forked from NPM/numass-framework
42 lines
1.5 KiB
Markdown
42 lines
1.5 KiB
Markdown
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---
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content_type: "doc_shard"
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title: "Meta-data object structure"
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chapter: "meta"
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ordering: 4
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label: "meta_structure"
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version: 1.1
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date: 27.08.2015
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published: true
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---
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<table>
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<tr>
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<td>
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<img src="${img 'meta.svg'}" alt="Meta structure"/>
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</td>
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<td>
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<p>
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The Meta object is a tree-like structure, which can contain other meta objects as branches (which are
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called
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elements) and <a href="#value">Value</a> objects as leafs.
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Both Values and Meta elements are organized in String-keyed maps. And each map element is a list of
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appropriate type. By requesting single Value or Meta element one is supposed to request first element of
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this list.
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</p>
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<hr>
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<p><strong>Note</strong> that such lists are always immutable. Trying to change it may cause a error.</p>
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<hr>
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<p>
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While meta itself does not have any write methods and is considered to be immutable, some of its
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extensions do have methods that can change meta structure. One should be careful not to use mutable meta
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elements when one need immutable one.
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</p>
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<p>
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In order to conveniently edit meta, there is MetaBuilder class.
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</p>
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</td>
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<tr>
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</table>
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The naming of meta elements and values follows basic DataForge [naming and navigation](#navigation) convention.
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Meaning that elements and values could be called like `child_name.grand_child_name.value_name`.
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One can event use numbers as queries in such paths like `child_name.grand_child_name[3].value_name`.
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