Feature: support tables without a primary key

[Diggsey]

Pretty self explanatory - there's not really a reason to prevent inserting into a table without a primary key. Not supporting operations requiring Identifiable is fine.

[sgrif]

This isn't possible until Diesel 2.0. We may eventually try to generalize "data source" as a supertrait of Table, which has no primary key (e.g. views), but tables should always have some form of primary key.

[Diggsey]

Is that because it would require breaking changes? AFAICT, the only part of diesel currently using knowledge of the primary key is the find() method. Everything else works equally well without a primary key.

[weiznich]

It will require a breaking change because we need do separate Table in such a way that there is a supertrait of Table that contains the AllColumns associated type and the all_columns function. The Table trait would than contain only the PrimaryKey associated type and the primary_key function. It is a breaking change because this would break all code that currently implements Table.

@sgrif Maybe we should introduce a diesel 2.0 tag to have a list of things we may want to fix in 2.0?

[Diggsey]

Not calling it a Table seems confusing - whether or not something has a primary key is incidental to whether it's a table.

I currently have a table which implements a "set" data structure - the "value" is not the primary key because for reasons relating to locking, it is preferable to allow transient duplicate items than to enforce uniqueness (which could cause "insert" operations to have to wait on "remove" transactions, which are slow).

[sgrif]

@Diggsey You can just tell Diesel some random column is the primary key

[KeenS]

Is this planned to be developed for diesel 2.0? (And is diesel 2.0 is planned?)

I want to use partitioned tables, which doesn't support primary key.

[KeenS]

I found diesel_cli supports table filtering.
https://github.com/diesel-rs/diesel/blob/master/diesel_cli/tests/print_schema/print_schema_except_tables/diesel.toml
I'm going to use it until diesel 2.0 get released