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Changes between Version 6 and Version 8 of IntroductionToWidgets


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Timestamp:
07/13/06 12:57:07 (13 years ago)
Author:
plewis
Comment:

revert to v4 (despam)

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  • IntroductionToWidgets

    v6 v8  
    1  
    21= Introduction =  
    32 
     
    65= The Fooball Application = 
    76 
    8 We're going to create a web application that tracks statistics for the entirely fictitious sport of "Fooball".  Fooball is a very simple game: players on teams do unspecified things to score as many points as possible before the end of the game. The team with the most points at the end wins. The player with the most points at the end gets lucrative sponsorship deals, but that's outside the scope of this tutorial. 
     7We're going to create a web application that tracks statistics for the entirely fictitious sport of "Fooball".  Fooball is a very simple game: players on teams do unspecified things to score as many points as possible before the end of the game. The team with the most points at the end wins. The player with the most points at the end gets lucrative sponsorship deals, but that's outside the scope of this tutorial. 
    98 
    109The front page will contain a list of teams and a list of all league players and their stats.  The list of teams will contain links to individual team pages, each listing stats for the players on that team.  Simple enough. 
    1110 
    12 I'll assume that you know enough TurboGears to "quickstart" the application; if not, see the TurboGears documentation. I'm going to quickstart the application using 'fooball' for both the application and module name, and I'll assume that you've properly configured the database connection in your "dev.cfg" file (I'm using an SQLite backend on Windows XP). 
    13  
    14 Now, let's define our data model in  
     11I'll assume that you know enough TurboGears to "quickstart" the application; if not, see the TurboGears documentation. I'm going to quickstart the application using 'fooball' for both the application and module name, and I'll assume that you've properly configured the database connection in your "dev.cfg" file (I'm using an SQLite backend on Windows XP). 
     12 
     13Now, let's define our data model in {{{model.py}}}: 
     14 
     15{{{ 
     16#!python 
     17import datetime 
     18 
     19class Player(SQLObject): 
     20   name = StringCol(length=40, alternateID=True) 
     21   birthdate = DateCol(notNull=True) 
     22 
     23   team = ForeignKey('Team') 
     24 
     25   points = IntCol(default=0) 
     26 
     27class Team(SQLObject): 
     28   city = StringCol(length=20, notNull=True) 
     29   nickname = StringCol(length=20, notNull=True, alternateID=True) 
     30    
     31   players = MultipleJoin('Player') 
     32}}} 
     33 
     34From the model, you can see that teams are uniquely identified by their nickname (although a city can host multiple teams), and all players forever belong to one team (Fooball players haven't discovered free agency yet, to the delight of Fooball team owners). 
     35 
     36We'll create the database using "tg-admin sql create", and define some data using "tg-admin shell". You could use !ModelDesigner and Catwalk to do this, but for simplicity we'll use the command line tools. 
     37 
     38{{{ 
     39#!python 
     40>>> import datetime 
     41>>> t1 = Team(city='Pittsburgh', nickname='Ferrous Metals') 
     42>>> t2 = Team(city='Seattle', nickname='Seagulls') 
     43>>> Player(name='Bob Waffleburger', birthdate=datetime.date(1982,3,2), team=t1, points=21) 
     44<Player 1 name='Bob Waffleburger' birthdate='datetime.date(198...)' teamID=1 points=21> 
     45>>> Player(name='Mike Handleback', birthdate=datetime.date(1975,9,25), team=t2, points=10) 
     46<Player 2 name='Mike Handleback' birthdate='datetime.date(197...)' teamID=2 points=10> 
     47>>> hub.commit() 
     48}}} 
     49 
     50Good enough for now. (Any resemblance to real teams, players, or final scores is purely coincidental, but I'm sure you knew that.) 
     51 
     52Now we'll cobble up a simple front page by editing the body of {{{\fooball\fooball\templates\welcome.kid}}}: 
     53 
     54{{{ 
     55<h1>International Fooball League Stats</h1> 
     56<h2>Teams</h2> 
     57<table border="1"> 
     58  <tr> 
     59    <th>City</th> 
     60    <th>Team Name</th> 
     61  </tr> 
     62  <tr py:for="team in teams"> 
     63    <td py:content="team.city"/> 
     64    <td py:content="team.nickname"/> 
     65  </tr> 
     66</table> 
     67 
     68<h2>Players</h2> 
     69<table border="1"> 
     70  <tr> 
     71    <th>Name</th> 
     72    <th>Birthdate</th> 
     73    <th>Team</th> 
     74    <th>Points</th> 
     75  </tr> 
     76  <tr py:for="player in players"> 
     77    <td py:content="player.name"/> 
     78    <td py:content="player.birthdate"/> 
     79    <td py:content="player.team"/> 
     80    <td py:content="player.points"/> 
     81  </tr> 
     82</table> 
     83}}} 
     84 
     85Since our template uses the {{{teams}}} and {{{players}}} variables, add them to the Root controller's index method in {{{controllers.py}}}: 
     86 
     87{{{ 
     88#!python 
     89from model import Team, Player 
     90 
     91class Root(controllers.RootController): 
     92    @expose(template="fooball.templates.welcome") 
     93    def index(self): 
     94        return dict(teams=Team.select(), 
     95                    players=Player.select()) 
     96}}} 
     97 
     98= The First Attempt = 
     99 
     100Now, start the app, and take a look at the front page: 
     101 
     102***screenshot*** 
     103 
     104Ugh.  Well, the teams look fine, but the players show an ugly SQLObject representation for their team name.  We could fix this by changing the {{{player.team}}} to {{{players.team.city}}}, but then we'd have to make sure we do it everywhere we want to show a {{{Player.team}}}.  And make sure we always do it the same way.  That's a recipe for mistakes. When programming, it's best to follow the maxim, "Don't Repeat Yourself". 
     105 
     106Instead, we'll tell the {{{Team}}} object how to display itself by adding a string-izing method to the class: 
     107 
     108{{{ 
     109#!python 
     110def __str__(self): 
     111    return "%s %s" % (self.city, self.nickname) 
     112}}} 
     113 
     114And look: reuse! We can get rid of that ugly "City/Name" table by doing the same thing there in the {{{welcome.kid}}} template: 
     115 
     116{{{ 
     117<h2>Teams</h2> 
     118<table border="1"> 
     119  <tr> 
     120    <th>Team</th> 
     121  </tr> 
     122  <tr py:for="team in teams"> 
     123    <td py:content="team"/> 
     124  </tr> 
     125</table> 
     126}}} 
     127 
     128***screenshot*** 
     129 
     130Much better. Now let's make pages for each team.  A new controller method will do the trick: 
     131 
     132{{{ 
     133#!python 
     134    @expose(template="fooball.templates.team") 
     135    def team(self, team_id, *args, **kw): 
     136        return dict(team=Team.get(int(team_id))) 
     137}}} 
     138 
     139With a new template called "team.kid", whose body looks like this: 
     140 
     141{{{ 
     142<h1 py:content="team"/> 
     143<h2>Players</h2> 
     144<table border="1"> 
     145  <tr> 
     146    <th>Name</th> 
     147    <th>Birthdate</th> 
     148    <th>Points</th> 
     149  </tr> 
     150  <tr py:for="player in team.players"> 
     151    <td py:content="player.name"/> 
     152    <td py:content="player.points"/> 
     153    <td py:content="player.birthdate"/> 
     154  </tr> 
     155</table> 
     156}}} 
     157 
     158And a way to get to the team page, courtesy of a quick change to the welcome template: 
     159 
     160{{{ 
     161<h2>Teams</h2> 
     162<table border="1"> 
     163  <tr> 
     164    <th>Team</th> 
     165  </tr> 
     166  <tr py:for="team in teams"> 
     167    <td><a href="${'/team/%d' % team.id}">${team}</a></td> 
     168  </tr> 
     169</table> 
     170}}} 
     171 
     172And... 
     173 
     174***welcome screenshot*** 
     175 
     176Ok, let's look at the team page for Pittsburgh: 
     177 
     178***team screenshot*** 
     179 
     180Whoops. Haha. I don't think "Big Bob" was born on 0, and he certainly didn't earn 1983-03-02=1975 points. When I typed the second table, I switched the order of two columns. 
     181 
     182This again illustrates the "Don't Repeat Yourself" point. Every time you write the same code again, you run the risk of introducing bugs. And if you want to change the way the table looks (say, by showing 'age' instead of 'birthday', you have to repeat the change each time. 
     183 
     184= Enter the Widget =  
     185 
     186Rather than retype (or copy and paste) that table every time we want to show a grid of players, let's create a reusable widget. We'll create the simplest possible widget that we can use in both the front page and the team page.  We'll add it to {{{controllers.py}}} for now: 
     187 
     188{{{ 
     189#!python 
     190from turbogears import widgets 
     191from model import Team, Player 
     192 
     193class SimpleRosterWidget(widgets.Widget): 
     194    template = ''' 
     195    <table xmlns:py="http://purl.org/kid/ns#" class="simpleroster" border="1"> 
     196      <tr> 
     197      <th>Name</th> 
     198        <th>Birthdate</th> 
     199        <th>Team</th> 
     200        <th>Points</th> 
     201      </tr> 
     202      <tr py:for="player in value"> 
     203        <td py:content="player.name"/> 
     204        <td py:content="player.birthdate"/> 
     205        <td py:content="player.team"/> 
     206        <td py:content="player.points"/> 
     207      </tr> 
     208    </table> 
     209''' 
     210}}} 
     211 
     212And that's it. Not a drop of code to be found. You'll note that the template references "value", which is the standard TurboGears name used to apply data to the widget. I also added a CSS class to the widget; I like to do that because it's easier to apply per-widget CSS styles down the road. 
     213 
     214Let's provide the widget in the controllers: 
     215 
     216{{{ 
     217#!python 
     218players_widget = SimpleRosterWidget() 
     219 
     220class Root(controllers.RootController): 
     221    @expose(template="fooball.templates.welcome") 
     222    def index(self): 
     223        return dict(teams=Team.select(), 
     224                    players=Player.select(), 
     225                    players_widget=players_widget) 
     226 
     227    @expose(template="fooball.templates.team") 
     228    def team(self, team_id, *args, **kw): 
     229        return dict(team=Team.get(int(team_id)), 
     230                    players_widget=players_widget) 
     231}}} 
     232 
     233And change the welcome template to use the widget: 
     234 
     235{{{ 
     236<h2>Players</h2> 
     237${players_widget.display(players)} 
     238}}} 
     239 
     240***screenshot*** 
     241 
     242= Template Parameters =  
     243 
     244This looks good so far. Let's do the same to the team template: 
     245 
     246{{{ 
     247<h2>Players</h2> 
     248${players_widget.display(team.players)} 
     249}}} 
     250 
     251***screenshot*** 
     252 
     253Hmm.  Well, it works, but it seems a bit silly to specify the team column for the team roster, since it will always be the same. We could create separate widgets for each page, but that defeats the reusability of widgets.  So let's add a parameter to the {{{SimpleRosterWidget}}} class to disable the team column: 
     254 
     255{{{ 
     256#!python 
     257class SimpleRosterWidget(widgets.Widget): 
     258    template_vars=['with_team'] 
     259     
     260    def __init__(self, with_team=True, *args, **kw): 
     261        super(SimpleRosterWidget,self).__init__(*args, **kw) 
     262        self.with_team=with_team 
     263         
     264    template = ''' 
     265    <table xmlns:py="http://purl.org/kid/ns#" class="simpleplayer" border="1"> 
     266      <tr> 
     267      <th>Name</th> 
     268        <th>Birthdate</th> 
     269        <th py:if="with_team">Team</th> 
     270        <th>Points</th> 
     271      </tr> 
     272      <tr py:for="player in value"> 
     273        <td py:content="player.name"/> 
     274        <td py:content="player.birthdate"/> 
     275        <td py:if="with_team" py:content="player.team"/> 
     276        <td py:content="player.points"/> 
     277      </tr> 
     278    </table> 
     279''' 
     280}}} 
     281 
     282There's a bit going on here: 
     283 
     284 * We added a class attribute called {{{template_vars}}} ('''NOTE''' 0.9a5 will call this same attribute {{{params}}}. It will issue a {{{DeprecationWarning}}} to remind you that you should update your code).  When TurboGears renders the template, it looks for this attribute. Any attribute names in this list that exist on the template instance will be added to the variables provided to the template.  So at render time, if the template has a {{{with_team}}} attribute, the template will be able to access it. 
     285  
     286 * We added an {{{__init__}}} method that calls the parent class ({{{Widget}}}, in this case), and stores the {{{with_team}}} argument (if any).  Since we don't want to worry about what the base class is, we use Python's {{{super}}} function, and since we don't want to worry about what arguments might be there, we use {{{*args}}} and {{{**kw}}} to pass along any extra positional or keyword arguments to the base class. 
     287  
     288 * Since we've added "with_team" to the template_vars, we can use its value to determine whether or not to display the team name: 
     289 
     290then inside the team template: 
     291 
     292{{{ 
     293<h2>Players</h2> 
     294${players_widget.display(team.players, with_team=False)} 
     295}}} 
     296 
     297***screenshot*** 
     298 
     299Great.  Now we're done.  
     300 
     301But, as Mr. Jobs is so fond of saying, there's "one more thing..." 
     302 
     303= Now, Don't Do That! = 
     304 
     305Now that you've seen how to create your own table-based, customizable widget, I'm going to tell you not to do that. Creating your own widgets is a fast and easy way to create reusable and customizable user interfaces, but if you're just doing a simple table layout like our roster grid, the TurboGears widgets library already gives you a great, pre-made widget: {{{DataGrid}}}. 
     306 
     307To use {{{DataGrid}}}, just change the {{{index}}} and {{{team}}} controller methods: 
     308 
     309{{{ 
     310#!python 
     311class Root(controllers.RootController): 
     312    @expose(template="fooball.templates.welcome") 
     313    def index(self): 
     314        player_fields = [('Name', 'name'), 
     315                         ('Birth Date', 'birthdate'), 
     316                         ('Team', 'team'), 
     317                         ('Points', 'points')] 
     318        return dict(teams=Team.select(), 
     319                    players=Player.select(), 
     320                    players_widget=widgets.DataGrid(fields=player_fields)) 
     321 
     322    @expose(template="fooball.templates.team") 
     323    def team(self, team_id, *args, **kw): 
     324        player_fields = [('Name', 'name'), 
     325                         ('Birth Date', 'birthdate'), 
     326                         ('Points', 'points')] 
     327        return dict(team=Team.get(int(team_id)), 
     328                    players_widget=widgets.DataGrid(fields=player_fields)) 
     329}}} 
     330 
     331Now you can delete your {{{SimpleRosterWidget}}}, and voila! Instant table widget: 
     332 
     333***screenshot*** 
     334 
     335Note that we didn't need to change the Kid template at all.  Like our {{{SimpleRosterGrid}}}, {{{DataGrid}}} is derived from {{{widgets.Widget}}}. That means that it gets called the same way (via the display call).  It uses the {{{fields}}} parameter to decide what to display. {{{fields}}} is a list of tuples; each tuple contains the header string and either a string or a callable object (like a function, for example).  
     336 
     337If you provide a string, the {{{DataGrid}}} uses it as an attribute name on data object. If you provide a callable object, {{{DataGrid}}} calls it, passing the data item as the only parameter. The callable can return either a string (which is escaped and displayed by Kid) or an {{{Element}}} (from the elementtree library), which is rendered and then displayed. 
     338 
     339That's a mouthful. Let's figure it out by converting our hand-coded teams table on the front page to a {{{DataGrid}}}. The nicely-styled players table is making it look unfashionably plain, anyway. 
     340 
     341Add this to the imports of controllers.py: 
     342 
     343{{{ 
     344#!python 
     345from elementtree import ElementTree 
     346}}} 
     347 
     348Now, just before the Root class definition, add a function to create a link ('a') {{{Element}}} from a {{{Team}}} object: 
     349 
     350{{{ 
     351#!python 
     352def makeTeamLink(team): 
     353    link = ElementTree.Element('a', 
     354                               href='/team/%d' % team.id) 
     355    link.text = team 
     356    return link 
     357}}} 
     358 
     359Add the teams widget to the index controller. Note that I'm using the {{{makeTeamLink}}} function itself as the field value for the team name, and not a call to the function: 
     360 
     361{{{ 
     362#!python 
     363class Root(controllers.RootController): 
     364    @expose(template="fooball.templates.welcome") 
     365    def index(self): 
     366        team_fields = [('Name', makeTeamLink)] 
     367        player_fields = [('Name', 'name'), 
     368                         ('Birth Date', 'birthdate'), 
     369                         ('Team', 'team'), 
     370                         ('Points', 'points')] 
     371         
     372        return dict(teams=Team.select(), 
     373                    teams_widget=widgets.DataGrid(fields=team_fields), 
     374                    players=Player.select(), 
     375                    players_widget=widgets.DataGrid(fields=player_fields)) 
     376}}} 
     377 
     378Now just make one quick change to the welcome template: 
     379 
     380{{{ 
     381<body> 
     382<h1>International Fooball League Stats</h1> 
     383<h2>Teams</h2> 
     384${teams_widget.display(teams)} 
     385<h2>Players</h2> 
     386${players_widget.display(players)} 
     387}}} 
     388 
     389***screenshot*** 
     390 
     391That's pretty. And we've taken just about all the HTML out of our controller, which is even better. 
     392 
     393Incidentally, if the visual style of {{{DataGrid}}} looks familiar, it is: it uses the same CSS-based styling as CatWalk. If you like that style, you get it for free just by using the {{{DataGrid}}}.  If not, you can always change it in your web app's own CSS. 
     394 
     395For example, I like links to look like links, and the default CSS fragment for DataGrid removes the underline decoration.  To fix this, just add a line to your application's stylesheet: 
     396 
     397{{{ 
     398.grid td a {text-decoration:underline} 
     399}}} 
    15400 
    16401= Conclusion = 
    17402 
    18 Widgets are a powerful addition to the TurboGears tool set. They ''can'' be complex to write and use (especially when you get into the &#34;form&#34; and &#34;fastdata&#34;) libraries, but they don't ''have'' to be. Wrapping custom display elements in simple widgets is quick and easy, and can help you develop faster and with fewer errors and display inconsistencies. 
     403Widgets are a powerful addition to the TurboGears tool set. They ''can'' be complex to write and use (especially when you get into the "form" and "fastdata") libraries, but they don't ''have'' to be. Wrapping custom display elements in simple widgets is quick and easy, and can help you develop faster and with fewer errors and display inconsistencies.