如何在typescript中使用SelectMany

我犯了這個錯誤，我不知道為什么。我看到this.dayscalendar.Days是一個包含數據的數組。我正在嘗試使用SelectMany并選擇一個匹配的記錄。

linq.js:152 1未捕獲錯誤：單個：沒有元素滿足條件。

Enumerable.From(this.dayscalendar.Days)
    ArrayEnumerable {source: Array(7)}
    source
    : 
    Array(7)
    0: {Day: 'Sun', IsSelected: false}
    1: {Day: 'Mon', IsSelected: false}
    2: {Day: 'Tues', IsSelected: false}
    3: {Day: 'Wed', IsSelected: false}
    4: {Day: 'Thus', IsSelected: false}
    5: {Day: 'Fri', IsSelected: false}
    6: {Day: 'Sat', IsSelected: false}

行獲取錯誤

Enumerable.From(this.dayscalendar.Days).SelectMany(w => w.day).Single(d => d.day === 'Wed');