I have 2 different Entity Class as below :

@Table(name = "tableA")
public class EntityA{

    @PartitionKey
    @Column(name = "age")
    int age;

    @PartitionKey
    @Column(name = "class")
    int class;

    @Column(name = "rollNo")
    int rollNo;

}

@Table(name = "tableB")
public class EntityA{

    @PartitionKey
    @Column(name = "class")
    int class;

    @Column(name = "rollNo")
    int rollNo;

    // one column less 
}

Now based on some condition I need to persist the data in both the tables.

In my service layer I have a List of EntityA :: List<EntityA> which I am passing to the DAOImpl method where I insert the data as below :

public void insertListItems(List<EntityA> entityAList) {
    // here I need to convert the List<EntityA>  to List<EntityB>
    // before table insert operation.
}

How I can make that conversion where in the EnitityB I have one column less. I don't want to write boilerplate code for the conversion as my entity class is big in actual. Instead use some library that helps with the mapping.

CodePudding user response：

You could try to get a Map like this Map<String, List<String> columns;

The first value (key) is the column name and the second value (value) is a list of all values of this column.

Then you can just use if statements for selecting a column or not.

So:

1. Load all columns and their values
2. Use a loop with if statements.
3. In this loop, you could also integrate a list of Strings, which are the unallowed or allowed column names.

CodePudding user response：

如果目的是单纯的存储数据我感觉其实不用转换,不如直接写原生sql更好.我的英语不好我使用翻译软件,希望能帮到你

If the purpose is purely to store data, I feel that it is better to write native SQL without converting. My English is not good, I use translation software, I hope it can help you

CodePudding user response：

You can use Jackson's ObjectMapper library to achieve this. In order for this to work you must have getters declared in both EntityA and EntityB class, as well as a default (empty) constructor.

import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.Collections;
import java.util.List;
import java.util.Objects;
import java.util.Optional;
import java.util.stream.Collectors;

/**
 * Function converts list of objects to another list of objects
 * which' type is specified by the clazz attribute. Clazz attribute
 * must not be null, or it will throw a NullPointerException.
 * 
 * @param list List of target objects
 * @param clazz Class to map list objects to
 * @param <T> Target class
 * @param <F> From class
 * @return F.class List converted to T.class List
 */
public static <T, F> List<T> convertList(List<F> list, Class<T> clazz) {
    Objects.requireNonNull(clazz);
    ObjectMapper mapper = new ObjectMapper();

    // Important: this must be declared so mapper doesn't throw 
    // an exception for all properties which it can't map.
    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

    return Optional.ofNullable(list)
            .orElse(Collections.emptyList())
            .stream()
            .map(obj -> mapper.convertValue(obj, clazz))
            .collect(Collectors.toList());
}

public void insertListItems(List<EntityA> entityAList) {
    List<EntityB> entityBList = convertList(entityAList, EntityB.class);
    // Continue with table insert operation
}