I am trying to insert data that is stored in an array of struct into a MongoDB using the go.mongodb.org/mongo-driver library. My struct is
type Statement struct {
ProductID string `bson:"product_id" json:"product_id"`
ModelNum string `bson:"model_num" json:"model_num"`
Title string `bson:"title" json:"title"`
}
and my insertion code is
func insert(stmts []Statement) {
client, err := mongo.NewClient(options.Client().ApplyURI("mongodb://127.0.0.1:27017"))
if err != nil {
log.Fatal(err)
}
ctx, _ := context.WithTimeout(context.Background(), 10*time.Second)
err = client.Connect(ctx)
if err != nil {
log.Fatal(err)
}
defer client.Disconnect(ctx)
quickstartDatabase := client.Database("quickstart")
testCollection := quickstartDatabase.Collection("test")
testCollection.InsertMany(ctx, stmts) // This is giving error
}
The compiler gives the error cannot use stmts (variable of type []Statement) as []interface{} value in argument to testCollection.InsertMany at the InsertMany command.
I have tried marshalling the struct before inserting using bson.Marshal but even that doesn't work. How do I insert this data into the DB?
insertMany accept []interface{}
i would make like this
newValue := make([]interface{}, len(statements))
for i := range statements {
newValue[i] = statements[i]
}
col.InsertMany(ctx, newValue)
Related
I'm trying to convert the structure I'm decoding with my query to map[string]interface.
Here is my code:
var m map[string]interface
var result []Result
type Result struct {
Id ResultId `bson:"_id"`
Filename string `bson:"filename"`
}
type ResultId struct {
Host string `bson:"host"`
}
group := bson.D{{"$group", bson.D{{"_id", bson.D{{"host","$host"}}}, {"filename", bson.D{{"$last","$filename"}}}}}}
collection := client.Database("mongodb").Collection("Meta")
cursor, err := collection.Aggregate(ctx, mongo.Pipeline{group})
if err != nil {
return c.JSON(http.StatusInternalServerError, err)
}
defer cursor.Close(ctx)
if err = cursor.All(ctx, &results); err != nil {
fmt.Printf("cursor.All() error:", err)
return c.JSON(http.StatusInternalServerError, err)
}
for _, value := range results {
m = append(m,&bson.M{value.Id.Host:value.Filename})
}
But it does not return a map[string]interface and for information I use the go.mongodb.org package.
append only works on slices, (refer to effective go's section for more on append)
The way to add elements to a map, is simply:
m["key"] = value
Also keep in mind maps need to be initialised which I don't see in your code. Either with make or by giving an initial value (can be an empty value)
I am writing an abstraction over the official mongo driver which consists of a struct containing a pointer to the collection needed and CRUD methods on it. In order to be able to work with multiple types(all of which have bson adnotations) I use an interface called Storable, but I don't see a way in which I could decode the field without knowing the type exactly. Code snippet:
func (c *Collection) GetAll() ([]models.Storable, error) {
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()
cursor, err := c.coll.Find(ctx, bson.M{})
if err != nil {
return nil, err
}
var result []models.Storable
for cursor.Next(ctx) {
var doc models.Storable
err = cursor.Decode(&doc)
if err != nil {
return nil, err
}
result = append(result, doc)
}
return result, nil
}
type example:
type User struct {
ID primitive.ObjectID `json:"id" bson:"_id,omitempty"`
FirstName string `json:"firstName" bson:"firstName"`
LastName string `json:"lastName" bson:"lastName"`
Email string `json:"email" bson:"email"`
Password string `json:"password" bson:"password"`
}
You need to pass in the correct type to decode to somehow. To be able to pass in different types you could use the empty interface{}. However if you pass in the entire slice (e.g. []User) into interface{} you cannot append to it any more without complex usage of reflection.
Using a function to create a new row
As #mkopriva mentioned in the comments, we could pass a function creating a new row to it (or pass it to the collection on initialisation):
func (c *Collection) GetAll(newRow func() models.Storable) ([]models.Storable, error) {
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()
cursor, err := c.coll.Find(ctx, bson.M{})
if err != nil {
return nil, err
}
var result []models.Storable
for cursor.Next(ctx) {
nRow := newRow()
err = cursor.Decode(nRow)
if err != nil {
return nil, err
}
result = append(result, nRow.(models.Storable))
}
return result, nil
}
You would then call with a function returning the correct type (must be a pointer):
rows, err := c.GetAll(func() models.Storable {
return new(User)
})
Here my reference implementation using json decoding to test this: Playground
Using reflection to create a new row
You could pass in the variable type for a single row:
func (c *Collection) GetAll(row models.Storable) ([]models.Storable, error) {
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()
cursor, err := c.coll.Find(ctx, bson.M{})
if err != nil {
return nil, err
}
var result []models.Storable
for cursor.Next(ctx) {
nRow := reflect.New(reflect.TypeOf(p)).Interface()
err = cursor.Decode(nRow)
if err != nil {
return nil, err
}
result = append(result, nRow.(models.Storable))
}
return result, nil
}
You would then call this with the correct type:
var user User
rows, err := c.GetAll(user)
Note that I don't use a pointer type here! The pointer is taken via reflection in the function.
Here my reference implementation using json decoding to test this: Playground
The downside of the "one function for all" is that you now have a slice of models.Storable with different data inside and you have to use a type switch or type assertion to work with the data.
For this reason I don't use generic functions for database calls but create a new function for every call I need: e.g. GetAllUsers, GetUserByID, GetAllContacts, etc.
Note: this is one of the things I will rethink when generics get added to Go.
I am trying to create a function where it gets all the documents from a Mongo Collection and queries them to declared structs. To achieve this I set the parameters for the function of type interface so it can work with two structs. Here is my code:
In package entities:
type Project struct {
Title string
Position string
....
}
type Projects struct {
Projects []Project
}
In the current package:
var docs entities.Projects
var doc entities.Project
//doc represents a document from Mongo Collection
//docs represents an array of documents, each element is a document
//collection has type *mongo.Collection and points to the desired collection on MongoDB.
createQuery(&doc, &docs, collection)
func createQuery(doc interface{}, docs interface{}, c *mongo.Collection) {
documents := reflect.ValueOf(docs).Elem()
document := reflect.ValueOf(doc)
cur, err := c.Find(context.Background(), bson.D{{}})
if err != nil {
log.Fatal(err)
}
for cur.Next(context.Background()) {
err = cur.Decode(document.Interface())
if err != nil {
log.Fatal(err)
}
//Error is thrown here
documents.Set(reflect.Append(documents, document))
fmt.Println(doc)
}
if err := cur.Err(); err != nil {
log.Fatal(err)
}
if err != nil {
fmt.Printf("oh shit this is the error %s \n", err)
}
cur.Close(context.Background())
fmt.Printf("documents: %+v\n", documents.Interface())
fmt.Printf("document: %+v\n", document.CanSet())
}
---ERROR OUTPUT---
panic: reflect: call of reflect.Append on struct Value
I was able to set data to doc using the document variable, although when doing document.CanSet() is false (so it may not even work). Where the program breaks is when I try to append the document to the documents interface.
The code in the question passes the struct docs to a function that expects a slice. Pass the address of the slice field in docs instead of docs itself.
The createQuery function can determine the slice element type from the slice itself. There's no need to pass in an example value.
var docs entities.Projects
createQuery(&docs.Projects, collection)
for _, doc := range docs.Projects {
fmt.Println(doc.Title)
}
The call to cur.Decode requires a pointer to an uninitialized value. Use reflect.New to create that value.
func createQuery(docs interface{}, c *mongo.Collection) {
docsv := reflect.ValueOf(docs).Elem()
doct := docsv.Type().Elem()
cur, err := c.Find(context.Background(), bson.D{{}})
if err != nil {
log.Fatal(err)
}
for cur.Next(context.Background()) {
docpv := reflect.New(doct)
err = cur.Decode(docpv.Interface())
if err != nil {
log.Fatal(err)
}
docsv.Set(reflect.Append(docsv, docpv.Elem()))
}
if err := cur.Err(); err != nil {
log.Fatal(err)
}
cur.Close(context.Background())
}
As an aside, the entities.Projects struct type is not needed if that struct type will only ever have one field. Use []Project instead:
var docs []entities.Project
createQuery(&docs, collection)
for _, doc := range docs {
fmt.Println(doc.Title)
}
I tried to follow documentation here and here but had no luck.
I want to get a singleResult from FindOne on the Collection named moviesCollection and then use Decode or Unmarshal to put those values into a struct. The values in the struct JSONData are exactly the same as in each Document
I am using the official mongodb driver github.com/mongodb/mongo-go-driver
Here is an example of what I have tried:
mongoContext, cancelContext := context.WithTimeout(context.Background(), 10*time.Second)
defer cancelContext()
mongoClient, _ := mongo.Connect(mongoContext, options.Client().ApplyURI("mongodb://localhost:27017"))
moviesCollection := mongoClient.Database("Entertainment").Collection("Movies")
moviesCollection.InsertOne(mongoContext, bson.M{"_id": "Deadpool", "Path": "path/to/file"})
singleResult := moviesCollection.FindOne(mongoContext, bson.M{"_id": "Deadpool"})
if singleResult.Err() != nil {
log.Println("Find error: ", singleResult.Err())
}
JSONData := struct {
Path string `json:"Path"`
}{}
decodeError := singleResult.Decode(&JSONData)
if decodeError != nil {
log.Println("Decode error: ", decodeError)
}
fmt.Println("Path: ", JSONData.Path)
However no errors are produced and JSON.Path produces and empty string.
I have also tried using bson.D{{"_id", "Deadpool"}} instead of bson.M{"_id": "Deadpool"}
I can confirm that JSON.Path is not empty string as I have checked the database natively using MongoDB Compass. The entry contains the following:
{"_id":"Deadpool","Path":"path/to/file"}
Internally, MongoDB uses bson. Change your struct as below should work.
From
JSONData := struct {
Path string `json:"Path"`
}{}
to
JSONData := struct {
Path string `bson:"Path"`
}{}
Hey so as simagix mentioned you should be able to change your tag from JSON to bson:
`bson:"Path"`
Another option, incase you need to obtain a more generic result is to pass it a D object like so:
JSONData := &bson.D{}
decodeError := singleResult.Decode(JSONData)
You can then obtain all the information through a map using the JSON.Data.Map function.
If you are using mongo-go-driver >= v.0.1.0 then, taking a look to the go-doc it looks pretty straightforward:
filter := bson.D{{"hello", "world"}}
err := collection.FindOne(context.Background(), filter).Decode(&result)
if err != nil { return err }
// do something with result...
So, what you need is:
package main
import (
"context"
"github.com/mongodb/mongo-go-driver/bson"
"github.com/mongodb/mongo-go-driver/mongo
)
func main() {
ctx := context.Background()
client, err := mongo.NewClient("mongodb://localhost:27017")
if err != nil {
...
}
if err := client.Connect(ctx); err != nil {
...
}
defer client.Disconnect(ctx)
collection := client.Database("myDb").Collection("movies")
filter := bson.D{{"_id", "sometitle"}}
var result JSONData
err := collection.FindOne(ctx, filter).Decode(&result)
if err != nil {
...
}
// Do Something cool here
}
I see you are using Title to filter the doc. Pay attention.
So here is my question. I have an array which are stored the _ids of mongodbs objects. Whats the right way to retrieve them all in one query using the mgo and bson package?
So if the array is like that: ids:=["543d171c5b2c12420dd016","543d171c5b2dd016"]
How we make the query ? I tried that but I know its wrong.
query := bson.M{"_id": bson.M{"$in": ids}}
c.Find(query).All()
Thanks in advance
If the documents are stored with string ids, then the code looks correct.
The ids look like hex encoded object ids. If the object identifiers are object ids, then you need to the convert the hex strings to object ids:
oids := make([]bson.ObjectId, len(ids))
for i := range ids {
oids[i] = bson.ObjectIdHex(ids[i])
}
query := bson.M{"_id": bson.M{"$in": oids}}
MongoDB syntax for go.mongodb.org/mongo-driver has been updated, this should work using the official driver.
oids := make([]primitive.ObjectID, len(ids))
for i := range ids {
objID, err := primitive.ObjectIDFromHex(ids[i])
if err == nil {
oids = append(oids, objID)
}
}
This is to convert back to a struct that can be used through out the app
type MongoUser struct {
ID *primitive.ObjectID `json:"id" bson:"_id"`
FirstName string `json:"first_name" bson:"firstName"`
LastName string `json:"last_name" bson:"lastName"`
Email string `json:"email" bson:"email"`
}
This is a helper method that takes your slice of ids and turns it into the object id type.
func formatObjectIdMultiple(hex []string) ([]primitive.ObjectID, error) {
var list []primitive.ObjectID
oids := make([]primitive.ObjectID, len(hex))
for _, i := range hex {
objectId, err := primitive.ObjectIDFromHex(i)
if err != nil {
return nil, err
}
oids = append(oids, objectId)
}
return list, nil
}
Here is my method for the db. Its important you use bson.M for some reason bson.D does not work with this. Also dont forget to close your cursor the defer function will close it at the end of your GetMultipleUser function.
func (mongo *Mongo) GetMultipleUser(ids []string) ([]*MongoUser, error) {
objectIDs, err := formatObjectIdMultiple(ids)
if err != nil {
return nil, err
}
query := bson.M{"_id": bson.M{"$in": objectIDs}}
coll := mongo.Con.Database("dbName").Collection("users")
cursor, err := coll.Find(context.Background(), query)
if err != nil {
return nil, err
}
defer func() {
cursor.Close(context.Background())
}()
var output []*MongoUser
for cursor.Next(context.Background()) {
var temp *MongoUser
cursor.Decode(&temp)
output = append(output, temp)
}
return output, nil
}