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I'm one of the engineers who work on the data service > about metadata: in Postgrest .. We don't want to restrict the data service to a particular schema. You
by 0x777 10y ago
I'm one of the engineers who work on the data service
> about metadata: in Postgrest ..
We don't want to restrict the data service to a particular schema. You can add a table from any schema to be tracked, say information_schema or pg_catalog. In fact, that is how introspection works (you can look at the queries made by the console). This means that the schema cache in memory would be quite large because of the number of tables in information_schema/pg_catalog if we were to auto load all these. There is also the issue that you may not want to expose some tables. We can definitely have a console button which will let you import all the tables in public schema.
Sure, you can infer relationships from the foreign key constraints. But, how would you come up with names that do not conflict with the existing columns? What if you add a new column with the same name as an inferred relationship? With the data service, you can also define relationships on/to views across schemas (1). Making metadata explicit goes with one of our core principles, 'no magic'.
> what postgrest does for protection: a - no fancy joins,
explicit joins are not allowed even with our data service. The joins that happen are the implicit ones because of the relationships. We do the same thing if we need any custom joins/aggregations. Define a view and expose it.
> b -
you can't do anything other than selecting columns and relationships with the api.
> c -
the permission layer can be used to prevent these to some extent (like not allowing an anonymous user to filter on a particular column).
1. https://hasura.io/_docs/platform/0.6/getting-started/5-data-aggregations-views.html https://hasura.io/_docs/platform/0.6/getting-started/5-data-...
- ruslan_talpa 10y agoall the things i explained about metadata are implemented in postgrest and they work, and there is no loss of flexibility sinceyou can expose any table you want from any schema by explicitly creating a "mirror" view in the exposed schema. and relations are detected across tables and views and there is a way to deal with collisions. I am not saying that your way is bad (having a metadata file), just saying there is a way to automatically create it. - b,c that's good that you don't expose the entire SQL
- 0x777 10y agoI guess we'll need to have 'auto generate relationships' tooling. Just curious, how do you infer the relationships between a table and a view?
- ruslan_talpa 10y agocan't reply to your question so doing it here. the code is OS so you can look it up :) the idea is this - detect table relations based on FK - for each view check where each column comes from (view column usage) based on the info above you know all the relations in the system, even view to view also there is a way to do it in a single query but that is not yet implemented in postgrest
- 0x777 10y agoWhile we can get the information on the columns used in a view, we can't infer if the uniqueness properties propagate to the view which guarantee the semantics of relationships. I guess it might be convenient to do this (determine relationships across views), but the users should be aware of the guarantees offered in this scenario.
- ruslan_talpa 10y agoI am not sure i understand what you are saying about guarantees. If there is a FK, there is a relation. It's the user that is driving the relations by specifying what columns are FK, it's the same thing as defining relations in a GUI, only you do it at the database level
- ruslan_talpa 10y agoanyway, good luck with your product. As i mentioned, it's the only thing out there close to the concept of postgrest, and that's a good thing :)
- 0x777 10y agoThanks ! If I remember correctly, postgrest was started about the same time we started work on the data service. In fact, both these projects were pushing the limits of the then hasql library with the whole dynamic query generation.