无法使用 dexie 示例代码动态更新索引答案

【问题标题】：Can't update index dynamically with dexie sample code无法使用 dexie 示例代码动态更新索引
【发布时间】：2019-07-10 18:06:52
【问题描述】：

我一直在尝试动态更新数据库索引，但一直失败，卡了几天。我正在使用 angular7 & type 脚本和最新的 dexie 版本。当我尝试使用相同的代码时，它给了我错误：

我应该做些什么来让它工作吗？谢谢！

ERROR Error: Uncaught (in promise): UpgradeError: Dexie specification of currently installed DB version is missing
UpgradeError: Dexie specification of currently installed DB version is missing

我只是在这里复制粘贴示例代码：

 changeSchema(db, schemaChanges) {
    db.close();
    const newDb = new Dexie(db.name);
    newDb.version(db.verno + 1).stores(schemaChanges);
    return newDb.open();
  }

  // Open database dynamically:
  async playAround() {
    let db = new Dexie('FriendsDatabase');
    if (!(await Dexie.exists(db.name))) {
      db.version(1).stores({});
    }
    await db.open();

    // Add a table with some indexes:
    db = await this.changeSchema(db, { friends: 'id, name' });

    // Add another index in the friends table
    db = await this.changeSchema(db, { friends: 'id, name, age' });

    // Remove the age index again:
    db = await this.changeSchema(db, { friends: 'id, name' });

    // Remove the friends table
    db = await this.changeSchema(db, { friends: null });
  }

【问题讨论】：

标签： dexie

【解决方案1】：

此示例有问题。我已经使用工作示例更新了文档：

async function changeSchema(db, schemaChanges) {
  db.close();
  const newDb = new Dexie(db.name);

  newDb.on('blocked', ()=>false); // Silence console warning of blocked event.

  // Workaround: If DB is empty from tables, it needs to be recreated
  if (db.tables.length === 0) {
    await db.delete();
    newDb.version(1).stores(schemaChanges);
    return await newDb.open();
  }

  // Extract current schema in dexie format:
  const currentSchema = db.tables.reduce((result,{name, schema}) => {
    result[name] = [
      schema.primKey.src,
      ...schema.indexes.map(idx => idx.src)
    ].join(',');
    return result;
  }, {});

  console.log("Version: " + db.verno);
  console.log("Current Schema: ", currentSchema);

  // Tell Dexie about current schema:
  newDb.version(db.verno).stores(currentSchema);
  // Tell Dexie about next schema:
  newDb.version(db.verno + 1).stores(schemaChanges);
  // Upgrade it:
  return await newDb.open();    
}

// Open database dynamically:
async function playAround() {
  let db = new Dexie ('FriendsDatabase2');
  if (!(await Dexie.exists(db.name))) {
      console.log("Db does not exist");
      db.version(1).stores({});
  }
  await db.open();
  console.log("Could open DB")

  // Add a table with some indexes:
  db = await changeSchema(db, {friends: 'id, name'});
  console.log("Could enforce friends table with id and name")

  // Add another index in the friends table
  db = await changeSchema(db, {friends: 'id, name, age'});
  console.log("Could add the age index")

  // Remove the age index again:
  db = await changeSchema(db, {friends: 'id, name'})
  console.log("Could remove age index")

  // Remove the friends table
  db = await changeSchema(db, {friends: null});
  console.log("Could delete friends table")
}

playAround().catch(err => console.error(err));

小提琴：

https://jsfiddle.net/dfahlander/jzf2mc7n/

【讨论】：