Allowlist based conversion

[zhulik]

Is your feature request related to a problem? Please describe.

In my project, I have a generated struct which looks like this:

type AssetSetter struct {
	UUID                          *uuid.UUID           `db:"uuid,pk" `
	...
	DeactivationReason            *sql.Null[string]    `db:"deactivation_reason" `
	CreatedAt                     *time.Time           `db:"created_at" `
	UpdatedAt                     *time.Time           `db:"updated_at" `
	DeactivatedAt                 *sql.Null[time.Time] `db:"deactivated_at" `
}

It's used to create and update records in the sql table. Is case of insert operation - all fields must present(except those which are nullable), in case of update - only non-nil ones will be updated.

I have a corresponding struct in the domain model which has the same fields, but may have different types and so on. I use goverter to generate converters from the domain struct to the setter.

The problem is that I have cases when I only want to update a subset of fields given the entire domain struct. In case of deactivation, I want to make sure that only DeactivatedAt is converted from the domain struct to the setter:

domain.Asset{
<skipped non-nil and non-zero fields> 
  DeactivatedAt: time.Now(),
  DeactivationReason: &"deleted",
}

should be converted into

AssetSetter{DeactivatedAt: <from the domain struct>, DeactivationReson: <from the domain struct>}

All the rest of the fields for the setter should remain nils.

Describe the solution you'd like

It would be awesome to have a possibility to convert values based on an allow list:

type Converter{
  // goverter:ignoreAll <- a new comment
  // goverter:map DeactivatedAt DeactivatedAt <- may have only one argument, may have a diffent name like goverter:allow
  // goverter:map DeactivationReason DeactivationReason
  Convert(domain.Asset) db.AssetSetter
}

Only fields allowed explicitly will be converted.

Describe alternatives you've considered
I tried goverter:ignore, but the more fields the output struct has, the more ignores I should add, it quickly turns into a burden

[jmattheis]

This seems like a edge-case and I don't think many users need this. I'd wait for feedback from other users on this.

Generally, it seems weird to me to reuse the structs there. You could use specialized structs which only contain the needed fields (DeactivatedAt, DeactivationReason) and then you could already achieve similar things without changes needed in goverter.

[zhulik]

I wish I could use specialized structs, but, as I mentioned, the setter struct is generated, by the Bob ORM to be precise and it simply includes all fields of a table, that's by design.

I'm building an application with event sourcing where bob is exclusively used to interact with the database. The domain model uses it's own structs for entities, usually similar to bob's models. Most of my entities have a "deactivation" feature, which is essentially a soft delete.

My idea is to have a converter generated with goverter per entity per event, the event is a context and is only used to distinguish between different converter functions eg:

// goverter comments are omitted
type AssetConverters interface {
  CreatedAssetToSetter(asset core.Asset, event Created) models.AssetSetter // <- allows all fields. only goverter:map and autoMap are used
  UpdatedAssetToSetter(asset core.Asset, event Updated) models.AssetSetter // <- allows all fields with exceptions depending on the entity. goverter:map, autoMap and ignore are used
  DeactivatedToSetter(asset core.Asset, event Deactivated) models.AssetSetter // <- only DeactivatedAt, DeactivationReason and UpdatedAt are allowed, currently cannot be implemented.
}

I hope this explains my motivation better