我有一个名为Trade的实体,可以映射到包含属性的表。此实体也有一个字段,用于存储另一个表中的值。我的交易表包含第二个表的主键。我知道如何将整个第二个表作为我的Trade实体中的实体,但我只想要那一列。
@Entity
@Immutable
@Table(name = "Trade table")
@SecondaryTables(value = {
@SecondaryTable(name = "2nd table", pkJoinColumns = @PrimaryKeyJoinColumn(referencedColumnName = "id", foreignKey = @ForeignKey(name = "2ndtableID"))),
@SecondaryTable(name = "3rd table", pkJoinColumns = @PrimaryKeyJoinColumn(referencedColumnName = "id", foreignKey = @ForeignKey(name = "3rdtableID"))) })
public class TradeSearchResult {
@Id
@Column(name = "ID")
private Long primaryKey;
@Column(name = "col2", table = "2nd table")
private String valuefrom2ndtable;
@Column(name = "col3", table = "3rd table")
private String valuefrom3ndtable;
}
正如您所见,我尝试使用@SecondaryTables
,但是联接是在Trade实体的primaryKey上执行的。如何使用注释从交易表中选择外键,将其连接到第2 /第3表并直接从col2 / col3中获取值?任何建议表示赞赏
表贸易:
ID col1 fk1 fk2
------------------------
1 abc 12 43
2 def 23 32
3 ghi 34 21
表2:
ID col2
----------
12 a
23 b
34 c
表3:
ID col3
-----------
43 d
32 e
21 f
现在我的Trade类应具有属性:
Long id;
String col1;
String col2;
String col3;
hibernate查询:from Trade
应该在这个示例中为我提供3个具有以下属性的交易:
Trade1: 1, "abc","a","d"
Trade2: 2, "def","b","e"
Trade3: 3, "ghi","c","f"
并且我不想创建实体,只能访问属性col2
和col3
编辑:
select语句如下所示:
select trade.ID,TICKET,table2.col2,table3.col2 from trade join table 3 on table3.ID=trade.FKtable3 join table2 on table2.ID=trade.FKtable2
如果我在sql server中执行此语句,它会给我想要的结果。我想映射我的类,以便hibernate生成这个语句。
答案 0 :(得分:0)
根据javadoc example,您应该使用pkJoinColumn
和foreignKey
来定义应该用于加入表格的女巫列。
//编辑:
在你的版本之后,我试图制造一些魔法:
@Entity
@Immutable
@Table(name = "\"Trade table\"")
@SecondaryTables(value = {
@SecondaryTable(name = "2nd table", pkJoinColumns = @PrimaryKeyJoinColumn(name = "col2", referencedColumnName = "id")),
@SecondaryTable(name = "3rd table", pkJoinColumns = @PrimaryKeyJoinColumn(name = "col3", referencedColumnName = "id"))
})
public class Trade {
@Id
@Column(name = "id")
private Long primaryKey;
@Column(name = "col2")
private String valuefrom2ndtable;
@Column(name = "col3")
private String valuefrom3ndtable;
}
@Entity
@Table(name = "\"2nd table\"")
public class Table2 {
@Id
private long id;
}
@Entity
@Table(name = "\"3rd table\"")
public class Table3 {
@Id
private long id;
}
我得到的SQL就像:
create table "2nd table" (
id bigint not null,
col2 bigint not null,
primary key (col2)
);
create table "3rd table" (
id bigint not null,
col3 bigint not null,
primary key (col3)
);
create table "trade table" (
id bigint not null,
col2 varchar(255),
col3 varchar(255),
primary key (id)
);
alter table "3rd table"
add constraint FK7tkn132p8joplte47ce169h82
foreign key (col3)
references "trade table";
alter table "2nd table"
add constraint FK9jsoykrvn4d0v4aor03g1l324
foreign key (col2)
references "trade table";
这看起来像你想做的事情,但我并非100%确定......
答案 1 :(得分:0)
我不明白你为什么这样做?如果您的Trade
课程中有映射的实体,则可以随时访问其属性,但我会尝试提供解决方案来回答您的问题。
您可以这样做,但您应该在两个实体之间使用OneToMany
映射(因此您也应该存储整个映射的实体),并使用此表中的FK作为实体和地图中的属性它是这样的:
@JoinColumn(name="2ndtableID")
@ManyToOne(targetEntity=SecondTable.class,fetch=FetchType.LAZY)
private Message message;
@Column(name="2ndtableID")
private Long secondTableID;
答案 2 :(得分:0)
我解决此问题的方法是不将TradeSearchResult
映射到任何表格,并使用Criteria
/ CriteriaQuery
API来获取我需要的数据。我的Trade
类完美映射到交易表,并保存对其他表的对象的引用。现在来看如何构建查询:
CriteriaBuilder cb = emf.getCriteriaBuilder();
CriteriaQuery<TradeSearchResult> query = cb.createQuery(TradeSearchResult.class); //type is the entity you want to map to
Root<Trade> r = query.from(Trade.class); //root must be entity from which you can access all data
List<Predicate> predicates = new ArrayList<Predicate>(); //new list of predicates
predicates.add(cb.like(r.join("2ndTableEntityName").<String>get("valuefrom2ndtable"),"value to search for"));
//get the needed value from 2nd table and map it to the field
query.multiselect(r.get("2ndTableEntityName")).where(predicates.toArray(new Predicate[] {}));
//create the query and execute it
EntityManager em = emf.createEntityManager();
List<TradeSearchResult> results = em.createQuery(query).getResultList();
em.close();
return results; //return results
此代码返回仅包含所需字段的TradeSearchResult
实体列表,而不返回其他类中的整个对象