October 2024
Intermediate to advanced
270 pages
8h 13m
Spanish
Content preview from 97 cosas que todo programador Java debe saber
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Capítulo 21. Adoptar el pensamiento SQL
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Dean Wampler
Mira en esta consulta:
SELECT c.id, c.name, c.address, o.items FROM customers c JOIN orders o ON o.customer_id = c.id GROUP BY c.id
Adquirimos todos los clientes que tienen pedidos, incluidos sus nombres y direcciones, junto con los detalles de sus pedidos. Cuatro líneas de código. Cualquiera con un poco de experiencia en SQL, incluidos los no programadores, puede entender esta consulta.
Ahora piensa en una implementación Java. Podríamos declarar clases para Customer y Order. Recuerdo a consultores bienintencionados diciendo que también deberíamos crear clases para encapsular colecciones de ellas, en lugar de utilizar colecciones Java "desnudas". Seguimos necesitando consultar la base de datos, así que recurrimos a una herramienta de mapeo objeto-relacional (ORM) y escribimos código para ello. Cuatro líneas de código se convierten rápidamente en docenas o incluso cientos de líneas. Los pocos minutos que tardamos en escribir y refinar la consulta SQL se convierten en horas o días de edición, escritura de pruebas unitarias, revisión del código, etcétera.
¿No podemos implementar toda la solución sólo con la consulta SQL? ¿Estamos seguros de que no podemos? Incluso si realmente no podemos, ¿podemos eliminar el despilfarro ...
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