Join data from an ES index with data from logstash

I have indexed data from a referential (a list of providers, with their full name) from a file.
With logstash, I index data from a DB that contains also the ID of providers.

I want, when reading data from DB with logstash, populate the full name of the provider, in order to have an index with denormalized data.

How can I do this ?

I worked with another search engine and I have realized a customized plugin, reading data from an index and storing then in memory, so, on the fly, I could add data during the load in the index.

If the data is in ES then you can use the ES filter to do something like this.
Otherwise look at the translate plugin.