How to update an item using a struct containing only some items.

[chackett]

So, my use case is for multi step registration:

User submits first form with details I want to use to "create" a user item:

type UserStageOne struct {
UserID *string json:"userID,omitempty"
Name *string json:"name,omitempty"
Email *string json:"email,omitempty"
Password *string json:"password,omitempty"
SignUpIP *string json:"signUpIP,omitempty"
RegisteredTime time.Time json:"registeredTime,omitempty"
Verified bool json:"verified,omitempty"
}

So when the user submits the first firm the above item is created. The user is then presented with a second form which contains the following struct. I now want to "update" the item created from the first request to include the new fields from the following struct:

type UserFinal struct {
UserID *string json:"userID,omitempty" dynamo:"UserID"
RegData1 *string json:"regData1,omitempty"
RegData2 *string json:"regData2,omitempty"
RegData3 *string json:"regData3,omitempty"
AgreedTerms bool json:"agreedTerms,omitempty"
}

How can I achieve that? PUT isn't appropriate and I can't seem to get UPDATE to work as I would like. I don't want to have to enumerate the various fields etc.

Thank you.

[guregu]

Right now there isn't a super easy way to do this. But I think this is an interesting use case and I would like to add support.

In the meantime, I wonder if something like this would work? Totally untested.

func UpdateFromItem(table dynamo.Table, hashKey string, item interface{}) (*dynamo.Update, error) {
	m, err := dynamo.MarshalItem(item)
	if err != nil {
		return nil, err
	}
	u := table.Update(hashKey, m[hashKey])
	for k, v := range m {
		if k == hashKey {
			continue
		}
		u.Set(k, v)
	}
	return u, nil
}

you would use it like update, err := UpdateFromItem(table, "UserID", userFinalData) and then run the update.

If you wanted logic that ignored nils and stuff you could include it in the loop over m.

[chackett]

Yea that would probably work alright. I'll give it a go the next time i'm working on that piece of code.

In the end I ended up just retrieving the record and updating the fields then calling update. Crude.