JPA 注解以及pojo转为表 2
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7.一对多映射关系
有T_One和T_Many两个表,他们是一对多的关系,注解范例如下
主Pojo
01.@Entity
02.@Table(name = "T_ONE")
03.public class One implements Serializable {
04.private static final long serialVersionUID = 1L;
05.@Id
06.@Column(name = "ONE_ID", nullable = false)
07.private String oneId;
08.@Column(name = "DESCRIPTION")
09.private String description;
10.@OneToMany(cascade = CascadeType.ALL, mappedBy = "oneId")//指向多的那方的pojo的关联外键字段
11.private Collection<Many> manyCollection;
子Pojo
01.@Entity
02.@Table(name = "T_MANY")
03.public class Many implements Serializable {
04.private static final long serialVersionUID = 1L;
05.@Id
06.@Column(name = "MANY_ID", nullable = false)
07.private String manyId;
08.@Column(name = "DESCRIPTION")
09.private String description;
10.
11.@JoinColumn(name = "ONE_ID", referencedColumnName = "ONE_ID")//设置对应数据表的列名和引用的数据表的列名
12.@ManyToOne//设置在“一方”pojo的外键字段上
13.private One oneId;
8.多对多映射关系
貌似多对多关系不需要设置级联,以前用hibernate的时候着实为多对多的级联头疼了一阵子,JPA的多对多还需要实际的尝试一下才能有所体会。
估计JPA的多对多也是可以转换成两个一对多的。
第一个Pojo
01.@Entity
02.@Table(name = "T_MANYA")
03.public class ManyA implements Serializable {
04.private static final long serialVersionUID = 1L;
05.@Id
06.@Column(name = "MANYA_ID", nullable = false)
07.private String manyaId;
08.@Column(name = "DESCRIPTION")
09.private String description;
10.@ManyToMany
11.@JoinTable(name = "TMANY1_TMANY2", joinColumns = {@JoinColumn(name = "MANYA_ID", referencedColumnName = "MANYA_ID")}, inverseJoinColumns = {@JoinColumn(name = "MANYB_ID", referencedColumnName = "MANYB_ID")})
12.private Collection<ManyB> manybIdCollection;
第二个Pojo
01.@Entity
02.@Table(name = "T_MANYB")
03.public class ManyB implements Serializable {
04.private static final long serialVersionUID = 1L;
05.@Id
06.@Column(name = "MANYB_ID", nullable = false)
07.private String manybId;
08.@Column(name = "DESCRIPTION")
09.private String description;
10.@ManyToMany(mappedBy = "manybIdCollection")
11.private Collection<ManyA> manyaIdCollection;
9.一对一映射关系
主Pojo
01.@Entity
02.@Table(name = "T_ONEA")
03.public class OneA implements Serializable {
04.private static final long serialVersionUID = 1L;
05.@Id
06.@Column(name = "ONEA_ID", nullable = false)
07.private String oneaId;
08.@Column(name = "DESCRIPTION")
09.private String description;
10.@OneToOne(cascade = CascadeType.ALL, mappedBy = "oneA")//主Pojo这方的设置比较简单,只要设置好级联和映射到从Pojo的外键就可以了。
11.private OneB oneB;
从Pojo
01.@Entity
02.@Table(name = "T_ONEB")
03.public class OneB implements Serializable {
04.private static final long serialVersionUID = 1L;
05.@Id
06.@Column(name = "ONEA_ID", nullable = false)
07.private String oneaId;
08.@Column(name = "DESCRIPTION")
09.private String description;
10.@JoinColumn(name = "ONEA_ID", referencedColumnName = "ONEA_ID", insertable = false, updatable = false)//设置从方指向主方的关联外键,这个ONEA_ID其实是表T_ONEA的主键
11.@OneToOne
12.private OneA oneA;
10 大字段
01.@Lob //对应Blob字段类型
02.@Column(name = "PHOTO")
03.private Serializable photo;
04.@Lob //对应Clob字段类型
05.@Column(name = "DESCRIPTION")
06.private String description;
11.瞬时字段
不需要与数据库映射的字段,在保存的时候不需要保存倒数据库
01.@Transient
02.private int tempValue;
03.
04.public int getTempValue(){
05.get tempValue;
06.}
07.
08.public void setTempValue(int value){
09.this.tempValue = value;
10.}
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