Field-equals

Create a RecordPredicate that returns true when a record contains a field whose key and value both match exactly. Use it for stable attribute-based routing.

Interface

pub fn field_equals(key : String, value : String) -> RecordPredicate {}

input

• key : String - Field key to inspect.
• value : String - Exact value expected for that key.

output

• RecordPredicate - Predicate that matches records containing a field with the expected key and value.

Explanation

Detailed rules explaining key parameters and behaviors

• Matching requires both field.key == key and field.value == value.
• The predicate returns true on the first matching field.
• This helper is useful for routing records by environment, tenant, operation name, or fixed tags.
• It is stricter than has_field(...) because presence alone is not enough.

How to Use

Here are some specific examples provided.

When Keep One Tenant Stream

When log routing should isolate one tenant:

let logger = Logger::new(console_sink())
  .with_filter(field_equals("tenant", "acme"))

In this example, records for other tenants are excluded.

When Combine With Exact Target Matching

When field and target must both match:

let predicate = all_of([
  target_is("billing"),
  field_equals("region", "cn"),
])

In this example, only billing records tagged for the cn region remain.

Error Case

e.g.:

• If key or value is empty, matching still uses exact equality and may produce no results unless records contain the same empty string.

• If a record contains the key with multiple values, any one exact match is enough for the predicate to return true.

Notes

1. Prefer exact field matching over message substring matching for long-term routing rules.

2. Keep field naming stable across producers if this predicate is reused in shared configs.