JSONPath で JSON をクエリする方法

问题

大きな深くネストされた JSON ドキュメントから、トラバーサルコードを自作せずに特定のフィールドを抽出する必要があります。

前提条件

• JSON 構造の理解
• パス式への習熟

ステップ

1. 1. Learn the JSONPath syntax

   JSONPath uses dot notation for object keys ($.store.book) and brackets for array indices ([0]) or filters ([?(@.price < 10)]). The $ represents the root. Wildcards (*) match all elements. This is similar to XPath for XML.

   入力

   $.store.book[0].title

   输出

   first book's title

2. 2. Write and test the expression

   Construct the JSONPath expression for the data you want to extract. Test it against your JSON document. Filters use @ to reference the current element. Multiple matches return an array of results.

   入力

   $.store.book[?(@.price<10)].title

   输出

   titles of books under $10

3. 3. Handle edge cases

   Not all JSONPath implementations support the full spec. Filters, recursive descent ($..), and script expressions may vary. Check your implementation's capabilities. Handle missing paths gracefully — they return empty results, not errors.

   入力

   $..author

   输出

   all authors at any depth

期待される結果

JSONPath 式にマッチする値を JSON ドキュメントから抽出した結果。

よくあるエラー

Filter syntax not supported

Different JSONPath implementations support different filter syntaxes. Check the documentation for your specific implementation.

Path returns empty unexpectedly

Verify the path matches the JSON structure. Check for case sensitivity in keys and correct array indices.

トラブルシューティング指引

• If the path returns nothing, print the JSON structure and verify each segment exists.
• Use recursive descent ($..) to find keys at any depth if you are unsure of the exact path.

セキュリティ上の制限

• JSONPath is a read-only query language. It does not modify data or execute code.
• All querying is local.