what is client property of knexfile.js - postgresql

Question

In knex documentation of configuration of knexfile.js for PostgreSQL, they have a property called client, which looks this way:
...
client: 'pg'
...
However, going through some other projects that utilize PostgreSQL I noticed that they have a different value there, which looks this way:
...
client: 'postgresql'
...
Does this string correspond to the name of some sort of command line tool that is being used with the project or I misunderstand something?

Answer 1

Postgresql is based on a server-client model as described in 'Architectural Fundamentals'
psql is the standard cli client of postgres as mentioned here in the docs.
A client may as well be a GUI such as pg-admin, or a node-package such as 'pg' - here's a list.
The client parameter is required and determines which client adapter will be used with the library.
You should also read the docs of 'Server Setup and Operation'
To initialize the library you can do the following (in this case on localhost):
var knex = require('knex')({
client: 'mysql',
connection: {
host : '127.0.0.1',
user : 'your_database_user',
password : 'your_database_password',
database : 'myapp_test'
}
})
The standard user of the client deamon ist 'postgres' - which you can use of course, but its highly advisable to create a new user as stated in the docs and/or apply a password to the standard user 'postgres'.
On Debian stretch i.E.:
# su - postgres
$ psql -d template1 -c "ALTER USER postgres WITH PASSWORD 'SecretPasswordHere';"
Make sure you delete the command line history so nobody can read out your pwd:
rm ~/.psql_history
Now you can add a new user (i.E. foobar) on the system and for postgres
# adduser foobar
and
# su - postgres
$ createuser --pwprompt --interactive foobar
Lets look at the following setup:
module.exports = {
development: {
client: 'xyz',
connection: { user: 'foobar', database: 'my_app' }
},
production: { client: 'abc', connection: process.env.DATABASE_URL }
};
This basically tells us the following:
In dev - use the client xyz to connect to postgresqls database my_app with the user foobar (in this case without pwd)
In prod - retrieve the globalenv the url of the db-server is set to and connect via the client abc
Here's an example how node's pg-client package opens a connection pool:
const pool = new Pool({
user: 'foobar',
host: 'someUrl',
database: 'someDataBaseName',
password: 'somePWD',
port: 5432,
})
If you could clarify or elaborate your setup or what you like to achieve a little more i could give you some more detailed info - but i hope that helped anyways..