SpringDataJPA筆記(12)-Table註解詳解

由於在實際使用中，有時候會遇到需要訪問同一臺服務器上別的數據庫，但是又不想配置多數據源的情況，Table註解給我們提供了這種便利的操作

JPA在根據實體自動生成數據表關聯的時候，如果實體類與其映射的數據庫表名不同名時，則需要使用到Table註解來標註映射的表名，除此之外還可以指定表所屬的數據庫目錄或模式

首先來看一下Table註解的屬性

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface Table {
    String name() default "";

    String catalog() default "";

    String schema() default "";

    UniqueConstraint[] uniqueConstraints() default {};

    Index[] indexes() default {};
}

name

name屬性用於指定數據庫表名稱

若不指定則以實體類名稱作爲表名

例如如下代碼

@Entity
@Table
public class TableEntity extends AnimalEntity<Long> {
}

生成的數據庫名爲table_entity

catalog

catalog屬性用於指定數據庫實例名

一般來說數據庫實例在數據源配置的時候指定了，不配置就默認使用數據源配置的默認庫

如果使用catalog屬性設置名稱時，若數據庫存在和指定名稱一致的實例，新創建的表將出現在該實例中

若不存在，則會在啓動的時候拋出異常

 WARN 3304 --- [           main] o.h.t.s.i.ExceptionHandlerLoggedImpl     : GenerationTarget encountered exception accepting command : Error executing DDL "create table aaaadb.table_entity (id bigint not null auto_increment, age integer, gmt_create datetime not null, gmt_update datetime, height integer, name varchar(255), pid bigint, sex varchar(255), weight integer, primary key (id)) engine=InnoDB" via JDBC Statement

org.hibernate.tool.schema.spi.CommandAcceptanceException: Error executing DDL "create table aaaadb.table_entity (id bigint not null auto_increment, age integer, gmt_create datetime not null, gmt_update datetime, height integer, name varchar(255), pid bigint, sex varchar(255), weight integer, primary key (id)) engine=InnoDB" via JDBC Statement
	at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:67) ~[hibernate-core-5.4.12.Final.jar:5.4.12.Final]
	at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.applySqlString(AbstractSchemaMigrator.java:559) [hibernate-core-5.4.12.Final.jar:5.4.12.Final]
	at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.applySqlStrings(AbstractSchemaMigrator.java:504) [hibernate-core-5.4.12.Final.jar:5.4.12.Final]
	at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.createTable(AbstractSchemaMigrator.java:277) [hibernate-core-5.4.12.Final.jar:5.4.12.Final]
	at org.hibernate.tool.schema.internal.GroupedSchemaMigratorImpl.performTablesMigration(GroupedSchemaMigratorImpl.java:71) [hibernate-core-5.4.12.Final.jar:5.4.12.Final]
	at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.performMigration(AbstractSchemaMigrator.java:207) [hibernate-core-5.4.12.Final.jar:5.4.12.Final]
	at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.doMigration(AbstractSchemaMigrator.java:114) [hibernate-core-5.4.12.Final.jar:5.4.12.Final]
	at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.performDatabaseAction(SchemaManagementToolCoordinator.java:184) [hibernate-core-5.4.12.Final.jar:5.4.12.Final]
	at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.process(SchemaManagementToolCoordinator.java:73) [hibernate-core-5.4.12.Final.jar:5.4.12.Final]
	at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:314) [hibernate-core-5.4.12.Final.jar:5.4.12.Final]
	at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:468) [hibernate-core-5.4.12.Final.jar:5.4.12.Final]
	at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:1237) [hibernate-core-5.4.12.Final.jar:5.4.12.Final]
	at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:58) [spring-orm-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:365) [spring-orm-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:391) [spring-orm-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:378) [spring-orm-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.afterPropertiesSet(LocalContainerEntityManagerFactoryBean.java:341) [spring-orm-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1855) [spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1792) [spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:595) [spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) [spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) [spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) [spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) [spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1108) ~[spring-context-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:868) ~[spring-context-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.2.4.RELEASE.jar:5.2.4.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141) ~[spring-boot-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747) ~[spring-boot-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) ~[spring-boot-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) ~[spring-boot-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) ~[spring-boot-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) ~[spring-boot-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at com.mt.demo.jpa.SpringBootJpaDemoApplication.main(SpringBootJpaDemoApplication.java:10) ~[classes/:na]
Caused by: java.sql.SQLSyntaxErrorException: Unknown database 'aaaadb'
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:120) ~[mysql-connector-java-8.0.19.jar:8.0.19]
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97) ~[mysql-connector-java-8.0.19.jar:8.0.19]
	at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122) ~[mysql-connector-java-8.0.19.jar:8.0.19]
	at com.mysql.cj.jdbc.StatementImpl.executeInternal(StatementImpl.java:764) ~[mysql-connector-java-8.0.19.jar:8.0.19]
	at com.mysql.cj.jdbc.StatementImpl.execute(StatementImpl.java:648) ~[mysql-connector-java-8.0.19.jar:8.0.19]
	at com.zaxxer.hikari.pool.ProxyStatement.execute(ProxyStatement.java:95) ~[HikariCP-3.4.2.jar:na]
	at com.zaxxer.hikari.pool.HikariProxyStatement.execute(HikariProxyStatement.java) ~[HikariCP-3.4.2.jar:na]
	at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:54) ~[hibernate-core-5.4.12.Final.jar:5.4.12.Final]
	... 34 common frames omitted

uniqueConstraints

uniqueConstraints屬性用於設定約束條件

例如

@Table(uniqueConstraints={@UniqueConstraint(name = "name_key", columnNames={"name"})})

查看數據庫，對應SQL語句

UNIQUE KEY `name_key` (`name`)

這裏建議指定name屬性，以防止在不同情況下生成的name不同，引起一些問題

聯合約束

@Table(uniqueConstraints={@UniqueConstraint(name = "name_age_key", columnNames={"name", "age"})})

對應數據庫語句

UNIQUE KEY `name_age_key` (`name`,`age`)

indexes

表的索引，通過使用 @Index 註解來聲明，僅在允許自動更新數據庫表結構的場景中起到作用，默認沒有其他額外的索引

例如，默認是不唯一的

@Table(indexes={@Index(name = "name_index", columnList="name")})

數據庫對應SQL語句

KEY `name_index` (`name`)

如果添加了unique = true，則和約束的效果是一樣的

@Table(indexes={@Index(name = "name_index", columnList="name", unique = true)})

數據庫語句爲

UNIQUE KEY `name_index` (`name`)

聯合索引

@Table(indexes={@Index(name = "name_age_index", columnList="name, age", unique = true)})

同樣和約束時一樣的SQL

UNIQUE KEY `name_age_index` (`name`,`age`)

schema

目前schema在mysql中的作用未知，怎麼設置好像都沒有什麼用處，後續有空再研究看看

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SpringDataJPA筆記(12)-Table註解詳解

name

catalog

uniqueConstraints

indexes

schema

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