insert/update from web server or database

I have a data-model on the front-end that I want to insert/update in the database which of the following approaches (or neither!) is considered best practice:

# in webserver

some_model = {json}

some_url_executed('/', db_exec("select update_model(some_model);")

-- in database
create function update_model(json)

/* multiple tables to update for the model */
insert/update tables from json data

or option 2:

# in webserver

some_model = {json};

db_exec("begin transaction");
foreach field in some_model {
    db_exec("update some_table set value = some_model.value
}
dbexec("commit or rollback");

My data-model, if it matters, looks like:

{ fld1: {},
  ...
  fld5: { 'sub-fields' : { 'nested':'values' } } 
  fld6: [ {...}, {...} ]
}

I like the idea of letting the database handle this because I can grant permissions on that function to the user/group in the database (they shouldn’t be allowed to navigate to the url anyway) but, yea – could use some guidance.

Back to the question, is it a bad idea to loop through a json object and insert/update from a stored procedure? Where does this logic belong? I’m using postgresql 9.5.