mongodb - 环回: Saving one-to-many relations in MongoDB

Question

从我阅读文档和模型关系示例中，我没有看到如何在 MongoDB 中保存一对多关系。我有以下型号:

1. Category
2. Post

Category 有很多 Posts 并且 Post 属于 Category 我使用的外键是“categoryId”

我使用以下脚本将示例数据插入 MongoDB:

create-categories.js:

var categories = [
        {"title" : "Technology Matters", "description": "Blogs on latest technologies"},
        {"title" : "Innovative Ideas", "description": "Innovative ideas on the next project"},
        {"title" : "Comments on Hot Topics", "description": "My comments on the hot topics"}
];
module.exports = function(server) {
        var dataSource = server.dataSources.mongoDatastore;
        dataSource.automigrate('Category', function(err) {
                if (err) throw err;
                var Model = server.models.Category;
                //create some sample data
                var count = categories.length;
                categories.forEach(function(category) {
                        Model.create(category, function(er, result) {
                                if (er) return;
                                console.log('Category created: ', result);
                                count--;
                                if (count == 0) {
                                        console.log('Categories all created!');
                                        dataSource.disconnect();
                                }
                        });
                        //could define a model scope here
                });
        });
};

create-posts.js:

var posts = [
        {"title" : "Post 1 Title", "bodyText": "body text for blog post 1", "dateCreated": new Date(), "categoryId": 1},
        {"title" : "Post 2 Title", "bodyText": "body text for blog post 2", "dateCreated": new Date(), "categoryId": 1},
        {"title" : "Post 3 Title", "bodyText": "body text for blog post 3", "dateCreated": new Date(), "categoryId": 2},
        {"title" : "Post 4 Title", "bodyText": "body text for blog post 4", "dateCreated": new Date(), "categoryId": 2},
        {"title" : "Post 5 Title", "bodyText": "body text for blog post 5", "dateCreated": new Date(), "categoryId": 1},
        {"title" : "Post 6 Title", "bodyText": "body text for blog post 6", "dateCreated": new Date(), "categoryId": 3},
        {"title" : "Post 7 Title", "bodyText": "body text for blog post 7", "dateCreated": new Date(), "categoryId": 2},
        {"title" : "Post 8 Title", "bodyText": "body text for blog post 8", "dateCreated": new Date(), "categoryId": 3},
        {"title" : "Post 9 Title", "bodyText": "body text for blog post 9", "dateCreated": new Date(), "categoryId": 1},
        {"title" : "Post 10 Title", "bodyText": "body text for blog post 10", "dateCreated": new Date(), "categoryId": 2}
];
module.exports = function(server) {
        var dataSource = server.dataSources.mongoDatastore;
        dataSource.automigrate('Post', function(err) {
                if (err) throw err;
                var Model = server.models.Post;
                //create some sample data
                var count = posts.length;
                posts.forEach(function(post) {
                        Model.create(post, function(er, result) {
                                if (er) return;
                                console.log('Post created: ', result);
                                count--;
                                if (count == 0) {
                                        console.log('Posts all created!');
                                        dataSource.disconnect();
                                }
                        });
                        //could define a model scope here
                });
        });
};

请注意上面每个帖子对象中伪造的“categoryId”只是临时的，我希望将实际的categoryId从MongoDB保存到每个帖子对象。

我的问题是:将每个帖子对象保存到 MongoDB 时，如何获取所有者的 ID(在本例中为categoryId)。我的MongoDB中保存的类别如下，每个类别都有一个ObjectId类型的_id。 Post集合中是否需要将类别ObjectId保存为外键？如果是，怎么做？

{
        "_id" : ObjectId("55355f076ed9d911089ea0a7"),
        "title" : "Technology Matters",
        "description" : "Blogs on latest technologies"
}
{
        "_id" : ObjectId("55355f076ed9d911089ea0a8"),
        "title" : "Innovative Ideas",
        "description" : "Innovative ideas on the next project"
}
{
        "_id" : ObjectId("55355f076ed9d911089ea0a9"),
        "title" : "Comments on Hot Topics",
        "description" : "My comments on the hot topics"
}

Answer 1

托尼给你一些建议，

1. NoSQL 不相信标准化。在许多地方存储相同的数据是可以的。
2. 在 MongoDB 中，如果一对多关系不太大，则可以在单个文档中处理一对多关系，即 one < many而不是one << many和cardinality of one is not very high .

您的问题的解决方案可能是，一个类别可以有多个帖子，但总共会出现多少个类别。在我看来，与帖子相比，一个(类别)的数量要少得多。

存储数据的更好方法是，

创建一个名为 posts 的集合，例如，

{
      "title" : "Post 1 Title", 
      "bodyText": "body text for blog post 1", 
      "dateCreated": new Date(), 
      "category": "movie"
}

在某些情况下，帖子可能会分为 2 个类别

{
      "title" : "Post 1 Title", 
      "bodyText": "body text for blog post 1", 
      "dateCreated": new Date(), 
      "category": ["movie","drama"]
}

这仍然是一个很好的设计，并且可以很好地处理大量数据。由于所有相关数据都存储在单个位置，因此操作性能也将得到改善，这正是 NoSQL 的真正优势。