我想尝试一个简单的 Spring Boot Hibernate 示例。
我有这个数据库：
create or replace table treasurelog.categories
(
id bigint auto_increment
primary key,
name varchar(20) null
);
我想使用 JPA Hibernate 从中获取数据。 访问是通过 CategoryController 和 JPARepository 进行的。
如上所示，我的DB中的Table Category，只有ID为PK和名称。
然后我写了这个控制器：
@RestController
public class FindingController {
private CategoryRepository categoryRepository;
public FindingController(CategoryRepository categoryRepository) {
this.categoryRepository = categoryRepository;
}
@GetMapping(value = "/categories")
public List<Category> getCategories() {
return categoryRepository.findAll();
}
}
使用此存储库
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import java.util.List;
public interface CategoryRepository extends JpaRepository<Category, Integer> {
@Query("select Category as category from Category ")
public List<Category> findAll();
}
这个实体：
@Getter
@Setter
@Entity
@Table(name = "categories")
public class Category {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id", nullable = false)
private Long id;
@Size(max = 20)
@Column(name = "name", length = 20)
private String name;
}
但是我在尝试 GET 时总是遇到此错误：
ava.lang.NullPointerException: Cannot invoke "org.hibernate.metamodel.mapping.DiscriminatorType.getJdbcJavaType()" because "this.discriminatorType" is null
at org.hibernate.sql.ast.tree.expression.EntityTypeLiteral.createSqlSelection(EntityTypeLiteral.java:132) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.sql.ast.tree.expression.EntityTypeLiteral.createDomainResult(EntityTypeLiteral.java:123) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.sql.BaseSqmToSqlAstConverter.lambda$visitSelection$23(BaseSqmToSqlAstConverter.java:2287) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at java.base/java.util.Collections$SingletonList.forEach(Collections.java:4966) ~[na:na]
at org.hibernate.query.sqm.sql.BaseSqmToSqlAstConverter.visitSelection(BaseSqmToSqlAstConverter.java:2282) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.sql.BaseSqmToSqlAstConverter.visitSelectClause(BaseSqmToSqlAstConverter.java:2200) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.sql.BaseSqmToSqlAstConverter.visitQuerySpec(BaseSqmToSqlAstConverter.java:2044) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.sql.BaseSqmToSqlAstConverter.visitQuerySpec(BaseSqmToSqlAstConverter.java:434) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.tree.select.SqmQuerySpec.accept(SqmQuerySpec.java:125) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.spi.BaseSemanticQueryWalker.visitQueryPart(BaseSemanticQueryWalker.java:221) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.sql.BaseSqmToSqlAstConverter.visitQueryPart(BaseSqmToSqlAstConverter.java:1902) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.sql.BaseSqmToSqlAstConverter.visitSelectStatement(BaseSqmToSqlAstConverter.java:1587) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.sql.BaseSqmToSqlAstConverter.visitSelectStatement(BaseSqmToSqlAstConverter.java:434) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.tree.select.SqmSelectStatement.accept(SqmSelectStatement.java:222) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.sql.BaseSqmToSqlAstConverter.translate(BaseSqmToSqlAstConverter.java:770) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.internal.ConcreteSqmSelectQueryPlan.buildCacheableSqmInterpretation(ConcreteSqmSelectQueryPlan.java:345) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.internal.ConcreteSqmSelectQueryPlan.withCacheableSqmInterpretation(ConcreteSqmSelectQueryPlan.java:268) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.internal.ConcreteSqmSelectQueryPlan.performList(ConcreteSqmSelectQueryPlan.java:244) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.sqm.internal.QuerySqmImpl.doList(QuerySqmImpl.java:518) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.spi.AbstractSelectionQuery.list(AbstractSelectionQuery.java:367) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.hibernate.query.Query.getResultList(Query.java:119) ~[hibernate-core-6.2.7.Final.jar:6.2.7.Final]
at org.springframework.data.jpa.repository.query.JpaQueryExecution$CollectionExecution.doExecute(JpaQueryExecution.java:129) ~[spring-data-jpa-3.1.3.jar:3.1.3]
at org.springframework.data.jpa.repository.query.JpaQueryExecution.execute(JpaQueryExecution.java:92) ~[spring-data-jpa-3.1.3.jar:3.1.3]
at org.springframework.data.jpa.repository.query.AbstractJpaQuery.doExecute(AbstractJpaQuery.java:148) ~[spring-data-jpa-3.1.3.jar:3.1.3]
at org.springframework.data.jpa.repository.query.AbstractJpaQuery.execute(AbstractJpaQuery.java:136) ~[spring-data-jpa-3.1.3.jar:3.1.3]
at org.springframework.data.repository.core.support.RepositoryMethodInvoker.doInvoke(RepositoryMethodInvoker.java:136) ~[spring-data-commons-3.1.3.jar:3.1.3]
at org.springframework.data.repository.core.support.RepositoryMethodInvoker.invoke(RepositoryMethodInvoker.java:120) ~[spring-data-commons-3.1.3.jar:3.1.3]
at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.doInvoke(QueryExecutorMethodInterceptor.java:164) ~[spring-data-commons-3.1.3.jar:3.1.3]
at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.invoke(QueryExecutorMethodInterceptor.java:143) ~[spring-data-commons-3.1.3.jar:3.1.3]
在我看到的教程中没有任何关于 DecriminatorType 的内容。
我希望有人能给我一些信息。
谢谢。
首先在存储库界面中将
<Category, Integer><Category, Long>Long控制器中的第二个更改字段声明来自
private CategoryRepository categoryRepository
到
private final CategoryRepository categoryRepository
如果你想要构造函数注入
实体类中的最后一个
Category