I know the title says interface array, but that's how the data is being printed.
I have a field in mongodb called "devices" which is of type object. This object contains a bunch of random key values pairs. The keys are just randomly generated integers and the value are a string.
So I've written some code which retrieves the data from the db, after I've retrieved the data I want to get all the keys from theses objects and store them in an array and I can't seem to figure out how to do that.
First I assume my issue lies with the way I'm getting the data since I'm storing it into an interface{} and not an array. The data prints out like an array but when I change the structure to retrieve an array it comes back empty so I scrapped that idea.
Function
type Data struct {
Devices interface{} `json:"devices" bson:"devices"`
}
client := db.ConnectClient()
col := client.Database("Users").Collection("User")
var deviceIds Data
_ = col.FindOne(context.TODO(), bson.D{}).Decode(&deviceIds)
log.Print(deviceIds.Devices)
Output
2020/10/29 21:28:07 [{123456789 Plant} {456753121 Money Bringer} {798745321 Hello}]
Also I have tried changing that struct to
type Data struct {
Devices map[int]interface{} `json:"devices" bson:"devices"`
}
which gives an output of
2020/10/29 21:35:10 map[123456789:Plant 456753121:Money Bringer 798745321:Hello]
but again I don't know how to extract the keys from them
So as I just finished writing this question I figured out the map was the correct way to get my data.
Posted the question and answering it myself because I thought it would be useful for others
type Data struct {
Devices map[int]interface{} `json:"devices" bson:"devices"`
}
for key, value := range deviceIds.Devices {
fmt.Println(key, value)
}
Changing the struct to the above map and then looping through it with range worked perfectly
I would like to change order my documents in Mongo DB using Go. I have valid json string code and i can marshal it successfully in to map[string]int. The sample of this type just like:
[{year 1}, {lastupdated -1}]. The value presents order year field ascending and lastupdated field descending. This struct is aspect of MongoDB understands. Also I'm pass this data into bson.D type. Here is my code:
if queries["order"] != nil {
var unmarshalledOrder map[string]int
json.Unmarshal(queries["order"].([]byte), &unmarshalledOrder)
docRes := make(bson.D, 0)
for field, sort := range unmarshalledOrder {
docRes = append(docRes, bson.DocElem{field, sort})
}
log.Println(docRes)
}
When I print docRes, everthing goes well. But i pass the data to options.Sort function, the function throws interface conversion: interface {} is runtime.errorString, not string panic. Is it a bug on mongo go driver or am i wrong?
Can you post the code you've written which uses the driver? Based on the use of bson.DocElem, I think you're using mgo, but mgo's Query.Sort method takes strings, not documents (https://pkg.go.dev/github.com/globalsign/mgo?tab=doc#Query.Sort).
For the record, I'm learning Go. I'm trying to use and the mgo package and I'd like to insert a new document and return this newly created document to user (I'm trying to write a basic API). I've wrote the following code:
EDIT: Here's the struct for the model:
type Book struct {
ISBN string `json:"isbn"`
Title string `json:"title"`
Authors []string `json:"authors"`
Price string `json:"price"`
}
session := s.Copy()
defer session.Close()
var book Book
decoder := json.NewDecoder(r.Body)
err := decoder.Decode(&book)
if err != nil {
ErrorWithJSON(w, "Incorrect body", http.StatusBadRequest)
return
}
c := session.DB("store").C("books")
info, err := c.Upsert(nil, book)
if err != nil {
ErrorWithJSON(w, "Database error", http.StatusInternalServerError)
log.Println("Failed insert book: ", err)
return
}
respBody, err := json.MarshalIndent(info, "", " ")
if err != nil {
log.Fatal(err)
}
ResponseWithJSON(w, respBody, http.StatusOK)
Please note that Book is a struct I have created earlier. The above code does work but what it returns is the upsert result like so:
{
"Updated": 1,
"Removed": 0,
"Matched": 1,
"UpsertedId": null
}
Which is not the recently created object. How can I get the the recently created object to return as a response (please note that ideally I'd like the confirmation that the document was successfully inserted. I have seen other questions where the ID is generated beforehand but for what I've seen it doesn't confirm that the document was created was it?)
Let's clear the concepts first. In MongoDB, each document must have an _id property which acts as its unique document identifier inside a collection. Either you provide the value of this _id or it is assigned automatically by MongoDB.
So it would be ideal (or it's strongly recommended) for your model types to include a field for the _id document identifier. Since we're talking about books here, books already have a unique identifier called ISBN, which you may opt to use as the value of the _id field.
The mapping between MongoDB fields and Go struct fields must be specified using the bson tag (not json). So you should provide bson tag values along with json tags.
So change your model to:
type Book struct {
ISBN string `json:"isbn" bson:"_id"`
Title string `json:"title" bson:"title"`
Authors []string `json:"authors" bson:"authors"`
Price string `json:"price" bson:"price"`
}
If you want to insert a new document (a new book), you should always use Collection.Insert().
And what will be the ID of the newly inserted document? The field you set to the Book.ISBN field as we declared it to be the document ID with the bson:"_id" tag.
You should only use Collection.Upsert() if you are not sure whether the document already exists, but either way you want it to be the document you have at hand. Collection.Upsert() will try to find a document to update, and if one is found, that will be updated. If no document is found, then an insert operation will be performed. The first parameter is the selector to find the document to be updated. Since you passed nil, that means any document may qualify, so one will be selected "randomly". So if you already have books saved, any may get selected and get overwritten. This is certainly not want you want.
Since now the ISBN is the ID, you should specify a selector that filters by ISBN, like this:
info, err := c.Upsert(bson.M{"_id": book.ISBN}, book)
Or since we're filtering by ID, use the more convenient Collection.UpsertId():
info, err := c.UpsertId(book.ISBN, book)
If you want to update an existing document, for that you may use Collection.Update(). This is similar to Collection.Upsert(), but the difference is that if no documents match the selector, an insert will not be performed. Updating a document matched by ID can also be done with the more convenient Collection.UpdateId() (which is analogue to Collection.UpsertId()).
For other documents which do not have a unique identifier naturally (like books having ISBN), you may use generated IDs. The mgo library provides the bson.NewObjectId() function for such purpose, which returns you a value of type bson.ObjectId. When saving new documents with Collection.Insert(), you can acquire a new unique ID with bson.NewObjectId() and assign it to the struct field that is mapped to the MongoDB _id property. If the insert succeeds, you can be sure the document's ID is what you just set before calling Collection.Insert(). This ID generation is designed to work even in a distributed environment, so it will generate unique IDs even if 2 of your nodes attempt to generate an ID at the same time.
So for example if you don't have the ISBN for a book when saving it, then you must have a separate, designated ID field in your Book type, for example:
type Book struct {
ID bson.ObjectId `bson:"_id"`
ISBN string `json:"isbn" bson:"isbn"`
Title string `json:"title" bson:"title"`
Authors []string `json:"authors" bson:"authors"`
Price string `json:"price" bson:"price"`
}
And when saving a new book:
var book Book
// Fill what you have about the book
book.ID = bson.NewObjectId()
c := session.DB("store").C("books")
err = c.Insert(book)
// check error
// If no error, you can refer to this document via book.ID
Banged my head for a while on this.
info, err := c.Upsert(nil, book)
The nil selector for the upsert will match everything so if your collection is empty the selector won't match and all will be fine, the info object will contain the ObjectId in the UpsertedId field, but on every following upsert with nil selector the collection will have records and the nil selector for the upsert will match, therefore it won't return you the UpsertedId and you will be updating the first matched record.
You could use never matching selector for the upsert (which was my solution), but note that this way you will only insert and get the inserted ObjectId and never update a record.
You can checkout the following test:
func TestFoo(t *testing.T) {
foo := struct {
Bar string `bson:"bar"`
}{
Bar: "barrr",
}
session, _ := mgo.DialWithInfo(&mgo.DialInfo{
Addrs: []string{"127.0.0.1:27017"},
})
coll := session.DB("foo").C("bar")
coll.DropCollection()
info, _ := coll.Upsert(nil, foo) // will insert
count, _ := coll.Count()
fmt.Printf("%+v, collecton records:%v\n", info, count) // &{Updated:0 Removed:0 Matched:0 UpsertedId:ObjectIdHex("5c35e8ee1f5b80c932b44afb")}, collection records:1
info, _ = coll.Upsert(bson.M{}, foo) // will update
count, _ = coll.Count()
fmt.Printf("%+v, collecton records:%v\n", info, count) // &{Updated:1 Removed:0 Matched:1 UpsertedId:<nil>}, collection records:1
info, _ = coll.Upsert(bson.M{"nonsense": -1}, foo) // will insert duplicate record (due to the selector that will never match anything)
count, _ = coll.Count()
fmt.Printf("%+v, collecton records:%v\n", info, count) // &{Updated:0 Removed:0 Matched:0 UpsertedId:ObjectIdHex("5c35ea2a1f5b80c932b44b1d")}, collection records:2
foo.Bar = "baz"
info, _ = coll.Upsert(nil, foo) // will update the first matched (since the selector matches everything)
count, _ = coll.Count()
fmt.Printf("%+v, collecton records:%v\n", info, count)
// after the test the collection will have the following records
//> use foo
//> db.bar.find()
//{ "_id" : ObjectId("5c35ebf41f5b80c932b44b81"), "bar" : "baz" } // the first matched on the last update with nil selector
//{ "_id" : ObjectId("5c35ebf41f5b80c932b44b86"), "bar" : "barrr" } // the duplicated record with the selector that never matches anything
}
EDIT: Note that you should have an index on the never matching field, or your insert query will take too long if you have many records, because the upsert on not indexed filed will scan all the documents in the collection.
I am new to GO language and I am using MongoDB with it. I am creating a backend for an application and its frontend on Angular 4. I want to check if collection exists or not.
Here is my code and I have checked it using nil.
collection := GetCollection("users")
fmt.Println("collection", collection)
if collection == nil {
fmt.Println("Collection is empty")
}
I have created a GetCollection function which return a collection when we pass it a collection name.
So when if there is no collection how can I check that if it exists or not?
I have tried many things but failed.
You may simply use the Database.CollectionNames() method which returns the collection names present in the given db. It returns a slice in which you have to check if your collection is listed.
sess := ... // obtain session
db := sess.DB("") // Get db, use db name if not given in connection url
names, err := db.CollectionNames()
if err != nil {
// Handle error
log.Printf("Failed to get coll names: %v", err)
return
}
// Simply search in the names slice, e.g.
for _, name := range names {
if name == "collectionToCheck" {
log.Printf("The collection exists!")
break
}
}
But as Neil Lunn wrote in his comments, you shouldn't need this. You should change your logic to use MongoDB not to rely on this check. Collections are created automatically if you try to insert a document, and querying from non-existing collections yields no error (and no result of course).
I'm still new to go and while I see multiple questions on SO similar to this, I'm unable to reproduce the output some OP's had requested (this answer looking the closest).
I'm doing something fairly simple, I'm hitting a users collection in mongo and all I want to do is get the _id value back as a string. I'm going to eventually push these _id's up to NSQ but that's the brunt of my task.
var users []bson.M
err = sess.DB("db_name").C("users").Find(bson.M{}).All(&users)
if err != nil {
os.Exit(1)
}
for _, user := range users {
fmt.Printf("%+v \n", user["_id"])
}
Today this outputs:
ObjectIdHex("537f700b537461b70c5f0000")
ObjectIdHex("537f700b537461b70c600000")
ObjectIdHex("537f700b537461b70c610000")
ObjectIdHex("537f700b537461b70c620000")
I went through the bson#m docs and thought I was correctly using the map in order to extra the value. So I think, my query results in:
{"_id" : ObjectIdHex("Some_ID") }
but if ObjectIdHex("ID") is the value, how do I simply get the string within there.
So ideal output:
"537f700b537461b70c5f0000"
"537f700b537461b70c600000"
"537f700b537461b70c610000"
"537f700b537461b70c620000"
The value associated with key "_id" is of type bson.ObjectId which is simply a string.
bson.M is a type map[string]interface{}, so you need Type assertion to get the id as an ObjectId:
objid, ok := m["_id"].(ObjectId)
if !ok {
panic("Not ObjectId")
}
And the ObjectId has a ObjectId.Hex() method which returns exactly what you want: the object id as a "pure" hex string:
fmt.Println(objid.Hex())
Alternatives
objid can simply be converted to string because its underlying type is string. So you can use a number of further options to convert it to a hex string:
hexid := fmt.Sprintf("%x", string(objid))
If you just want to print it, you can do directly:
fmt.Printf("%x", string(objid))
Note: Converting it to string is important else the fmt package would call its String() method which results in a string like ObjectIdHex("537f700b537461b70c5f0000") and this is what would be converted to hex which is clearly not what you want.
Alternatively you can use the encoding/hex package and the hex.EncodeToString() function:
hexid := hex.EncodeToString([]byte(objid))