gen: expose table's primary key and/or constraint names for use in `im.OnConflict()`/`im.OnConflictOnConstraint()`

[edigaryev]

The recent 0.29.0 release made some pretty substantial changes to the generated code's API (and I hope for the good), one of which was the deprecation of Upsert() in favor of Insert() with some mods.

Assuming that one now has to use im.OnConflict() or im.OnConflictOnConstraint() to achieve the same behavior, the table's primary key and/or constraint names needs to be specified explicitly for use in these mods.

Whereas before this was handled automatically by the Upsert(), when passing conflictCols equal to nil:

bob/dialect/sqlite/table.go

Lines 205 to 207 in 09c8491

	if len(conflictCols) == 0 {
	conflictCols = t.pkCols
	}

As a result, one now has to type these constraints by hand, which makes things more error-prone than they were before.

[stephenafamo]

This is on the radar.

In the CHANGELOG, you may notice that constraints and indexes are now being loaded with even a bit more information than before (e.g. CHECK constraints are now loaded too).

In the near future, the plan is to generate code with this information so that it can be used in queries.

In the meantime, you can supply your own templates and generate any code you need.