将当前行与上一行进行比较。 Java

Question

我想将当前行与上一行进行比较，如果匹配，则进行计算。如果不是，则分配 0.0 我的代码只计算而不接受条件。

例如我有table：石油 oil 包含月份、日期和指标

它必须看起来像：

Month      Values  Date        |formula              |Growth
september   100     01.09.2020  |(100/nan - 1) * 100  |infinity
september   80      08.09.2020  |(80/100-1) * 100     |-20
september   100     15.09.2020  |(100/80-1) * 100     |25     
october     118     01.10.2020  |september != october |0
october     120     08.10.2020  |(120/118-1) * 100    |1.69                 
october     123     15.10.2020  |(123/120-1) * 100    |2.5
november    122     01.11.2020  |october != november  |0
november    122     08.11.2020  |(122/122-1) * 100    |0

我的class模特：

@Entity
@Table(name = "oper_mon_oil_price")

public class OilModel {

@Id
@GeneratedValue(strategy =  GenerationType.IDENTITY)
private long id;
@Column(name = "o_year")
private String oyear;
@Column(name = "o_month")
private String omonth;
@Column(name = "o_date_event")
private String odateEvent;
@Column(name = "o_period")
private String operiod;
@Column(name = "o_area")
private String oarea;
@Column(name = "o_unit")
private String ounit;
@Column(name = "o_ai_92")
public Double oai92;
@Column(name = "o_ai_95")
public Double oai95;
@Column(name = "o_diesel_winter")
private Double odieselWinter;
@Column(name = "o_diesel_fuel_offseason")
private Double odieselFuelOffseason;
@Column(name = "growth_ai_92")
public Double growthAi92;
@Column(name = "growth_ai_95")
public Double growthAi95;
@Column(name = "growth_diesel_winter")
public Double growthDieselWinter;
@Column(name = "growth_diesel_fuel_offseason")
public Double growthDieselFuelOffseason;
 
getters/setters
}

class 存储库：

@Repository
@Mapper
public interface OilProdTovRepo {

@Select("SELECT * FROM oper_mon_prod_tov ORDER BY o_year ASC, o_month ASC, o_date_event ASC ")
@Results(value ={
        @Result(property = "id",column = "id"),
        @Result(property = "area",column = "o_area"),
        @Result(property = "year",column = "o_year"),
        @Result(property = "month",column = "o_month"),
        @Result(property = "period",column = "o_period"),
        @Result(property = "dateEvent",column = "o_date_event"),
        @Result(property = "unit",column = "o_unit"),
        @Result(property = "wheatFlourFirstGrade",column = "o_wheat_flour_first_grade"),
        @Result(property = "wheatBread",column = "o_wheat_bread"),
        @Result(property = "horns",column = "o_horns"),
        @Result(property = "buckwheat",column = "o_buckwheat"),
        @Result(property = "polishedRice",column = "o_polished_rice"),
        @Result(property = "potato",column = "o_potato"),
        @Result(property = "carrots",column = "o_carrots"),
        @Result(property = "onion",column = "o_onion"),
        @Result(property = "cabbageWhite",column = "o_cabbage_white"),
        @Result(property = "sugar",column = "o_sugar"),
        @Result(property = "oil",column = "o_oil"),
        @Result(property = "beef",column = "o_beef"),
        @Result(property = "chickenMeat",column = "o_chicken_meat"),
        @Result(property = "milk",column = "o_milk"),
        @Result(property = "kefir",column = "o_kefir"),
        @Result(property = "butter",column = "o_butter"),
        @Result(property = "egg",column = "o_egg"),
        @Result(property = "salt",column = "o_salt"),
        @Result(property = "cottageCheese",column = "o_cottage_cheese"),
        @Result(property = "growthWheatFlourFirstGrade",column = "o_growth_wheat_flour_first_grade"),

})
List<OilProdTovModel> getOilProdTovModel();

@Update("UPDATE oper_mon_prod_tov SET o_growth_wheat_flour_first_grade=#{growthWheatFlourFirstGrade} WHERE id=#{id}")
void updateWheatFlourFirstGrade(OilProdTovModel oilProdTovModel);
}

和主要class，服务：

@Service
public class OilProdTovService {
@Autowired
public OilProdTovRepo oilProdTovRepo;

public List<OilProdTovModel> allOilProdTov() {
    List<OilProdTovModel> oilProdTovModels = oilProdTovRepo.getOilProdTovModel();
    Double first = 0.0;
    Double result;
    for (OilProdTovModel oilProdTovModel : oilProdTovModels) {
        if (oilProdTovModel.getMonth().equals("September")) {
            Double wheatFlourFirstGrade = oilProdTovModel.getWheatFlourFirstGrade();
            result = (wheatFlourFirstGrade / first - 1) * 100;
            first = wheatFlourFirstGrade;
            wheatFlourFirstGrade = result;
            oilProdTovModel.setGrowthWheatFlourFirstGrade(wheatFlourFirstGrade);
        } else if (oilProdTovModel.getMonth().equals("October")) {
            Double wheatFlourFirstGrade = oilProdTovModel.getWheatFlourFirstGrade();
            result = (wheatFlourFirstGrade / first - 1) * 100;
            first = wheatFlourFirstGrade;
            wheatFlourFirstGrade = result;
            oilProdTovModel.setGrowthWheatFlourFirstGrade(wheatFlourFirstGrade);
        }
        else if (oilProdTovModel.getMonth().equals("November")) {
            Double wheatFlourFirstGrade = oilProdTovModel.getWheatFlourFirstGrade();
            result = (wheatFlourFirstGrade / first - 1) * 100;
            first = wheatFlourFirstGrade;
            wheatFlourFirstGrade = result;
            oilProdTovModel.setGrowthWheatFlourFirstGrade(wheatFlourFirstGrade);
        }
        else {
            oilProdTovModel.setGrowthWheatFlourFirstGrade(0.0);
        }
        
        oilProdTovRepo.updateWheatFlourFirstGrade(oilProdTovModel);
    }
    return oilProdTovRepo.getOilProdTovModel();
}
}

我如何修改我的代码？

Answer 1

由于您似乎难以获得列表中彼此跟随的 2 个实体，因此您可以这样做：

使用“foreach”：

List<OilProdTovModel> oilProdTovModels = ...
OilProdTovModel prev = null;
for (OilProdTovModel oilProdTovModel : oilProdTovModels) {
  if( prev != null ) {
    //compare oilProdTovModel and prev here
  }

  prev = oilProdTovModel; //keep track of the current element to serve as prev for the next iteration
}

使用传统的 for 循环：

for (int i = 1; i < oilProdTovModels.size(); i++) {
  OilProdTovModel prev = oilProdTovModels.get(i - 1);
  OilProdTovModel current = oilProdTovModels.get(i);

  //compare both - if you need to handle the first element without any comparison then do that before the loop 
  //(or iterate from 0 to size() - 1 and handle the last element after the loop if needed)
}

将当前行与上一行进行比较。 Java

Comparing the current line with the previous one. Java

java

spring

spring-boot

if-statement

spring-mybatis