db filter odoo

db filter is very important in odoo,Odoo is a multi-tenant system: a single Odoo system may run and serve a number of database instances. It is also highly customizable, with customizations (starting from the modules being loaded) depending on the “current database”.However it is an issue for non-logged users (portal, website) which aren’t bound to a database: Odoo needs to know which database should be used to load the website page or perform the operation. If multi-tenancy is not used that is not an issue, there’s only one database to use, but if there are multiple databases accessible Odoo needs a rule to know which one it should use.

dbfilter = ^%d$

suppose a user has domain      shop1.xyz.com,  shop2.xyz.com so it will work with above case but make sure make db name like shop1, shop2
note: you have to set nginx as well and in add dns entries in domain panel as well for those subdomain

you may face issue related to reject db filter so the issue nginx you have to add this 
location /longpolling {
    proxy_pass  http://odoo:8072 ;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;

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