猫鼬 - 根据条件从查询中排除嵌入文档

Question

我正在使用猫鼬。我的数据库中有以下文档：

question: {
    "id": "60ab9bd0d40a362189e842ff",
    "deletedAt": null
        "answers": [
        {
            "id": "60ab9e4e58a72f4768c5f63b",
            "deletedAt": "2021-05-28T20:23:30.409Z",
        },
        {
            "id": "60ab9e4e58a72f4768c5f64c",
            "deletedAt": null,
        },
    }
}

我想获得deletedAt 字段为空的所有问题，以及deletedAt 字段为空的所有答案。 所以我的查询结果应该是这样的：

question: {
    "id": "60ab9bd0d40a362189e842ff",
    "deletedAt": null
        "answers": [
         {
            "id": "60ab9e4e58a72f4768c5f64c",
            "deletedAt": null,
        },
    }
}

我尝试过的：

Question.aggregate([
    { $match: { deletedAt: null }},
    { $project: {
        answers: { 
          $filter: {
            input: "$answers",
            as: "answer",
            cond: { "$$answer.deletedAt": null }
          }
        }
      }
    },
    { $sort: sort },
    { $limit: limit + 1 }
]}

如果能提供任何帮助，我将不胜感激！

Answer 1

使用$eq 运算符匹配$filter 运算符中的条件，

    { $project: {
        answers: { 
          $filter: {
            input: "$answers",
            as: "answer",
            cond: { 
              $eq: ["$$answer.deletedAt", null]
            }
          }
        }
      }
    },