As a user, I want the exists operator to be prepended to the query

[tloubrieu-jpl]

Checked for duplicates

No - I haven't checked

🧑‍🔬 User Persona(s)

User

💪 Motivation

...so that I can more intuitively use the exists operator with a syntax that reads naturally in English (prefix notation) and combine it cleanly with the not operator.

📖 Additional Details

Feedback from the API Working Group meeting on 01-28-2026.

The current postfix syntax (implemented in #406) requires awkward constructions for negation:

• Current (postfix): pds:Target/pds:name exists
• Current negation: not (pds:Investigation/pds:stop_date_time exists)

The new prefix syntax is more intuitive and reads naturally:

• New (prefix): (exists pds:Target/pds:name)
• New negation: (not exists pds:Citation_Information/pds:author_list)

Examples of new syntax:

Use Case	New Syntax
Check field exists	(exists pds:Target/pds:name)
Check field does NOT exist	(not exists pds:Investigation/pds:stop_date_time)
Regex pattern matching	(exists "pds:Target.*")
Combined with other conditions	(exists pds:Target/pds:name) and pds:Target/pds:type eq "Planet"
Complex query	(exists pds:Target/pds:name) and (not exists pds:Citation_Information/pds:author_list)

Acceptance Criteria

Given I am querying the registry API
When I use (exists field_name) with the prefix syntax
Then the API returns only documents where the specified field exists and has a non-null/non-empty value

Given I am querying the registry API
When I use (not exists field_name) in my query
Then the API returns only documents where the specified field does not exist or is null/empty

Given I want to check for fields matching a regex pattern
When I use (exists "regex_pattern") with a quoted string
Then the API matches the regex against known field names and returns documents where any matched field exists

Given I combine exists with other query operators
When I use queries like (exists pds:Target/pds:name) and pds:Target/pds:type eq "Planet"
Then the API correctly applies both conditions and returns matching documents

⚙️ Engineering Details

This change requires updates to the ANTLR4 lexer grammar (Search.g4) in the lexer module:

1. Grammar Changes: Modify the EXISTS rule from postfix to prefix notation:

   • Current grammar: comparison : FIELD EXISTS | STRINGVAL EXISTS | ...
   • New grammar: comparison : EXISTS FIELD | EXISTS STRINGVAL | ...

2. Listener Updates: Update Antlr4SearchListener.java in the service module to handle the new parse tree structure where EXISTS precedes the field/pattern.

3. NOT handling: Ensure NOT EXISTS works as a combined prefix operator (not just NOT wrapping the entire expression).

4. Backward Compatibility: Determine whether to support both syntaxes during a transition period or deprecate the postfix syntax immediately.

5. Integration Tests: Update Postman collection in the registry repository with tests for the new syntax.

Files likely to be modified:

• lexer/src/main/antlr4/gov/nasa/pds/api/registry/lexer/Search.g4
• service/src/main/java/gov/nasa/pds/api/registry/search/Antlr4SearchListener.java

🎉 I&T

Update integration tests in the registry repository Postman collection to use the new prefix syntax for exists queries.