appypod-rattail/fields/ref.py

# ------------------------------------------------------------------------------
# This file is part of Appy, a framework for building applications in the Python
# language. Copyright (C) 2007 Gaetan Delannay

# Appy is free software; you can redistribute it and/or modify it under the
# terms of the GNU General Public License as published by the Free Software
# Foundation; either version 3 of the License, or (at your option) any later
# version.

# Appy is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE. See the GNU General Public License for more details.

# You should have received a copy of the GNU General Public License along with
# Appy. If not, see <http://www.gnu.org/licenses/>.

# ------------------------------------------------------------------------------
import sys, re
from appy.fields import Field, No
from appy.px import Px
from appy.gen.layout import Table
from appy.gen import utils as gutils
from appy.shared import utils as sutils

# ------------------------------------------------------------------------------
class Ref(Field):
    # Some default layouts. "w" stands for "wide": those layouts produce tables
    # of Ref objects whose width is 100%.
    wLayouts = Table('lrv-f', width='100%')
    # "d" stands for "description": a description label is added.
    wdLayouts = {'view': Table('l-d-f', width='100%')}

    # This PX displays the title of a referenced object, with a link on it to
    # reach the consult view for this object. If we are on a back reference, the
    # link allows to reach the correct page where the forward reference is
    # defined. If we are on a forward reference, the "nav" parameter is added to
    # the URL for allowing to navigate from one object to the next/previous on
    # ui/view.
    pxObjectTitle = Px('''
     <x var="navInfo='ref.%s.%s:%s.%d.%d' % (zobj.UID(), field.name, \
               field.pageName, loop.ztied.nb + startNumber, totalNumber);
             navInfo=not field.isBack and navInfo or '';
             cssClass=ztied.getCssFor('title')">
      <x>::ztied.getSupTitle(navInfo)</x>
      <a var="pageName=field.isBack and field.back.pageName or 'main';
              fullUrl=ztied.getUrl(page=pageName, nav=navInfo)"
         href=":fullUrl" class=":cssClass">:(not includeShownInfo) and \
         ztied.Title() or field.getReferenceLabel(ztied.appy())
      </a><span name="subTitle" style=":showSubTitles and 'display:inline' or \
            'display:none'">::ztied.getSubTitle()"</span>
     </x>''')

    # This PX displays icons for triggering actions on a given referenced object
    # (edit, delete, etc).
    pxObjectActions = Px('''
     <table class="noStyle" var="isBack=field.isBack">
      <tr>
       <!-- Arrows for moving objects up or down -->
       <td if="not isBack and (len(zobjects)&gt;1) and changeOrder and canWrite"
          var2="objectIndex=field.getIndexOf(zobj, ztied);
                ajaxBaseCall=navBaseCall.replace('**v**','%s,%s,{%s:%s,%s:%s}'%\
                  (q(startNumber), q('ChangeRefOrder'), q('refObjectUid'),
                   q(ztied.UID()), q('move'), q('**v**')))">
        <img if="objectIndex &gt; 0" class="clickable" src=":url('arrowUp')"
             title=":_('move_up')"
             onclick=":ajaxBaseCall.replace('**v**', 'up')"/>
        <img if="objectIndex &lt; (totalNumber-1)" class="clickable"
             src=":url('arrowDown')" title=":_('move_down')"
             onclick=":ajaxBaseCall.replace('**v**', 'down')"/>
       </td>
       <!-- Workflow transitions -->
       <td if="ztied.showTransitions('result')"
           var2="targetObj=ztied">:targetObj.appy().pxTransitions</td>
       <!-- Edit -->
       <td if="not field.noForm and ztied.mayEdit() and field.delete">
        <a var="navInfo='ref.%s.%s:%s.%d.%d' % (zobj.UID(), field.name, \
                        field.pageName, loop.ztied.nb+startNumber, totalNumber)"
           href=":ztied.getUrl(mode='edit', page='main', nav=navInfo)">
         <img src=":url('edit')" title=":_('object_edit')"/></a>
       </td>
       <!-- Delete -->
       <td if="not isBack and field.delete and canWrite and ztied.mayDelete()">
        <img class="clickable" title=":_('object_delete')" src=":url('delete')"
             onclick=":'onDeleteObject(%s)' % q(ztied.UID())"/>
       </td>
       <!-- Unlink -->
       <td if="not isBack and field.unlink and canWrite">
        <img class="clickable" title=":_('object_unlink')" src=":url('unlink')"
             onclick=":'onUnlinkObject(%s,%s,%s)' % (q(zobj.UID()), \
                        q(field.name), q(ztied.UID()))"/>
       </td>
      </tr>
     </table>''')

    # Displays the button allowing to add a new object through a Ref field, if
    # it has been declared as addable and if multiplicities allow it.
    pxAdd = Px('''
      <input if="showPlusIcon" type="button" class="button"
        var2="navInfo='ref.%s.%s:%s.%d.%d' % (zobj.UID(), \
                field.name, field.pageName, 0, totalNumber);
              formCall='goto(%s)' % \
                q('%s/do?action=Create&amp;className=%s&amp;nav=%s' % \
                  (folder.absolute_url(), linkedPortalType, navInfo));
              formCall=not field.addConfirm and formCall or \
                'askConfirm(%s,%s,%s)' % (q('script'), q(formCall), \
                                          q(addConfirmMsg));
              noFormCall=navBaseCall.replace('**v**', \
                           '%d,%s' % (startNumber, q('CreateWithoutForm')));
              noFormCall=not field.addConfirm and noFormCall or \
                'askConfirm(%s, %s, %s)' % (q('script'), q(noFormCall), \
                                            q(addConfirmMsg))"
        style=":url('buttonAdd', bg=True)" value=":_('add_ref')"
        onclick=":field.noForm and noFormCall or formCall"/>''')

    # This PX displays, in a cell header from a ref table, icons for sorting the
    # ref field according to the field that corresponds to this column.
    pxSortIcons = Px('''
     <x if="changeOrder and canWrite and ztool.isSortable(field.name, \
            zobjects[0].meta_type, 'ref')"
        var2="ajaxBaseCall=navBaseCall.replace('**v**', '%s,%s,{%s:%s,%s:%s}'% \
               (q(startNumber), q('SortReference'), q('sortKey'), \
                q(field.name), q('reverse'), q('**v**')))">
      <img class="clickable" src=":url('sortAsc')"
           onclick=":ajaxBaseCall.replace('**v**', 'False')"/>
      <img class="clickable" src=":url('sortDesc')"
           onclick=":ajaxBaseCall.replace('**v**', 'True')"/>
     </x>''')

    # This PX is called by a XmlHttpRequest (or directly by pxView) for
    # displaying the referred objects of a reference field.
    pxViewContent = Px('''
     <div var="field=zobj.getAppyType(req['fieldName']);
               innerRef=req.get('innerRef', False) == 'True';
               ajaxHookId=zobj.UID() + field.name;
               startNumber=int(req.get('%s_startNumber' % ajaxHookId, 0));
               info=field.getLinkedObjects(zobj, startNumber);
               zobjects=info.objects;
               totalNumber=info.totalNumber;
               batchSize=info.batchSize;
               batchNumber=len(zobjects);
               folder=zobj.getCreateFolder();
               linkedPortalType=ztool.getPortalType(field.klass);
               canWrite=not field.isBack and zobj.allows(field.writePermission);
               showPlusIcon=zobj.mayAddReference(field.name);
               atMostOneRef=(field.multiplicity[1] == 1) and \
                            (len(zobjects)&lt;=1);
               addConfirmMsg=field.addConfirm and \
                             _('%s_addConfirm' % field.labelId) or '';
               navBaseCall='askRefField(%s,%s,%s,%s,**v**)' % \
                            (q(ajaxHookId), q(zobj.absolute_url()), \
                             q(field.name), q(innerRef));
               changeOrder=field.changeOrderEnabled(zobj);
               showSubTitles=req.get('showSubTitles', 'true') == 'true'"
          id=":ajaxHookId">

      <!-- The definition of "atMostOneRef" above may sound strange: we
           shouldn't check the actual number of referenced objects. But for
           back references people often forget to specify multiplicities. So
           concretely, multiplicities (0,None) are coded as (0,1). -->
      <!-- Display a simplified widget if at most 1 referenced object. -->
      <table if="atMostOneRef">
       <tr valign="top">
        <!-- If there is no object -->
        <x if="not zobjects">
         <td class="discreet">:_('no_ref')</td>
         <td>:field.pxAdd</td>
        </x>
        <!-- If there is an object -->
        <x if="zobjects">
         <td for="ztied in zobjects"
             var2="includeShownInfo=True">:field.pxObjectTitle</td>
        </x>
       </tr>
      </table>

      <!-- Display a table in all other cases -->
      <x if="not atMostOneRef">
       <div if="not innerRef or showPlusIcon" style="margin-bottom: 4px">
        (<x>:totalNumber</x>)
        <x>:field.pxAdd</x>
        <!-- The search button if field is queryable -->
        <input if="zobjects and field.queryable" type="button" class="button"
               style=":url('buttonSearch', bg=True)" value=":_('search_title')"
               onclick=":'goto(%s)' % \
                 q('%s/ui/search?className=%s&amp;ref=%s:%s' % \
                 (ztool.absolute_url(), linkedPortalType, zobj.UID(), \
                  field.name))"/>
       </div>

       <!-- Appy (top) navigation -->
       <x>:obj.pxAppyNavigate</x>

       <!-- No object is present -->
       <p class="discreet" if="not zobjects">:_('no_ref')</p>

       <table if="zobjects" class=":innerRef and 'innerAppyTable' or ''"
              width="100%">
        <tr valign="bottom">
         <td>
          <!-- Show forward or backward reference(s) -->
          <table class="not innerRef and 'list' or ''"
                 width=":innerRef and '100%' or field.layouts['view']['width']"
                 var="columns=zobjects[0].getColumnsSpecifiers(\
                        field.shownInfo, dir)">
           <tr if="field.showHeaders">
            <th for="column in columns" width=":column['width']"
                align="column['align']"
                var2="field=column['field']">
             <span>:_(field.labelId)</span>
             <x>:field.pxSortIcons</x>
             <x var="className=linkedPortalType">:obj.pxShowDetails</x>
            </th>
           </tr>
           <tr for="ztied in zobjects" valign="top"
               class=":loop.ztied.odd and 'even' or 'odd'">
            <td for="column in columns"
                width=":column['width']" align=":column['align']"
                var2="field=column['field']">
             <!-- The "title" field -->
             <x if="python: field.name == 'title'">
              <x>:field.pxObjectTitle</x>
              <div if="ztied.mayAct()">:field.pxObjectActions</div>
             </x>
             <!-- Any other field -->
             <x if="field.name != 'title'">
              <x var="zobj=ztied; obj=ztied.appy(); layoutType='cell';
                      innerRef=True"
                 if="zobj.showField(field.name, \
                                    layoutType='result')">:field.pxView</x>
             </x>
            </td>
           </tr>
          </table>
         </td>
        </tr>
       </table>

       <!-- Appy (bottom) navigation -->
       <x>:obj.pxAppyNavigate</x>
      </x>
     </div>''')

    pxView = pxCell = Px('''
     <x var="x=req.set('fieldName', field.name)">:field.pxViewContent</x>''')

    pxEdit = Px('''
     <select if="field.link"
             var2="requestValue=req.get(name, []);
                   inRequest=req.has_key(name);
                   zobjects=field.getSelectableObjects(obj);
                   uids=[o.UID() for o in \
                         field.getLinkedObjects(zobj).objects];
                   isBeingCreated=zobj.isTemporary()"
             name=":name" size="isMultiple and field.height or ''"
             multiple="isMultiple and 'multiple' or ''">
      <option value="" if="not isMultiple">:_('choose_a_value')"></option>
      <option for="ztied in zobjects" var2="uid=ztied.o.UID()"
              selected=":inRequest and (uid in requestValue) or \
                                       (uid in uids)"
              value=":uid">:field.getReferenceLabel(ztied)</option>
     </select>''')

    pxSearch = Px('''<x>
     <label lfor=":widgetName">:_(field.labelId)"></label><br/>&nbsp;&nbsp;
     <!-- The "and" / "or" radio buttons -->
     <x if="field.multiplicity[1] != 1"
        var2="operName='o_%s' % name;
              orName='%s_or' % operName;
              andName='%s_and' % operName">
      <input type="radio" name=":operName" id=":orName" checked="checked"
             value="or"/>
      <label lfor=":orName">:_('search_or')"></label>
      <input type="radio" name=":operName" id=":andName" value="and"/>
      <label lfor=":andName">:_('search_and')"></label><br/>
     </x>
     <!-- The list of values -->
     <select name=":widgetName" size=":field.sheight" multiple="multiple">
      <option for="v in ztool.getSearchValues(name, className)"
              var2="uid=v[0]; title=field.getReferenceLabel(v[1])" value=":uid"
              title=":title">:ztool.truncateValue(title,field.swidth)"></option>
     </select>
    </x>''')

    def __init__(self, klass=None, attribute=None, validator=None,
                 multiplicity=(0,1), default=None, add=False, addConfirm=False,
                 delete=None, noForm=False, link=True, unlink=None, back=None,
                 show=True, page='main', group=None, layouts=None,
                 showHeaders=False, shownInfo=(), select=None, maxPerPage=30,
                 move=0, indexed=False, searchable=False,
                 specificReadPermission=False, specificWritePermission=False,
                 width=None, height=5, maxChars=None, colspan=1, master=None,
                 masterValue=None, focus=False, historized=False, mapping=None,
                 label=None, queryable=False, queryFields=None, queryNbCols=1,
                 navigable=False, searchSelect=None, changeOrder=True,
                 sdefault='', scolspan=1, swidth=None, sheight=None):
        self.klass = klass
        self.attribute = attribute
        # May the user add new objects through this ref ?
        self.add = add
        # When the user adds a new object, must a confirmation popup be shown?
        self.addConfirm = addConfirm
        # May the user delete objects via this Ref?
        self.delete = delete
        if delete == None:
            # By default, one may delete objects via a Ref for which one can
            # add objects.
            self.delete = bool(self.add)
        # If noForm is True, when clicking to create an object through this ref,
        # the object will be created automatically, and no creation form will
        # be presented to the user.
        self.noForm = noForm
        # May the user link existing objects through this ref?
        self.link = link
        # May the user unlink existing objects?
        self.unlink = unlink
        if unlink == None:
            # By default, one may unlink objects via a Ref for which one can
            # link objects.
            self.unlink = bool(self.link)
        self.back = None
        if back:
            # It is a forward reference
            self.isBack = False
            # Initialise the backward reference
            self.back = back
            self.backd = back.__dict__
            back.isBack = True
            back.back = self
            back.backd = self.__dict__
            # klass may be None in the case we are defining an auto-Ref to the
            # same class as the class where this field is defined. In this case,
            # when defining the field within the class, write
            # myField = Ref(None, ...)
            # and, at the end of the class definition (name it K), write:
            # K.myField.klass = K
            # setattr(K, K.myField.back.attribute, K.myField.back)
            if klass: setattr(klass, back.attribute, back)
        # When displaying a tabular list of referenced objects, must we show
        # the table headers?
        self.showHeaders = showHeaders
        # When displaying referenced object(s), we will display its title + all
        # other fields whose names are listed in the following attribute.
        self.shownInfo = list(shownInfo)
        if not self.shownInfo: self.shownInfo.append('title')
        # If a method is defined in this field "select", it will be used to
        # filter the list of available tied objects.
        self.select = select
        # Maximum number of referenced objects shown at once.
        self.maxPerPage = maxPerPage
        # Specifies sync
        sync = {'view': False, 'edit':True}
        # If param p_queryable is True, the user will be able to perform queries
        # from the UI within referenced objects.
        self.queryable = queryable
        # Here is the list of fields that will appear on the search screen.
        # If None is specified, by default we take every indexed field
        # defined on referenced objects' class.
        self.queryFields = queryFields
        # The search screen will have this number of columns
        self.queryNbCols = queryNbCols
        # Within the portlet, will referred elements appear ?
        self.navigable = navigable
        # The search select method is used if self.indexed is True. In this
        # case, we need to know among which values we can search on this field,
        # in the search screen. Those values are returned by self.searchSelect,
        # which must be a static method accepting the tool as single arg.
        self.searchSelect = searchSelect
        # If changeOrder is False, it even if the user has the right to modify
        # the field, it will not be possible to move objects or sort them.
        self.changeOrder = changeOrder
        Field.__init__(self, validator, multiplicity, default, show, page,
                       group, layouts, move, indexed, False,
                       specificReadPermission, specificWritePermission, width,
                       height, None, colspan, master, masterValue, focus,
                       historized, sync, mapping, label, sdefault, scolspan,
                       swidth, sheight)
        self.validable = self.link

    def getDefaultLayouts(self):
        return {'view': Table('l-f', width='100%'), 'edit': 'lrv-f'}

    def isShowable(self, obj, layoutType):
        res = Field.isShowable(self, obj, layoutType)
        if not res: return res
        # We add here specific Ref rules for preventing to show the field under
        # some inappropriate circumstances.
        if (layoutType == 'edit') and \
           (self.mayAdd(obj) or not self.link): return False
        if self.isBack:
            if layoutType == 'edit': return False
            else: return getattr(obj.aq_base, self.name, None)
        return res

    def getValue(self, obj, type='objects', noListIfSingleObj=False,
                 startNumber=None, someObjects=False):
        '''Returns the objects linked to p_obj through this Ref field.
           - If p_type is "objects",  it returns the Appy wrappers;
           - If p_type is "zobjects", it returns the Zope objects;
           - If p_type is "uids",     it returns UIDs of objects (= strings).

           * If p_startNumber is None, it returns all referred objects.
           * If p_startNumber is a number, it returns self.maxPerPage objects,
             starting at p_startNumber.

           If p_noListIfSingleObj is True, it returns the single reference as
           an object and not as a list.

           If p_someObjects is True, it returns an instance of SomeObjects
           instead of returning a list of references.'''
        uids = getattr(obj.aq_base, self.name, [])
        if not uids:
            # Maybe is there a default value?
            defValue = Field.getValue(self, obj)
            if defValue:
                # I must prefix call to function "type" with "__builtins__"
                # because this name was overridden by a method parameter.
                if __builtins__['type'](defValue) in sutils.sequenceTypes:
                    uids = [o.o.UID() for o in defValue]
                else:
                    uids = [defValue.o.UID()]
        # Prepare the result: an instance of SomeObjects, that will be unwrapped
        # if not required.
        res = gutils.SomeObjects()
        res.totalNumber = res.batchSize = len(uids)
        batchNeeded = startNumber != None
        if batchNeeded:
            res.batchSize = self.maxPerPage
        if startNumber != None:
            res.startNumber = startNumber
        # Get the objects given their uids
        i = res.startNumber
        while i < (res.startNumber + res.batchSize):
            if i >= res.totalNumber: break
            # Retrieve every reference in the correct format according to p_type
            if type == 'uids':
                ref = uids[i]
            else:
                ref = obj.getTool().getObject(uids[i])
                if type == 'objects':
                    ref = ref.appy()
            res.objects.append(ref)
            i += 1
        # Manage parameter p_noListIfSingleObj
        if res.objects and noListIfSingleObj:
            if self.multiplicity[1] == 1:
                res.objects = res.objects[0]
        if someObjects: return res
        return res.objects

    def getLinkedObjects(self, obj, startNumber=None):
        '''Gets the objects linked to p_obj via this Ref field. If p_startNumber
           is None, all linked objects are returned. If p_startNumber is a
           number, self.maxPerPage objects will be returned, starting at
           p_startNumber.'''
        return self.getValue(obj, type='zobjects', someObjects=True,
                             startNumber=startNumber)

    def getFormattedValue(self, obj, value, showChanges=False):
        return value

    def getIndexType(self): return 'ListIndex'

    def getIndexValue(self, obj, forSearch=False):
        '''Value for indexing is the list of UIDs of linked objects. If
           p_forSearch is True, it will return a list of the linked objects'
           titles instead.'''
        if not forSearch:
            res = getattr(obj.aq_base, self.name, [])
            if res:
                # The index does not like persistent lists.
                res = list(res)
            else:
                # Ugly catalog: if I return an empty list, the previous value
                # is kept.
                res.append('')
            return res
        else:
            # For the global search: return linked objects' titles.
            res = [o.title for o in self.getValue(type='objects')]
            if not res: res.append('')
            return res

    def validateValue(self, obj, value):
        if not self.link: return None
        # We only check "link" Refs because in edit views, "add" Refs are
        # not visible. So if we check "add" Refs, on an "edit" view we will
        # believe that that there is no referred object even if there is.
        # If the field is a reference, we must ensure itself that multiplicities
        # are enforced.
        if not value:
            nbOfRefs = 0
        elif isinstance(value, basestring):
            nbOfRefs = 1
        else:
            nbOfRefs = len(value)
        minRef = self.multiplicity[0]
        maxRef = self.multiplicity[1]
        if maxRef == None:
            maxRef = sys.maxint
        if nbOfRefs < minRef:
            return obj.translate('min_ref_violated')
        elif nbOfRefs > maxRef:
            return obj.translate('max_ref_violated')

    def linkObject(self, obj, value, back=False):
        '''This method links p_value (which can be a list of objects) to p_obj
           through this Ref field.'''
        # p_value can be a list of objects
        if type(value) in sutils.sequenceTypes:
            for v in value: self.linkObject(obj, v, back=back)
            return
        # Gets the list of referred objects (=list of uids), or create it.
        obj = obj.o
        refs = getattr(obj.aq_base, self.name, None)
        if refs == None:
            refs = obj.getProductConfig().PersistentList()
            setattr(obj, self.name, refs)
        # Insert p_value into it.
        uid = value.o.UID()
        if uid not in refs:
            # Where must we insert the object? At the start? At the end?
            if callable(self.add):
                add = self.callMethod(obj, self.add)
            else:
                add = self.add
            if add == 'start':
                refs.insert(0, uid)
            else:
                refs.append(uid)
            # Update the back reference
            if not back: self.back.linkObject(value, obj, back=True)

    def unlinkObject(self, obj, value, back=False):
        '''This method unlinks p_value (which can be a list of objects) from
           p_obj through this Ref field.'''
        # p_value can be a list of objects
        if type(value) in sutils.sequenceTypes:
            for v in value: self.unlinkObject(obj, v, back=back)
            return
        obj = obj.o
        refs = getattr(obj.aq_base, self.name, None)
        if not refs: return
        # Unlink p_value
        uid = value.o.UID()
        if uid in refs:
            refs.remove(uid)
            # Update the back reference
            if not back: self.back.unlinkObject(value, obj, back=True)

    def store(self, obj, value):
        '''Stores on p_obj, the p_value, which can be:
           * None;
           * an object UID (=string);
           * a list of object UIDs (=list of strings). Generally, UIDs or lists
             of UIDs come from Ref fields with link:True edited through the web;
           * a Zope object;
           * a Appy object;
           * a list of Appy or Zope objects.'''
        # Standardize p_value into a list of Zope objects
        objects = value
        if not objects: objects = []
        if type(objects) not in sutils.sequenceTypes: objects = [objects]
        tool = obj.getTool()
        for i in range(len(objects)):
            if isinstance(objects[i], basestring):
                # We have a UID here
                objects[i] = tool.getObject(objects[i])
            else:
                # Be sure to have a Zope object
                objects[i] = objects[i].o
        uids = [o.UID() for o in objects]
        # Unlink objects that are not referred anymore
        refs = getattr(obj.aq_base, self.name, None)
        if refs:
            i = len(refs)-1
            while i >= 0:
                if refs[i] not in uids:
                    # Object having this UID must unlink p_obj
                    self.back.unlinkObject(tool.getObject(refs[i]), obj)
                i -= 1
        # Link new objects
        if objects:
            self.linkObject(obj, objects)

    def mayAdd(self, obj):
        '''May the user create a new referred object from p_obj via this Ref?'''
        # We can't (yet) do that on back references.
        if self.isBack: return No('is_back')
        # Check if this Ref is addable
        if callable(self.add):
            add = self.callMethod(obj, self.add)
        else:
            add = self.add
        if not add: return No('no_add')
        # Have we reached the maximum number of referred elements?
        if self.multiplicity[1] != None:
            refCount = len(getattr(obj, self.name, ()))
            if refCount >= self.multiplicity[1]: return No('max_reached')
        # May the user edit this Ref field?
        if not obj.allows(self.writePermission): return No('no_write_perm')
        # Have the user the correct add permission?
        tool = obj.getTool()
        addPermission = '%s: Add %s' % (tool.getAppName(),
                                        tool.getPortalType(self.klass))
        folder = obj.getCreateFolder()
        if not obj.getUser().has_permission(addPermission, folder):
            return No('no_add_perm')
        return True

    def checkAdd(self, obj):
        '''Compute m_mayAdd above, and raise an Unauthorized exception if
           m_mayAdd returns False.'''
        may = self.mayAdd(obj)
        if not may:
            from AccessControl import Unauthorized
            raise Unauthorized("User can't write Ref field '%s' (%s)." % \
                               (self.name, may.msg))

    def changeOrderEnabled(self, obj):
        '''Is changeOrder enabled?'''
        if isinstance(self.changeOrder, bool):
            return self.changeOrder
        else:
            return self.callMethod(obj, self.changeOrder)

    def getSelectableObjects(self, obj):
        '''This method returns the list of all objects that can be selected to
           be linked as references to p_obj via p_self.'''
        if not self.select:
            # No select method has been defined: we must retrieve all objects
            # of the referred type that the user is allowed to access.
            return obj.search(self.klass)
        else:
            return self.select(obj)

    xhtmlToText = re.compile('<.*?>', re.S)
    def getReferenceLabel(self, refObject):
        '''p_self must have link=True. I need to display, on an edit view, the
           p_refObject in the listbox that will allow the user to choose which
           object(s) to link through the Ref. The information to display may
           only be the object title or more if self.shownInfo is used.'''
        res = ''
        for fieldName in self.shownInfo:
            refType = refObject.o.getAppyType(fieldName)
            value = getattr(refObject, fieldName)
            value = refType.getFormattedValue(refObject.o, value)
            if refType.type == 'String':
                if refType.format == 2:
                    value = self.xhtmlToText.sub(' ', value)
                elif type(value) in sequenceTypes:
                    value = ', '.join(value)
            prefix = ''
            if res:
                prefix = ' | '
            res += prefix + value
        maxWidth = self.width or 30
        if len(res) > maxWidth:
            res = res[:maxWidth-2] + '...'
        return res

    def getIndexOf(self, obj, refObj):
        '''Gets the position of p_refObj within this field on p_obj.'''
        uids = getattr(obj.aq_base, self.name, None)
        if not uids: raise IndexError()
        return uids.index(refObj.UID())

def autoref(klass, field):
    '''klass.field is a Ref to p_klass. This kind of auto-reference can't be
       declared in the "normal" way, like this:

       class A:
           attr1 = Ref(A)

       because at the time Python encounters the static declaration
       "attr1 = Ref(A)", class A is not completely defined yet.

       This method allows to overcome this problem. You can write such
       auto-reference like this:

       class A:
           attr1 = Ref(None)
       autoref(A, A.attr1)
    '''
    field.klass = klass
    setattr(klass, field.back.attribute, field.back)
# ------------------------------------------------------------------------------