How to Query Unstructured MongoDB Collections in Go with mgo?

Handling Unstructured MongoDB Collections in Go with mgo

When querying a collection in MongoDB with mgo, it is possible to predefined the data that will be returned in a struct, as demonstrated with the Person struct example provided. However, there may be scenarios where the documents in the collection have a varying set of keys.

How to Handle Unstructured Collections in Go / mgo

There are multiple ways to handle unstructured collections in Go / mgo:

Using a map:

By using a bson.M type, which is a map[string]interface{}, you can store the document data directly without defining a specific struct.

var m bson.M
err := collection.Find(nil).One(&m)
check(err)
for key, value := range m {
    fmt.Println(key, value)
}

Using a document slice:

bson.D is a slice type that preserves the ordering of keys and provides an efficient mechanism for handling documents.

var d bson.D
err := collection.Find(nil).One(&d)
check(err)
for i, elem := range d {
    fmt.Println(elem.Name, elem.Value)
}

Using an inline map field:

By using the ,inline bson flag in a map field in a struct, you can combine the convenience of using a struct with the flexibility of handling unknown fields.

type Person struct {
    ID        bson.ObjectId `bson:"_id,omitempty"`
    Name      string
    Phone     string
    Extra     bson.M `bson:",inline"`
}

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