mirror of https://gitee.com/bigwinds/arangodb
54 lines
2.5 KiB
Plaintext
54 lines
2.5 KiB
Plaintext
!CHAPTER Attribute Names
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Users can pick attribute names for document attributes as desired, provided the
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following attribute naming constraints are not violated:
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- Attribute names starting with an underscore are considered to be system
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attributes for ArangoDB's internal use. Such attribute names are already used
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by ArangoDB for special purposes:
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- *_id* is used to contain a document's handle
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- *_key* is used to contain a document's user-defined key
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- *_rev* is used to contain the document's revision number
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- In edge collections, the
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- *_from*
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- *_to*
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attributes are used to reference other documents.
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More system attributes may be added in the future without further notice so
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end users should try to avoid using their own attribute names starting with
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underscores.
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* Attribute names should not start with the at-mark (*@*). The at-mark
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at the start of attribute names is reserved in ArangoDB for future use cases.
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* Theoretically, attribute names can include punctuation and special characters
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as desired, provided the name is a valid UTF-8 string. For maximum
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portability, special characters should be avoided though. For example,
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attribute names may contain the dot symbol, but the dot has a special meaning
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in Javascript and also in AQL, so when using such attribute names in one of
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these languages, the attribute name would need to be quoted by the end
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user. This will work but requires more work so it might be better to use
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attribute names which don't require any quoting/escaping in all languages
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used. This includes languages used by the client (e.g. Ruby, PHP) if the
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attributes are mapped to object members there.
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* ArangoDB does not enforce a length limit for attribute names. However, long
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attribute names may use more memory in result sets etc. Therefore the use
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of long attribute names is discouraged.
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* As ArangoDB saves document attribute names separate from the actual document
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attribute value data, the combined length of all attribute names for a
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document must fit into an ArangoDB shape structure. The maximum combined names
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length is variable and depends on the number and data types of attributes
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used.
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* Attribute names are case-sensitive.
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* Attributes with empty names (the empty string) are removed from the document
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when saving it.
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When the document is later requested, it will be returned without these
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attributes. For example, if this document is saved:
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{ "a" : 1, "" : 2, "b": 3 }
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and later requested, it will be returned like this:
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{ "a" : 1, "b": 3 }
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