Realm "cascade delete" on Android

Question

I did the search about "cascade delete" operation for the Realm. Sadly that feature has not been implemented yet. I made my own implementation of it and shared it here.

How to make generic code for the Realm "cascade delete" operation ?

Answer 1

1) Copy this code to your project

import android.util.Log;


import java.lang.reflect.Method;
import io.realm.RealmList;
import io.realm.RealmObject;
import com.company.project.models.IRealmCascade;

/**
 */

public class RealmUtils
{
public static void deleteCascade( RealmObject dataObject )
{
    if (dataObject == null)
    {
        return;
    }
    if( IRealmCascade.class.isAssignableFrom( dataObject.getClass() ) )
    {
        for( Method method : dataObject.getClass().getSuperclass().getDeclaredMethods() )
        {
            try {
                //Ignore generated methods
                if( (method.getName().contains("realmGet$")) || (method.getName().contains("access$super")) )
                {
                    continue;
                }
                Class<?> resultType = method.getReturnType();
                //Ignore non object members
                if (resultType.isPrimitive()) {
                    continue;
                }

                if (RealmObject.class.isAssignableFrom(resultType)) {
                    //Delete Realm object
                    try {
                        RealmObject childObject = (RealmObject) method.invoke(dataObject);
                        RealmUtils.deleteCascade(childObject);
                    } catch (Exception ex) {
                        Log.e("REALM", "CASCADE DELETE OBJECT: " + ex.toString());
                    }
                } else if (RealmList.class.isAssignableFrom(resultType)) {
                    //Delete RealmList items
                    try {
                        RealmList childList = (RealmList) method.invoke(dataObject);
                        while( childList.iterator().hasNext() )
                        {
                            RealmObject listItem = (RealmObject)childList.iterator().next();
                            RealmUtils.deleteCascade(listItem);
                        }
                    } catch (Exception ex) {
                        Log.e("REALM", "CASCADE DELETE LIST: " + ex.toString());
                    }
                }
            }
            catch (Exception ex)
            {
                Log.e("REALM", "CASCADE DELETE ITERATION: " + ex.toString());
            }
        }
    }
    dataObject.deleteFromRealm();
}

}

2) Add interface to your project. If your Realm object implement this interface all child objects will be deleted after call deleteCascade. If interface not implemented this function delete Realm object but don't delete child objects.

public interface IRealmCascade {
}

3) Declare your Realm object. Example below.

public class NodeModel extends RealmObject implements IRITSerializable, IRealmCascade {
    @PrimaryKey
    @SerializedName("id") private String objId;
    @SerializedName("parentId") private String parentId;
    @SerializedName("contentType") private String nodeType;
    @Required
    @SerializedName("name") private String name;

    @SerializedName("settings") private RealmList<ValueTypeModel> columns;

    public String getObjId() {
        return objId;
    }

    public void setObjId(String objId) {
        this.objId = objId;
    }

    public String getParentId() {
        return parentId;
    }

    public void setParentId(String parentId) {
        this.parentId = parentId;
    }

    public String getNodeType() {
        return nodeType;
    }

    public void setNodeType(String nodeType) {
        this.nodeType = nodeType;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public RealmList<ValueTypeModel> getColumns() {
        return columns;
    }

    public void setColumns(RealmList<ValueTypeModel> columns) {
        this.columns = columns;
    }
}

4) You need to call RealmUtils.deleteCascade(realmObject); instead realmObject.removeFromRealm(); Example below Update data in local database

for( NodeModel nodeItem: incomingData.getNodesList() )
{
    RealmResults<NodeModel> results = bgRealm.where(NodeModel.class).equalTo("objId", nodeItem.getObjId()).findAll();
    if (results.size() > 0)
    {
        RealmUtils.deleteCascade(results.first());
    }
    bgRealm.copyToRealm(nodeItem);
}

Enjoy your clean DB! :)