Dexie.js - 如何加入表格？

Question

我目前使用 Dexie.js 在本地存储数据。我有 3 个不同的表，它们通过使用外键相互连接。我设法设置了架构并插入了相应的数据。但是，当我要检索数据时，却找不到如何连接不同表的示例。

下面是一个例子：

var db = new Dexie('my-testing-db');
db.delete().then(function() {

  db.version(1).stores({
    genres: '++id,name',
    albums: '++id,name,year,*tracks',
    bands: '++id,name,*albumsId,genreId'
  });

  db.transaction('rw', db.genres, db.albums, db.bands, function() {
    var rock = db.genres.add({
        name: 'rock'
      }),
      jazz = db.genres.add({
        name: 'jazz'
      });

    var justLookAround = db.albums.add({
      name: 'Just Look Around',
      year: 1992,
      tracks: [
        'We want the truth', 'Locomotive', 'Shut me out'
      ]
    });

    var sickOfItAll = db.bands.add({
      name: 'Sick Of it All'
    });

    justLookAround.then(function(album_id) {
      rock.then(function(rock_id) {
        sickOfItAll.then(function(band_id) {
          db.bands.update(band_id, {
            genreId: rock_id,
            albumsId: [album_id]
          }).then(function(updated) {

          });
        });
      });
    });

  }).then(function() {
    //how to join the tables here????
    db.bands.each(function(band) {
      console.log(band);
    });
  });
});

Answer 1

以下是加入结果的方法。免责声明：代码未经测试！

\n

var all = Dexie.Promise.all;\n\nfunction joinBands (bandCollection) {\n\n    // Start by getting all bands as an array of band objects\n    return bandCollection.toArray(function(bands) {\n\n        // Query related properties:\n        var genresPromises = bands.map(function (band) {\n            return db.genres.get(band.genreId || 0);\n        });\n        var albumsPromises = bands.map(function (band) {\n            return db.albums.where('id').anyOf(band.albumsId || []).toArray();\n        });\n\n        // Await genres and albums queries:\n        return all ([\n            all(genresPromises),\n            all(albumsPromises)\xc2\xa8\n        ]).then(function (genresAndAlbums) {\n\n            // Now we have all foreign keys resolved and\n            // we can put the results onto the bands array\n            // before returning it:\n            bands.forEach(function (band, i) {\n                band.genre = genresAndAlbums[0][i];\n                band.albums = genresAndAlbums[1][i];\n            });\n            return bands;\n        });\n    });\n}\n\n// Join all:\njoinBands(db.bands.toCollection()).then(function (bands) {\n    alert ("All bands: " + JSON.stringify(bands, null, 4));\n}).catch(function (error) {\n    alert ("Oops: " + error);\n});\n\n// Query and join:\njoinBands(db.bands.where('genreId').anyOf([1,5,19]).limit(25)).then(function (bands) {\n    alert ("Some bands: " + JSON.stringify(bands, null, 4));\n}).catch (function (error) {\n    alert ("Oops: " + error);\n});\n

\n

最好从事务中调用 joinBands() 以加快查询速度并获得更可靠和原子的结果。

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