judo-runtimecustom-queries

name: judo-runtime:custom-queries description: Extend JUDO DAO RDBMS query translation with custom mappers. Use when adding custom query element handling, extending SQL generation, or implementing custom join strategies. metadata: author: BlackBelt Technology version: "${project.version}"

Custom Query Extensions

Guide for extending the JUDO DAO RDBMS query translation layer with custom mappers and translators.

Query Translation Architecture

flowchart TB
    subgraph "Query Translation"
        QM["Query Model<br/>(Abstract)"]
        MF["MapperFactory"]
        RB["RdbmsBuilder"]
        TR["Translator"]
        SQL["SQL Statement"]
    end
    
    QM --> MF
    MF --> RB
    RB --> TR
    TR --> SQL

Extension Points

1. MapperFactory - Query Element Mapping

Implement MapperFactory to register custom query element mappers:

public class CustomMapperFactory implements MapperFactory {
    
    @Override
    public Map<Class<?>, RdbmsMapper<?>> getMappers(RdbmsBuilder rdbmsBuilder) {
        Map<Class<?>, RdbmsMapper<?>> mappers = new HashMap<>();
        
        // Add custom mapper for your query element type
        mappers.put(CustomQueryElement.class, 
            new CustomQueryElementMapper(rdbmsBuilder));
        
        return mappers;
    }
}

2. RdbmsMapper - Element Translation

Extend RdbmsMapper for custom query elements:

public class CustomQueryElementMapper extends RdbmsMapper<CustomQueryElement> {
    
    public CustomQueryElementMapper(RdbmsBuilder rdbmsBuilder) {
        super(rdbmsBuilder);
    }
    
    @Override
    public RdbmsField map(CustomQueryElement element, 
                          RdbmsBuilderContext context) {
        // Translate to RDBMS field
        return RdbmsField.builder()
            .name(element.getFieldName())
            .sqlType(element.getSqlType())
            .build();
    }
}

3. Translator - Expression Translation

Add custom expression translators:

public class CustomExpressionTranslator 
    implements Function<CustomExpression, Expression> {
    
    @Override
    public Expression apply(CustomExpression expr) {
        // Transform custom expression to standard expression
        return new StringConstant(expr.evaluate());
    }
}

// Register with Translator
translator.register(CustomExpression.class, 
    new CustomExpressionTranslator());

Built-in Mappers

Mapper	Purpose
`AttributeMapper`	Maps attribute selectors to SQL columns
`FunctionMapper`	Maps function calls to SQL functions
`VariableMapper`	Maps variables to SQL parameters
`FilterMapper`	Maps filter expressions to WHERE clauses

Join Processors

Custom join strategies can be implemented via processors:

Processor	Use Case
`FilterJoinProcessor`	Filter-based joins
`ContainerJoinProcessor`	Container relationship joins
`SubSelectJoinProcessor`	Subquery-based joins
`CustomJoinProcessor`	Custom join conditions

Registration with Guice

public class CustomQueryModule extends AbstractModule {
    @Override
    protected void configure() {
        Multibinder<MapperFactory> mapperFactories = 
            Multibinder.newSetBinder(binder(), MapperFactory.class);
        mapperFactories.addBinding().to(CustomMapperFactory.class);
    }
}