如何在一个视图中链接更多文档

Question

有 3 种 CouchDB 文档类型：

用户

{ "_id: "user/author1", "type: "user", "name" : "Joe Doe"}

评论

{ "_id: "review/review1", "type" : "review", "content" : "..." }

产品

{ "_id": "product/awesomeproduct", "type" : "product", "reviews": [
   {
       "author": "author1",
       "review_id": "review/review1"
   },
   {
       "author": "author2",
       "review_id": "review/review2"
   }
  ]
}

如何从单一视图的文档中获取所有数据？

我尝试使用链接文档，但每次发出时只能使用一个（使用 include_docs=true）：

（咖啡稿）

(doc) ->
  if doc.type is "product"
    for review in doc.reviews
       emit [doc._id, review.author],{_id: "user/" + review.author}
       emit [doc._id, review.author],{_id: review.review_id}

但我想要这样的东西（在单次​​发射中获取用户和审查文档）：

 (doc) ->
  if doc.type is "product"
    for review in doc.reviews
       key = [doc._id, review.author]
       value = {"user:" {_id: "user/" + review.author},"review" :{_id: review.review_id}}
       emit key, value

有没有可能的方法来实现它？如何在单一视图中加入这些类型的文档？

我想得到这样的结果：

[
  key : ["product/awesomeproduct", "author1"], 
  value : {user: {_id: "user/author1"},review :{_id: "review/review1"}}
  doc: 
     {user: {"_id: "user/author1", "type: "user", "name" : "Joe Doe"},
      review: {"_id: "review/review1", "type" : "review", "content" : "..."}
     }

]

Answer 1

似乎是 reduce 函数的经典案例（抱歉，我没有咖啡 :)）：

地图

function(doc) {
    if(doc.type == "product") {
        for(review_i in doc.reviews) {
            var review = doc.reviews[review_i];
            emit([doc._id, review.author],{user: "user/" + review.author, review: review.review_id});
        }
    }
}

减少

function(keys, values) {
    return(values);
}

结果（?reduce=true[&group=exact]）：

key                                      value
["product/awesomeproduct", "author2"]    [{user: "user/author2", review: "review/review1"}]
["product/awesomeproduct", "author1"]    [{user: "user/author1", review: "review/review1"}]

您希望发出的数据究竟是什么样的？

回复上述评论 应该是可能的，除了您希望在视图返回的文档中显示数据的方式。 include_docs 表示按原样返回整个文档。似乎您希望在视图和返回的文档中表示相同的数据，因此可能将文档的结构更改为：

_id : ...
data : 
    {
        user: {"_id: "user/author1", "type: "user", "name" : "Joe Doe"},
        review: {"_id: "review/review1", "type" : "review", "content" : "..."}
    }

否则，如果你只希望view key,values是上面提到的结构，而不关心返回的doc的结构：

地图

function(doc) {
    if(doc.type == "product") {
        for(review_i in doc.reviews) {
            var review = doc.reviews[review_i];
            emit([doc._id, review.author],{
                            user: {_id: "user/" + review.author}, 
                            review: {_id: review.review_id}
                            });
        }
    }
}

这应该导致：

curl -X GET http://localhost:5984/testdb2/_design/test/_view/test?include_docs=true\&reduce=false

{
    "offset": 0,
    "rows": [
        {
            "doc": {
                "_id": "product/awesomeproduct",
                "_rev": "2-20f0c6cc663e03ab93f8646f09d87db2",
                "reviews": [
                    {
                        "author": "author1",
                        "review_id": "review/review1"
                    },
                    {
                        "author": "author2",
                        "review_id": "review/review1"
                    }
                ],
                "type": "product"
            },
            "id": "product/awesomeproduct",
            "key": [
                "product/awesomeproduct",
                "author1"
            ],
            "value": {
                "review": {
                    "_id": "review/review1"
                },
                "user": {
                    "_id": "user/author1"
                }
            }
        },
        {
            "doc": {
                "_id": "product/awesomeproduct",
                "_rev": "2-20f0c6cc663e03ab93f8646f09d87db2",
                "reviews": [
                    {
                        "author": "author1",
                        "review_id": "review/review1"
                    },
                    {
                        "author": "author2",
                        "review_id": "review/review1"
                    }
                ],
                "type": "product"
            },
            "id": "product/awesomeproduct",
            "key": [
                "product/awesomeproduct",
                "author2"
            ],
            "value": {
                "review": {
                    "_id": "review/review1"
                },
                "user": {
                    "_id": "user/author2"
                }
            }
        }
    ],
    "total_rows": 2
}

这并不是你要找的东西，但这是我的最佳猜测。

Answer 2

简短的回答...你不能。 Couchdb 只允许您一次发出一个文档。

有两种方法可以获取您需要的数据。

1. 保持结构不变，并在您的客户端代码中手动执行连接。
2. 非规范化您的数据。此处的非规范化类似于将评论放入您的产品文档中。

Data modeling considerations 适用于 Mongodb，但有关如何在 NoSQL 环境中构建数据的概念与适用于 CouchDB 的概念相同

Answer 3

你可以在下面做这样的事情，

function (doc) {
  if(doc.type is "product" && doc.reviews.length > 0){
    
    for(x=0; x<doc.reviews.length; x++){
       key = [doc._id, review.author]
       value = {"user:" {_id: "user/" + review.author},"review" :{_id: review.review_id}}
       emit ([key, value])
    }
  }
}

这将在您的相关视图中发出两个文档。