Cannot get unfetched attribute [group] from detached object error for manytoone relatation with sec$Group

I have my own table, and I add manytoone relationship to cuba.security.entity.Group.

    @Lookup(type = LookupType.SCREEN)
    @ManyToOne(fetch = FetchType.EAGER, optional = false)
    @JoinColumn(name = "GROUP_ID")
    protected Group group;

    public void setGroup(Group group) {
        this.group = group;
    }

    public Group getGroup() {
        return group;
    }

And in my webview code, I use pickerfield to select Group:

<pickerField id="code_group" metaClass="sec$Group"/> 

And i have my own code to save it to database:

            PickerField codeGroup = (PickerField) editBox.getComponent(CODE_GROUP);
            Group group = codeGroup.getValue();
            editedItem.setGroup(group);

It works and datasaved, I can edit this row successfully in entityInspector.browse page.

But while I try to edit it in my own code, it raise error: Cannot get unfetched attribute [group] from detached object.

I searched other topic, seems it related with view “_local”, but my page using view I created:

    <view class="cn.com.dataocean.cip.entity.ExcelTable"
          extends="_local"
          name="excelTable-view"
          systemProperties="true"/>

how to solve it?

The error detail is:

java.lang.IllegalStateException: Cannot get unfetched attribute [group] from detached object cn.com.dataocean.cip.entity.ExcelTable-63aa7dfe-5175-9976-9542-e880e8824968 [detached].
	at org.eclipse.persistence.internal.queries.EntityFetchGroup.onUnfetchedAttribute(EntityFetchGroup.java:98)
	at com.haulmont.cuba.core.sys.persistence.CubaEntityFetchGroup.onUnfetchedAttribute(CubaEntityFetchGroup.java:61)
	at org.eclipse.persistence.internal.jpa.EntityManagerImpl.processUnfetchedAttribute(EntityManagerImpl.java:2846)
	at com.haulmont.chile.core.model.impl.AbstractInstance._persistence_checkFetched(AbstractInstance.java)
	at cn.com.dataocean.cip.entity.ExcelTable._persistence_get_group(ExcelTable.java)
	at cn.com.dataocean.cip.entity.ExcelTable.getGroup(ExcelTable.java:102)

I fixed it by rewrite the view:

    <view class="cn.com.dataocean.cip.entity.ExcelTable"
          extends="_local"
          name="excelTable-view-with-group"
          systemProperties="true">
          <property name="group"
                  view="_minimal"/>
    </view>