[英]JPA Criteria API: select count(*) from subquery with joins and group by for pagination implementation
我想在从数据库返回的产品列表中实现分页功能。 所以我需要知道查询的总结果。
数据库表是:
PRODUCT TABLE
-----------------------------
ID NAME
-------------- --------------
1 Product 1
2 Product 2
PRODUCT SUPPLIER TABLE
--------------------------------------------
ID PRODUCT ID PRICE
-------------- -------------- --------------
1 1 35
2 1 30
3 2 70
4 2 75
期望的结果是不同供应商的最低价格的产品列表。
Product 1 30
Product 2 70
主要查询应该是这样的:
select p.name, min(ps.price) from product
inner join product_supplier ps on ps.product_id = p.id
group by p.name
所以计数查询应该是这样的:
select count(*) from (
select p.name, min(ps.price) from product
inner join product_supplier ps on ps.product_id = p.id
group by p.name
)
我用来获取分页结果的代码是:
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<Tuple> tupleQuery = cb.createTupleQuery();
Root<product> product = tupleQuery.from(product.class);
Join<product, productSupplier> productSuppliers = product.join("productSuppliers");
tupleQuery.multiselect(
product,
cb.min(productSuppliers.get("price")).alias("price")
);
tupleQuery.groupBy(product);
tupleQuery.orderBy(cb.asc(product.get("name")));
TypedQuery<Tuple> query = entityManager
.createQuery(tupleQuery)
.setMaxResults(pageable.getPageSize())
.setFirstResult(Long.valueOf(pageable.getOffset()).intValue());
List<Tuple> products = query.getResultList();
for (Tuple productResult : products) {
Product product = productResult.get(product);
Double minPrice = (Double)productResult.get("price");
ProductDTO productDTO = new ProductDTO(product, minPrice);
}
但我不确定如何从主查询中获取计数。 我正在使用的代码是:
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<Long> countQuery = cb.createQuery(Long.class)
Root<Product> product = countQuery.from(Product.class);
Join<Product, ProductSupplier> productSuppliers = product.join("productSuppliers");
countQuery.groupBy(product);
countQuery.select(cb.count(product));
long count = entityManager.createQuery(countQuery).getSingleResult();
但它会产生以下 SQL:
select
count(product0_.id) as col_0_0_
from
pu_products product0_
inner join
pu_product_suppliers productsu1_
on product0_.id=productsu1_.product_id
group by
product0_.id
返回多个结果,抛出以下异常:
org.springframework.dao.IncorrectResultSizeDataAccessException: query did not return a unique result: 31
所以我不知道如何让它工作。
谢谢。
像这样的命名查询怎么样:
select count(distinct ps.product) from product_supplier ps where ps.price is not null
似乎不可能从通过标准 API 的聚合查询中执行select count (*) from
:
所以最后我应用了这个答案中找到的这个解决方案:
select count(*) from ({final_query_string})
包裹它。select count (*) from
.问候。
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