().batch();
    for (DocumentSnapshot snapshot : querySnapshot) {
        batch.delete(snapshot.getReference());
    }
    Tasks.await(batch.commit());

    return querySnapshot.getDocuments();
}

即使 Firebase 团队不推荐删除操作，因为它对安全性和性能有负面影响，您仍然可以将其用于小型数据集。