CODEWITHSUNDEEP
node.jsredis
Woodsy
Woodsy

Reputation: 3377

Search an hmap for a value

If I have a redis hmap that looks like the following:

client.hset('test', 'one', 'aaa');
client.hset('test', 'two', 'bbb');
client.hset('test', 'three', 'ccc');
client.hset('test', 'four', 'ddd');

and I want to find if the map has a value like ccc whats the best way to do that?

I can call something like 

 client.hgetall('test', function(err, obj){
     for(id in obj){
         if(obj[id] == 'ccc'){
             return id;
         }
     }
  });

But this seems very inefficient, is there a search or find method in redis that would produce nicer solution?

Upvotes: 0

Views: 67

Answers (2)

for_stack
for_stack

Reputation: 22886

There's no built-in way to search by value. If you want to do it more efficient, you have to build an inverted index from value to key, e.g. inverted-test. Each time when you update the test hash, also update the inverted index.

HSET test one aaa
HSET inverted-test aaa one

NOTE

If in your original hash, multiple keys might have the same value. You might need to implement the inverted index with a LIST.

HSET test one aaa
LPUSH inverted-test:aaa one
HSET test two aaa
LPUSH inverted-test:aaa two

Upvotes: 1

Duarte Mendes
Duarte Mendes

Reputation: 161

You could use the filter method like this:

client.hgetall('test', (err, obj) => {
    // in here we create an array of the object obj properties
    const keys = Object.keys(obj);
    // and now we iterate that array with the filter method
    const wantedValues = keys.filter(key => obj[key] === 'ccc');
    // wantedValues is now a array with the keys of the object obj that have the value ccc
});

Upvotes: 0

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