JPA对于简单的查询操作确实很给力，但是涉及到多表、多条件、分页的场景就不是很好实现了。
可行的解决方案
1、多条件
public interface BaseRepository<T,ID extends Serializable> extends JpaRepository<T,ID>, JpaSpecificationExecutor<T>使用Specification来实现条件的拼接
2、多表
数据量不大的情况，可以考虑视图，视图实体配置和表的没有任何区别。
3、分页
可以自行实现分页逻辑，也可以使用框架的 Pageable 类。
核心代码示例
// 核心方法 拼接条件 public default Predicate getPredocate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder cb, DataQueryObject dqo) { List<Predicate> predicates = new ArrayList<>(); // 获取查询对象的所有属性 Field[] fields = dqo.getClass().getDeclaredFields(); for (Field field : fields) { field.setAccessible(true); String queryFiled = null; QueryType queryType = null; Object value = null; Predicate predicate = null; // 获取属性的 自定义注解类型 QueryField annotaion = field.getAnnotation(QueryField.class); // 如果没有注解 则跳过 if(annotaion == null) { continue; } // 如果注解中 name为空 则用字段名称作为属性名 if(!StringUtils.isEmpty(annotaion.name())) { queryFiled = annotaion.name(); } else { queryFiled = field.getName(); } queryType = annotaion.type(); try { value = field.get(dqo); } catch (IllegalArgumentException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } // 判断字段类型是否为空 if(value == null && queryType.isNotCanBeNull()) { logger.debug("查询类型：" + queryType + "不允许为空。"); continue; } // 判断注解中 的条件类型 switch (queryType) { case EQUAL: Path<Object> equal = getRootByQueryFiled(queryFiled, root); predicate = cb.equal(equal, value); predicates.add(predicate); break; case BEWTEEN: Path<Comparable> between = getRootByQueryFiledComparable(queryFiled, root); QueryBetween queryBetween = null; if(value instanceof QueryBetween) queryBetween = (QueryBetween) value; else continue; predicate = cb.between(between, queryBetween.after, queryBetween.before); predicates.add(predicate); break; case LESS_THAN: Path<Comparable> lessThan = getRootByQueryFiledComparable(queryFiled, root); if(value instanceof QueryBetween) queryBetween = (QueryBetween) value; else continue; predicate = cb.lessThan(lessThan, queryBetween.after); predicates.add(predicate); break; case LESS_THAN_EQUAL: Path<Comparable> lessThanOrEqualTo = getRootByQueryFiledComparable(queryFiled, root); if(value instanceof QueryBetween) queryBetween = (QueryBetween) value; else continue; predicate = cb.lessThanOrEqualTo(lessThanOrEqualTo, queryBetween.after); predicates.add(predicate); break; case GREATEROR_THAN: Path<Comparable> greaterThan = getRootByQueryFiledComparable(queryFiled, root); if(value instanceof QueryBetween) queryBetween = (QueryBetween) value; else continue; predicate = cb.greaterThan(greaterThan, queryBetween.after); predicates.add(predicate); break; case GREATEROR_THAN_EQUAL: Path<Comparable> greaterThanOrEqualTo = getRootByQueryFiledComparable(queryFiled, root); if(value instanceof QueryBetween) queryBetween = (QueryBetween) value; else continue; predicate = cb.lessThanOrEqualTo(greaterThanOrEqualTo, queryBetween.after); predicates.add(predicate); break; case NOT_EQUAL: Path<Object> notEqual = getRootByQueryFiled(queryFiled, root); predicate = cb.notEqual(notEqual, value); predicates.add(predicate); break; case IS_NULL: Path<Object> isNull = getRootByQueryFiled(queryFiled, root); predicate = cb.isNull(isNull); predicates.add(predicate); break; case IS_NOT_NULL: Path<Object> isNotNull = getRootByQueryFiled(queryFiled, root); predicate = cb.isNotNull(isNotNull); predicates.add(predicate); break; case LEFT_LIKE: Path<String> leftLike = getRootByQueryFiledString(queryFiled, root); predicate = cb.like(leftLike, "%" + value.toString()); predicates.add(predicate); break; case RIGHT_LIKE: Path<String> rightLike = getRootByQueryFiledString(queryFiled, root); predicate = cb.like(rightLike, value.toString() + "%"); predicates.add(predicate); break; case FULL_LIKE: Path<String> fullLike = getRootByQueryFiledString(queryFiled, root); predicate = cb.like(fullLike, "%" + value.toString() + "%"); predicates.add(predicate); break; case DEFAULT_LIKE: Path<String> like = getRootByQueryFiledString(queryFiled, root); predicate = cb.like(like, value.toString()); predicates.add(predicate); break; case NOT_LIKE: Path<String> notLike = getRootByQueryFiledString(queryFiled, root); predicate = cb.like(notLike, value.toString()); predicates.add(predicate); break; case IN: Path<Object> in = getRootByQueryFiled(queryFiled, root); In ins = cb.in(in); List inList = null; if(value instanceof List) { inList = (List) value; } for (Object object : inList) { ins.value(object); } predicates.add(ins); break; default: break; } } // 如果 为空 代表 没有任何有效的条件 if(predicates.size() == 0) { return cb.and(); } Object[] list = predicates.toArray(); Predicate[] t = new Predicate[predicates.size()]; Predicate[] result = predicates.toArray(t); return cb.and(result); } public default Path<Object> getRootByQueryFiled(String queryFiled, Root<T> root) { if(queryFiled.indexOf(".") < 0) { return root.get(queryFiled); } else { return getRootByQueryFiled(queryFiled.substring(queryFiled.indexOf(".") + 1, queryFiled.length()), root.get(queryFiled.substring(0, queryFiled.indexOf(".")))); } } public default Path<Object> getRootByQueryFiled(String queryFiled, Path<Object> path) { if(queryFiled.indexOf(".") < 0) { return path.get(queryFiled); } else { return getRootByQueryFiled(queryFiled.substring(queryFiled.indexOf(".") + 1, queryFiled.length()), path.get(queryFiled.substring(0, queryFiled.indexOf(".")))); } } public default Path<String> getRootByQueryFiledString(String queryFiled, Root<T> root) { if(queryFiled.indexOf(".") < 0) { return root.get(queryFiled); } else { return getRootByQueryFiledString(queryFiled.substring(queryFiled.indexOf(".") + 1, queryFiled.length()), root.get(queryFiled.substring(0, queryFiled.indexOf(".")))); } } public default Path<String> getRootByQueryFiledString(String queryFiled, Path<Object> path) { if(queryFiled.indexOf(".") < 0) { return path.get(queryFiled); } else { return getRootByQueryFiledString(queryFiled.substring(queryFiled.indexOf(".") + 1, queryFiled.length()), path.get(queryFiled.substring(0, queryFiled.indexOf(".")))); } } public default Path<Comparable> getRootByQueryFiledComparable(String queryFiled, Root<T> root) { if(queryFiled.indexOf(".") < 0) { return root.get(queryFiled); } else { return getRootByQueryFiledComparable(queryFiled.substring(queryFiled.indexOf(".") + 1, queryFiled.length()), root.get(queryFiled.substring(0, queryFiled.indexOf(".")))); } } public default Path<Comparable> getRootByQueryFiledComparable(String queryFiled, Path<Object> path) { if(queryFiled.indexOf(".") < 0) { return path.get(queryFiled); } else { return getRootByQueryFiledComparable(queryFiled.substring(queryFiled.indexOf(".") + 1, queryFiled.length()), path.get(queryFiled.substring(0, queryFiled.indexOf(".")))); } }自定义注解
@Retention(RetentionPolicy.RUNTIME) @Target(ElementType.FIELD) public @interface QueryField { QueryType type(); String name() default ""; }接收参数
@QueryField(type = QueryType.EQUAL, name = "redddlCode") @ApiModelProperty(value="XXX",name="redddlCode",example="S2344") private String redddlCode;
