带有外键的模型上的restful api

Question

TLDR; How to create REST api on model having Foreign key (or db relationship in general) in buffalo framework?

I am absolute beginner in go and I am trying to write an RESTFul service using buffalo framework following following example given on it official website. I am able to create RESTful api on models which have no database relationship. But I am stuck when I faced a situation where model has a foreign key. I am not able to find any documentation or reference on web. I concept on Go is also weak, you can also educate me on those thins.

Models: (ref: https://gobuffalo.io/en/docs/db/relations#example

type Composer struct {
    ID              uuid.UUID `json:"id" db:"id"`
    Name            string    `json:"name" db:"name"`
    Description     string    `json:"description" db:"description"`
    CreatedAt       time.Time `json:"created_at" db:"created_at"`
    UpdatedAt       time.Time `json:"updated_at" db:"updated_at"`

}


type Track struct {
    ID          uuid.UUID           `json:"id" db:"id"`
    Title       string              `json:"title" db:"title"`
    Description string              `json:"description" db:"description"`
    Composer    Composer            `has_one:"composer" fk_id:"id"`
    CreatedAt   time.Time           `json:"created_at" db:"created_at"`
    UpdatedAt   time.Time           `json:"updated_at" db:"updated_at"`
}

Resources: (ref: https://gobuffalo.io/en/docs/resources)

type TrackResource struct {
    buffalo.Resource
}


func (v TrackResource) List(c buffalo.Context) error {
    tx, ok := c.Value("tx").(*pop.Connection)
    if !ok {
        return errors.WithStack(errors.New("no transaction found"))
    }

    pieces := &models.Tracks{}

    q := tx.PaginateFromParams(c.Params())

    if err := q.All(pieces); err != nil {
        return errors.WithStack(err)
    }

    c.Set("pagination", q.Paginator)

    return c.Render(200, r.JSON(pieces))
}


func (v TrackResource) Show(c buffalo.Context) error {
    tx, ok := c.Value("tx").(*pop.Connection)
    if !ok {
        return errors.WithStack(errors.New("no transaction found"))
    }

    piece := &models.Track{}

    if err := tx.Find(piece, c.Param("track_id")); err != nil {
        return c.Render(404, r.JSON(err))
    }

    return c.Render(200, r.JSON(piece))
}


func (v TrackResource) Create(c buffalo.Context) error {

    piece := &models.Track{}

    if err := c.Bind(piece); err != nil {
        return errors.WithStack(err)
    }

    tx, ok := c.Value("tx").(*pop.Connection)
    if !ok {
        return errors.WithStack(errors.New("no transaction found"))
    }

    verrs, err := piece.Create(tx)
    if err != nil {
        return errors.WithStack(err)
    }

    if verrs.HasAny() {
        return c.Render(422, r.JSON(verrs))
    }

    return c.Render(201, r.Auto(c, piece))
}


func (v TrackResource) Update(c buffalo.Context) error {

    tx, ok := c.Value("tx").(*pop.Connection)
    if !ok {
        return errors.WithStack(errors.New("no transaction found"))
    }

    piece := &models.Track{}

    if err := tx.Find(piece, c.Param("track_id")); err != nil {
        return c.Error(404, err)
    }

    if err := c.Bind(piece); err != nil {
        return errors.WithStack(err)
    }

    verrs, err := piece.Update(tx)
    if err != nil {
        return errors.WithStack(err)
    }

    if verrs.HasAny() {
        return c.Render(422, r.JSON(verrs))
    }

    return c.Render(200, r.JSON(piece))
}


func (v TrackResource) Destroy(c buffalo.Context) error {

    tx, ok := c.Value("tx").(*pop.Connection)
    if !ok {
        return errors.WithStack(errors.New("no transaction found"))
    }

    piece := &models.Track{}

    if err := tx.Find(piece, c.Param("track_id")); err != nil {
        return c.Error(404, err)
    }

    if err := tx.Destroy(piece); err != nil {
        return errors.WithStack(err)
    }

    return c.Render(200, r.JSON(piece))
}

When I am trying to create a track. I am getting error:

json: cannot unmarshal string into Go struct field Track.Composer of type models.Composer
gitlab.com/****/****/actions.TrackResource.Create

Please help.

Answer 1

You're trying to bind a Track containing a Composer with its ID, but Composer is defined as a struct.

To make it work, you need to implement the Unmarshaler interface and define how to convert this ID into the Composer struct you want.