Combination of JsonMerge and JsonManagedReference fails

[miguelocarvajal]

I have an issue where if I use a List with both JsonMerge and JsonManagedReference annotations, the back reference is null.

I came up with the following test case:

Test class

package com.carvajalonline;

import java.util.List;

import com.fasterxml.jackson.databind.ObjectMapper;

public class Test {
    public static void main(String[] args) {
        ObjectMapper objectMapper = new ObjectMapper();

        try {
            Invoice invoice = objectMapper.readValue("{\"lines\": [{\"id\": 20, \"total\": \"$200.00\"}]}", Invoice.class);

            List<InvoiceLine> lines = invoice.getLines();
            for (InvoiceLine invoiceLine : lines) {
                System.out.println("line: " + invoiceLine.getId() + " - " + invoiceLine.getInvoice());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Invoice class

package com.carvajalonline;

import java.util.ArrayList;
import java.util.List;

import com.fasterxml.jackson.annotation.JsonManagedReference;
import com.fasterxml.jackson.annotation.JsonMerge;

public class Invoice {
    @JsonManagedReference("invoice")
    @JsonMerge
    private List<InvoiceLine> lines = new ArrayList<>();

    public Invoice() {
        lines.add(new InvoiceLine(10, "$100.00", this));
    }

    public List<InvoiceLine> getLines() {
        return lines;
    }

    public void setLines(List<InvoiceLine> lines) {
        this.lines = lines;
    }
}

InvoiceLine class

package com.carvajalonline;

import com.fasterxml.jackson.annotation.JsonBackReference;

public class InvoiceLine {
    private Integer id;
    private String total;
    @JsonBackReference("invoice")
    private Invoice invoice;

    public InvoiceLine() {

    }

    public InvoiceLine(Integer id, String total, Invoice invoice) {
        this.id = id;
        this.total = total;
        this.invoice = invoice;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getTotal() {
        return total;
    }

    public void setTotal(String total) {
        this.total = total;
    }

    public Invoice getInvoice() {
        return invoice;
    }

    public void setInvoice(Invoice invoice) {
        this.invoice = invoice;
    }
}

I expect the output to be:

line: 10 - com.carvajalonline.Invoice@XXXX line: 20 - com.carvajalonline.Invoice@XXXX

However, when I introduce the JsonMerge annotation, the output I get is: line: 10 - com.carvajalonline.Invoice@XXXX line: 20 - null (SHOULD NOT BE GETTING NULL HERE)

If I remove the JsonMerge annotation, I get this output line: 20 - com.carvajalonline.Invoice@XXXX

Obviously when the JsonMerge annotation is removed, line 10 no longer appears because the array is being replaced, however the invoice is no longer null.

I am using version 2.9.5 to produce this bug. Any pointers as to how this can be handled?

Thanks!

[miguelocarvajal]

Dug through the code and it seems the problem is in MergingSettableBeanProperty.

Since it doesn't call the delegate, because it expects the null provider to do so from what I gather. If I add the annotation @JsonSetter(nulls = Nulls.SKIP) to the @JsonManagedReference above, I get the following error:

java.lang.IllegalStateException: Should never try to reset delegate
    at com.fasterxml.jackson.databind.deser.impl.ManagedReferenceProperty.withDelegate(ManagedReferenceProperty.java:43)
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty$Delegating._with(SettableBeanProperty.java:663)
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty$Delegating.withNullProvider(SettableBeanProperty.java:678)
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty$Delegating.withNullProvider(SettableBeanProperty.java:678)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase._resolveMergeAndNullSettings(BeanDeserializerBase.java:919)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.resolve(BeanDeserializerBase.java:516)
    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:293)
    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:244)
    at com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:142)
    at com.fasterxml.jackson.databind.DeserializationContext.findRootValueDeserializer(DeserializationContext.java:477)
    at com.fasterxml.jackson.databind.ObjectMapper._findRootDeserializer(ObjectMapper.java:4190)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4009)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3004)

Just for testing I removed all of the if (value != null) checks in MergingSettableBeanProperty and removed the @JsonSetter(nulls = Nulls.SKIP) annotation and it works.

I am sure this is not the correct solution. Any thoughts?

[dududen]

in 2.14.2 version problem continues, any updates?

[cowtowncoder]

2.14.2 is an old version; should perhaps test with 2.17.1 (latest release).

But as a general rule: if issue has not updates, there is no update. This is likely the case here too. I am not aware of any back channels where updates would be made; fixes/changes should be reflected on issue.

One thing that would help here would be a proper test case (unit test) -- code sample uses print statements for manual verification; those would need to become assertions.

Beyond that, I am not sure combination of @JsonMerge and @JsonManagedReference can be made to work: it may be challenging to combine them.