public MongoIndex add(MongoIndex mongoIndex) {
        indexModels.add(new IndexModel(Indexes.compoundIndex(mongoIndex.getBson()), mongoIndex));
        return this;
    }
public MongoIndex add ( MongoIndex mongoIndex ) { indexModels . add ( new IndexModel ( Indexes . compoundIndex ( mongoIndex . getBson ( ) ) , mongoIndex ) ) ; return this ; }
/*组合索引