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Setting null or empty for #singular list in lombok

I have a list as
#Value
#Builder(toBuilder = true)
class Demo {
private BigInteger id;
#Singular
private List<String> name;
}
I have some data added in the name list. Now I want to set it to empty or null. How can I achieve it?
As per my understanding if I m using #Singular annotation it makes the list immutable.
I m using Java with Lombok.

As per my understanding if I m using #Singular annotation it makes the
list immutable.
It makes the list in the Demo instance immutable. It does not make the list immutable in the builder; it simply changes the API of the builder.
From the documentation:
with the #Singular annotation, lombok will treat that builder node
as a collection, and it generates 2 'adder' methods instead of a
'setter' method
As for emptying the list,
A 'clear' method is also generated.
In your case, clearNames (the list field should be called names, not name, otherwise Lombok complains).
If you want a mutable instance, don't use #Singular

As per my understanding if I m using #Singular annotation it makes the
list immutable
No, Lambok just create method for single add element, for you class (I strongly recommend change name to names). You just need to call method "clearNames"
#Value
#Builder(toBuilder = true)
class Demo {
private BigInteger id;
#Singular
private List<String> names;
}
Lambok generate following builder
public static class UserBuilder {
private BigInteger id;
private ArrayList<String> names;
UserBuilder() {
}
public User.UserBuilder name(String name) {
if (this.names == null) this.names = new ArrayList<String>();
this.names.add(name);
return this;
}
public User.UserBuilder names(Collection<? extends String> names) {
if (this.names == null) this.names = new ArrayList<String>();
this.names.addAll(names);
return this;
}
public User.UserBuilder clearNames() {
if (this.names != null)
this.names.clear();
return this;
}
...
public User build() {
...
}
public String toString() {
...
}
}

How to fix " Failed to instantiate 'className' using constructor NO_CONSTRUCTOR with arguments" in immutable class

I use MongoDBRepository in spring boot, and when I save some object in database everything is ok. but when I find object by id spring does not allow do that.
I try to change VehicleRoutingProblemSolution type to Object type, but VehicleRoutingProblemSolution have other object field PickupService and it without default constructor to. And yes, this class has immutable... I can't create default constructors, what can I do?
import com.fasterxml.jackson.annotation.JsonProperty;
import com.graphhopper.jsprit.core.problem.solution.VehicleRoutingProblemSolution;
import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;
#Document(collection = "vrp_solutions")
public class VrpSolutionHolder {
// Specifies the solution id
#Id
#JsonProperty("id")
private String id;
// Specifies the solution id
#JsonProperty("solution")
private VehicleRoutingProblemSolution vehicleRoutingProblemSolution;
// Created at timestamp in millis
#JsonProperty("created_at")
private Long created_at = System.currentTimeMillis();
public VrpSolutionHolder(String id, VehicleRoutingProblemSolution vehicleRoutingProblemSolution) {
this.id = id;
this.vehicleRoutingProblemSolution = vehicleRoutingProblemSolution;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public VehicleRoutingProblemSolution getVehicleRoutingProblemSolution() {
return vehicleRoutingProblemSolution;
}
public void setVehicleRoutingProblemSolution(VehicleRoutingProblemSolution vehicleRoutingProblemSolution) {
this.vehicleRoutingProblemSolution = vehicleRoutingProblemSolution;
}
public Long getCreated_at() {
return created_at;
}
public void setCreated_at(Long created_at) {
this.created_at = created_at;
}
}
org.springframework.web.util.NestedServletException: Request
processing failed; nested exception is
org.springframework.data.mapping.model.MappingInstantiationException:
Failed to instantiate
com.graphhopper.jsprit.core.problem.solution.VehicleRoutingProblemSolution
using constructor NO_CONSTRUCTOR with arguments

I ran into the exact same problem. A persistent immutable class containing other class instances, throwing that aforementioned exception when retrieved by this repository method:
public interface ProjectCodeCacheRepository extends MongoRepository<CachedCode, String> {
public CachedCode findByCode(String code);
public List<CachedCode> findByClientId(UUID clientId);
}
...
List<CachedCode> cachedForClient = this.codeCacheRepo.`**findByClientId**`(clientId);
...
Following Erwin Smouts hints, this is nicely fixed by giving it a special constructor annotated org.springframework.data.annotation.PersistenceConstructor like so:
#Document(collection="cachedcodes")
public class CachedCode {
#PersistenceConstructor
public CachedCode(String code, UUID clientId, LocalDateTime expiration) {
this.code = code;
this.clientId = clientId;
this.expiration = expiration;
}
public CachedCode(String code, UUID clientId, long secondsExpiring) {
this.code = code;
this.clientId = clientId;
this.expiration = LocalDateTime.now().plusSeconds(secondsExpiring);
}
public UUID getClientId( ) {
return this.clientId;
}
public String getCode() {
return this.code;
}
public boolean hasExpired(LocalDateTime now) {
return (expiration.isBefore(now));
}
...
#Id
private final String code;
private final UUID clientId;
private final LocalDateTime expiration;
}
So, you should check if your VehicleRoutingProblemSolution has a) a constructor that matches the database fields (check in mongo client) and b) is annotated to be the one used by the driver (or whichever piece of Spring magic under the hood).

If your framework tool requires (visible) no-arg constructors (plus accompanying setters), and the class you have is required to stay as is, then you could roll your own, say, MutableVehicleRoutingProblemSolution where in the setters you could have :
this.vehicleRoutingProblemSolution = new VehicleRoutingProblemSolution(vehicleRoutingProblemSolution.getId(), newSolution);
Thus your MutableVehicleRoutingProblemSolution wraps around the existing VehicleRoutingProblemSolution.
Hacky smell to it, but it fits the requirements.
(Or you could try to find a tool that is able to use, not annotations on the contained fields, but annotations on constructor arguments.)

This is a problem where the corresponding class does not have a no-arg constructor like - I was facing an issue with java.io.File.
Solution:
In general - change the declaration to Object class and convert where we are using the class.
from
class MyClass{
File myfile;
}
to
class MyClass{
Object myFile;
}

For anyone using lombok, you need to remove the #Builder annotation on your class and use #Data instead, or follow the above solution to provide a specialized constructor

Oddly, I received this when I attempted to decorate a custom interface with ...
#Document(collection = "Person")
Example:
package test.barry.interfaces;
import org.springframework.data.mongodb.core.mapping.Document;
import org.springframework.data.mongodb.core.query.Query;
import org.springframework.data.mongodb.core.query.UpdateDefinition;
#Document(collection = "Person")
public interface CustomRepository
{
void updatex(Query filterPredicate, UpdateDefinition updatePredicate);
}

Can I prefix a function with "get" in Springboot

I have a Mcq class associated to a MongoRepository, and I want to get an instance of my Mcq which apply several changes (Answers shuffle, Questions draw, etc). I declared my function "myMcq.getInstance()", but I can't do that because every time I want to send a Mcq in a ResponseEntity there is an error in the JSON output because Springboot thinks that there is a "instance" property in my class.
Here is my java class :
#Document(collection = "Mcqs")
public class Mcq {
#Id public String id;
#DBRef public User creator;
public String title;
public String categoryID;
public List<McqChapter> chapterList = new ArrayList<>();
public Difficulty difficulty;
public Mcq() {}
public Mcq(String title) {
this();
this.title = title;
}
public ArrayList<String> getQuestionsIDs() {
ArrayList<String> result = new ArrayList<>();
for (McqChapter chapter : chapterList) result.addAll(chapter.getQuestionIDs());
return result;
}
public McqInstance getInstance() {
return new McqInstance(this);
}
}

To prevent the error add #JsonIgnore to getInstance() method:
#JsonIgnore
public McqInstance getInstance() {
return new McqInstance(this);
}
Marker annotation that indicates that the annotated method or field is to be ignored by introspection-based serialization and deserialization functionality. That is, it should not be consider a "getter", "setter" or "creator".

save mongo entity to the different collections

I've been using Spring Data for saving entities to the mongo DB and my code at the moment looks like this:
I have a repo class:
public interface LogRepo extends MongoRepository<Log, String> {
}
and I have an Entity Log which looks like this:
#Document(
collection = "logs"
)
public class Log {
#Id
private String id;
private String jsonMessage;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getJsonMessage() {
return jsonMessage;
}
public void setJsonMessage(String jsonMessage) {
this.jsonMessage = jsonMessage;
}
}
and this work well for me, however this approach works only for the case if I want to save Log entities to "logs" collection. However it would be very nice for me to be able to save Log entity to different collections depending on the context. I mean it would be nice to define collection name in the runtime. Is it possible somehow?
Thanks, cheers

Try to use inheritance and define appropriate collection names in such way. May give you possibility to save in different collections but you will be still not able to specify dynamically collection names and resp. their amount at runtime.

#Document(
collection = "logs"
)
public class Log {
#Id
private String id;
private String jsonMessage;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getJsonMessage() {
return jsonMessage;
}
public void setJsonMessage(String jsonMessage) {
this.jsonMessage = jsonMessage;
}
}
#Document(
collection = "log_child"
)
public class LogChild extends Log{}
With the MongoOperations save method you can choose which class to use and
based on the class it will choose the appropriate collection.

#Document(collection = "collection_#{T(com.github.your_project.DBUtils).getCollectionName()}")
public Class Collection
You can change the name in real time using a static getter
#UtilityClass
public class DBUtils {
private String collectionName;
public String getCollectionName() {
return collectionName;
}
public void setCollectionName(String collectionName) {
DBUtils.collectionName = collectionName;
}
}

Persisting a Collection class with ORMLite in android

I have two classes setup like the following. I am confused as to when I need to annotate something as an foreign collection and when I do not. This may also sound silly, but nowhere in the ORMLite documentation does it say whether or not a non-foreign collection is allowed. What if I have a List of ints which get autoboxed into Integers? can I just persist this using a standard #DatabaseField above the Collection? A foreign collection, according to ORMLite, must also have back reference for it to work (a reference to the parent, given a one to many realtionship). For the example below, I am assuming you should annotate myBList as a foreign collection as well as making myA a foreign object, but how could you handle myStringList?
I Have seen sample code here but it doesn't answer my questions: http://ormlite.com/docs/examples
public class A {
private Set<B> myBList = new HashSet<B>();
private List<String> myStringList = new ArrayList<String>();
private long id;
public A(){}
public Set<B> getMyBList() {
return myBList;
}
public void setMyBList(Set<B> myBList) {
this.myBList = myBList;
}
public List<String> getMyStringList() {
return myStringList;
}
public void setMyStringList(List<String> myStringList) {
this.myStringList = myStringList;
}
public void setId(long id){
this.id = id;
}
public long getId(){
return id;
}
}
public class B {
private int myInt;
private String myString;
private A myA;
private long id;
public B(){}
public A getMyA(){
return myA;
}
public A setMyA(A a){
myA = a;
}
public int getMyInt() {
return myInt;
}
public void setMyInt(int myInt) {
this.myInt = myInt;
}
public String getMyString() {
return myString;
}
public void setMyString(String myString) {
this.myString = myString;
}
public void setId(long id){
this.id = id;
}
public long getId(){
return id;
}
}

#Robert is correct. When hibernate persists a collection (or even an array), it does so with hidden extra tables with foreign ids -- in other words hidden foreign collections. ORMLite tries to adhere to the KISS principle and so has you define the foreign collections "by hand" instead.
I've added more details about storing collections.
http://ormlite.com/docs/foreign-collection
This means that you cannot persist an Integer type because there is no foreign-id. Also, your code can define a foreign collection Collection<Order> or ForeignCollection<Order>. Either one will be set with a ForeignCollection. ORMLite does not support lists or other collection types.

If you want to save a Collection (such as an ArrayList) of objects to ORMLite the easiest way is this:
#DatabaseField(dataType = DataType.SERIALIZABLE)
private SerializedList<MyObject> myObjects;
and to get my list of objects:
public List<MyObject> getMyObjects() {
return myObjects;
}