Support COUNT(THIS) in string-based query execution

[otaviojava]

Jakarta Query defines the following grammar rule for aggregate expressions:

aggregate_expression : 'COUNT' '(' 'THIS' ')';

This allows for string-based queries such as:

SELECT COUNT(THIS) FROM Word

Eclipse JNoSQL currently supports parsing and executing string-based queries via Jakarta Query integration. However, support for this aggregation expression is not yet implemented.

Goal

Enable SELECT COUNT(THIS) FROM Entity in string-based queries and ensure it is correctly interpreted and executed within Eclipse JNoSQL.

Technical Context

Eclipse JNoSQL already provides an internal mechanism to handle count-based queries through:

SelectQuery.isCount()

Reference:
SelectQuery.java#L86–L88

When the parser detects COUNT(THIS), it should toggle the SelectQuery's isCount flag accordingly.

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💡 Usage Example

SELECT COUNT(THIS) FROM Word WHERE term = 'java'

This functionality must also be compatible with Jakarta Data repositories:

@Repository
public interface WordRepository {
    @Query("SELECT COUNT(THIS) FROM Word WHERE term = 'java'")
    Long countJava();
}

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✅ Tasks

• Update the Jakarta Query parser integration in Eclipse JNoSQL to recognize the COUNT(THIS) aggregate expression.
• When COUNT(THIS) is parsed, set SelectQuery.count to true.
• Ensure the communication layer processes queries with isCount = true correctly.
• Add tests to validate COUNT(THIS) queries return correct results across supported databases.
• Verify compatibility with Jakarta Data's @Query syntax.