fetching the data from a mongodb in golang - mongodb

Question

I'm trying to fetch data from mongodb in golang using the gopkg.in/mgo.v2 driver, the format of the data is not fixed , as in few rows will be containing some fields which other rows might not.
here is the code for the same
session, err := mgo.Dial("mongodb://root:root#localhost:27017/admin")
db := session.DB("test")
fmt.Println(reflect.TypeOf(db))
CheckError(err,"errpor")
result := make(map[string]string)
//query := make(map[string]string)
//query["_id"] = "3434"
err1 := db.C("mycollection").Find(nil).One(&result)
CheckError(err1,"error")
for k := range result {
fmt.Println(k)
}
Now the data contained in the collection is { "_id" : "3434", "0" : 1 }, however the for loop gives the output as _id , shouldn't there be two keys '_id' and '0' ? or am I doing something wrong here.

Answer 1

oh I found the solution
the "result" variable should be of type bson.M and then you can typecast accordingly as you go deep into the nesting structure.

Answer 2

Give a try with the following piece of code. This will help you fetching matching records from the Database using BSON Object.
Do not forget to rename the Database name and Collection name of your MongoDB in the below code. Also needs to change the query parameter accordingly.
Happy Coding...
package main
import (
"context"
"fmt"
"time"
"go.mongodb.org/mongo-driver/bson"
"go.mongodb.org/mongo-driver/mongo"
"go.mongodb.org/mongo-driver/mongo/options"
)
// This is a user defined method to close resourses.
// This method closes mongoDB connection and cancel context.
func close(client *mongo.Client, ctx context.Context, cancel context.CancelFunc) {
defer cancel()
defer func() {
if err := client.Disconnect(ctx); err != nil {
panic(err)
}
}()
}
// This is a user defined method that returns
// a mongo.Client, context.Context,
// context.CancelFunc and error.
// mongo.Client will be used for further database
// operation. context.Context will be used set
// deadlines for process. context.CancelFunc will
// be used to cancel context and resourse
// assositated with it.
func connect(uri string) (*mongo.Client, context.Context, context.CancelFunc, error) {
ctx, cancel := context.WithTimeout(context.Background(),
30*time.Second)
client, err := mongo.Connect(ctx, options.Client().ApplyURI(uri))
return client, ctx, cancel, err
}
// query is user defined method used to query MongoDB,
// that accepts mongo.client,context, database name,
// collection name, a query and field.
// datbase name and collection name is of type
// string. query is of type interface.
// field is of type interface, which limts
// the field being returned.
// query method returns a cursor and error.
func query(client *mongo.Client, ctx context.Context, dataBase, col string, query, field interface{}) (result *mongo.Cursor, err error) {
// select database and collection.
collection := client.Database(dataBase).Collection(col)
// collection has an method Find,
// that returns a mongo.cursor
// based on query and field.
result, err = collection.Find(ctx, query,
options.Find().SetProjection(field))
return
}
func main() {
// Get Client, Context, CalcelFunc and err from connect method.
client, ctx, cancel, err := connect("mongodb://localhost:27017")
if err != nil {
panic(err)
}
// Free the resource when mainn dunction is returned
defer close(client, ctx, cancel)
// create a filter an option of type interface,
// that stores bjson objects.
var filter, option interface{}
// filter gets all document,
// with maths field greater that 70
filter = bson.D{
{"_id", bson.D{{"$eq", 3434}}},
}
// option remove id field from all documents
option = bson.D{{"_id", 0}}
// call the query method with client, context,
// database name, collection name, filter and option
// This method returns momngo.cursor and error if any.
cursor, err := query(client, ctx, "YourDataBaseName",
"YourCollectioName", filter, option)
// handle the errors.
if err != nil {
panic(err)
}
var results []bson.D
// to get bson object from cursor,
// returns error if any.
if err := cursor.All(ctx, &results); err != nil {
// handle the error
panic(err)
}
// printing the result of query.
fmt.Println("Query Reult")
for _, doc := range results {
fmt.Println(doc)
}
}