java 使用一个 JPQL 查询连接多个表
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Join multiple tables with one JPQL query
提问by acroscene
I got this sql-query I want to create as query in JPQL but I cannot get it right. I got a manytoone relationship between QuestionAnswers and QuizQuestions:
我得到了这个 sql 查询，我想在 JPQL 中创建为查询，但我做对了。我在 QuestionAnswers 和 QuizQuestions 之间有一个多对一的关系：
SQL:
查询语句：
SELECT quizName, question, answer FROM Quiz
JOIN QuizQuestions on Quiz.quizId = QuizQuestions.Quiz_QuizId
JOIN QuestionAnswers on QuizQuestions.questionId = QuestionAnswers.question_questionId
WHERE quiz.quizId = 1;
JPQL query:
JPQL 查询：
Query query = entityManager.createQuery("SELECT q.quizName, f.question, a.answer FROM Quiz q, QuizQuestions f, QuestionAnswers a LEFT JOIN QuestionAnswers ON f.questionId=a.question.questionId");
I get syntax error in Intellij.
我在 Intellij 中遇到语法错误。
What can be wrong?
有什么问题？
Im using EclipseLink
我正在使用 EclipseLink
EDITsolved it like this with just one join:
EDIT只用一个连接就解决了这个问题：
Query query = entityManager.createQuery("SELECT f.quiz.quizName FROM QuizQuestions f JOIN QuestionAnswers qa WHERE f.questionId = qa.question.questionId");
回答by Dherik
Probably, you are looking for a JPQL like this:
可能您正在寻找这样的 JPQL：
SELECT quiz.name, quizquestion.question, questionasnswer.answer FROM Quiz quiz
JOIN quiz.quizQuestions quizquestion
JOIN quizquestion.questionAnswers questionasnswer
WHERE quiz.id = 1;
I would evict solutions with qa.question.questionId(tableA.tableB.column), because the JPA framework not always generate nice SQLs from this. Always explicit the JOINs in the JPQL.
我会用qa.question.questionId(tableA.tableB.column)驱逐解决方案，因为 JPA 框架并不总是从中生成好的 SQL。始终在 JPQL 中显式显示 JOIN。
