使用 lodash 创建多级查找表

Question

Lets pretend an api is returning the structure in apiResult , and I want to create a two-level index for looking up what comments a given author have made on a given article.

The lookup table for the authors, articles and comments it self is easy enough, but I struggle with the CommentsByArticleAndAuthor -lookup.

In the mapped structure, I'm showing how I'm making the lookup index for the three 'easy' parts, and also how I want the CommentsByArticleAndAuthor to look.

How can I go forward generating this index?

 var apiResult = { Authors: [ { Id: "author-id-1", Name: "Author One" }, { Id: "author-id-2", Name: "Author Two" } ], Articles: [ { Id: "article-id-1", Title: "This Great Article" } ], Comments: [ { Id: "comment-id-1", AuthorId: "author-id-1", ArticleId: "article-id-1", Comment: "that great, hu?" }, { Id: "comment-id-2", AuthorId: "author-id-2", ArticleId: "article-id-1", Comment: "yes, that great" } ] } var mapped = { Authors: _.keyBy(apiResult.Authors, 'Id'), Articles: _.keyBy(apiResult.Articles, 'Id'), Comments: _.keyBy(apiResult.Comments, 'Id'), CommentsByArticleAndAuthor: { "article-id-1": { "author-id-1": [ "comment-id-1" ], "author-id-2": [ "comment-id-2" ] } } } console.log(JSON.stringify(mapped, null, 2));

 <script src="https://cdn.jsdelivr.net/lodash/4.17.4/lodash.min.js"></script>

Answer 1

You could iterate the comments and build a hierarchical object strcture.

 var apiResult = { Authors: [{ Id: "author-id-1", Name: "Author One" }, { Id: "author-id-2", Name: "Author Two" }], Articles: [{ Id: "article-id-1", Title: "This Great Article" }], Comments: [{ Id: "comment-id-1", AuthorId: "author-id-1", ArticleId: "article-id-1", Comment: "that great, hu?" }, { Id: "comment-id-2", AuthorId: "author-id-2", ArticleId: "article-id-1", Comment: "yes, that great" }] }, mapped = { CommentsByArticleAndAuthor: {} }; apiResult.Comments.forEach(function (o) { var ref = mapped.CommentsByArticleAndAuthor; ref[o.ArticleId] = ref[o.ArticleId] || {}; ref[o.ArticleId][o.AuthorId] = ref[o.ArticleId][o.AuthorId] || []; ref[o.ArticleId][o.AuthorId].push(o.Id); }); console.log(mapped);

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For a more dynamic approach, you could use an array for the hierarchy and an object for the default values.

 var apiResult = { Authors: [{ Id: "author-id-1", Name: "Author One" }, { Id: "author-id-2", Name: "Author Two" }], Articles: [{ Id: "article-id-1", Title: "This Great Article" }], Comments: [{ Id: "comment-id-1", AuthorId: "author-id-1", ArticleId: "article-id-1", Comment: "that great, hu?" }, { Id: "comment-id-2", AuthorId: "author-id-2", ArticleId: "article-id-1", Comment: "yes, that great" }] }, mapped = { CommentsByArticleAndAuthor: {} }; apiResult.Comments.forEach(function (o) { ['ArticleId', 'AuthorId'].reduce(function (r, k) { return r[o[k]] = r[o[k]] || { AuthorId: [] }[k] || {}; }, mapped.CommentsByArticleAndAuthor).push(o.Id); }); console.log(mapped);

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Answer 2

You can reduce the apiResult.Comments into the desired result:

CommentsByArticleAndAuthor: apiResult.Comments.reduce((result, comment) => Object.assign(result, {
  [comment.ArticleId]: Object.assign(result[comment.ArticleId] || {}, {
    [comment.AuthorId]: result[comment.ArticleId] && result[comment.ArticleId][comment.AuthorId]
      ? result[comment.ArticleId][comment.AuthorId].push(comment.Id)
      : [comment.Id]
  })
}), {})

Your example:

 var apiResult = { Authors: [ { Id: "author-id-1", Name: "Author One" }, { Id: "author-id-2", Name: "Author Two" } ], Articles: [ { Id: "article-id-1", Title: "This Great Article" } ], Comments: [ { Id: "comment-id-1", AuthorId: "author-id-1", ArticleId: "article-id-1", Comment: "that great, hu?" }, { Id: "comment-id-2", AuthorId: "author-id-2", ArticleId: "article-id-1", Comment: "yes, that great" } ] } var mapped = { CommentsByArticleAndAuthor: { "article-id-1": { "author-id-1": [ "comment-id-1" ], "author-id-2": [ "comment-id-2" ] } }, CommentsByArticleAndAuthor: apiResult.Comments.reduce((result, comment) => Object.assign(result, { [comment.ArticleId]: Object.assign(result[comment.ArticleId] || {}, { [comment.AuthorId]: result[comment.ArticleId] && result[comment.ArticleId][comment.AuthorId] ? result[comment.ArticleId][comment.AuthorId].push(comment.Id) : [comment.Id] }) }), {}) } console.log(mapped);

 <script src="https://cdn.jsdelivr.net/lodash/4.17.4/lodash.min.js"></script>

Answer 3

Thanks to Ninas great answer I came up with this generic solution:

 const apiResult = { Authors: [{ Id: "author-id-1", Name: "Author One" }, { Id: "author-id-2", Name: "Author Two" }], Articles: [{ Id: "article-id-1", Title: "This Great Article" }], Comments: [{ Id: "comment-id-1", AuthorId: "author-id-1", ArticleId: "article-id-1", Comment: "that great, hu?" }, { Id: "comment-id-2", AuthorId: "author-id-2", ArticleId: "article-id-1", Comment: "yes, that great" }] }; const mapped = {}; const indexBy = function(collection, keys, map = (item) => item) { let result = {}; collection.forEach((item) => { keys.reduce((r, k, idx) => { let value = _.get(item, k); if (idx === keys.length - 1) return r[value] = [...r[value] || [], map(item)]; return r[value] = r[value] || {} }, result); }); return result; } mapped.CommentsByArticlesAndAuthor = indexBy(apiResult.Comments, ['ArticleId', 'AuthorId'], (item) => item.Id); mapped.CommentsByAuthorAndArticle = indexBy(apiResult.Comments, ['AuthorId', 'ArticleId'], (item) => item.Id); console.log(mapped);

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 <script src="https://cdn.jsdelivr.net/lodash/4.17.4/lodash.min.js"></script>

It let me index on as many levels that I want, and it let me transform the item indexed, defaulting to just store the full item. It also utilize get from lodash to support nested key values, eg Author.Id instead of AuthorId .