C#オブジェクトがIndexedDBに着くまで｜Blazor WASM永続化のデータ形式の旅

private static MusicDataModel ToDataModel(Music music)
{
    return new MusicDataModel
    {
        Version = 3,
        Id = music.Id,
        Metadata = new MusicMetadataModel
        {
            Title = music.Metadata.Title,
            LastModified = DateTime.UtcNow,
        },
        Settings = new MusicSettingsModel
        {
            Tempo = music.Settings.Tempo,
            Numerator = music.Settings.Numerator,
            Denominator = music.Settings.Denominator,
        },
        Tracks = music.Tracks.Select(TrackToV2).ToArray(),
    };
}

public byte[] Write(Music music)
{
    var model = ToDataModel(music);
    var bin = MessagePackSerializer.Serialize(model);
    return bin;
}

public class MusicsDataBase(IJSRuntime js)
{
    private readonly IJSRuntime _js = js;
    private IJSObjectReference? _db;

    private async Task<IJSObjectReference> EnsureDbAsync()
    {
        if (_db is null)
        {
            var dbModule = await _js.InvokeAsync<IJSObjectReference>("import", "/db.js");
            _db = await dbModule.InvokeAsync<IJSObjectReference>("useDatabase");
        }
        return _db;
    }

    public async Task SetAsync(int musicId, byte[] pimData)
    {
        var db = await EnsureDbAsync();
        await db.InvokeVoidAsync("setItem", musicId, pimData);
    }
}

const runTransaction = (mode, fn) =>
    new Promise((resolve, reject) => {
        const tx = db.transaction(MUSIC_STORE_NAME, mode);
        const store = tx.objectStore(MUSIC_STORE_NAME);
        const request = fn(store);
        request.onsuccess = () => resolve(request.result);
        request.onerror = () => reject(request.error);
    });

async function setItem(musicId, pimData) {
    // pimData は C# 側から Uint8Array として届く
    await runTransaction("readwrite", (store) => store.put(pimData, musicId));
}

request.onupgradeneeded = (event) => {
    const db = event.target.result;
    if (!db.objectStoreNames.contains(MUSIC_STORE_NAME)) {
        db.createObjectStore(MUSIC_STORE_NAME);
    }
};

if (navigator.storage && navigator.storage.persist) {
    const isPersisted = await navigator.storage.persisted();
    if (!isPersisted) {
        const granted = await navigator.storage.persist();
        console.log(`[Picom] Storage persistence ${granted ? 'granted' : 'denied'}`);
    }
}

async function getAllItems() {
    // PIM v3 からは ID がバイナリ内に埋め込まれているため、外側のキーは不要。
    // store.getAll() で値（Uint8Array）配列を一括取得する。
    return await runTransaction("readonly", (store) => store.getAll());
}

public async Task<List<Music>> ReadAllFromLocalStorageAsync()
{
    var stored = await _storage.GetAllAsync();
    var musics = new List<Music>(stored.Count);

    foreach (var bin in stored)
    {
        var (result, music) = Read(bin);
        if (result is ReadResult.Success && music is not null)
        {
            musics.Add(music);
        }
    }

    return musics;
}