一、配置
依赖
org.springframework.boot
spring-boot-starter-data-jpa
配置文件
数据库版本需要与database-platform对应，我这里使用的数据库是mysql5.7。
spring:
datasource:
url: jdbc:mysql://127.0.0.1:3306/springboot_test
username: root
password: abc123
driver-class-name: com.mysql.cj.jdbc.Driver
jpa:
#配置数据库类型
database: MYSQL
#指定数据库的引擎
database-platform: org.hibernate.dialect.MySQL57Dialect
#配置是否打印sql
show-sql: true
#Hibernate相关配置
hibernate:
#配置级联等级
# ddl-auto: create
ddl-auto: update
open-in-view: false
# jackson:
# property-naming-strategy: CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES
可选参数
- create 启动时删数据库中的表，然后创建，退出时不删除数据表
- create-drop 启动时删数据库中的表，然后创建，退出时删除数据表 如果表不存在报错
- update 每次运行程序，没有表格会新建表格，表内有数据不会清空，只会更新
- validate 项目启动表结构进行校验 如果不一致则报错
实体类
@Entity
@Table(name = "person") //自动创建的表的表名 @TableName是mybatisplus的注解
public class Person {
@Id //@TableId是mybatisplus的注解
@GeneratedValue(strategy = GenerationType.IDENTITY) //主键id需要添加该注解
private Long id;
@Column(length =50,name = "name")
private String name;
private String email;
private String gender;
private String address;
}
@Entity
@Entity 注解和 @Table 注解都是 Java Persistence API 中定义的一种注解
@Entity默认的ORM映射关系为：类名与数据库中的表名相映射
如果没有 @javax.persistence.Entity 和 @javax.persistence.Id 这两个注解的话，它完全就是一个典型的 POJO 的 Java 类，现在加上这两个注解之后，就可以作为一个实体类与数据库中的表相对应。他在数据库中的对应的表为：@Table
如果同时使用了 @Entity(name=“student”) 和 @Table(name=“students”)，最终的对应的表名必须是哪个？答案是 students，这说明优先级：@Table > @Entity。@column
@Column来改变class中字段名与db中表的字段名的映射规则
二、使生成的表字段有序
由于JPA源码中的PropertyContainer表中使用TreeMap保存字段，因此实际生成的表字段是升序排列的。我们只需要将TreeMap改为LinkedHashMap即可（在项目中创建相同的包，将org.hibernate.hibernate-core依赖中的org.hibernate.cfg.PropertyContainer包下的PropertyContainer类复制到自己创建的包下，将TreeMap修改为LinkedHashMap即可，运行时会使用我们创建的类）。
具体步骤
- 创建包org.hibernate.cfg
- 在包下创建类PropertyContainer
package org.hibernate.cfg;
import java.util.*;
import javax.persistence.Access;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.OneToOne;
import javax.persistence.Transient;
import org.hibernate.AnnotationException;
import org.hibernate.annotations.Any;
import org.hibernate.annotations.ManyToAny;
import org.hibernate.annotations.Target;
import org.hibernate.annotations.Type;
import org.hibernate.annotations.common.reflection.XClass;
import org.hibernate.annotations.common.reflection.XProperty;
import org.hibernate.boot.MappingException;
import org.hibernate.boot.jaxb.Origin;
import org.hibernate.boot.jaxb.SourceType;
import org.hibernate.cfg.annotations.HCANNHelper;
import org.hibernate.internal.CoreMessageLogger;
import org.hibernate.internal.util.StringHelper;
import org.jboss.logging.Logger;
/**
* @author CJ
* @date: 2021/4/14 9:34
*/
public class PropertyContainer {
private static final CoreMessageLogger LOG = (CoreMessageLogger) Logger.getMessageLogger(CoreMessageLogger.class, org.hibernate.cfg.PropertyContainer.class.getName());
private final XClass xClass;
private final XClass entityAtStake;
private final AccessType classLevelAccessType;
private final LinkedHashMap persistentAttributeMap;
PropertyContainer(XClass clazz, XClass entityAtStake, AccessType defaultClassLevelAccessType) {
this.xClass = clazz;
this.entityAtStake = entityAtStake;
if (defaultClassLevelAccessType == AccessType.DEFAULT) {
defaultClassLevelAccessType = AccessType.PROPERTY;
}
AccessType localClassLevelAccessType = this.determineLocalClassDefinedAccessStrategy();
assert localClassLevelAccessType != null;
this.classLevelAccessType = localClassLevelAccessType != AccessType.DEFAULT ? localClassLevelAccessType : defaultClassLevelAccessType;
assert this.classLevelAccessType == AccessType.FIELD || this.classLevelAccessType == AccessType.PROPERTY;
this.persistentAttributeMap = new LinkedHashMap();
List fields = this.xClass.getDeclaredProperties(AccessType.FIELD.getType());
List getters = this.xClass.getDeclaredProperties(AccessType.PROPERTY.getType());
this.preFilter(fields, getters);
Map persistentAttributesFromGetters = new LinkedHashMap();
this.collectPersistentAttributesUsingLocalAccessType(this.persistentAttributeMap, persistentAttributesFromGetters, fields, getters);
this.collectPersistentAttributesUsingClassLevelAccessType(this.persistentAttributeMap, persistentAttributesFromGetters, fields, getters);
}
private void preFilter(List fields, List getters) {
Iterator propertyIterator = fields.iterator();
XProperty property;
while (propertyIterator.hasNext()) {
property = (XProperty) propertyIterator.next();
if (mustBeSkipped(property)) {
propertyIterator.remove();
}
}
propertyIterator = getters.iterator();
while (propertyIterator.hasNext()) {
property = (XProperty) propertyIterator.next();
if (mustBeSkipped(property)) {
propertyIterator.remove();
}
}
}
private void collectPersistentAttributesUsingLocalAccessType(LinkedHashMap persistentAttributeMap, Map persistentAttributesFromGetters, List fields, List getters) {
Iterator propertyIterator = fields.iterator();
XProperty xProperty;
Access localAccessAnnotation;
while (propertyIterator.hasNext()) {
xProperty = (XProperty) propertyIterator.next();
localAccessAnnotation = (Access) xProperty.getAnnotation(Access.class);
if (localAccessAnnotation != null && localAccessAnnotation.value() == javax.persistence.AccessType.FIELD) {
propertyIterator.remove();
persistentAttributeMap.put(xProperty.getName(), xProperty);
}
}
propertyIterator = getters.iterator();
while (propertyIterator.hasNext()) {
xProperty = (XProperty) propertyIterator.next();
localAccessAnnotation = (Access) xProperty.getAnnotation(Access.class);
if (localAccessAnnotation != null && localAccessAnnotation.value() == javax.persistence.AccessType.PROPERTY) {
propertyIterator.remove();
String name = xProperty.getName();
XProperty previous = (XProperty) persistentAttributesFromGetters.get(name);
if (previous != null) {
throw new MappingException(LOG.ambiguousPropertyMethods(this.xClass.getName(), HCANNHelper.annotatedElementSignature(previous), HCANNHelper.annotatedElementSignature(xProperty)), new Origin(SourceType.ANNOTATION, this.xClass.getName()));
}
persistentAttributeMap.put(name, xProperty);
persistentAttributesFromGetters.put(name, xProperty);
}
}
}
private void collectPersistentAttributesUsingClassLevelAccessType(LinkedHashMap persistentAttributeMap, Map persistentAttributesFromGetters, List fields, List getters) {
Iterator var5;
XProperty getter;
if (this.classLevelAccessType == AccessType.FIELD) {
var5 = fields.iterator();
while (var5.hasNext()) {
getter = (XProperty) var5.next();
if (!persistentAttributeMap.containsKey(getter.getName())) {
persistentAttributeMap.put(getter.getName(), getter);
}
}
} else {
var5 = getters.iterator();
while (var5.hasNext()) {
getter = (XProperty) var5.next();
String name = getter.getName();
XProperty previous = (XProperty) persistentAttributesFromGetters.get(name);
if (previous != null) {
throw new MappingException(LOG.ambiguousPropertyMethods(this.xClass.getName(), HCANNHelper.annotatedElementSignature(previous), HCANNHelper.annotatedElementSignature(getter)), new Origin(SourceType.ANNOTATION, this.xClass.getName()));
}
if (!persistentAttributeMap.containsKey(name)) {
persistentAttributeMap.put(getter.getName(), getter);
persistentAttributesFromGetters.put(name, getter);
}
}
}
}
public XClass getEntityAtStake() {
return this.entityAtStake;
}
public XClass getDeclaringClass() {
return this.xClass;
}
public AccessType getClassLevelAccessType() {
return this.classLevelAccessType;
}
public Collection getProperties() {
this.assertTypesAreResolvable();
return Collections.unmodifiableCollection(this.persistentAttributeMap.values());
}
private void assertTypesAreResolvable() {
Iterator var1 = this.persistentAttributeMap.values().iterator();
XProperty xProperty;
do {
if (!var1.hasNext()) {
return;
}
xProperty = (XProperty) var1.next();
} while (xProperty.isTypeResolved() || discoverTypeWithoutReflection(xProperty));
String msg = "Property " + StringHelper.qualify(this.xClass.getName(), xProperty.getName()) + " has an unbound type and no explicit target entity. Resolve this Generic usage issue or set an explicit target attribute (eg @OneToMany(target=) or use an explicit @Type";
throw new AnnotationException(msg);
}
private AccessType determineLocalClassDefinedAccessStrategy() {
AccessType hibernateDefinedAccessType = AccessType.DEFAULT;
AccessType jpaDefinedAccessType = AccessType.DEFAULT;
org.hibernate.annotations.AccessType accessType = (org.hibernate.annotations.AccessType) this.xClass.getAnnotation(org.hibernate.annotations.AccessType.class);
if (accessType != null) {
hibernateDefinedAccessType = AccessType.getAccessStrategy(accessType.value());
}
Access access = (Access) this.xClass.getAnnotation(Access.class);
if (access != null) {
jpaDefinedAccessType = AccessType.getAccessStrategy(access.value());
}
if (hibernateDefinedAccessType != AccessType.DEFAULT && jpaDefinedAccessType != AccessType.DEFAULT && hibernateDefinedAccessType != jpaDefinedAccessType) {
throw new org.hibernate.MappingException("@AccessType and @Access specified with contradicting values. Use of @Access only is recommended. ");
} else {
AccessType classDefinedAccessType;
if (hibernateDefinedAccessType != AccessType.DEFAULT) {
classDefinedAccessType = hibernateDefinedAccessType;
} else {
classDefinedAccessType = jpaDefinedAccessType;
}
return classDefinedAccessType;
}
}
private static boolean discoverTypeWithoutReflection(XProperty p) {
if (p.isAnnotationPresent(OneToOne.class) && !((OneToOne) p.getAnnotation(OneToOne.class)).targetEntity().equals(Void.TYPE)) {
return true;
} else if (p.isAnnotationPresent(OneToMany.class) && !((OneToMany) p.getAnnotation(OneToMany.class)).targetEntity().equals(Void.TYPE)) {
return true;
} else if (p.isAnnotationPresent(ManyToOne.class) && !((ManyToOne) p.getAnnotation(ManyToOne.class)).targetEntity().equals(Void.TYPE)) {
return true;
} else if (p.isAnnotationPresent(ManyToMany.class) && !((ManyToMany) p.getAnnotation(ManyToMany.class)).targetEntity().equals(Void.TYPE)) {
return true;
} else if (p.isAnnotationPresent(Any.class)) {
return true;
} else if (p.isAnnotationPresent(ManyToAny.class)) {
if (!p.isCollection() && !p.isArray()) {
throw new AnnotationException("@ManyToAny used on a non collection non array property: " + p.getName());
} else {
return true;
}
} else if (p.isAnnotationPresent(Type.class)) {
return true;
} else {
return p.isAnnotationPresent(Target.class);
}
}
private static boolean mustBeSkipped(XProperty property) {
return property.isAnnotationPresent(Transient.class) || "net.sf.cglib.transform.impl.InterceptFieldCallback".equals(property.getType().getName()) || "org.hibernate.bytecode.internal.javassist.FieldHandler".equals(property.getType().getName());
}
}
三、常用注解和索引创建
@Entity 标注用于实体类声明语句之前，指出该Java类为实体类，将映射到指定的数据库表。
@Table(name = "xxx") 当实体类与其映射的数据库表名不同名时使用@Table标注说明
@Id 声明一个实体类的属性映射为数据库的主键列。
@GeneratedValue 标注主键的生成策略
- IDENTITY：采用数据库ID自增长的方式来自增主键字段，Oracle不支持这种方式（oracle12g后，应该支持了。）；
- AUTO：JPA自动选择合适的策略，是默认选项；
- SEQUENCE：通过序列产生主键，通过@SequenceGenerator(strategy=GenerationType.AUTO) 注解指定序列名，MySql不支持这种方式。
- TABLE 通过表产生键，框架借助由表模拟序列产生主键，使用该策略可以使应用更易于数据库移植。
@Column(name="xxx",nullable=false,length=64,unique=false,) 当实体的属性与其映射的数据库表的列不同名时使用。@Column标注也可以置于属性的getter方法之前。
@Basic(fetch="",optional="") 表示一个简单的属性到数据库表的字段的映射，对于没有任何标注的getXxx()方法，默认即为Basic。fetch表示该属性的读取策略，有EAGER和LAZY两种，分别表示主支抓取和延迟加载，默认为EAGER。optional表示该属性是否允许为null,默认为true。
@Transient 表示该属性并非一个到数据库表的字段的映射，ORM框架将忽略该属性。类似@TableField(exist = false)。
@Temporal(TemporalType.TIMESTAMP) 使用@Temporal注解来调整Date精度
索引
1.创建联合唯一索引
@Table(uniqueConstraints = {@UniqueConstraint(columnNames={"category_name", "sec_category_name"})})
注意：还需要再对应的字段上添加@Column(name = "category_name") , @Column(name = "sec_category_name")
2.添加唯一索引约束
@Table(name = "UserOrgUnit",uniqueConstraints = @UniqueConstraint(name = "uni_resmodule", columnNames = {"resModule"}) )
3.添加普通索引
@Table(name = "order", indexes = {@Index(columnList = "applyMemberId"), @Index(columnList = "orgUnitId")})
@Table(name = "cooked_nutrition_detail",indexes = {@Index(name = "idx_cooked_parameter_id",columnList = "cooked_parameter_id"), @Index(name = "idx_ingredient_id",columnList = "ingredient_id")})
复合索引配置，注意 name 相同就可以了。
复合索引字段顺序就是 @Index中字段的顺序，注意 最佳左前缀特性。