MongoDB fetching all the documents in a collection gives an empty slice of structs using mgo

Question

I have inserted data into mongodb in the following way

  {
     "_id" : ObjectId("5c80e9cc3bf127cfc80ba5dc"),
     "resp" : [
         {
             "name" : "by",
             "gender" : "synced",
             "age" : "response",
             "hobby" : "submitted",
             "mobile" : "revision"
         },
        {
            "name" : "byoooooo",
            "gender" : "sytewed",
            "age" : "se",
            "hobby" : "subed",
            "mobile" : "revissaaon"
        }
    ]
  }

Using this method

func (d *CollectDAO) Insert(responses []*models.FormData) error {
  resp := models.Responses{
      Data: responses,
  }
  err := db.C(formsCollection).Insert(resp)
  return err
}

This is the struct used in the insert method

type FormData struct {
  Name     string `csv:"name" json:"name" bson:"name"`
  Gender   string `csv:"gender" json:"gender" bson:"gender"`
  Age      string `csv:"age" json:"age" bson:"age"`
  Hobby    string `csv:"hobby" json:"hobby" bson:"hobby"`
  MobileNo string `csv:"mobile" json:"mobile" bson:"mobile"`
}

The handler reads sample csv data from a file. This is the csv data

name,gender,age,hobby,mobile
by,synced,response,submitted,revision
byoooooo,sytewed,se,subed,revissaaon

And then inserts that into mongo

When querying all the documents of my collection I get an empty response

func (d *CollectDAO) FindAll() (models.Responses, error) {
    var responses []models.Responses
    err := db.C(formsCollection).Find(nil).All(&responses)
    if err != nil {
        log.Fatal(err)
    }

    log.Printf("all docs %v\n", responses)

    return responses, err
}

When I try to log the value of the struct I get an empty struct. This is the responses struct that I am using at the end to put the slice of response in.

type Responses struct {
  Data []*FormData `json:"response"`
}

What am I doing wrong? I just need to implement a handler that will return all the data in a collection as a struct.

On the client side I get this error

unexpected end of JSON input
{ObjectIdHex("") []}

Answer 1

The mgo package uses the bson tag to map struct fields to document fields in MongoDB.

So your Responses type should look something like this:

type Responses struct {
    Data []*FormData `json:"response" bson:"resp"`
}

Note that you have to save documents with this struct (with bson tag) to be able to fetch results into values of this type.