PHP Redis: Get Key Where Value (Detailed Guide w/ Code Examples)

Use Case(s)

In PHP, interacting with Redis often involves using the phpredis extension. A typical situation where you might want to get a key based on its associated value is when you are trying to reverse lookup values. Please note Redis doesn't inherently support this operation but it can be achieved by maintaining a mirror of your data where the values are keys and vice versa.

Code Examples

The following examples will show how to set a key-value pair in Redis and then perform a reverse lookup.

Setting a key-value pair:

$redis = new Redis();
$redis->connect('127.0.0.1', 6379);
$redis->set('key', 'value');

To maintain a mirror of the data for reverse lookup, you'd store the 'value' as the key and 'key' as the value:

$redis->set('value', 'key');

Now, you can get the key by searching for the value:

$key = $redis->get('value'); // returns 'key'

Best Practices

Ensure that the mirrored data is always updated along with the main data. This way, the reverse lookup will provide the correct results. Also, remember that while this method can be useful in certain situations, it can consume twice the memory because you're storing each pair twice.

Common Mistakes

Not updating the mirrored data when the original data changes, leading to inaccurate reverse lookups.

FAQs

Q: Can I get a key from a value in Redis directly? A: No, Redis does not support this operation natively. The workaround is to maintain a mirror of your data where the values are keys and vice versa. However, this method can consume twice the memory because you're storing each pair twice.