Object Mapping without losing existing data

Usually Object Mappers are for scenarios to map a larger set of data to small set (example: Entity object has a lot of data but we want to return only a few of them).

Entity

Object mappers usually create a new Instance of destination object of small set and set the required fields from source object with larger set, but I have opposite scenario: I have a destination object which already contains some data and now I need to map a new source object with smaller data set into destination object.

Source Class

public class SrcObj {
private String name;
private int i;


Destination Class

public class DestObj {
private String name;
private int i;
private float f;
private boolean b;


DesObj already contains the value of int i and float f, SrcObj has String name and int, i need to save SrcObj data into DestObj without losing existing data.

Model Mapper always creating a new Object of DestObj which will map SrcObj into it but rest of the fields are null.

public class ObjectMapper {
public static void main(String args) {
SrcObj src = new SrcObj("src name", 1);
DestObj dest = new DestObj(null, 0, 1, true);
ModelMapper modelMapper = ObjectMapper.modelMapper();
dest = modelMapper.map(src, DestObj.class);
System.out.println(dest);
}

private static ModelMapper modelMapper() {
ModelMapper modelMapper = new ModelMapper();
PropertyMap<SrcObj, DestObj> orderMap = new PropertyMap<SrcObj, DestObj>() {
protected void configure() {
// map().setI(destination.getI());
map().setI(source.getI());
System.out.println("model mapper");
map().setName(source.getName());
}
};

modelMapper.addMappings(orderMap);
return modelMapper;
}
}


there is an option in Model mapper to use destination, commented above but it's not working.

how can i have destObj containing all values
destObj[name="src name", i=1,f=1.1,b=true]

You forgot to ask a question....
– Joakim Danielson
Jun 30 at 5:41

modelmapper.org/javadoc/org/modelmapper/…. But in my experience, such mappers should be avoided at all cost: they only save you a few lines of trivial code to copy properties from one object to another, but make things a lot harder when dealing with more complex mappings, imutable objects, etc. And most importantly, they fail silently when you rename a property in the source class and don't apply the same refactoring on the destination class (or vice-versa), leading to plenty of bugs that don' happen if you code the copy by yourself.
– JB Nizet
Jun 30 at 5:45

@JBNizet I already went through the documentation but didn't succeed. yes, I know the implications but right now I have simple objects so it doesn't matter.
– shrikant.sharma
Jun 30 at 5:48

Then post a complete minimal example of what you tried after using the method I linked to, and tell precisely what you expected to happen, and what happened instead.
– JB Nizet
Jun 30 at 5:50

HI @JBNizet I hope this is what you are saying modelMapper.map(src, dest); but its giving compile time error Type mismatch: cannot convert from void to DestObj because this overloaded method return type is void.
– shrikant.sharma
Jun 30 at 6:05

modelMapper.map(src, dest);

2 Answers
2

First, if you don't want to use getter/setter in your classes, you can just enable the field matching feature.

modelMapper.getConfiguration()
.setFieldMatchingEnabled(true)
.setFieldAccessLevel(AccessLevel.PRIVATE);


And you can simply modelMapper.map(src, dest) that will update the dest's properties from source.

modelMapper.map(src, dest)

@Chun Han Hsiao thanks for your response, it worked, just for the sake of solution.

SrcObj src = new SrcObj("src name", 1);
DestObj dest = new DestObj(null, 0, 1, true);
ModelMapper modelMapper = ObjectMapper.modelMapper();
modelMapper.map(src, dest);
System.out.println(dest);


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