This is not clear enough from current documentation

Thanks for the great project!
How do i make a side effect for the model initialization (i need to store it in the database)?

I'm currently using this package for test fixture generation
and it happens quite often that i get the same email in just few repetitive calls, which prevents from using it 'as is' and requiring to add some random part manually.

It would be really useful to provide options for nested attributes in subfactories.

For example, I propose the dot . as a delimiter for attributes nesting. Following with the subfactory example, we should be able to declare a user with a specific name for its group:

func main() {
  for i := 0; i < 3; i++ {
    user := UserFactory.MustCreateWithOption(map[string]any{"Group.Name": "group-x"}).(*User)
    fmt.Println(
      "ID:", user.ID, " Name:", user.Name, " Location:", user.Location,
      " Group.ID:", user.Group.ID, " Group.Name", user.Group.Name)
  }
}

Output

ID: 1  Name: user-1  Location: Tokyo  Group.ID: 1  Group.Name group-x
ID: 2  Name: user-2  Location: Tokyo  Group.ID: 2  Group.Name group-x
ID: 3  Name: user-3  Location: Tokyo  Group.ID: 1  Group.Name group-x

This is already implemented on other libraries, for example within Model Bakery. At draftea we are extensibely using factory-go, so I would be excited to have this built in.
We could carry out the job, but first I wan't to be sure you also think this is a good idea and is in tune with you long-term aspirations for the project.

Intro

Hi!
For some time we have been using this library at my company, and the dot notation for nested field setting on subfactories has proven really useful. It make really the declaration of new instances with fixed data really elegant.

Now, I think a similar strategy could be carried over for slice nested fields.
If you like the idea, I could PR it myself.

Example

Context

For example (borrowed from our codebase):

type Player struct {
  ID          string
  FirstName   string
  LastName    string
  ExternalIds []ExternalID
}

type ExternalID struct {
  ID       string
  Provider string
}

our factories look like:

func playerFactoryBuilder(model any) *factory.Factory {
  return factory.NewFactory(
    model,
  ).Attr(
    "ID",
      AlphanumericGenerator(10),
  ).Attr(
    "FirstName", FirstNameGenerator,
  ).Attr(
    "LastName", LastNameGenerator,
  ).SubSliceFactory(
    "ExternalIds",
    externalIDFactory,
    func() int { return 2 },
  )
}

var externalIDFactory = NewFactory(
  models.ExternalID{},
).Attr(
  "Provider",
  ConstantGenerator("somewhat"),
).Attr(
  "ID",
  AlphanumericGenerator(10),
)

Proposal:

My proposal would work like this:

Scenario 1: Dot notation for nested array fields

func main() {
  for i := 0; i < 3; i++ {
    player := PlayerFactory.MustCreateWithOption(map[string]any{"ExternalIds.Provider": "some-provider"}).(*Player)
    for i, _ := range player.externalIds {
      fmt.Println("ID:", player.ExternalIds.[i].ID, " Provider:", player.ExternalIds[i].Provider)
    }
  }
}

would affect all slice generated instances, printing something like

ID: 12ad23d4bn  Provider: some-provider
ID: 32ad23d4bn  Provider: some-provider

Scenario 2: Dot notation for nested array fields on specific index in slice subfactory bounds

func main() {
  for i := 0; i < 3; i++ {
    player := PlayerFactory.MustCreateWithOption(map[string]any{"ExternalIds.1.Provider": "some-provider"}).(*Player)
    for i, _ := range player.externalIds {
      fmt.Println("ID:", player.ExternalIds.[i].ID, " Provider:", player.ExternalIds[i].Provider)
    }
  }
}

would affect only the instance generated at the specified index, printing something like

ID: 12ad23d4bn  Provider: somewhat
ID: 32ad23d4bn  Provider: some-provider

Scenario 3: Dot notation for nested array fields on specific index out of slice subfactory bounds

func main() {
  for i := 0; i < 3; i++ {
    player := PlayerFactory.MustCreateWithOption(map[string]any{"ExternalIds.2.Provider": "some-provider"}).(*Player)
    for i, _ := range player.externalIds {
      fmt.Println("ID:", player.ExternalIds.[i].ID, " Provider:", player.ExternalIds[i].Provider)
    }
  }
}

would panic with an error.

As part of the usage to calls like SeqInt(...) and SeqString(...) is it possible to get access to the args.Context() at all?

I want to pass in data that I need to the use as part of these builders.

This is sample code.

type User struct {
	Fullname  string
	Firstname string
	Lastname  string
}

var UserFactory = factory.NewFactory(
	&User{},
).Attr("Firstname", func(args factory.Args) (interface{}, error) {
	return "John", nil
}).Attr("Lastname", func(args factory.Args) (interface{}, error) {
	return "Doe", nil
}).Attr("Fullname", func(args factory.Args) (interface{}, error) {
	user := args.Instance().(*User)
	return fmt.Sprintf("%v %v", user.Firstname, user.Lastname), nil
})

user := UserFactory.MustCreate().(*User)
fmt.Println("Fullname:", user.Fullname, " Firstname:", user.Firstname, " Lastname:", user.Lastname)

Expect: Fullname: John Doe Firstname: John Lastname: Doe
Actual : Fullname: Firstname: John Lastname: Doe

I think when this work in order that define in struct. It generate Fullname first. In that time, Firstname and Lastname is not generated yet. So, Fullname is empty.

First off just want to say thanks, this project has been super helpful to me as I've been testing a DB backed application that features a complex graph of related models.

One feature that would be very helpful is if I could pass an explicit parent into a factory create method. This would let me use a factory as both a subfactory in a chain of related factories and in isolation to create a new instance of a model to add to an existing chain of related models.

Let me know what you think!

I have a struct like below

type Model struct {
    ID uuid.UUID
}

type User struct {
    Model
    Name string
}

and I am trying to do something like this

var UserFactory = factory.NewFactory(&models.User{}).
    Attr("ID", func(args factory.Args) (interface{}, error) {
        id := uuid.NewV4()
        return id, nil
    })

and I got this No such attribute name: ID, I don't have idea how to resolve this.

Each group of tests should have its own fixtures so we do not need to make modifications to other tests test data

as it is in in factorygirl, would be very useful if factory-fo support setting options for related objects (separated by dot):

user := factory.UserFactory.MustCreateWithOption(map[string]interface{}{"Role.RoleId": 2})