How to "sort" and "limit" results in mongodb? - mongodb

Question

I'm trying to execute a query with "sort" and "limit". With mgo you could do Find(nil).Sort(“-when”).Limit(10) but the new, official mongo driver has no such methods. How can I sort and "limit" with the new driver?

Answer 1

In the current version mongo-go-driver v1.0.3, the options are simplified. For example to perform find, sort and limit:
import (
"go.mongodb.org/mongo-driver/bson"
"go.mongodb.org/mongo-driver/mongo"
"go.mongodb.org/mongo-driver/mongo/options"
)
options := options.Find()
// Sort by `_id` field descending
options.SetSort(bson.D{{"_id", -1}})
// Limit by 10 documents only
options.SetLimit(10)
cursor, err := collection.Find(context.Background(), bson.D{}, options)
See more available options on godoc.org/go.mongodb.org/mongo-driver/mongo/options. Especially FindOptions for all possible options for Find().

Answer 2

The official driver is not straightforward as mgo. You can do sort and limit using the findopt.Limit and findopt.Sort.
You can see examples from the official repository.
https://github.com/mongodb/mongo-go-driver/blob/5fea1444e52844a15513c0d9490327b2bd89ed7c/mongo/crud_spec_test.go#L364

Answer 3

You can use
findOptions := options.Find()
findOptions.SetLimit(2)
findOptions.SetSkip(2)
...
cursor, err := collection.Find(context.Background(), bson.M{}, findOptions)
resource at https://www.mongodb.com/blog/post/mongodb-go-driver-tutorial

Answer 4

you need import "github.com/mongodb/mongo-go-driver/options" package to build a findOptions.
import github.com/mongodb/mongo-go-driver/options
findOptions := options.Find() // build a `findOptions`
findOptions.SetSort(map[string]int{"when": -1}) // reverse order by `when`
findOptions.SetSkip(0) // skip whatever you want, like `offset` clause in mysql
findOptions.SetLimit(10) // like `limit` clause in mysql
// apply findOptions
cur, err := collection.Find(context.TODO(), bson.D{}, findOptions)
// resolve err
for cur.Next(context.TODO()) {
// call cur.Decode()
}

Answer 5

The sort-option apparently requires you to add a map[string]interface{} where you can specify a field as key and a sortOrder as value (where 1 means ascending and -1 means descending) as following:
sortMap := make(map[string]interface{})
sortMap["version"] = 1
opt := findopt.Sort(sortMap)
As far as I can see this means that you are only able to properly sort results by one sortField because keys in a go map are stored in a random order.

Answer 6

ONE LINE OPTION
I know there is already a lot of answers but you can do it as one line (if you need it for any case of yours)
// From the Doc
// func (f *FindOptions) SetSort(sort interface{}) *FindOptions
cursor, err := collection.Find(context.Background(), bson.M{}, options.Find().SetSort(map[string]int{"when": -1}).SetLimit(10))
SetSort() and the others currently returns the parent pointer itself