I want to save a slice of structs in Google Cloud Datastore (Firestore in Datastore mode).
Take this Phonebook and Contact for example.
type Contact struct {
Key *datastore.Key `json:"id" datastore:"__key__"`
Email string `json:"email" datastore:",noindex"`
Name string `json:"name" datastore:",noindex"`
}
type Phonebook struct {
Contacts []Contact
Title string
}
Saving and loading this struct is no problem as the Datastore library takes care of it.
Due to the presence of some complex properties in my actual code, I need to implement PropertyLoadSaver methods.
Saving the Title property is straightforward. But I have problems storing the slice of Contact structs.
I tried using the SaveStruct method:
func (pb *Phonebook) Save() ([]datastore.Property, error) {
ps := []datastore.Property{
{
Name: "Title",
Value: pb.Title,
NoIndex: true,
},
}
ctt, err := datastore.SaveStruct(pb.Contacts)
if err != nil {
return nil, err
}
ps = append(ps, datastore.Property{
Name: "Contacts",
Value: ctt,
NoIndex: true,
})
return ps, nil
}
This code compiles but doesn't work.
The error message is datastore: invalid entity type
Making a slice of Property explicitly also does not work:
func (pb *Phonebook) Save() ([]datastore.Property, error) {
ps := []datastore.Property{
{
Name: "Title",
Value: pb.Title,
NoIndex: true,
},
}
cttProps := datastore.Property{
Name: "Contacts",
NoIndex: true,
}
if len(pb.Contacts) > 0 {
props := make([]interface{}, 0, len(pb.Contacts))
for _, contact := range pb.Contacts {
ctt, err := datastore.SaveStruct(contact)
if err != nil {
return nil, err
}
props = append(props, ctt)
}
cttProps.Value = props
}
ps = append(ps, cttProps)
return ps, nil
}
Making a slice of Entity does not work either:
func (pb *Phonebook) Save() ([]datastore.Property, error) {
ps := []datastore.Property{
{
Name: "Title",
Value: pb.Title,
NoIndex: true,
},
}
cttProps := datastore.Property{
Name: "Contacts",
NoIndex: true,
}
if len(pb.Contacts) > 0 {
values := make([]datastore.Entity, len(pb.Contacts))
props := make([]interface{}, 0, len(pb.Contacts))
for _, contact := range pb.Contacts {
ctt, err := datastore.SaveStruct(contact)
if err != nil {
return nil, err
}
values = append(values, datastore.Entity{
Properties: ctt,
})
}
for _, v := range values {
props = append(props, v)
}
cttProps.Value = props
}
ps = append(ps, cttProps)
return ps, nil
}
Both yielded the same error datastore: invalid entity type
Finally I resorted to using JSON. The slice of Contact is converted into a JSON array.
func (pb *Phonebook) Save() ([]datastore.Property, error) {
ps := []datastore.Property{
{
Name: "Title",
Value: pb.Title,
NoIndex: true,
},
}
var values []byte
if len(pb.Contacts) > 0 {
js, err := json.Marshal(pb.Contacts)
if err != nil {
return nil, err
}
values = js
}
ps = append(ps, datastore.Property{
Name: "Contacts",
Value: values,
NoIndex: true,
})
return ps, nil
}
Isn't there a better way of doing this other than using JSON?
