Data store : retreive a value by key

Hi all,

I’m trying to use the datastore to manage user UI preferences.
After the user is logged in, i load pref’s from the database with a SC and store it in datastore.
The datastore structure is very simple like this:

It’s works perfectly, BUT, i do not figure out how to retreive a user pref value from the datastrore with a key (which is “code”).
For example, i want to hide a Label if the user pref code BOOKS_EMP is equal to 1. I treid to put this in the dynamic attribute of the label:

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But it doesn’t work ?

Can you help me please !