Spring data redis - How to use hashOperation's scan method to get keys or values based on pattern?

Question

I have never worked on Redis and Spring boot. I want to use Redis as a cache.

I have been using hashOperations for get/set operations. I have configured the RedisTemplate to stop weird hashes from getting prepended to a key.

I have a class called Post which I am caching. A user can create multiple posts. The key gets generated like this : userId::postId and the post data gets cached.

How to use scan method of RedisTemplate to get all posts of a particular user? I tried ScanOptions and the pattern * but I am certainly doing something wrong as I am not getting any data. There aren't many links or youtube videos on scan and ScanOptions so I am finding it difficult to implement.

This is what I have wrote for getting all posts of a user:

public List<Post> getPostsByUid(String uid) {
 String key = uid + "::";
 ScanOptions scanOptions = ScanOptions.scanOptions().match("*").count(20).build();
 Cursor cursor = hashOperations.scan(key, scanOptions);
 List<Post> posts = new ArrayList<>();
 while(cursor.hasNext()) {
 posts.add((Post)cursor.next());
 }
 return posts;
}

This is the savePost method

public Post savePost(Post post) {
 String key = post.getUid() + "::" + post.getPostid();
 hashOperations.put(key, "", post);
 return post;
}

Thanks for helping!

Answer 1

hashOperations.scan scans within a hash. But you want to scan within whole database (Redis).

String keyPattern = uid + "::" + "*";
ScanOptions scanOptions = ScanOptions.scanOptions().match(keyPattern).count(20).build();
Cursor c = redisConnection.scan(options); // scanning in db
while (c.hasNext()) {
 // c.next() is Redis key. Use this in hashOperations to get your Post.
}

• echoaman: Can we use hashOperations when Redis is used as a cache or is it only used when Redis is used as a database?
• sazzad: Always. hashOperations just means the operations will be done on Redis hash data structure.
• Giampiero Poggi: how can i inject redisConnection? thanks