未知运算符：mgo中的“ $ or”

Question

I'm getting unknown operator: $or error with code below and couldn't figure out why.

vc := &storers.VCategory{}

err = mndb.
    C("virtualcategoryprototypes").
    Find(bson.M{
        "children":   nil,
        "deleted_by": nil,
        "indexCycleNo": bson.M{"$or": []bson.M{
            bson.M{"$exists": false},
            bson.M{"$lt": cycle}}}}).
    One(vc)

Answer 1

An $or expression is a series (array) of other conditions which are valid on their own (and which will be evaluated using logical OR connection), and the result of the $or expression will be in logical AND connection with other conditions at the same level.

So you have to move the $or operator up one level, its value must be a slice or array, and the elements of $or will be in your case indexCycleNo: {$exists: false} and indexCycleNo: {$lt: cycle}:

err = mndb.
    C("virtualcategoryprototypes").
    Find(bson.M{
        "children":   nil,
        "deleted_by": nil,
        "$or": []bson.M{
            {"indexCycleNo": bson.M{"$exists": false}},
            {"indexCycleNo": bson.M{"$lt": cycle}},
        },
    }).
    One(vc)