import logging
from flask import Blueprint, session, flash, render_template
from .forms import GeneralModelConverter
from .widgets import FormWidget, ShowWidget, ListWidget, SearchWidget
from .actions import ActionItem
from .urltools import *

log = logging.getLogger(__name__)


def expose(url='/', methods=('GET',)):
    """
        Use this decorator to expose views on your view classes.
       
        :param url:
            Relative URL for the view
        :param methods:
            Allowed HTTP methods. By default only GET is allowed.
    """

    def wrap(f):
        if not hasattr(f, '_urls'):
            f._urls = []
        f._urls.append((url, methods))
        return f
    return wrap



class BaseView(object):
    """
        All views inherit from this class. it's constructor will register your exposed urls on flask as a Blueprint.

        This class does not expose any urls, but provides a common base for all views.
        
        Extend this class if you want to expose methods for your own templates        
    """

    appbuilder = None
    blueprint = None
    endpoint = None

    route_base = None
    """ Override this if you want to define your own relative url """

    template_folder = 'templates'
    """ The template folder relative location """
    static_folder = 'static'
    """  The static folder relative location """
    base_permissions = None
    """
        List with allowed base permission.
        Use it like this if you want to restrict your view to readonly::

            class MyView(ModelView):
                base_permissions = ['can_list','can_show']
    """

    default_view = 'list'
    """ the default view for this BaseView, to be used with url_for (method name) """
    extra_args = None
    """ dictionary for injecting extra arguments into template """

    def __init__(self):
        """
            Initialization of base permissions
            based on exposed methods and actions

            Initialization of extra args
        """
        if self.base_permissions is None:
            self.base_permissions = set()
            for attr_name in dir(self):
                if hasattr(getattr(self, attr_name), '_permission_name'):
                    permission_name = getattr(getattr(self, attr_name), '_permission_name')
                    self.base_permissions.add('can_' + permission_name)
            self.base_permissions = list(self.base_permissions)
        if not self.extra_args:
            self.extra_args = dict()

    def create_blueprint(self, appbuilder,
                         endpoint=None,
                         static_folder=None):
        """
            Create Flask blueprint. You will generally not use it
            
            :param appbuilder:
               the AppBuilder object
            :param endpoint:
               endpoint override for this blueprint, will assume class name if not provided
            :param static_folder:
               the relative override for static folder, if ommited application will use the appbuilder static
        """
        # Store appbuilder instance
        self.appbuilder = appbuilder

        # If endpoint name is not provided, get it from the class name
        self.endpoint = endpoint or self.__class__.__name__

        if self.route_base is None:
            self.route_base = '/' + self.__class__.__name__.lower()

        self.static_folder = static_folder
        if not static_folder:
            # Create blueprint and register rules
            self.blueprint = Blueprint(self.endpoint, __name__,
                                       url_prefix=self.route_base,
                                       template_folder=self.template_folder)
        else:
            self.blueprint = Blueprint(self.endpoint, __name__,
                                       url_prefix=self.route_base,
                                       template_folder=self.template_folder,
                                       static_folder=static_folder)
        self._register_urls()
        return self.blueprint

    def _register_urls(self):
        for attr_name in dir(self):
            attr = getattr(self, attr_name)
            if hasattr(attr, '_urls'):
                for url, methods in attr._urls:
                    self.blueprint.add_url_rule(url,
                                                attr_name,
                                                attr,
                                                methods=methods)

    def render_template(self, template, **kwargs):
        """
            Use this method on your own endpoints, will pass the extra_args
            to the templates.

            :param template: The template relative path
            :param kwargs: arguments to be passed to the template
        """
        kwargs['base_template'] = self.appbuilder.base_template
        kwargs['appbuilder'] = self.appbuilder
        return render_template(template, **dict(list(kwargs.items()) + list(self.extra_args.items())))

    def _prettify_name(self, name):
        """
            Prettify pythonic variable name.

            For example, 'HelloWorld' will be converted to 'Hello World'

            :param name:
                Name to prettify.
        """
        return re.sub(r'(?<=.)([A-Z])', r' \1', name)

    def _prettify_column(self, name):
        """
            Prettify pythonic variable name.

            For example, 'hello_world' will be converted to 'Hello World'

            :param name:
                Name to prettify.
        """
        return re.sub('[._]', ' ', name).title()

    def update_redirect(self):
        """
            Call it on your own endpoint's to update the back history navigation.
            If you bypass it, the next submit or back will go over it.
        """
        page_history = Stack(session.get('page_history', []))
        page_history.push(request.url)
        session['page_history'] = page_history.to_json()

    def get_redirect(self):
        """
            Returns the previous url.
        """
        index_url = self.appbuilder.get_url_for_index
        page_history = Stack(session.get('page_history', []))

        if page_history.pop() is None:
            return index_url
        session['page_history'] = page_history.to_json()
        url = page_history.pop() or index_url
        return url


class BaseModelView(BaseView):
    """
        The base class of ModelView and ChartView, all properties are inherited
        Customize ModelView and ChartView overriding this properties

        This class supports all the basics for query
    """

    datamodel = None
    """ 
        Your sqla model you must initialize it like::
        
            class MyView(ModelView):
                datamodel = SQLAModel(MyTable)
    """

    title = 'Title'

    search_columns = None
    """ 
        List with allowed search columns, if not provided all possible search columns will be used 
        If you want to limit the search (*filter*) columns possibilities, define it with a list of column names from your model::
        
            class MyView(ModelView):
                datamodel = SQLAModel(MyTable, db.session)
                search_columns = ['name','address']
             
    """
    label_columns = None
    """ 
        Dictionary of labels for your columns, override this if you want diferent pretify labels 
        
        example (will just override the label for name column)::
        
            class MyView(ModelView):
                datamodel = SQLAModel(MyTable, db.session)
                label_columns = {'name':'My Name Label Override'}
        
    """
    search_form = None
    """ To implement your own add WTF form for Search """
    base_filters = None
    """ 
        Filter the view use: [['column_name',BaseFilter,'value'],]
    
        example::
        
            def get_user():
                return g.user
        
            class MyView(ModelView):
                datamodel = SQLAModel(MyTable, db.session)
                base_filters = [['created_by', FilterEqualFunction, get_user],
                                ['name', FilterStartsWith, 'a']]
    
    """

    base_order = None
    """
        Use this property to set default ordering for lists ('col_name','asc|desc')::

            class MyView(ModelView):
                datamodel = SQLAModel(MyTable, db.session)
                base_order = ('my_column_name','asc')

    """
    search_widget = SearchWidget
    """ Search widget you can override with your own """

    _base_filters = None
    """ Internal base Filter from class Filters will always filter view """
    _filters = None
    """ Filters object will calculate all possible filter types based on search_columns """

    def __init__(self, **kwargs):
        """
            Constructor
        """
        datamodel = kwargs.get('datamodel', None)
        if datamodel:
            self.datamodel = datamodel
        self._init_properties()
        self._init_forms()
        self._init_titles()
        super(BaseModelView, self).__init__(**kwargs)

    def _gen_labels_columns(self, list_columns):
        """
            Auto generates pretty label_columns from list of columns
        """
        for col in list_columns:
            if not self.label_columns.get(col):
                self.label_columns[col] = self._prettify_column(col)

    def _init_titles(self):
        pass

    def _init_properties(self):
        self.label_columns = self.label_columns or {}
        self.base_filters = self.base_filters or []
        self._base_filters = self.datamodel.get_filters().add_filter_list(self.base_filters)
        list_cols = self.datamodel.get_columns_list()
        self.search_columns = self.search_columns or self.datamodel.get_search_columns_list()
        self._gen_labels_columns(list_cols)
        self._filters = self.datamodel.get_filters(self.search_columns)

    def _init_forms(self):
        conv = GeneralModelConverter(self.datamodel)
        if not self.search_form:
            self.search_form = conv.create_form(self.label_columns, self.search_columns)


    def _get_search_widget(self, form=None, exclude_cols=None, widgets=None):
        exclude_cols = exclude_cols or []
        widgets = widgets or {}
        widgets['search'] = self.search_widget(route_base=self.route_base,
                                               form=form,
                                               include_cols=self.search_columns,
                                               exclude_cols=exclude_cols,
                                               filters=self._filters
        )
        return widgets

    def _label_columns_json(self):
        """
            Prepares dict with labels to be JSON serializable
        """
        ret = {}
        for key, value in list(self.label_columns.items()):
            ret[key] = str(value)
        return ret



class BaseCRUDView(BaseModelView):
    """
        The base class for ModelView, all properties are inherited
        Customize ModelView overriding this properties
    """

    related_views = None
    """ 
        List with ModelView classes
        Will be displayed related with this one using relationship sqlalchemy property::

            class MyView(ModelView):
                datamodel = SQLAModel(Group, db.session)
                related_views = [MyOtherRelatedView]
                
    """
    _related_views = None
    """ internal list with ref to instantiated view classes """
    list_title = ""
    """ List Title, if not configured the default is 'List ' with pretty model name """
    show_title = ""
    """ Show Title , if not configured the default is 'Show ' with pretty model name """
    add_title = ""
    """ Add Title , if not configured the default is 'Add ' with pretty model name """
    edit_title = ""
    """ Edit Title , if not configured the default is 'Edit ' with pretty model name """

    list_columns = None
    """
        A list of columns (or model's methods) to be displayed on the list view.
        Use it to control the order of the display
    """
    show_columns = None
    """
        A list of columns (or model's methods) to be displayed on the show view.
        Use it to control the order of the display
    """
    add_columns = None
    """
        A list of columns (or model's methods) to be displayed on the add form view.
        Use it to control the order of the display
    """
    edit_columns = None
    """
        A list of columns (or model's methods) to be displayed on the edit form view.
        Use it to control the order of the display
    """
    order_columns = None
    """ Allowed order columns """

    page_size = 10
    """ 
        Use this property to change default page size 
    """

    show_fieldsets = None
    """ 
        show fieldsets django style [(<'TITLE'|None>, {'fields':[<F1>,<F2>,...]}),....]
        
        ::
        
            class MyView(ModelView):
                datamodel = SQLAModel(MyTable, db.session)

                show_fieldsets = [
                    ('Summary',{'fields':['name','address','group']}),
                    ('Personal Info',{'fields':['birthday','personal_phone'],'expanded':False}),
                    ]

    """
    add_fieldsets = None
    """ 
        add fieldsets django style (look at show_fieldsets for an example)
    """
    edit_fieldsets = None
    """ 
        edit fieldsets django style (look at show_fieldsets for an example)
    """

    description_columns = None
    """ 
        Dictionary with column descriptions that will be shown on the forms::
        
            class MyView(ModelView):
                datamodel = SQLAModel(MyTable, db.session)

                description_columns = {'name':'your models name column','address':'the address column'}
    """
    validators_columns = None
    """ Dictionary to add your own validators for forms """
    add_form_extra_fields = None
    """
        A dictionary containing column names and a WTForm
        Form fields to be added to the Add form, these fields do not
        exist on the model itself ex::

        extra_fields={'some_col':BooleanField('Some Col', default=False)}

    """
    edit_form_extra_fields = None
    """ Dictionary to add extra fields to the Edit form using this property """
    add_form_query_cascade = None
    """
        FUTURE FEATURE, Don't use it yet
        
        Implements query cascade related fields. Will user relate fields
        with multiple values.

        Grammar: [('Parent field','Child field', SQLAModel(ChildModel, Session),
                [['child field rel to parent',Filter,'parent'],...]),...]

            class ContactModelView(ModelView):
                datamodel = SQLAModel(Contact, db.session)
                add_form_query_cascade = [('model', 'manufacture'
                        SQLAModel(Product, db.session),
                        [['manufacture_id',FilterEqual,'id']]
                        )]

    """
    edit_form_query_cascade = None
    """
        FUTURE FEATURE, Don't use it yet
    """
    add_form_query_rel_fields = None
    """
        Add Customized query for related fields to add form.
        Assign a dictionary where the keys are the column names of
        the related models to filter, the value for each key, is a list of lists with the
        same format as base_filter
        {'relation col name':[['Related model col',FilterClass,'Filter Value'],...],...}
        Add a custom filter to form related fields::

            class ContactModelView(ModelView):
                datamodel = SQLAModel(Contact, db.session)
                add_form_query_rel_fields = [('group':[['name',FilterStartsWith,'W']]}

    """
    edit_form_query_rel_fields = None
    """
        Add Customized query for related fields to edit form.
        Assign a dictionary where the keys are the column names of
        the related models to filter, the value for each key, is a list of lists with the
        same format as base_filter
        {'relation col name':[['Related model col',FilterClass,'Filter Value'],...],...}
        Add a custom filter to form related fields::

            class ContactModelView(ModelView):
                datamodel = SQLAModel(Contact, db.session)
                add_form_query_rel_fields = [('group':[['name',FilterStartsWith,'W']]}

    """

    add_form = None
    """ To implement your own, assign WTF form for Add """
    edit_form = None
    """ To implement your own, assign WTF form for Edit """

    list_template = 'appbuilder/general/model/list.html'
    """ Your own add jinja2 template for list """
    edit_template = 'appbuilder/general/model/edit.html'
    """ Your own add jinja2 template for edit """
    add_template = 'appbuilder/general/model/add.html'
    """ Your own add jinja2 template for add """
    show_template = 'appbuilder/general/model/show.html'
    """ Your own add jinja2 template for show """

    list_widget = ListWidget
    """ List widget override """
    edit_widget = FormWidget
    """ Edit widget override """
    add_widget = FormWidget
    """ Add widget override """
    show_widget = ShowWidget
    """ Show widget override """

    actions = None

    def __init__(self, **kwargs):
        super(BaseCRUDView, self).__init__(**kwargs)
        # collect and setup actions
        self.actions = {}
        for attr_name in dir(self):
            func = getattr(self, attr_name)
            if hasattr(func, '_action'):
                action = ActionItem(*func._action, func=func)
                self.base_permissions.append(action.name)
                self.actions[action.name] = action

    def _init_forms(self):
        """
            Init forms for Add and Edit
        """
        super(BaseCRUDView, self)._init_forms()
        conv = GeneralModelConverter(self.datamodel)
        if not self.add_form:
            self.add_form = conv.create_form(self.label_columns,
                                             self.add_columns,
                                             self.description_columns,
                                             self.validators_columns,
                                             self.add_form_extra_fields,
                                             self.add_form_query_rel_fields)
        if not self.edit_form:
            self.edit_form = conv.create_form(self.label_columns,
                                              self.edit_columns,
                                              self.description_columns,
                                              self.validators_columns,
                                              self.edit_form_extra_fields,
                                              self.edit_form_query_rel_fields)

    def _init_titles(self):
        """
            Init Titles if not defined
        """
        super(BaseCRUDView, self)._init_titles()
        class_name = self.datamodel.model_name
        if not self.list_title:
            self.list_title = 'List ' + self._prettify_name(class_name)
        if not self.add_title:
            self.add_title = 'Add ' + self._prettify_name(class_name)
        if not self.edit_title:
            self.edit_title = 'Edit ' + self._prettify_name(class_name)
        if not self.show_title:
            self.show_title = 'Show ' + self._prettify_name(class_name)
        self.title = self.list_title

    def _init_properties(self):
        """
            Init Properties
        """
        super(BaseCRUDView, self)._init_properties()
        # Reset init props
        self.related_views = self.related_views or []
        self._related_views = self._related_views or []
        self.description_columns = self.description_columns or {}
        self.validators_columns = self.validators_columns or {}
        self.add_form_extra_fields = self.add_form_extra_fields or {}
        self.edit_form_extra_fields = self.edit_form_extra_fields or {}
        # Generate base props
        list_cols = self.datamodel.get_user_columns_list()
        self.list_columns = self.list_columns or [list_cols[0]]
        self._gen_labels_columns(self.list_columns)
        self.order_columns = self.order_columns or self.datamodel.get_order_columns_list(list_columns=self.list_columns)
        if self.show_fieldsets:
            self.show_columns = []
            for fieldset_item in self.show_fieldsets:
                self.show_columns = self.show_columns + list(fieldset_item[1].get('fields'))
        else:
            if not self.show_columns:
                self.show_columns = list_cols
        if self.add_fieldsets:
            self.add_columns = []
            for fieldset_item in self.add_fieldsets:
                self.add_columns = self.add_columns + list(fieldset_item[1].get('fields'))
        else:
            if not self.add_columns:
                self.add_columns = list_cols
        if self.edit_fieldsets:
            self.edit_columns = []
            for fieldset_item in self.edit_fieldsets:
                self.edit_columns = self.edit_columns + list(fieldset_item[1].get('fields'))
        else:
            if not self.edit_columns:
                self.edit_columns = list_cols

    """
    -----------------------------------------------------
            GET WIDGETS SECTION
    -----------------------------------------------------        
    """

    def _get_related_view_widget(self, item, related_view,
                                 order_column='', order_direction='',
                                 page=None, page_size=None):

        fk = related_view.datamodel.get_related_fk(self.datamodel.obj)
        filters = related_view.datamodel.get_filters()
        # Check if it's a many to one model relation
        if related_view.datamodel.is_relation_many_to_one(fk):
            filters.add_filter_related_view(fk, self.datamodel.FilterRelationOneToManyEqual,
                                        self.datamodel.get_pk_value(item))
        # Check if it's a many to many model relation
        elif related_view.datamodel.is_relation_many_to_many(fk):
            filters.add_filter_related_view(fk, self.datamodel.FilterRelationManyToManyEqual,
                                        self.datamodel.get_pk_value(item))
        else:
            log.error("Can't find relation on related view {0}".format(related_view.name))
            return None
        return related_view._get_view_widget(filters=filters,
                                             order_column=order_column,
                                             order_direction=order_direction,
                                             page=page, page_size=page_size)

    def _get_related_views_widgets(self, item, orders=None,
                                   pages=None, page_sizes=None,
                                   widgets=None, **args):
        """
            :return:
                Returns a dict with 'related_views' key with a list of
                Model View widgets
        """
        widgets = widgets or {}
        widgets['related_views'] = []
        for view in self._related_views:
            if orders.get(view.__class__.__name__):
                order_column, order_direction = orders.get(view.__class__.__name__)
            else:
                order_column, order_direction = '', ''
            widgets['related_views'].append(self._get_related_view_widget(item, view,
                                                                          order_column, order_direction,
                                                                          page=pages.get(view.__class__.__name__),
                                                                          page_size=page_sizes.get(
                                                                              view.__class__.__name__)))
        return widgets

    def _get_view_widget(self, **kwargs):
        """
            :return:
                Returns a Model View widget
        """
        return self._get_list_widget(**kwargs).get('list')

    def _get_list_widget(self, filters,
                         actions=None,
                         order_column='',
                         order_direction='',
                         page=None,
                         page_size=None,
                         widgets=None,
                         **args):

        """ get joined base filter and current active filter for query """
        widgets = widgets or {}
        actions = actions or self.actions
        page_size = page_size or self.page_size
        if not order_column and self.base_order:
            order_column, order_direction = self.base_order
        joined_filters = filters.get_joined_filters(self._base_filters)
        count, lst = self.datamodel.query(joined_filters, order_column, order_direction, page=page, page_size=page_size)
        pks = self.datamodel.get_keys(lst)
        widgets['list'] = self.list_widget(label_columns=self.label_columns,
                                           include_columns=self.list_columns,
                                           value_columns=self.datamodel.get_values(lst, self.list_columns),
                                           order_columns=self.order_columns,
                                           page=page,
                                           page_size=page_size,
                                           count=count,
                                           pks=pks,
                                           actions=actions,
                                           filters=filters,
                                           modelview_name=self.__class__.__name__)
        return widgets

    def _get_show_widget(self, id, widgets=None, actions=None, show_fieldsets=None):
        widgets = widgets or {}
        actions = actions or self.actions
        show_fieldsets = show_fieldsets or self.show_fieldsets
        item = self.datamodel.get(id)
        widgets['show'] = self.show_widget(pk=id,
                                           label_columns=self.label_columns,
                                           include_columns=self.show_columns,
                                           value_columns=self.datamodel.get_values_item(item, self.show_columns),
                                           actions=actions,
                                           fieldsets=show_fieldsets,
                                           modelview_name=self.__class__.__name__
        )
        return widgets


    def _get_add_widget(self, form, exclude_cols=None, widgets=None):
        exclude_cols = exclude_cols or []
        widgets = widgets or {}
        widgets['add'] = self.add_widget(form=form,
                                         include_cols=self.add_columns,
                                         exclude_cols=exclude_cols,
                                         fieldsets=self.add_fieldsets
        )
        return widgets

    def _get_edit_widget(self, form, exclude_cols=None, widgets=None):
        exclude_cols = exclude_cols or []
        widgets = widgets or {}
        widgets['edit'] = self.edit_widget(form=form,
                                           include_cols=self.edit_columns,
                                           exclude_cols=exclude_cols,
                                           fieldsets=self.edit_fieldsets
        )
        return widgets

    """
    -----------------------------------------------------
            CRUD functions behaviour
    -----------------------------------------------------        
    """
    def _list(self):
        """
            list function logic, override to implement different logic
            returns list and search widget
        """
        if get_order_args().get(self.__class__.__name__):
            order_column, order_direction = get_order_args().get(self.__class__.__name__)
        else:
            order_column, order_direction = '', ''
        page = get_page_args().get(self.__class__.__name__)
        page_size = get_page_size_args().get(self.__class__.__name__)
        get_filter_args(self._filters)
        widgets = self._get_list_widget(filters=self._filters,
                                        order_column=order_column,
                                        order_direction=order_direction,
                                        page=page,
                                        page_size=page_size)
        form = self.search_form.refresh()
        self.update_redirect()
        return self._get_search_widget(form=form, widgets=widgets)


    def _show(self, pk):
        """
            show function logic, override to implement diferent logic
            returns show and related list widget
        """
        pages = get_page_args()
        page_sizes = get_page_size_args()
        orders = get_order_args()

        widgets = self._get_show_widget(pk)
        item = self.datamodel.get(pk)
        self.update_redirect()
        return self._get_related_views_widgets(item, orders=orders,
                                               pages=pages, page_sizes=page_sizes, widgets=widgets)

    def _add(self):
        """
            Add function logic, override to implement diferent logic
            returns add widget or None
        """
        is_valid_form = True
        get_filter_args(self._filters)
        exclude_cols = self._filters.get_relation_cols()
        form = self.add_form.refresh()

        if request.method == 'POST':
            self._fill_form_exclude_cols(exclude_cols, form)
            if form.validate():
                item = self.datamodel.obj()
                form.populate_obj(item)
                self.pre_add(item)
                if self.datamodel.add(item):
                    self.post_add(item)
                flash(*self.datamodel.message)
                return None
            else:
                is_valid_form = False
        if is_valid_form:
            self.update_redirect()
        return self._get_add_widget(form=form, exclude_cols=exclude_cols)

    def _edit(self, pk):
        """
            Edit function logic, override to implement diferent logic
            returns Edit widget and related list or None
        """
        is_valid_form = True
        pages = get_page_args()
        page_sizes = get_page_size_args()
        orders = get_order_args()
        get_filter_args(self._filters)
        exclude_cols = self._filters.get_relation_cols()

        item = self.datamodel.get(pk)
        # convert pk to correct type, if pk is non string type.
        pk = self.datamodel.get_pk_value(item)

        if request.method == 'POST':
            form = self.edit_form.refresh(request.form)
            # fill the form with the suppressed cols, generated from exclude_cols
            self._fill_form_exclude_cols(exclude_cols, form)
            # trick to pass unique validation
            form._id = pk
            if form.validate():
                form.populate_obj(item)
                self.pre_update(item)
                if self.datamodel.edit(item):
                    self.post_update(item)
                flash(*self.datamodel.message)
                return None
            else:
                is_valid_form = False
        else:
            # Only force form refresh for select cascade events
            form = self.edit_form.refresh(obj=item)
        widgets = self._get_edit_widget(form=form, exclude_cols=exclude_cols)
        widgets = self._get_related_views_widgets(item, filters={},
                                                  orders=orders, pages=pages, page_sizes=page_sizes, widgets=widgets)
        if is_valid_form:
            self.update_redirect()
        return widgets

    def _delete(self, pk):
        """
            Delete function logic, override to implement diferent logic
            deletes the record with primary_key = pk

            :param pk:
                record primary key to delete
        """
        item = self.datamodel.get(pk)
        self.pre_delete(item)
        if self.datamodel.delete(item):
            self.post_delete(item)
        flash(*self.datamodel.message)
        self.update_redirect()

    """
    ------------------------------------------------
                HELPER FUNCTIONS
    ------------------------------------------------
    """

    def _fill_form_exclude_cols(self, exclude_cols, form):
        """
            fill the form with the suppressed cols, generated from exclude_cols
        """
        for filter_key in exclude_cols:
            filter_value = self._filters.get_filter_value(filter_key)
            rel_obj = self.datamodel.get_related_obj(filter_key, filter_value)
            field = getattr(form, filter_key)
            field.data = rel_obj


    def pre_update(self, item):
        """
            Override this, will be called before update
        """
        pass

    def post_update(self, item):
        """
            Override this, will be called after update
        """
        pass

    def pre_add(self, item):
        """
            Override this, will be called before add
        """
        pass

    def post_add(self, item):
        """
            Override this, will be called after update
        """
        pass

    def pre_delete(self, item):
        """
            Override this, will be called before delete
        """
        pass

    def post_delete(self, item):
        """
            Override this, will be called after delete
        """
        pass
