如何使用 jpa 条件 api 编写此查询？

Question

Select c.id,
    (Select c2.value from customer_table c2 Where c2.id = c.id And c2.key = 'test') as "test",
    (Select c2.value from customer_table c2 Where c2.id = c.id And c2.key = 'service-category') as "service-category",
    (Select c2.value from customer_table c2 Where c2.id = c.id And c2.key = 'exam') as "exam"
From customer_table c
Group By c.id;

Answer 1

假设 customerTable 实体存在并正确建模，它的关系和值是 String 类型，实现将是这样的：

CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<YourPojo> cq = cb.createQuery(YourPojo.class);

Root<CustomerTable> root = cq.from(CustomerTable.class);

//Subquery 1
Subquery<String> sqVal1 = cq.subquery(String.class);
Root<CustomerTable> sq1Root = sqVal1.from(CustomerTable.class);
sqVal1.where(
    cb.and(
        cb.equal(root.get("id"),sq1Root.get("id")),
        cb.equal(sq1Root.get("key"),"test")
    )
);
sqVal1.select(sq1Root.get("value"));

//Subquery 2
Subquery<String> sqVal2 = cq.subquery(String.class);
Root<CustomerTable> sq2Root = sqVal2.from(CustomerTable.class);
sqVal2.where(
    cb.and(
        cb.equal(root.get("id"),sq2Root.get("id")),
        cb.equal(sq2Root.get("key"),"service-category")
    )
);
sqVal2.select(sq2Root.get("value"));

//Subquery 3
Subquery<String> sqVal3 = cq.subquery(String.class);
Root<CustomerTable> sq3Root = sqVal3.from(CustomerTable.class);
sqVal3.where(
    cb.and(
        cb.equal(root.get("id"),sq3Root.get("id")),
        cb.equal(sq3Root.get("key"),"exam")
    )
);
sqVal3.select(sq3Root.get("value"));

cq.groupBy(root.get("id"));

cq.multiselect(
    root.get("id"),
    sqVal1.getSelection(),
    sqVal2.getSelection(),
    sqVal3.getSelection()
);

您需要一个带有构造函数的 pojo，其参数（顺序和类型）与多选子句相同

public class YourPojo {
    public YourPojo(String id, String val1, String val2, String val3){
       [...]
    }
}

建议使用元模型来访问实体的属性，这将导致替换以下代码

root.get("id");

与另一个

root.get(CustomerTable_.id);

使用元模型而不深入主题的众多优点之一是能够auto-complete 属性命名并减少此时出错的机会。

如何使用 jpa 条件 api 编写此查询？

how to write this query using jpa criteria api?

java

hibernate

jpa

criteria-api

spring-boot