我搜索了关于 Realm 的“级联删除”操作。遗憾的是，该功能尚未实现。我自己实现了它并在此处分享。

如何为 Realm 的“级联删除”操作编写通用代码？

最佳答案

1) 将这段代码复制到你的项目中

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) 为您的项目添加接口(interface)。如果您的 Realm 对象实现了此接口(interface)，则在调用 deleteCascade 后所有子对象都将被删除。如果接口(interface)未实现此功能，则删除 Realm 对象但不删除子对象。

public interface IRealmCascade {
}

3) 声明您的 Realm 对象。示例如下。

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) 你需要调用RealmUtils.deleteCascade(realmObject);代替 realmObject.removeFromRealm(); 下面的例子 更新本地数据库中的数据

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);
}

享受干净的数据库吧! :)

关于android - Android 上的 Realm "cascade delete"，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/36992703/