Code-pattern for Creating Mind-blowing Tabular Reports on Visualforce (With Sample code)

Salesforce.com has a mind-blowing reporting structure but it limits on data that is available on the system. Can we report on Data that is not present in the system?
For e.g., in a time-sheet management system, can we identify the people who have not filled time-sheets for a particular day? Can we report on data that is not present in the system? Can we identify records that are not created?

There is one thing I have learned working on Force.com platform for last 7 years, there is No No answer in Salesforce. Think a little bit and the answer will reach you. It is somewhat like climbing mount Everest, can you do it? Sure yes, in how many days depends on how fit I am (or how crazy I am)

Ok that Everest thing came up because someone did ask me that a few weeks back, moving on. Someone did also ask me about creating a report on missing details and I gave it a thought. The short answer is Yes we can, the long answer is we write a Visualforce page, anyone can tell you that. But what I really wanted to do was create a reusable code that I could use for a generic tabular report component.

The code is fairly simple, the pseudo code for the code is.
1. Generate a set of String for Rows
2. Generate a set of String for Columns
3. Prepare a map with Key as Row+Column and store the data accordingly.
4. Create a Dynamic table on Visualforce.

Apex Class for the page

public with sharing class TabularReportController {
    
    public Set rows{get;set;}
    public Set Cols {get;set;}
    public Map dataMap {get;set;}

 public TabularReportController(){
  prepareDataForReport();
 }

  public string getURLParam(String paramName){
            return ApexPages.currentPage().getParameters().get(paramName);
 }
 
 //Get the data for the rows
 public Map getrow(){
     return new Map([Select id, name, Accountid from Contact]);
 }
 
 
 //Get the data for the columns
 public Map getColumns(){
       return new Map([Select id, name from Account]);
 }


    //This is where the magic happens
 public void prepareDataForReport(){
     rows= new Set();
     cols= new Set();
     dataMap= new Map();
     Map columnsData=getColumns();
     Map rowData= getRow();
     
     //Geronimo
     for(Account a: columnsData.values()){
         cols.add(a.name);
         for(Contact c: rowData.values()){
             rows.add(c.name);
             String key= a.name+c.name; //Key is the key in which we set the data that we want to display.
                //Do some hazy logic here. This is where the key lies, you perfom your calculations and simply prepare the data
                //For display
                //For this example I am going to check if Contact is related to account
                if(c.accountid==a.id){
                    dataMap.put(key,'Related');
                }else{
                    dataMap.put(key,'Unrelated');
                }
         }
     }
     
 }
}

Visualforce page for the code

 <apex:page controller="TabularReportController" sidebar="false">  
 <style type="text/css">  
      .Related {  
            background-color: #0B610B;  
            color: #FBF8EF !important;  
      }  
      .Unrelated{  
            background-color: #A4A4A4;  
      }  
   </style>  
 <apex:sectionHeader title="Documents" subtitle="Report"/>  
 <apex:form >  
 <apex:pageBlock id="TheTable" title="Are the Accounts and Contact related?">  
 <table border="0" cellpadding="2" cellspacing="2" style="table-layout:auto" class="list">  
      <colgroup span="2"></colgroup>   
      <thead class="">  
      <tr class=" headerRow">  
           <th class=" headerRow" scope="col" colspan="1">Contact</th>            
           <apex:repeat value="{!rows}" var="row">  
           <th class=" headerRow">{!row}</th>  
      </apex:repeat>  
      </tr>  
 </thead>  
  <tbody >  
 <apex:repeat value="{!cols}" var="col">  
 <tr class="dataRow">  
      <td class="dataCell" colspan="1" style="white-space:nowrap"><span>{!col}</span></td>  
      <apex:repeat value="{!rows}" var="row" >  
&lt;!-- This is the Key, so to speak, for the entire page. Generating the key on the visualforce page --&gt;
      <apex:variable var="key" value="{!col}{!row}"/>  
      <td class="{!dataMap[key]}">{!dataMap[key]}</td>       
 </apex:repeat>  
 </tr>  
 </apex:repeat>  
 </tbody>  
 </table>  
 </apex:pageBlock>  
 </apex:form>  
 </apex:page>  

You can see the output of the report here

You can enhance the code using the same structure. Here are couple different thing I tried

1. Adding a link to the data using wrapper
2. Model window editing for the data
3. Adding complex many to many relationships
4. Plotting records that are not present

The list can go on.