I'm looking to have a database containing the locations and materials,... required to operate a warehouse.
The client wants to have a local Edge to make sure they can keep operating everything but Edge can't use databases on it's own.
Is it possible to have a named query tag via remote tag provider to use this info in the Edge?
How would it respond when the connection is gone, you continue making modifications in the tag and then the connection comes online?
Sometimes Edge isn't the answer.
If you want DB access without a connection to "central," install a limited license set of the full version locally.
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You really want to use standard Ignition in the facility with such a system, and have the database local as well. Really.
If there were already a full Ignition gateway on-premises, and you were looking at adding an Edge instance for a process area within the warehouse, then yes - there are discussion points - majority of which would involve a messaging scheme between Edge <--> Full gateways (Edge cannot query DB directly, but can request that another gateway run the query and return the results, which may be stored in a dataset tag for use locally).
In general, Edge shouldn't be considered if there is not a full gateway to accompany.
Oy! Never do this. If uptime/fallback is a concern, add a redundant backup server to the full Ignition install, not an Edge instance.
...because? Edge has limitations, but operating as a standalone (periods of offline access) gateway isn't one of them.
In the same facility, an offline situation should never happen. If the local network is not reliable, fix the local network !! Add multiple link paths moderated by RSTP or your favorite branded equivalent, if necessary.
Edge as a fallback solution requires dramatically more engineering to deploy, and to maintain. It may be a good deal for an integrator advising an end-user, but is not a good deal for the end-user.
Can't say I've experienced much hardship with fallback regarding Full+Edge architecture (trivial by comparison to Full-Full). This is another case where details matter. Lots to speculate on. To get back to the topic & better answer the OP:
An Edge gateway cannot connect to DB. Since an Edge gateway can have only one tag provider (and, it cannot be a remote tag provider), I believe the answer is No.
Can a remote (full) gateway write to tags on an Edge gateway? Sure...please don't do this.
See above. If you need an Edge gateway (really, any gateway) to operate standalone, then ensure information is stored locally. The request for the information should always originate where the data is to be stored, where possible.
While a full Ignition gateway and local DB is the preferred route for a new installation, know that Edge is perfectly capable of scaling out an existing architecture:
- Sending cached historical data that's been accumulating during an outage (via native store & forward - up to 35 days).
- Requesting information from a full gateway (using native methods)
After all, that's what it was designed for: "...from the plant floor to independent remote sites..."