golang convert primative.D to struct

[Matthew Shaver]

In go I am storing a structure with an interface{} field to be able to store different sub structures in the mongodb record. When I read back the record into the struct I can see the interface{} field has type primitive.D. 

I can convert that data to a specific struct type using the following steps but I want to know if this is the recommended / most efficient method

type Record struct {

  Type         string

  SubStruct interface{}

}

type SubRec struct {

  Val1 int

  Val2 int

}

rec, err := jobs.Find(StdDb, insertId)

subPrimativeD := rec.SubStruct.(primitive.D)

temp, err := bson.MarshalExtJSON(subPrimativeD, true, true)

var subRec SubRec

err := bson.UnmarshalExtJSON(temp, true, &subRec)

[Wan Bachtiar]

In go I am storing a structure with an interface{} field to be able to store different sub structures in the mongodb record. When I read back the record into the struct I can see the interface{} field has type primitive.D.

Hi Matthew,

Not exactly sure what the problem here, but other than interface you can also use either bson.D (ordered), or bson.M (unordered). For example:

type Record struct {
    Type string
    SubStruct bson.D
}

And you can just call Cursor.Decode() instead of the marshal/unmarshal, for example:

cursor, err := collection.Find(context.TODO(), bson.D{})
if err != nil {
    log.Fatal(err)
}
defer cursor.Close(context.TODO())
for cursor.Next(context.Background()) {
    doc := &Record{}
    err = cursor.Decode(doc)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(doc)
}

The above is assuming you’re using the current version of MongoDB Go driver v1.0.3. If you have further question, please include the driver version that you’re using.

Regards,
Wan.

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