Composite literal uses unkeyed fields

Question

I am working with new official mongodb driver for golang. I have created one complex query to insert the data into mongo db and then sort it according to an element value. I am using a filter in which I have created the bson type using :-

filter := bson.D{{"autorefid", "100"}}

But It is showing a warning saying:

primitive.E composite literal uses unkeyed fields

The warnings are creating a mess in my code.

Answer 1

The warnings can be stopped by setting the check flag to false.

$ go doc cmd/vet

By default all checks are performed. If any flags are explicitly set to true, only those tests are run. Conversely, if any flag is explicitly set to false, only those tests are disabled. Thus -printf=true runs the printf check, -printf=false runs all checks except the printf check.

Unkeyed composite literals

Flag: -composites

Composite struct literals that do not use the field-keyed syntax.

But the warning is due to not providing the keys name when setting the value in primitive.E struct.

Setting keys for primitive.E struct will remove the warning messages. For example

filter := bson.D{primitive.E{Key: "autorefid", Value: "100"}}

Package primitive contains types similar to Go primitives for BSON types can do not have direct Go primitive representations.

type E struct {
    Key   string
    Value interface{}
}

E represents a BSON element for a D. It is usually used inside a D.

For more information have a look at primitive.E

Answer 2

Since no one else has pointed this out — the warning is there to safeguard you from changes in the third-party API breaking your code silently.

Ignoring this vet warning has the potential to lead to really nasty and hard to track down runtime bugs, so you'd be better off if you were to always specify the keys of 3rd party structs explicitly.

Such would be the case if the maintainers of the library you are using decided to change the order of elements in their struct for whatever reason. For example, switching Key with Value, in the OP case. Your code would still appear to compile just fine, but what you intended to be the key would now be passed as the value and vice versa, and things would just start breaking in unexpected ways.

Answer 3

You can simply change:

filter := bson.D{{"autorefid", "100"}}

to:

filter := bson.D{{Key: "autorefid", Value: "100"}}

//Skip primitive.E as said by Chris W