Mongodb MongoError:无法识别的管道阶段名称：'$添加字段'；

MongoError:无法识别的管道阶段名称：“$addFields”。 “猫鼬”：“^4.5.8” 我的源代码：

                Post.aggregate(
                    [{
                        $addFields: {
                            userName: { $concat: [ "$author.firstName", " ", "$author.lastName" ] }
                        }
                        //$project: { userName: { $concat: [ "$author.firstName", " ", "$author.lastName" ] } } //this is ok!
                    }],
                    function (err, result) {
                        if (err) {
                            console.log(err);
                            return;
                        }
                        console.log(result);
                    }
                )

后模型：

let schema = {
id: "post",
properties: {
    content: {type: "string"},
    author: {
        type: "object",
        id: {type: "string"},
        avatar: {type: "string"},
        firstName: {type: "string"},
        lastName: {type: "string"},
        status: {type: "string"}
    },
    category: {
        type: "object",
        id: {type: "string"},
        name: {type: "string"}
    },
    images: {
        type: "array",
        items: {
            type: "object",
            properties: {
                filePath: {type: "string"},
            }
        }
    },
    video: {
        type: "object",
        thumbnail: {type: "string"},
        filePath: {type: "string"}
    },
    likes: {
        type: "array",
        items: {
            type: "object",
            properties: {
                userId: {type: "string"},
                status: {type: "string"},
                _id   : {type: "string", default: null}
            }
        }
    },
    shares: {
        type: "array",
        items: {
            type: "object",
            properties: {
                userId: {type: "string"},
                status: {type: "string"},
                destination: {type: "string"}, //FACEBOOK|TWISTER|GOOGLE
                _id        : {type: "string", default: null}
            }
        }
    },
    favorites: {
        type: "array",
        items: {
            type: "object",
            properties: {
                userId: {type: "string"},
                status: {type: "string"},
                _id   : {type: "string", default: null}
            }
        }
    },
    comments: {
        type: "array",
        items: {
            type: "object",
            properties: {
                commentId: {type: "string"},
                _deleted: {type: "Date", default: ''},
                _id     : {type: "string", default: null}
            }
        }
    },
    _created: {type: "Date", default: Date.now},
    _deleted: {type: "Date", default: ''},
    _updated: {type: "Date", default: ''}
}

在Mongo3.4版本中引入。正如您所评论的，您正在使用mongo 3.2.9，所提到的查询将不起作用

如果由于某种原因无法更新mongo版本，则必须使用以下方法，其中需要迭代每个文档并设置新字段

Post.find({}).forEach(function(post){
  post.findOneAndUpdate({_id: post._id}, 
      {$set: {userName: post.author.firstName + " " + post.author.lastName }})
});

---

mongodb上的版本是什么

$addFields

在3.4mongodb的版本是^4.5.8，在packge.json中：“mongoose”：“^4.5.8”，“mongoose json select”：“^0.2.1”，“mongoose unique validator”：“^1.0.2”，使用我检查过的问题的答案检查版本，mongodb的版本是3.2.9。非常感谢。修改原始文档是一个糟糕的解决方法。OP问题中注释掉的

$project

是正确的解决方法。非常感谢！我更新了mongo版本并解决了我的问题problem@JohnnyHK你能解释一下为什么$project解决方案是正确的吗？我正在寻找这个问题的答案：