我正在努力创建一个使用多个表的 jpa 查询。我似乎无法理解如何将表格连接在一起。这是我要创建的查询:
SELECT algm.m_l_i, algnsm.n_s_i
FROM algm, alg, algnsm, mal
WHERE algm.l_g_i = alg.l_g_i
AND alg.l_g_t = 'xxx'
AND algnsm.l_g_i = algm.l_g_i
AND mal.c_l_i = algm.m_l_i
AND mal.p_l_i = 'yyy';
我尝试了几种方法,从使用连接运算符到在键上使用 where 运算符。我无法在网上找到足够的关于加入的信息来提供帮助。一旦我尝试加入超过一张 table 的深度,我就会卡住。一些建议或技巧真的很有用。 谢谢
CriteriaBuilder b = em.getCriteriaBuilder();
CriteriaQuery<Tuple> q = builder.createTupleQuery();
Root<MAL> malRoot = query.from(MAL.class);
Root<ALGM> algmRoot = query.from(ALGM.class);
// error
algmRoot.join(ML_.mLI);
// error
malRoot.join(ML_.mLI);
Predicate e1 = builder.equal(malRoot.get(MAL_.pL).get(ML_.mLI), "abc");
Predicate e2 = builder.equal(malRoot.get(MAL_.cL), algmRoot.get(ALGM_.mL));
query.where(builder.and(e1, e2));
query.select(builder.tuple(malRoot.get(MAL_.pL), malRoot.get(MAL_.cL), algmRoot.get(ALGM_.aLG).get(ALG_.lGT)));
@Entity
@Table(name = "M_A_L")
public class MAL implements Serializable {
@EmbeddedId
protected MALPK malPK;
@Basic(optional = false)
@Column(name = "ENTRY_IND")
private String entryInd;
@JoinColumn(name = "P_L_I", referencedColumnName = "M_L_I", insertable = false, updatable = false)
@ManyToOne(optional = false)
private ML pL;
@JoinColumn(name = "C_L_I", referencedColumnName = "M_L_I", insertable = false, updatable = false)
@ManyToOne(optional = false)
private ML cL;
...
}
@Entity
@Table(name = "A_L_G_M")
public class ALGM implements Serializable {
@EmbeddedId
protected ALGMPK algmPK;
@JoinColumn(name = "M_L_I", referencedColumnName = "M_L_I", insertable = false, updatable = false)
@ManyToOne(optional = false, fetch = FetchType.EAGER)
private ML mL;
@JoinColumn(name = "L_G_I", referencedColumnName = "L_G_I", insertable = false, updatable = false)
@ManyToOne(optional = false)
private ALG aLG;
....
}
public class ALGM_ {
public static volatile SingularAttribute<ALGM, ML> mL;
public static volatile SingularAttribute<ALGM, ALGMPK> aLGMPK;
public static volatile SingularAttribute<ALGM, ALG> aLG;
}
public class MAL_ {
public static volatile SingularAttribute<MAL, String> eI;
public static volatile SingularAttribute<MAL, MALPK> mALPK;
public static volatile SingularAttribute<MAL, ML> pL;
public static volatile SingularAttribute<MAL, ML> cL;
}
public class ALG_ {
public static volatile CollectionAttribute<ALG, MW> mWC;
public static volatile SingularAttribute<ALG, ALGCM> aLGCM;
public static volatile SingularAttribute<ALG, ALGAVM> aLGAVM;
public static volatile SingularAttribute<ALG, TR> tZ;
public static volatile CollectionAttribute<ALG, ALGM> aLGMC;
public static volatile SingularAttribute<ALG, String> d;
public static volatile SingularAttribute<ALG, String> lGT;
public static volatile SingularAttribute<ALG, String> lGI;
public static volatile SingularAttribute<ALG, ALGNSM> aLGNSM;
public static volatile SingularAttribute<ALG, ALGFVM> aLGFVM;
public static volatile SingularAttribute<ALG, ALGNAM> aLGNAM;
}
最佳答案
JPA 查询中的连接是这样的:
创建从 A 到 B 的连接:
Root<A> root ....
CriteriaQuery<?> query .....
CriteriaBuilder builder.....
Join<A, B> BTable = root.join(SingularAttribute<A, B>);
或
Join<A, B> BTable = root.join(A_.B);
一旦获得 bTable 的引用,就可以将其用于路径变量。
关于java - 具有多个连接的 JPA 条件生成器,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/3870944/