我从 Java 开始,想将查询转换为 Lambda 中的 SQL 或 Java 8 中的 Stream。
按照下面的查询。
SELECT * FROM Correspondencia c, (SELECT entidadeOrigem, MAX(m1) similaridadeMaxima FROM Correspondencia WHERE m1 <> 0 GROUP BY entidadeOrigem) r WHERE c.entidadeOrigem = r.entidadeOrigem AND c.m1 =
r.similaridadeMaxima
我使用下面的 getter 和 setter 创建了 Correpondencia 类:
public class Correspondencia {
int codigo;
String nome;
String entidadeOrigem;
String EntidadeDestino;
double m1;
double m2;
double m3;
double medMax;
double dem;
public int getCodigo() {
return codigo;
}
public void setCodigo(int codigo) {
this.codigo = codigo;
}
public String getNome() {
return nome;
}
public void setNome(String nome) {
this.nome = nome;
}
public String getEntidadeOrigem() {
return entidadeOrigem;
}
public void setEntidadeOrigem(String entidadeOrigem) {
this.entidadeOrigem = entidadeOrigem;
}
public String getEntidadeDestino() {
return EntidadeDestino;
}
public void setEntidadeDestino(String entidadeDestino) {
EntidadeDestino = entidadeDestino;
}
public double getM1() {
return m1;
}
public void setM1(double m1) {
this.m1 = m1;
}
public double getM2() {
return m2;
}
public void setM2(double m2) {
this.m2 = m2;
}
public double getM3() {
return m3;
}
public void setM3(double m3) {
this.m3 = m3;
}
public double getMedMax() {
return medMax;
}
public void setMedMax(double medMax) {
this.medMax = medMax;
}
public double getDem() {
return dem;
}
public void setDem(double dem) {
this.dem = dem;
}
}
我创建了一个列表:
List<Correspondencia> cor = new ArrayList<Correspondencia>();
cor.add(new Correspondencia(41,"Paper_Organization","Paper", "Organization",0,0.14,0.04,0.23,0.08));
cor.add(new Correspondencia(22,"Paper_Organization","Paper", "Organization",0,0.15,0.04,0.23,0.08));
cor.add(new Correspondencia(22,"Paper_Organization","Paper", "Organization",0,0.36,0.04,0.23,0.08));
cor.add(new Correspondencia(11,"email_hasanemail","email", "hasanemail",0.19,0.21,0.19,0.,0.12));
cor.add(new Correspondencia(11,"email_hasanemail","email", "hasanemail",0.25,0.21,0.19,0.,0.12));
cor.add(new Correspondencia(11,"email_hasanemail","email", "hasanemail",0.37,0.21,0.19,0.,0.12));
cor.add(new Correspondencia(31,"Review_Reviewer","Review","Reviewer",0.36,0.5,0.41,0.,0.25));
cor.add(new Correspondencia(31,"Review_Reviewer","Review","Reviewer",0.38,0.5,0.41,0.,0.25));
cor.add(new Correspondencia(31,"Review_Reviewer","Review","Reviewer",0.37,0.5,0.41,0.,0.25));
cor.add(new Correspondencia(32,"email_hasanemail","email", "hasanemail",0.36,0.5,0.41,0.,0.25));
cor.add(new Correspondencia(01,"PaperAbstract_Abstract","PaperAbstract","Abstract", 0.33,0.45,0.32,0.,0.22));
cor.add(new Correspondencia(01,"PaperAbstract_Abstract","PaperAbstract","Abstract", 0.37,0.45,0.32,0.,0.22));
现在我想根据以下查询使用 Lambda 或 Stream 过滤类(class):
SELECT * FROM Correspondencia c, (SELECT entidadeOrigem, MAX(m1) similaridadeMaxima FROM Correspondencia WHERE m1 <> 0 GROUP BY entidadeOrigem) r WHERE c.entidadeOrigem = r.entidadeOrigem AND c.m1 = r.similaridadeMaxima
这将返回按 entidadeOrigem 的项目分组的 m1 的最大值作为结果:
22,"Paper_Organization","Paper", "Organization",0,0.36,0.04,0.23,0.08
11,"email_hasanemail","email", "hasanemail",0.37,0.21,0.19,0.,0.12
31,"Review_Reviewer","Review","Reviewer",0.38,0.5,0.41,0.,0.25
01,"PaperAbstract_Abstract","PaperAbstract","Abstract", 0.37,0.45,0.32,0.,0.22
一位同事在下面给了我以下代码:
Correspondencia maxM1 = cor.stream()
.filter(x -> x.getM1() != 0)
.max(Comparator.comparing(x -> x.getM1()))
.get();
System.out.println(maxM1);
但是,它只返回 entidadeOrigem 的最大 m1 值。
而我需要的是根据下面的 SQL 返回由 entidadeOrigem 分组的 m1 的每个重复项的最大值。
SELECT * FROM Correspondencia c, (SELECT entidadeOrigem, MAX(m1)
similaridadeMaxima FROM Correspondencia WHERE m1 <> 0 GROUP BY
entidadeOrigem) r WHERE c.entidadeOrigem = r.entidadeOrigem AND c.m1 =
r.similaridadeMaxima
最佳答案
首先根据entidadeOrigem
进行分组场成Map<String,List<Correspondencia>>
, 从每个列表中获取最大值
List<Correspondencia> result = cor.stream()
.collect(Collectors.groupingBy(Correspondencia::getEntidadeOrigem))
.values()
.stream()
.map(c->c.stream().max(Comparator.comparingDouble(Correspondencia::getM1)))
.filter(p->p.isPresent())
.map(Optional::get)
.collect(Collectors.toList());
关于java - 如何将 SQL 查询转换为 Lambda 或 Stream (Java 8)?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/56212748/