How to Create Nested OR/AND Query Filters in MongoDB with the Go Driver?

MongoDB Nested OR/AND Query Filter in Go

The MongoDB Go driver allows you to create complex query filters using the $or and $and operators. However, if you need to create nested operators within these top-level operators, the process can be a bit confusing due to the driver's use of bson.D and bson.E elements.

The following example demonstrates how to create a nested OR/AND query filter:

package main

import (
    "context"
    "fmt"
    "time"

    "go.mongodb.org/mongo-driver/bson"
    "go.mongodb.org/mongo-driver/mongo"
)

func main() {
    ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
    defer cancel()

    client, err := mongo.NewClient(options.Client().ApplyURI("mongodb://localhost:27017"))
    if err != nil {
        panic(err)
    }
    defer client.Disconnect(ctx)

    collection := client.Database("test").Collection("people")

    // Create a nested OR/AND query filter
    filter := bson.D{
        {
            "$and", bson.A{
                bson.D{{"age", 30}},
                bson.D{{"$or", bson.A{
                    bson.D{{"name", "John"}},
                    bson.D{{"name", "Jane"}},
                }}},
            },
        },
    }

    // Find all people matching the filter
    cur, err := collection.Find(ctx, filter)
    if err != nil {
        panic(err)
    }
    defer cur.Close(ctx)

    // Iterate through the results and print each person's name
    for cur.Next(ctx) {
        var result bson.M
        if err := cur.Decode(&result); err != nil {
            panic(err)
        }
        fmt.Println(result["name"])
    }

    if err := cur.Err(); err != nil {
        panic(err)
    }
}

In this example:

• The top-level $and operator is represented by a bson.D slice.
• The $or operator within the $and operator is also represented by a bson.D slice.
• Each condition in the $or operator is represented by a bson.D element.

It's important to note that the $and operator is the default, so you don't have to explicitly specify it. However, if you want to nest other operators within $and, you'll need to use a bson.A slice to represent the array of conditions.

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