带有 bean 映射器的嵌套对象 jdbi 3 为空答案

【问题标题】：Nested objects jdbi 3 with bean mapper is null带有 bean 映射器的嵌套对象 jdbi 3 为空
【发布时间】：2022-10-03 06:44:54
【问题描述】：

我有一个子类，其成员变量嵌套如下定义。但是，当我跑步时

val child = childRepo[1]

child.parent 是 null。如何自动获取嵌套成员变量？

模型.kt

import org.jdbi.v3.core.mapper.Nested
data class Child(
        var id: Int = -1,

        @Nested
        var parent: Parent? = null,

        var created: Instant? = null
)

data class Parent(
        var id: Int = -1,
)

ChildRepo.kt

import org.jdbi.v3.sqlobject.config.RegisterBeanMapper
import org.jdbi.v3.sqlobject.statement.SqlQuery
@SqlQuery(\"\"\"
        SELECT 
            c.id as c_id, c.created as c_created,
            p.id as p_id 
        FROM child as c
            INNER JOIN parent p on p.id = c.parent_id
        WHERE c.id = :id
        \"\"\")
@RegisterBeanMapper(value = Child::class, prefix = \"c\")
@RegisterBeanMapper(value = Parent::class, prefix = \"p\")
operator fun get(id: Int): Child?

标签： jdbi jdbi3

【解决方案1】：

如果您还为这两个类注册了JoinRowMapper（例如使用@RegisterJoinRowMapper），您将获得最接近您的存储库sn-p 的东西。您的get 方法的返回类型将是JoinRow，您可以从中检索两个值。

这里有更多信息和一些例子：https://jdbi.org/#_joins

如果您愿意在类定义中设置前缀，则可能更简单的方法是将 @Nested("p") 放在 parent 的 Child 字段上，并在存储库方法上仅添加以下注释：

@SqlQuery("""
    SELECT 
        c.id as id, c.created as created,
        p.id as p_id 
    FROM child as c
        INNER JOIN parent p on p.id = c.parent_id
    WHERE c.id = :id
    """)
@RegisterBeanMapper(value = Child::class)

【讨论】：

【解决方案2】：

已注册映射器中的前缀适用于顶级 bean。因此，您的 Child bean 使用“c”前缀正确映射。但是，“@Nested”注释不提供任何附加信息，哪些列用于嵌套 bean。因此，JDBI 尝试将带有“c”前缀的列映射到“Parent”bean，这不起作用。将 @Nested 注释替换为 @Nested("p") 以向 JDBI 发出该嵌套 bean 使用不同前缀的信号。然而，由于这是一个嵌套 Bean，JDBI 使用一个嵌套前缀（即 c_p）。因此，将父级的列选择为p_id as c_p_id。

此代码适用于 JDBI 3.33.0（其中对 bean 映射逻辑进行了一些更改）：

    @Test
    void testParentChild() {
        handle.execute("create table child (id integer not null, parent_id integer, created timestamp)");
        handle.execute("create table parent(id integer, created timestamp)");
        handle.execute("insert into parent (id, created) values (1, now())");
        handle.execute("insert into parent (id, created) values (2, now())");
        handle.execute("insert into parent (id, created) values (3, now())");

        handle.execute("insert into child(id, parent_id, created) values(1, 1, now())");
        handle.execute("insert into child(id, parent_id, created) values(2, 1, now())");
        handle.execute("insert into child(id, parent_id, created) values(3, 1, now())");
        handle.execute("insert into child(id, parent_id, created) values(4, 2, now())");
        handle.execute("insert into child(id, parent_id, created) values(5, 2, now())");
        handle.execute("insert into child(id, parent_id, created) values(6, 2, now())");
        handle.execute("insert into child(id, parent_id, created) values(7, 3, now())");
        handle.execute("insert into child(id, parent_id, created) values(8, 3, now())");
        handle.execute("insert into child(id, parent_id, created) values(9, 3, now())");

        ParentChildDao dao = handle.attach(ParentChildDao.class);

        Child c = dao.getChild(4);

        assertThat(c).isNotNull();
        assertThat(c.getParent()).isNotNull();
        assertThat(c.getParent().getId()).isEqualTo(2);

    }

    public static class Child {
        private int id;
        private Parent parent;
        private Instant created;

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        public Parent getParent() {
            return parent;
        }

        @Nested("p")
        public void setParent(Parent parent) {
            this.parent = parent;
        }

        public Instant getCreated() {
            return created;
        }

        public void setCreated(Instant created) {
            this.created = created;
        }
    }

    public static class Parent {
        private int id;
        private Instant created;

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        public Instant getCreated() {
            return created;
        }

        public void setCreated(Instant created) {
            this.created = created;
        }
    }

    public interface ParentChildDao {
        @SqlQuery("SELECT  c.id as c_id, c.created as c_created,p.id as c_p_id  FROM child as c INNER JOIN parent p on p.id = c.parent_id WHERE c.id = :id")
        @RegisterBeanMapper(value=Child.class, prefix="c")
        @RegisterBeanMapper(value=Parent.class)
        Child getChild(int id);
    }

【讨论】：