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features/json_pointer.md
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@@ -18,6 +18,40 @@ Consider the following JSON document
}
```
Select a pointer (or a node of the tree) to walk it through this document; each segment of the pointer goes one level
deeper. The table below lists the same pointers.
<div class="nj-pointer-walk" data-nj-pointer-walk data-doc="{&quot;array&quot;:[&quot;A&quot;,&quot;B&quot;,&quot;C&quot;],&quot;nested&quot;:{&quot;one&quot;:1,&quot;two&quot;:2,&quot;three&quot;:[true,false]}}" role="group" aria-label="Pointer walker for the example document">
<p class="nj-pointer-static">Highlighted: the path of the pointer <code>/nested/three/1</code>, which identifies <code>false</code>.</p>
<ul class="nj-pointer-tree">
<li data-p="" class="is-on"><span class="nj-pointer-n"><span class="nj-pointer-k">root</span> <span class="nj-pointer-t">object</span></span>
<ul>
<li data-p="/array" class="is-pass"><span class="nj-pointer-n"><span class="nj-pointer-k">&quot;array&quot;</span> <span class="nj-pointer-t">array</span></span>
<ul>
<li data-p="/array/0"><span class="nj-pointer-n"><span class="nj-pointer-k">0</span>: <span class="nj-pointer-v nj-pointer-v--s">&quot;A&quot;</span></span></li>
<li data-p="/array/1"><span class="nj-pointer-n"><span class="nj-pointer-k">1</span>: <span class="nj-pointer-v nj-pointer-v--s">&quot;B&quot;</span></span></li>
<li data-p="/array/2"><span class="nj-pointer-n"><span class="nj-pointer-k">2</span>: <span class="nj-pointer-v nj-pointer-v--s">&quot;C&quot;</span></span></li>
</ul>
</li>
<li data-p="/nested" class="is-on"><span class="nj-pointer-n"><span class="nj-pointer-k">&quot;nested&quot;</span> <span class="nj-pointer-t">object</span></span>
<ul>
<li data-p="/nested/one" class="is-pass"><span class="nj-pointer-n"><span class="nj-pointer-k">&quot;one&quot;</span>: <span class="nj-pointer-v nj-pointer-v--n">1</span></span></li>
<li data-p="/nested/two" class="is-pass"><span class="nj-pointer-n"><span class="nj-pointer-k">&quot;two&quot;</span>: <span class="nj-pointer-v nj-pointer-v--n">2</span></span></li>
<li data-p="/nested/three" class="is-on"><span class="nj-pointer-n"><span class="nj-pointer-k">&quot;three&quot;</span> <span class="nj-pointer-t">array</span></span>
<ul>
<li data-p="/nested/three/0" class="is-pass"><span class="nj-pointer-n"><span class="nj-pointer-k">0</span>: <span class="nj-pointer-v nj-pointer-v--b">true</span></span></li>
<li data-p="/nested/three/1" class="is-on is-target"><span class="nj-pointer-n"><span class="nj-pointer-k">1</span>: <span class="nj-pointer-v nj-pointer-v--b">false</span></span></li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
<p class="nj-caption" markdown>The highlighted nodes are the path from the root to the selected level, and the line below the tree shows the value the pointer resolves to. Select a segment in the pointer bar to stop at a shallower level, or a node of the tree to select its pointer.</p>
Then every value inside the JSON document can be identified as follows:
| JSON Pointer | JSON value |
@@ -138,12 +172,74 @@ The reverse function, [`unflatten`](../api/basic_json/unflatten.md) recreates th
auto j_original = j_flat.unflatten();
```
Each leaf of the document becomes one key of the flat object, and `unflatten()` reverses the mapping:
<div class="nj-fig-wrap" markdown>
<svg class="nj-fig nj-pointer-fl" viewBox="0 0 760 442" role="img" aria-labelledby="fig-flat-title" xmlns="http://www.w3.org/2000/svg">
<title id="fig-flat-title">flatten() turns the nested example document into a flat object, and unflatten() turns it back. Left, the document as a tree: array with the elements A, B, C, and nested with one = 1, two = 2, and three with the elements true and false. Right, the flat object with one key per leaf: /array/0 = A, /array/1 = B, /array/2 = C, /nested/one = 1, /nested/two = 2, /nested/three/0 = true, /nested/three/1 = false. Each leaf is joined to its key by a line.</title>
<defs><marker id="fig-flat-arrow" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto"><path class="fg-head" d="M0 1 L10 5 L0 9 z"/></marker></defs>
<text class="fg-h" x="20" y="26">nested value</text>
<text class="fg-h" x="470" y="26">flat object: key = J&#8203;SON Pointer</text>
<line class="fg-arrow" x1="250" y1="52" x2="450" y2="52" marker-end="url(#fig-flat-arrow)"/>
<text class="nj-pointer-fl-op" x="350" y="44">flatten()</text>
<line class="fg-arrow" x1="450" y1="420" x2="250" y2="420" marker-end="url(#fig-flat-arrow)"/>
<text class="nj-pointer-fl-op" x="350" y="412">unflatten()</text>
<path class="nj-pointer-fl-edge" d="M25 99 V115 H42"/>
<path class="nj-pointer-fl-edge" d="M51 127 V143 H68"/>
<path class="nj-pointer-fl-edge" d="M51 127 V171 H68"/>
<path class="nj-pointer-fl-edge" d="M51 127 V199 H68"/>
<path class="nj-pointer-fl-edge" d="M25 99 V227 H42"/>
<path class="nj-pointer-fl-edge" d="M51 239 V255 H68"/>
<path class="nj-pointer-fl-edge" d="M51 239 V283 H68"/>
<path class="nj-pointer-fl-edge" d="M51 239 V311 H68"/>
<path class="nj-pointer-fl-edge" d="M77 323 V339 H94"/>
<path class="nj-pointer-fl-edge" d="M77 323 V367 H94"/>
<path class="nj-pointer-fl-link nj-pointer-fl--s" d="M139.6 143 C259.6 143 340 171 460 171"/>
<circle class="nj-pointer-fl-dot nj-pointer-fl--s" cx="139.6" cy="143" r="3.5"/>
<text class="fg-code" x="470" y="176" xml:space="preserve"><tspan class="nj-pointer-fl-key">"/array/0"</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--s">"A"</tspan></text>
<path class="nj-pointer-fl-link nj-pointer-fl--s" d="M139.6 171 C259.6 171 340 199 460 199"/>
<circle class="nj-pointer-fl-dot nj-pointer-fl--s" cx="139.6" cy="171" r="3.5"/>
<text class="fg-code" x="470" y="204" xml:space="preserve"><tspan class="nj-pointer-fl-key">"/array/1"</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--s">"B"</tspan></text>
<path class="nj-pointer-fl-link nj-pointer-fl--s" d="M139.6 199 C259.6 199 340 227 460 227"/>
<circle class="nj-pointer-fl-dot nj-pointer-fl--s" cx="139.6" cy="199" r="3.5"/>
<text class="fg-code" x="470" y="232" xml:space="preserve"><tspan class="nj-pointer-fl-key">"/array/2"</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--s">"C"</tspan></text>
<path class="nj-pointer-fl-link nj-pointer-fl--n" d="M158.8 255 C278.8 255 340 255 460 255"/>
<circle class="nj-pointer-fl-dot nj-pointer-fl--n" cx="158.8" cy="255" r="3.5"/>
<text class="fg-code" x="470" y="260" xml:space="preserve"><tspan class="nj-pointer-fl-key">"/nested/one"</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--n">1</tspan></text>
<path class="nj-pointer-fl-link nj-pointer-fl--n" d="M158.8 283 C278.8 283 340 283 460 283"/>
<circle class="nj-pointer-fl-dot nj-pointer-fl--n" cx="158.8" cy="283" r="3.5"/>
<text class="fg-code" x="470" y="288" xml:space="preserve"><tspan class="nj-pointer-fl-key">"/nested/two"</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--n">2</tspan></text>
<path class="nj-pointer-fl-link nj-pointer-fl--b" d="M175.2 339 C295.2 339 340 311 460 311"/>
<circle class="nj-pointer-fl-dot nj-pointer-fl--b" cx="175.2" cy="339" r="3.5"/>
<text class="fg-code" x="470" y="316" xml:space="preserve"><tspan class="nj-pointer-fl-key">"/nested/three/0"</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--b">true</tspan></text>
<path class="nj-pointer-fl-link nj-pointer-fl--b" d="M184.8 367 C304.8 367 340 339 460 339"/>
<circle class="nj-pointer-fl-dot nj-pointer-fl--b" cx="184.8" cy="367" r="3.5"/>
<text class="fg-code" x="470" y="344" xml:space="preserve"><tspan class="nj-pointer-fl-key">"/nested/three/1"</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--b">false</tspan></text>
<text class="fg-h" x="20" y="92">root</text>
<text class="fg-code nj-pointer-fl-inner" x="46" y="120">"array"</text>
<text class="fg-code" x="72" y="148" xml:space="preserve"><tspan class="nj-pointer-fl-k">0</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--s">"A"</tspan></text>
<text class="fg-code" x="72" y="176" xml:space="preserve"><tspan class="nj-pointer-fl-k">1</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--s">"B"</tspan></text>
<text class="fg-code" x="72" y="204" xml:space="preserve"><tspan class="nj-pointer-fl-k">2</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--s">"C"</tspan></text>
<text class="fg-code nj-pointer-fl-inner" x="46" y="232">"nested"</text>
<text class="fg-code" x="72" y="260" xml:space="preserve"><tspan class="nj-pointer-fl-k">"one"</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--n">1</tspan></text>
<text class="fg-code" x="72" y="288" xml:space="preserve"><tspan class="nj-pointer-fl-k">"two"</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--n">2</tspan></text>
<text class="fg-code nj-pointer-fl-inner" x="72" y="316">"three"</text>
<text class="fg-code" x="98" y="344" xml:space="preserve"><tspan class="nj-pointer-fl-k">0</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--b">true</tspan></text>
<text class="fg-code" x="98" y="372" xml:space="preserve"><tspan class="nj-pointer-fl-k">1</tspan>: <tspan class="nj-pointer-fl-v nj-pointer-fl--b">false</tspan></text>
</svg>
</div>
<p class="nj-caption" markdown>Left: the example document as a tree; right: the flat object it becomes. `flatten()` converts from left to right, `unflatten()` from right to left.</p>
## See also
- Class [`json_pointer`](../api/json_pointer/index.md)
- Functions [`value`](../api/basic_json/value.md), [`contains`](../api/basic_json/contains.md), and
[`at`](../api/basic_json/at.md) accept JSON Pointers; see [Nested values](element_access/default_value.md#nested-values)
- Function [`flatten`](../api/basic_json/flatten.md)
- Function [`unflatten`](../api/basic_json/unflatten.md)
- [`json_pointer`](../api/json_pointer/index.md) - the JSON Pointer class
- [Nested values](element_access/default_value.md#nested-values) - [`value`](../api/basic_json/value.md),
[`contains`](../api/basic_json/contains.md), and [`at`](../api/basic_json/at.md) accept JSON Pointers
- [`flatten`](../api/basic_json/flatten.md) - convert a value to an object of JSON Pointers and primitive values
- [`unflatten`](../api/basic_json/unflatten.md) - restore a value from a flattened object
- [JSON Patch](json_patch.md) - paths inside a patch are JSON Pointers
- [JSON Merge Patch](merge_patch.md) - an alternative patch format that does not use JSON Pointer
- [`operator""_json_pointer`](../api/operator_literal_json_pointer.md) - user-defined literal to create a JSON pointer
- [Element Access](element_access/index.md) - other ways to access elements