Question
How can I list databases only with the given prefix (prefix_)?
Example:
package main
import (
"context"
"fmt"
"go.mongodb.org/mongo-driver/bson"
"go.mongodb.org/mongo-driver/mongo"
"go.mongodb.org/mongo-driver/mongo/options"
"log"
)
type foo struct {
Value string
}
func main() {
clientOptions := options.Client().ApplyURI("mongodb://10.0.12.76:27018")
client, err := mongo.Connect(context.TODO(), clientOptions)
if err != nil {
log.Fatal(err)
}
db := [3]string{"prefix_foo", "prefix_bar", "bar"}
for _, element := range db {
_, err := client.Database(element).Collection("placeholder").InsertOne(context.TODO(), foo{"sth"})
if err != nil {
log.Fatal(err)
}
}
filter := bson.D{{}}
dbs, err := client.ListDatabaseNames(context.TODO(), filter)
if err != nil {
log.Fatal(err)
}
fmt.Printf("%+v\n", dbs)
}
Output:
[admin bar config local prefix_bar prefix_foo]
Expected output:
[prefix_bar prefix_foo]
Bonus:
It is possible to create a database without defining new struct in my case foo?
My goal is to run a query on databases only with a prefix, so maybe better solution exists than listing dbs and then run a query on each database?
Simply filter by the name property, which denotes the database name. And to list databases starting with a given prefix, you may use a regexp being ^prefix_:
filter := bson.M{"name": primitive.Regex{Pattern: "^prefix_"}}
Other filter options are listed on the listDatabases command page:
You can specify a condition on any of the fields in the output of listDatabases:
name
sizeOnDisk
empty
shards
And you may use an empty bson.M{} to insert an empty document (_id will be added of course).
Related
In golang..
I get list mongodb database name below..
filter := bson.D{{}}
dbs, _ := client.ListDatabaseNames(context.TODO(), filter)
fmt.Printf("%+v\n", dbs)
But, I want to get list collections name.
How about ListCollectionNames?
Here's an example from the documentation. I added some placeholder lines that you need to replace by your client connection code and getting a database:
package main
import (
"context"
"fmt"
"log"
"go.mongodb.org/mongo-driver/bson"
"go.mongodb.org/mongo-driver/mongo"
)
func main() {
// Placeholder:
//
// Connect to MongoDB, handle error
client, err := mongo.connect(....)
if err != nil {
log.Fatal(err)
}
// Obtain the DB, by name. db will have the type
// *mongo.Database
db := client.Database("name-of-your-DB")
// use a filter to only select capped collections
result, err := db.ListCollectionNames(
context.TODO(),
bson.D{{"options.capped", true}})
if err != nil {
log.Fatal(err)
}
for _, coll := range result {
fmt.Println(coll)
}
}
Question
How can I list databases only with the given prefix (prefix_)?
Example:
package main
import (
"context"
"fmt"
"go.mongodb.org/mongo-driver/bson"
"go.mongodb.org/mongo-driver/mongo"
"go.mongodb.org/mongo-driver/mongo/options"
"log"
)
type foo struct {
Value string
}
func main() {
clientOptions := options.Client().ApplyURI("mongodb://10.0.12.76:27018")
client, err := mongo.Connect(context.TODO(), clientOptions)
if err != nil {
log.Fatal(err)
}
db := [3]string{"prefix_foo", "prefix_bar", "bar"}
for _, element := range db {
_, err := client.Database(element).Collection("placeholder").InsertOne(context.TODO(), foo{"sth"})
if err != nil {
log.Fatal(err)
}
}
filter := bson.D{{}}
dbs, err := client.ListDatabaseNames(context.TODO(), filter)
if err != nil {
log.Fatal(err)
}
fmt.Printf("%+v\n", dbs)
}
Output:
[admin bar config local prefix_bar prefix_foo]
Expected output:
[prefix_bar prefix_foo]
Bonus:
It is possible to create a database without defining new struct in my case foo?
My goal is to run a query on databases only with a prefix, so maybe better solution exists than listing dbs and then run a query on each database?
Simply filter by the name property, which denotes the database name. And to list databases starting with a given prefix, you may use a regexp being ^prefix_:
filter := bson.M{"name": primitive.Regex{Pattern: "^prefix_"}}
Other filter options are listed on the listDatabases command page:
You can specify a condition on any of the fields in the output of listDatabases:
name
sizeOnDisk
empty
shards
And you may use an empty bson.M{} to insert an empty document (_id will be added of course).
I am trying to get some familiarity with the official mongo-go-driver and the right syntax for UpdateOne.
My simplest full example follows:
(NOTE: in order to use this code you will need to substitute in your own user and server names as well as export the login password to the environment as MONGO_PW):
package main
import (
"context"
"fmt"
"os"
"go.mongodb.org/mongo-driver/bson"
"go.mongodb.org/mongo-driver/bson/primitive"
"go.mongodb.org/mongo-driver/mongo"
"go.mongodb.org/mongo-driver/mongo/options"
)
type DB struct {
User string
Server string
Database string
Collection string
Client *mongo.Client
Ctx context.Context
}
var db = DB{
User: <username>,
Server: <server_IP>,
Database: "test",
Collection: "movies",
Ctx: context.TODO(),
}
type Movie struct {
ID primitive.ObjectID `bson:"_id" json:"id"`
Name string `bson:"name" json:"name"`
Description string `bson:"description" json:"description"`
}
func main() {
if err := db.Connect(); err != nil {
fmt.Println("error: unable to connect")
os.Exit(1)
}
fmt.Println("connected")
// The code assumes the original entry for dunkirk is the following
// {"Name":"dunkirk", "Description":"a world war 2 movie"}
updatedMovie := Movie{
Name: "dunkirk",
Description: "movie about the british evacuation in WWII",
}
res, err := db.UpdateByName(updatedMovie)
if err != nil {
fmt.Println("error updating movie:", err)
os.Exit(1)
}
if res.MatchedCount < 1 {
fmt.Println("error: update did not match any documents")
os.Exit(1)
}
}
// UpdateByName changes the description for a movie identified by its name
func (db *DB) UpdateByName(movie Movie) (*mongo.UpdateResult, error) {
filter := bson.D{{"name", movie.Name}}
res, err := db.Client.Database(db.Database).Collection(db.Collection).UpdateOne(
db.Ctx,
filter,
movie,
)
if err != nil {
return nil, err
}
return res, nil
}
// Connect assumes that the database password is stored in the
// environment variable MONGO_PW
func (db *DB) Connect() error {
pw, ok := os.LookupEnv("MONGO_PW")
if !ok {
fmt.Println("error: unable to find MONGO_PW in the environment")
os.Exit(1)
}
mongoURI := fmt.Sprintf("mongodb+srv://%s:%s#%s", db.User, pw, db.Server)
// Set client options and verify connection
clientOptions := options.Client().ApplyURI(mongoURI)
client, err := mongo.Connect(db.Ctx, clientOptions)
if err != nil {
return err
}
err = client.Ping(db.Ctx, nil)
if err != nil {
return err
}
db.Client = client
return nil
}
The function signature for UpdateOne from the package docs is:
func (coll *Collection) UpdateOne(ctx context.Context, filter interface{},
update interface{}, opts ...*options.UpdateOptions) (*UpdateResult, error)
So I am clearly making some sort of mistake in creating the update interface{} argument to the function because I am presented with this error
error updating movie: update document must contain key beginning with '$'
The most popular answer here shows that I need to use a document sort of like this
{ $set: {"Name" : "The Matrix", "Decription" "Neo and Trinity kick butt" } }
but taken verbatim this will not compile in the mongo-go-driver.
I think I need some form of a bson document to comply with the Go syntax. What is the best and/or most efficient syntax to create this bson document for the update?
After playing around with this for a little while longer I was able to solve the problem after A LOT OF TRIAL AND ERROR using the mongodb bson package by changing the UpdateByName function in my code above as follows:
// UpdateByName changes the description for a movie identified by its name
func (db *DB) UpdateByName(movie Movie) (*mongo.UpdateResult, error) {
filter := bson.D{{"name", movie.Name}}
update := bson.D{{"$set",
bson.D{
{"description", movie.Description},
},
}}
res, err := db.Client.Database(db.Database).Collection(db.Collection).UpdateOne(
db.Ctx,
filter,
update,
)
if err != nil {
return nil, err
}
return res, nil
}
Note the use of bson.D{{$"set", .... It is unfortunate the way MongoDB has implemented the bson package this syntax still does not pass the go-vet. If anyone has a comment to fix the lint conflict below it would be appreciated.
go.mongodb.org/mongo-driver/bson/primitive.E composite literal uses unkeyed fields
In many cases you can replace construction
filter := bson.D{{"name", movie.Name}}
with
filter := bson.M{"name": movie.Name}
if arguments order dowsn't matter
I'm trying to find a document by its auto generated _id field. Code below returns nothing:
var documentID bson.RawValue
documentID.Type = 7
documentID.Value = []byte("5c7452c7aeb4c97e0cdb75bf")
objID := documentID.ObjectID()
value := collection.FindOne(ctx, bson.M{"_id": objID})
The value I provided is a real document id I got from Mongo Express
"_id": ObjectID("5c7452c7aeb4c97e0cdb75bf")
In case you're wondering why I bother with RawValue, I found examples using bson.EC.ObjectID but bson package doesn't seem to have EC type, also I found some examples mentioning github.com/mongodb/mongo-go-driver/bson/objectid package, but I could not find that package either. I previously developed with mgo but I'm new to mongo-go-driver, so if you can point an easy way to declare an ObjectID.
As #Carlos mentioned, I changed my code as this and everything works well.
objID, _ := primitive.ObjectIDFromHex("5c7452c7aeb4c97e0cdb75bf")
value := collection.FindOne(ctx, bson.M{"_id": objID})
You can use some thing like this:
var userDB user
objectIDS, _ := primitive.ObjectIDFromHex(userID)
collectionUser := dBClient.Database("MyDatabase").Collection("Users")
filter := bson.M{"_id": objectIDS}
err := collectionUser.FindOne(ctx, filter).Decode(&userDB)
if err != nil {
fmt.Println("errror retrieving user userid : " + userID)
}
package main
import (
"fmt"
"go.mongodb.org/mongo-driver/bson"
"go.mongodb.org/mongo-driver/bson/primitive"
"context"
)
// get collection "users" from db() which returns *mongo.Client
var userCollection = db().Database("goTest").Collection("users")
func mongodriver_find_by_id() {
objectId, err1 := primitive.ObjectIDFromHex("6041c3a6cfcba2fb9c4a4fd2")
if err1 != nil {fmt.Println(err1)}
findone_result := userCollection.FindOne(context.TODO(), bson.M{"_id":objectId})
var bson_obj bson.M
if err2 := findone_result.Decode(&bson_obj); err2 != nil {fmt.Println(err2)}
fmt.Println("bson_obj:", bson_obj)
}
I am using Golang and Postgres, Postgres has an advance feature where it can return your queries in Json format. What I want to do is get that Json query results and return it but I am having trouble since it has to be a String in order to return it. This is my code
package main
import(
"fmt"
"database/sql"
_ "github.com/lib/pq"
"log"
)
func HelloServer(w http.ResponseWriter, req *http.Request) {
db, err := sql.Open("postgres", "user=postgres password=password dbname=name sslmode=disable")
if err != nil {
log.Fatal(err)
}
defer db.Close()
rows, err := db.Query("select To_Json(t) (SELECT * from cars)t")
io.WriteString(w, "hello, world!\n")
}
func main() {
http.HandleFunc("/hello", HelloServer)
log.Fatal(http.ListenAndServe(":12345", nil))
}
The Rows element returns a Json array how can I turn that Rows element into a String ? For C# and Java I would just append the .ToString() method to it and it would make it a string . As you can see from the code above the io.WriteString takes a String as a second parameter so I want to make the Rows variable a String after it has the Json returned so that I can display it in the browser by passing it to the method. I want to replace the Hello World with the String Rows.
Rows is a sql.Rows type. In order to use the data returned by your database query you will have to iterated over the "rows".
An example from the docs
age := 27
rows, err := db.Query("SELECT name FROM users WHERE age=?", age)
if err != nil {
log.Fatal(err)
}
defer rows.Close()
for rows.Next() {
var name string
if err := rows.Scan(&name); err != nil {
log.Fatal(err)
}
fmt.Printf("%s is %d\n", name, age)
}
if err := rows.Err(); err != nil {
log.Fatal(err)
}
You should instead use QueryRow because you are expecting the database to return one result. In either case once you have used "Scan" to put the data into your own variable then you can either parse the JSON or print it out.