Support explicit insert of primary key field

[spalladino]

I'd need to explicitly insert the ID field when creating a new record, since I'm not using autoincremental IDs. Following up the changes needed in the postgres adapter, they seem quite simple: just removing a few conditions regarding primary_field in lines 46, 46 and 128.

Do you think that supporting this case would be useful? If so, how do you think it could be specified that in the model DSL? Something like primary explicit id : Int? If you think it's worthwhile, I can try to set something up and send you a PR.

[waterlink]

Hi @spalladino

What is the current behavior, when someone operates on the table without auto-increment and supplies id explicitly? My assumption, that it should just work, at least for postgres adapter, not sure about mysql and sqlite adapters though.

[spalladino]

Currently the adapter deletes the ID field from the fields to insert, and the insert fails due to a non-null constraint on the PK. See here where the primary_field is removed from the list of fields in the INSERT clause. Also, the number of field_refs ($1, $2, etc) generated is equal to the number of fields, minus one (the PK field).

[waterlink]

Here update functionality removes primary_field too. I believe that is okay.

So it looks like the difference in the behavior have to be on the adapter's side (create(fields) function).

Maybe second overload abstract def create(id, fields) for the adapter protocol would be good here, which would indicate creation with explicit id value. And on the side of the active_record shard it should be used when id is specified explicitly.

I like the idea of primary explicit id : Int. (probably simpler to have explicit_primary id : Int)