How to insert array of struct into MongoDB

Question

I am trying to insert data that is stored in an array of struct into a MongoDB using the go.mongodb.org/mongo-driver library. My struct is

type Statement struct {
    ProductID        string `bson:"product_id" json:"product_id"`
    ModelNum         string `bson:"model_num" json:"model_num"`
    Title            string `bson:"title" json:"title"`
}

and my insertion code is

func insert(stmts []Statement) {
    client, err := mongo.NewClient(options.Client().ApplyURI("mongodb://127.0.0.1:27017"))
    if err != nil {
        log.Fatal(err)
    }
    ctx, _ := context.WithTimeout(context.Background(), 10*time.Second)
    err = client.Connect(ctx)
    if err != nil {
        log.Fatal(err)
    }
    defer client.Disconnect(ctx)

    quickstartDatabase := client.Database("quickstart")
    testCollection := quickstartDatabase.Collection("test")
    testCollection.InsertMany(ctx, stmts) // This is giving error
}

The compiler gives the error cannot use stmts (variable of type []Statement) as []interface{} value in argument to testCollection.InsertMany at the InsertMany command.

I have tried marshalling the struct before inserting using bson.Marshal but even that doesn't work. How do I insert this data into the DB?

Have you tried creating a list of interface{} and cast your Statement? Something like: interfaceStmts := []interface{}{} for _, s := range stmts{ interfaceStmts = append(interfaceStmts, s) } — Mihai, Feb 28 '21 at 18:06
@Mihai Yes, that worked. Thank you. But doesn't iterate over every element in the array? Which is the fastest way to do this? — khateeb, Feb 28 '21 at 18:22
It does iterate over the elements in the array unfortunately. There is no nice and easy way to do the conversion. I think the good news is that the big O complexity of the code will not change with this extra iteration since the lib will also iterate over the batch so complexity is still O(n). This post https://stackoverflow.com/questions/12753805/type-converting-slices-of-interfaces/12754757#12754757 should cover the reason behind the language design. — Mihai, Feb 28 '21 at 21:09

score 3 · Answer 1 · edited Sep 03 '22 at 13:59

3

insertMany accept []interface{}

i would make like this

newValue := make([]interface{}, len(statements))

for i := range statements {
  newValue[i] = statements[i]
}

col.InsertMany(ctx, newValue)

edited Sep 03 '22 at 13:59

user8555937

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answered Mar 03 '21 at 02:54

Pocket

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Note: if you make using len(statements), then the first len(statements) records will be nil in newValue – yayayahei Apr 18 '22 at 12:44

How to insert array of struct into MongoDB

1 Answers1