MongoDB 驱动程序 Java：服务器上的“未知操作员：$project”

Question

我有以下

java

代码，用于创建

Bson

过滤器（按预期工作）。

但是，当我尝试将

projection

添加到我的过滤器时，我得到：

'unknown operator: $project' on server

我的代码中存在什么问题？

 private Bson createFilter(String name) {

        List<Bson> collectionFilters = new ArrayList<>();

        if (name != null) {
            filters.add(eq("person_name", name));
        }

        collectionFilters.add(projectCollectionFields());

        return and(collectionFilters);
    }

    private Bson projectCollectionFields() {
        return Aggregates.project(new Document()
                .append("_id", new Document("$cond", Arrays.asList(
                        new Document("$ne", Arrays.asList("$_id", null)),
                        "$_id",
                        "$$REMOVE"
                )))
                .append("name", new Document("$cond", Arrays.asList(
                        new Document("$ne", Arrays.asList("$person_name", null)),
                        "$person_name",
                        "$$REMOVE"
                )))
                .append("date", new Document("$cond", Arrays.asList(
                        new Document("$ne", Arrays.asList("$date_added", null)),
                        "$date_added",
                        "$$REMOVE"
                ))));
    }

Answer 1

在您的 projectCollectionFields() 中，您正在尝试聚合，您必须仅投影您想要的字段，例如

private Bson projectCollectionFields() {
    return Projections.fields(
        Projections.include("person_name", "date_added"),
        Projections.excludeId()
    );
}

修复createFilter()，例如：

private Bson createFilter(String name) {
    List<Bson> collectionFilters = new ArrayList<>();
    if (name != null) {
        collectionFilters.add(Filters.eq("person_name", name));
    }
    return Filters.and(collectionFilters);
}

然后：

Document doc = collection.find(createFilter(name))
                .projection(projectCollectionFields())
                .first();