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Nanaloveyuki
78 lines
2.3 KiB
Markdown
78 lines
2.3 KiB
Markdown
---
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name: record-with-fields
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group: api
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category: record
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update-time: 20260613
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description: Return a copy of a record with a replaced field array.
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key-word:
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- record
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- fields
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- transform
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- public
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---
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## Record-with-fields
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Return a copy of a `Record` with a different field array. This helper is the narrowest way to replace structured metadata while preserving the record's level, message, timestamp, and target.
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### Interface
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```moonbit
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pub fn Record::with_fields(self : Record, fields : Array[Field]) -> Record {}
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```
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#### input
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- `self : Record` - Base record whose field array should be replaced.
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- `fields : Array[Field]` - New structured field list for the returned record.
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#### output
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- `Record` - New record value carrying the updated fields.
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### Explanation
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Detailed rules explaining key parameters and behaviors
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- This helper returns a new record value instead of mutating the original one.
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- Only the `fields` array is replaced.
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- `level`, `message`, `timestamp_ms`, and `target` are preserved.
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- This is useful when one record should swap its metadata wholesale rather than append more fields.
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### How to Use
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Here are some specific examples provided.
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#### When Need To Replace Metadata Entirely
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When one record should keep its message and severity but use a new field set:
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```moonbit
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let rec = Record::new(Level::Info, "accepted", fields=[field("user", "alice")])
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let sanitized = rec.with_fields([field("user", "***")])
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```
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In this example, the original field array is replaced rather than extended.
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#### When Need To Clear Per-record Fields
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When structured metadata should be removed from one value:
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```moonbit
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let rec = Record::new(Level::Warn, "retry", fields=[field("job", "42")])
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let plain = rec.with_fields([])
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```
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In this example, the returned record keeps the same event identity but carries no fields.
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### Error Case
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e.g.:
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- If `fields` is empty, the returned record is still valid and simply carries no structured metadata.
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- If code should append or merge fields instead of replacing them, `append_fields(...)` or a custom patch is the better fit.
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### Notes
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1. Use this helper when one record should swap its entire field array.
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2. Use `append_fields(...)` when enrichment should preserve the original field list and add more entries afterward.
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