QueryDsl 获取延迟 属性
QueryDsl fetch lazy property
我有一个 属性 通常是延迟获取的:
@Entity
class Version(...,
@Basic(fetch = FetchType.LAZY)
@Type(type = "text")
var mappings: String? = null) {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private val id = 0
}
但有时我需要急切地获取它。我如何使用 QueryDsl 执行此操作?
这是我目前拥有的:
JPAQuery<Any>(entityManager).from(QVersion.version)
.where(...)
.select(QVersion.version)
.fetchOne()
但是当我稍后尝试访问 属性 时,这会导致异常:
org.hibernate.LazyInitializationException: Unable to perform requested lazy initialization [Version.mappings] - no session and settings disallow loading outside the Session
我建议将 table 拆分为两个单独的实体并定义一个 lazy OneToOne
关系,以便您可以在需要时通过 QueryDSL
急切地获取它。因此,对于您的示例,您可能有以下实体:
@Entity
@Table(name="version")
class Version{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private val id = 0;
@OneToOne(optional = false, fetch = FetchType.LAZY)
@JoinColumn(name = "id", referencedColumnName = "id")
private VersionMappings mappings;
}
@Entity
@Table(name="version")
VersionMappings{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private val id = 0;
@Basic(fetch = FetchType.LAZY)
@Type(type = "text")
var mappings: String? = null);
}
如果语法有误,请见谅;因为我不熟悉Kotlin
。然后就可以按如下方式进行预取:
QVersion version = QVersion.version;
Version versionWithEagerlyFetchedMapping = JPAQuery<>(entityManager).from(version).where(version.id.eq(id)).rightJoin(version.versionMapping).fetchJoin().select(version).fetchOne();
我准备按照 github repo 来展示我的建议。回购协议是一个 Spring 具有 3 个独立端点的引导应用程序:
/books-without-author/{id}
==> 获取没有作者的书
/books-with-author-exception/{id}
==> 尝试获取作者的书,但由于事务无法加载代理而抛出异常
/books-with-author/{id}
==> 按照我上面的建议,通过 QueryDSL
急切获取作者的书。
您可以检查控制台日志以查看预取的工作。当您调用上面的第三个端点时,您将看到生成以下查询:
select book0_.id as id1_0_0_, bookauthor1_.id as id1_0_1_, book0_.name as name2_0_0_, book0_.publish_year as publish_3_0_0_, book0_.version as version4_0_0_, bookauthor1_.author as author5_0_1_ from book book0_ right outer join book bookauthor1_ on book0_.id=bookauthor1_.id where book0_.id=?
另一方面,第一个端点将生成类似 select book0_.id as id1_0_0_, book0_.name as name2_0_0_, book0_.publish_year as publish_3_0_0_, book0_.version as version4_0_0_ from book book0_ where book0_.id=?
的查询
对此有一个非常简单的解决方案:.fetchAll()
JPAQuery<Any>(entityManager).from(QVersion.version)
.fetchAll() // <- here
.where(...)
.select(QVersion.version)
.fetchOne()
If you are using property-level lazy fetching (with bytecode instrumentation), it is possible to force Hibernate to fetch the lazy properties in the first query immediately using fetch all properties.
我有一个 属性 通常是延迟获取的:
@Entity
class Version(...,
@Basic(fetch = FetchType.LAZY)
@Type(type = "text")
var mappings: String? = null) {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private val id = 0
}
但有时我需要急切地获取它。我如何使用 QueryDsl 执行此操作? 这是我目前拥有的:
JPAQuery<Any>(entityManager).from(QVersion.version)
.where(...)
.select(QVersion.version)
.fetchOne()
但是当我稍后尝试访问 属性 时,这会导致异常:
org.hibernate.LazyInitializationException: Unable to perform requested lazy initialization [Version.mappings] - no session and settings disallow loading outside the Session
我建议将 table 拆分为两个单独的实体并定义一个 lazy OneToOne
关系,以便您可以在需要时通过 QueryDSL
急切地获取它。因此,对于您的示例,您可能有以下实体:
@Entity
@Table(name="version")
class Version{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private val id = 0;
@OneToOne(optional = false, fetch = FetchType.LAZY)
@JoinColumn(name = "id", referencedColumnName = "id")
private VersionMappings mappings;
}
@Entity
@Table(name="version")
VersionMappings{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private val id = 0;
@Basic(fetch = FetchType.LAZY)
@Type(type = "text")
var mappings: String? = null);
}
如果语法有误,请见谅;因为我不熟悉Kotlin
。然后就可以按如下方式进行预取:
QVersion version = QVersion.version;
Version versionWithEagerlyFetchedMapping = JPAQuery<>(entityManager).from(version).where(version.id.eq(id)).rightJoin(version.versionMapping).fetchJoin().select(version).fetchOne();
我准备按照 github repo 来展示我的建议。回购协议是一个 Spring 具有 3 个独立端点的引导应用程序:
/books-without-author/{id}
==> 获取没有作者的书/books-with-author-exception/{id}
==> 尝试获取作者的书,但由于事务无法加载代理而抛出异常/books-with-author/{id}
==> 按照我上面的建议,通过QueryDSL
急切获取作者的书。
您可以检查控制台日志以查看预取的工作。当您调用上面的第三个端点时,您将看到生成以下查询:
select book0_.id as id1_0_0_, bookauthor1_.id as id1_0_1_, book0_.name as name2_0_0_, book0_.publish_year as publish_3_0_0_, book0_.version as version4_0_0_, bookauthor1_.author as author5_0_1_ from book book0_ right outer join book bookauthor1_ on book0_.id=bookauthor1_.id where book0_.id=?
另一方面,第一个端点将生成类似 select book0_.id as id1_0_0_, book0_.name as name2_0_0_, book0_.publish_year as publish_3_0_0_, book0_.version as version4_0_0_ from book book0_ where book0_.id=?
对此有一个非常简单的解决方案:.fetchAll()
JPAQuery<Any>(entityManager).from(QVersion.version)
.fetchAll() // <- here
.where(...)
.select(QVersion.version)
.fetchOne()
If you are using property-level lazy fetching (with bytecode instrumentation), it is possible to force Hibernate to fetch the lazy properties in the first query immediately using fetch all properties.