Store user information in json or in a table in a database?

Question

I'm developing a site that has to store a user's contact list. So it will contain people's phone numbers, addresses and also messages sent to this contact. I obviously want to keep this information secure but it seems quite easy an efficient just giving each user a json file with an array of details.
I'm not too sure if this is a horrendously dangerous and insecure idea and if I should be using a table in a database, or something else. Using a table to store messages sent between users doesn't seem too intuitive though. So I was just wanted to know what the most sensible way I would store
i) User specific contact lists with sensitive information
ii) Messages sent between two contacts
I'm sorry if this is a widely known and not even talked about topic. I just couldn't really find a clear answer anywhere.

Answer 1

You should definitely use a database for this. If you store these values on files, then you will have to load all of the information per user every single time you need to access something as small as a single phone number.