java jOOQ 我可以将两个表的连接提取到各自的 POJO 中吗
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jOOQ can I fetch a join of two tables into the respective POJOs
提问by mat_boy
In jOOQ if I want to fetch a row of a table into a jOOQ autogenerated POJOs I do, for instance:
在 jOOQ 中，如果我想将表中的一行提取到 jOOQ 自动生成的 POJO 中，例如：
dsl.selectFrom(USER)
.where(USER.U_EMAIL.equal(email))
.fetchOptionalInto(User.class);
Now, suppose that I want to do a join between two tables, e.g. USERand ROLE, how can I fetch the result into the POJOs for these two tables?
现在，假设我想在两个表之间进行连接，例如USERand ROLE，我如何将结果提取到这两个表的 POJO 中？
回答by Lukas Eder
This is one solution using ResultQuery.fetchGroups(RecordMapper, RecordMapper)
这是使用的一种解决方案 ResultQuery.fetchGroups(RecordMapper, RecordMapper)
Map<UserPojo, List<RolePojo>> result =
dsl.select(USER.fields())
.select(ROLE.fields())
.from(USER)
.join(USER_TO_ROLE).on(USER.USER_ID.eq(USER_TO_ROLE.USER_ID))
.join(ROLE).on(ROLE.ROLE_ID.eq(USER_TO_ROLE.ROLE_ID))
.where(USER.U_EMAIL.equal(email))
.fetchGroups(
// Map records first into the USER table and then into the key POJO type
r -> r.into(USER).into(UserPojo.class),
// Map records first into the ROLE table and then into the value POJO type
r -> r.into(ROLE).into(RolePojo.class)
);
Note, if you want to use LEFT JOINinstead (in case a user does not necessarily have any roles, and you want to get an empty list per user), you'll have to translate NULLroles to empty lists yourself.
请注意，如果您想LEFT JOIN改用（以防用户不一定具有任何角色，并且您想为每个用户获取一个空列表），则必须自己将NULL角色转换为空列表。
Make sure you have activated generating equals()and hashCode()on your POJOs in order to be able to put them in a HashMapas keys:
确保您已在 POJO 上激活生成equals()和hashCode()，以便能够将它们HashMap作为键放入 a中：
<pojosEqualsAndHashCode>true</pojosEqualsAndHashCode>
