DDD Remove a Text Value Object from A List of Value Object

Question

I have entity with a list of value object like this:
(I'm using Go, but I hope it generally makes sense)

// this is my Crop entity
type Crop struct {
    UID uuid.UUID
    Name string
    Type string
    Notes []CropNote // This is a list of value object.
} 

// This is my CropNote value object
type CropNote struct {
    Content string
    CreatedDate time.Time
}

I have Crop behaviour for AddNewNote(content string). But the business process needs to have remove note behaviour too. I'm thinking something like RemoveNote(content string) behaviour. So I will iterate my Crop.Notes, find the row with the same content, then remove that row from the Crop.Notes list. But I think that finding the value by its note's content is error-prone. And its weird from the API point of view too because I need to send the content to the params.

My question is, how can I implement my Remove Note behaviour above?

EDIT: Sorry I think I'm not clearly explain myself.
I know how to remove a value from a slice.
My issue is about the DDD. About how to remove Value Object that only have fields above from the Crop.Notes list. Because we know that Value Object cannot have Identifier.
And if I really can only use Content and CreatedDate fields from my Value Object, then I should send that Content or CreatedDate value to the endpoint when I do REST API request which is weird.

score 1 · Accepted Answer · answered Jan 22 '18 at 01:37

Just use the instance of CropNote itself :

/* sorry for sudo code, not up with GO */
func (c Crop) removeNote(noteToRemove CropNote) {
    c.Notes= c.Notes.RemoveItem(noteToRemove); /* RemoveItem() is your own array manipulation code */
}

Now its up to your Application layer to identify and call the removal of the note.

Additional thing to think about:

Why is crop notes part of the Crop aggregate root? is the behavior of a Crop influenced by the notes or does Crop behavior influence the notes? Don't try and rebuild your data model inside your domain, it wont make sense. If your system requires the independent adding/removing/updating of crop notes, they may work better as their own aggregate roots that are indirectly dependent on an existing crop entity eg:

/*again, not proficiant with GO - treat as sudo code */
private type CropNote struct {
    UID uuid.UUID
    CropUID uuid.UUID
    Content string
    CreatedDate time.Time
}

function NewCropNote(crop Crop, content string) *CropNote{
    cn := new(CropNote)
    cn.UUID = uuid.new()
    cn.CropUID = crop.UUID
    cn.CreatedDate = now()
    cn.Content = content
    return cn
}

score 0 · Answer 2 · answered Jan 15 '18 at 04:53

In addition to @WeiHuang 's answer: If your notes is an unordered list, you can use swap instead of append or copy.

func (c Crop) removeNote(content string) {
    j:=len(c.Notes)
    for i:=0;i<j;i++ {
        if c.Notes[i]==content {
            j--
            c.Notes[j],c.Notes[i]=c.Notes[j],c.Notes[i]
        }
    }
    c.Notes=c.Notes[:j]
}

DDD Remove a Text Value Object from A List of Value Object

2 Answers2