JPA 注解以及pojo转为表 (二)
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.}