这种排序不存在索引 - couchDB

Question

使用排序方法访问数据时出错

错误是

No index exists for this sort

创建索引代码为

db.createIndex({
    index: { fields: ["timestamp", "upVote"] },
}).then(() => {
    this.intitialDatafromDB(db);
});

查找函数是

db.find({
   selector: { upVote: { $gt: 5 } },
   sort: [{ upVote: "desc" }],
   fields: ["news"],
}).then((result: any) => {
    this.data = result.docs;
}).catch((err: any) => {
    console.log(err);
});

Answer 1

您的查询失败的原因是索引字段的顺序很重要。

来自 pouchdb 文档Indexing on more than one field

One thing to note is that the order of these fields matters when creating your index

通过这样指定索引

fields: ['timestamp','upVote']

索引看起来像这样

timestamp	upVote
1590399369500	3
1590399369600	4
1590399369700	1
1590399369700	2
1590399369700	3
1590399369800	1

注意时间戳 1590399369700，以及辅助字段 upVote 的排序方式。

如果您的索引字段是这样排序的

fields: ['upVote','timestamp']

鉴于上述理论数据，该指数将如下所示

upVote	timestamp
1	1590399369700
1	1590399369800
2	1590399369700
3	1590399369500
3	1590399369700
4	1590399369600

您的查询会 return 您期望的结果，如下面的代码片段所示。我建议阅读 Map/reduce queries；掌握该文档中提出的概念将有助于更深入地理解为什么会这样。

const g_result = 'result';
const getEl = id => document.getElementById(id);
let db;

async function view() {
  const view = getEl(g_result);

  const result = await db.find({
    selector: {
      upVote: {
        $gt: 5
      },
    },
    sort: [{
      'upVote': 'desc'
    }],
    fields: ['news','upVote']
  }, );

  view.innerText = JSON.stringify(result, undefined, 3);
}

// canned test documents
function getDocsToInstall() {
  return [{
      timestamp: 1590399369508,
      upVote: 3,
      news: "new item 1"
    },
    {
      timestamp: 1590399248600,
      upVote: 4,
      news: "new item 2"
    },
    {
      timestamp: 1590399248600,
      upVote: 5,
      news: "new item 3"
    },
    {
      timestamp: 1590399248700,
      upVote: 6,
      news: "new item 4"
    },
    {
      timestamp: 1590399248900,
      upVote: 7,
      news: "new item 5"
    },
    {
      timestamp: 1590399249000,
      upVote: 8,
      news: "new item 6"
    },
  ]
}

// init example db instance
async function initDb() {
  db = new PouchDB('test', {
    adapter: 'memory'
  });

  await db.bulkDocs(getDocsToInstall());
  await db.createIndex({
    index: {
      fields: ['upVote', 'timestamp']
    }
  });
};

(async() => {
  await initDb();
  await view();
})();

https: //whosebug.com/questions/69122670/no-index-exists-for-this-sort-couchdb#

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<script src="https://github.com/pouchdb/pouchdb/releases/download/7.1.1/pouchdb.memory.min.js"></script>
<script src="https://github.com/pouchdb/pouchdb/releases/download/7.1.1/pouchdb.find.min.js"></script>
<pre id='view'></pre>
<div style='margin-top:2em'></div>
<pre id='result'>
</pre>

这种排序不存在索引 - couchDB

No index exists for this sort - couchDB

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