帶有謂詞的XQuery表達式

Question

我正在嘗試使用帶有謂詞的表達式來顯示每個父節點的子節點（該練習看起來很愚蠢，因為這是測試數據：最終的解決方案必須從其他xml文件中提取數據）。

數據樣本如下：

<Schools>
<School>
<name>St John's</name>
<AcademicYear year = "2017"></AcademicYear>
<Subject>English</Subject>
<Subject>Geography</Subject>
<Subject>Maths</Subject>
<AcademicYear year = "2016"></AcademicYear>
<Subject>Maths</Subject>
<Subject>Textiles</Subject>
<Subject>English</Subject>
<AcademicYear year = "2015"></AcademicYear>
<Subject>History</Subject>
<Subject>French</Subject>
<Subject>Spanish</Subject>
</School>

<School>
<name>Marsh Academy</name>
<AcademicYear year = "2017"></AcademicYear>
<Subject>Science</Subject>
<Subject>Geography</Subject>
<Subject>Computer science</Subject>
<AcademicYear year = "2016"></AcademicYear>
<Subject>English</Subject>
<Subject>History</Subject>
<Subject>Maths</Subject>
<AcademicYear year = "2015"></AcademicYear>
<Subject>French</Subject>
<Subject>Geography</Subject>
<Subject>Art</Subject>
</School>

</Schools>

查詢如下：

<Schools>
{for $School in doc("test.xml")/Schools/School
return
<School>
  <Name>
  {$School/name}
  </Name>
  {for $i in doc("test.xml")/Schools/[School = $School]/AcademicYear
  return
  <AcademicYear>
    {$i/@year}
    <subject><teacher></teacher><scale></scale></subject>
  </AcademicYear>}
   </School>}
</Schools>

出現錯誤，顯示與第8行有關的“期望的節點，找到了數組”。我嘗試了一個for循環，並簡單地將一個表達式放在學年標記內，如下所示

{doc（“ test.xml”）/學校/ [學校= $學校] / AcademicYear / @ year}

抱歉-我敢肯定這很簡單。 我是初學者！

Answer 1

謂詞之前沒有子節點。

選擇School元素時，將其移動到謂詞外部作為從Schools元素中選擇的子節點，然后在謂詞過濾器內部，使用引用當前的School元素. ：

for $i in doc("test.xml")/Schools/School[. = $School]/AcademicYear

但是，如果要遍歷同一文檔中的元素，為什么不只使用已經選擇的$School ：

for $i in $School/AcademicYear