1 ==========================
2 HTML Templating Mechanisms
3 ==========================
5 :Version: $Revision: 1.12 $
7 Current Situation and Issues
8 ============================
10 Syntax
11 ------
13 Roundup currently uses an element-based HTML-tag-alike templating syntax::
15 <display call="checklist('status')">
17 The templates were initially parsed using recursive regular expression
18 parsing, and since no template tag could encapsulate itself, the parser
19 worked just fine. Then we got the ``<require>`` tag, which could have other
20 ``<require>`` tags inside. This forced us to move towards a more complete
21 parser, using the standard python sgmllib/htmllib parser. The downside of this
22 switch is that constructs of the form::
24 <tr class="row-<display call="plain('status')">">
26 don't parse as we'd hope. We can modify the parser to work, but that doesn't
27 another couple of issues that have arisen:
29 1. the template syntax is not well-formed, and therefore is a pain to parse
30 and doesn't play well with other tools, and
31 2. user requirements generally have to be anticipated and accounted for in
32 templating functions (like ``plain()`` and ``checklist()`` above), and
33 we are therefore artificially restrictive.
35 Arguments for switching templating systems:
37 *Pros*
39 - more flexibility in templating control and content
40 - we can be well-formed
42 *Cons*
44 - installed user base (though they'd have to edit their templates with the
45 next release anyway)
46 - current templating system is pretty trivial, and a more flexible system
47 is likely to be more complex
50 Templates
51 ---------
53 We should also take this opportunity to open up the flexibility of the
54 templates through:
56 1. allowing the instance to define a "page" template, which holds the overall
57 page structure, including header and footer
61 Possible approaches
62 ===================
64 Zope's PageTemplates
65 --------------------
67 Using Zope's PageTemplates seems to be the best approach of the lot.
68 In my opinion, it's the peak of HTML templating technology at present. With
69 appropriate infrastructure, the above two examples would read:
71 <span tal:replace="item/status/checklist">status checklist</span>
73 <tr tal:attributes="class string:row-${item/status/name}">
75 ... which doesn't look that much more complicated... honest...
77 Other fun can be had when you start playing with stuff like:
79 <table>
80 <tr tal:repeat="message item/msg/list">
81 <td tal:define="from message/from">
82 <a href="" tal:attributes="href string:mailto:${from/address}"
83 tal:content="from/name">mailto link</a>
84 </td>
85 <td tal:content="message/title">subject</td>
86 <td tal:content="message/created">received date</td>
87 </tr>
88 </table>
90 Note: even if we don't switch templating as a whole, this document may be
91 applied to the ZRoundup frontend.
93 PageTemplates in a Nutshell
94 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
96 PageTemplates consist of three technologies:
98 TAL - Template Attribute Language
99 This is the syntax which is woven into the HTML using the ``tal:`` tag
100 attributes. A TAL parser pulls out the TAL commands from the attributes
101 runs them using some expression engine.
103 TALES - TAL Expression Syntax
104 The expression engine used in this case is TALES, which runs the expressions
105 that form the tag attribute values. TALES expressions come in three
106 flavours:
108 Path Expressions - eg. ``item/status/checklist``
109 These are object attribute / item accesses. Roughly speaking, the path
110 ``item/status/checklist`` is broken into parts ``item``, ``status``
111 and ``checklist``. The ``item`` part is the root of the expression.
112 We then look for a ``status`` attribute on ``item``, or failing that, a
113 ``status`` item (as in ``item['status']``). If that
114 fails, the path expression fails. When we get to the end, the object we're
115 left with is evaluated to get a string - methods are called, objects are
116 stringified. Path expressions may have an optional ``path:`` prefix, though
117 they are the default expression type, so it's not necessary.
119 String Expressions - eg. ``string:hello ${user/name}``
120 These expressions are simple string interpolations (though they can be just
121 plain strings with no interpolation if you want. The expression in the
122 ``${ ... }`` is just a path expression as above.
124 Python Expressions - eg. ``python: 1+1``
125 These expressions give the full power of Python. All the "root level"
126 variables are available, so ``python:item.status.checklist()`` would be
127 equivalent to ``item/status/checklist``, assuming that ``checklist`` is
128 a method.
130 PageTemplates
131 The PageTemplates module glues together TAL and TALES.
134 Implementation
135 ~~~~~~~~~~~~~~
137 I'm envisaging an infrastructure layer where each template has the following
138 "root level" (that is, directly accessible in the TALES namespace) variables
139 defined:
141 *class*
142 The current class of node being displayed as an HTMLClass instance
144 *item*
145 The current node from the database, if we're viewing a specific node, as an
146 HTMLItem instance. If it doesn't exist, then we're on a new item page.
148 (*classname*)
149 this is one of two things:
151 1. the *item* is also available under its classname, so a *user* node
152 would also be available under the name *user*. This is also an HTMLItem
153 instance.
154 2. if there's no *item* then the current class is available through this
155 name, thus "user/name" and "user/name/menu" will still work - the latter
156 will pull information from the form if it can.
158 this is a dangerous attribute, and may cause us pain the long run (its name
159 may clash with other top-level variables ... it already clashed with the
160 proposed *user* variable). It might be safer to go with just *class* and
161 *item*, actually...
163 *form*
164 The current CGI form information as a mapping of form argument name to value
166 *request*
167 Includes information about the current request, including:
168 - the url
169 - the current index information (``filterspec``, ``filter`` args,
170 ``properties``, etc) parsed out of the form.
171 - methods for easy filterspec link generation
172 - *user*, the current user node as an HTMLItem instance
174 *instance*
175 The current instance
177 *db*
178 The current open database
180 *config*
181 The current instance config
183 *modules*
184 python modules made available (XXX: not sure what's actually in there tho)
186 Accesses through a class (either through *class* or *db.<classname>*)::
188 class HTMLClass:
189 def __getattr__(self, attr):
190 ''' return an HTMLItem instance '''
191 def classhelp(self, ...)
192 def list(self, ...)
193 def filter(self):
194 ''' Return a list of items from this class, filtered and sorted
195 by the current requested filterspec/filter/sort/group args
196 '''
198 Accesses through an *item*::
200 class HTMLItem:
201 def __getattr__(self, attr):
202 ''' return an HTMLItem instance '''
203 def history(self, ...)
204 def remove(self, ...)
206 Note: the above could cause problems if someone wants to have properties
207 called "history" or "remove"...
209 String, Number, Date, Interval HTMLProperty
210 a wrapper object which may be stringified for the current plain() behaviour
211 and has methods emulating all the current display functions, so
212 ``item/name/plain`` would emulate the current ``call="plain()``". Also,
213 ``python:item.name.plain(name=value)`` would work just fine::
215 class HTMLProperty:
216 def __init__(self, instance, db, ...)
217 def __str__(self):
218 return self.plain()
220 class StringHTMLProperty(HTLProperty):
221 def plain(self, ...)
222 def field(self, ...)
223 def stext(self, ...)
224 def multiline(self, ...)
225 def email(self, ...)
227 class NumberHTMLProperty(HTMLProperty):
228 def plain(self, ...)
229 def field(self, ...)
231 class BooleanHTMLProperty(HTMLProperty):
232 def plain(self, ...)
233 def field(self, ...)
235 class DateHTMLProperty(HTMLProperty):
236 def plain(self, ...)
237 def field(self, ...)
238 def reldate(self, ...)
240 class IntervalHTMLProperty(HTMLProperty):
241 def plain(self, ...)
242 def field(self, ...)
243 def pretty(self, ...)
245 Link HTMLProperty
246 the wrapper object would include the above as well as being able to access
247 the class information. Stringifying the object itself would result in the
248 value from the item being displayed. Accessing attributes of this object
249 would result in the appropriate entry from the class being queried for the
250 property accessed (so item/assignedto/name would look up the user entry
251 identified by the assignedto property on item, and then the name property of
252 that user)::
254 class LinkHTMLProperty(HTMLProperty):
255 ''' Be a HTMLItem too '''
256 def __getattr__(self, attr):
257 ''' return a new HTMLProperty '''
258 def download(self, ...)
259 def checklist(self, ...)
261 Multilink HTMLProperty
262 the wrapper would also be iterable, returning a wrapper object like the Link
263 case for each entry in the multilink::
265 class MultilinkHTMLProperty(HTMLProperty):
266 def __len__(self):
267 ''' length of the multilink '''
268 def __getitem(self, num):
269 ''' return a new HTMLItem '''
270 def checklist(self, ...)
271 def list(self, ...)
273 *request*
274 the request object will handle::
276 class Request:
277 def __init__(self, ...)
278 def filterspec(self, ...)
280 Accesses through the *user* attribute of *request*::
282 class HTMLUser(HTMLItem):
283 def hasPermission(self, ...)
285 (note that the other permission check implemented by the security module may
286 be implemented easily in a tal:condition, so isn't needed here)
288 Template files
289 ~~~~~~~~~~~~~~
291 Each instance will have the opportunity to supply the following templates:
293 page
294 This is the overall page look template, and includes at some point a TAL
295 command that includes the variable "content". This variable causes the actual
296 page content to be generated.
298 [classname].[template type]
299 Templates that have this form are applied to item data. There are three forms
300 of special template types:
302 [classname].index
303 This template is used when the URL specifies only the class, and not a node
304 designator. It displays a list of [classname] items from the database, and
305 a "filter refinement" form.
306 Would perform a TAL ``repeat`` command using the list supplied by
307 ``class/filter``. This deviates from the current situation in that currently
308 the index template specifies a single row, and the filter part is
309 automatically generated.
311 [classname].item
312 This template is used when the URL specifies an item designator. It's the
313 default template used (when no template is explicitly given). It displays
314 a single item from the database using the *classname* variable (that
315 is, the variable of the same name as the class being displayed. If
317 These two special template types may be overridden by the :template CGI
318 variable.
320 Note that the "newitem" template doesn't exist any more because the item
321 templates may determine whether the page has an existing item to render. The
322 new item page would be accessed by "/tracker/url/issue?:template=item".
323 The old "filter" template has been subsumed by the index template.
326 Integrating Code
327 ~~~~~~~~~~~~~~~~
329 We will install PageTemplates, TAL and ZTUtils in site-packages. If there is a
330 local Zope installation, it will use its own PageTemplates code (Zope modifies
331 the module search path to give precedence to its own module library).
333 We will then install the trivial MultiMapping and ComputedAttribute modules in
334 the Roundup package, and have some import trickery that determines whether
335 they are required, and if so they will be imported as if they were at the
336 "top level" of the module namespace.
338 New CGI client structure
339 ~~~~~~~~~~~~~~~~~~~~~~~~
341 Handling of a request in the CGI client will take three phases:
343 1. Determine user, pre-set "content" to authorisation page if necessary
344 2. Render main page, with callback to "content"
345 3. Render content - if not pre-set, then determine which content to render
348 Use Cases
349 ~~~~~~~~~
351 Meta/parent bug
352 Can be done with addition to the schema and then the actual parent heirarchy
353 may be displayed with a new template page ":dependencies" or something.
355 Submission wizard
356 Can be done using new templates ":page1", ":page2", etc and some additional
357 actions on the CGI Client class in the instance.