Visualforce Developer Guide

Introducing Visualforce
Tools for Visualforce Development
Getting a Quick Start with Visualforce
Customizing the Appearance and Output of Visualforce Pages
Standard Controllers
Standard List Controllers
Custom Controllers and Controller Extensions
What are Custom Controllers and Controller Extensions?
Building a Custom Controller
Building a Controller Extension
Building a Custom List Controller
Controller Methods
Controller Class Security
Working with Large Sets of Data
Setting Read-Only Mode for an Entire Page
Setting Read-Only Mode for Controller Methods
Considerations for Creating Custom Controllers and Controller Extensions
Order of Execution in a Visualforce Page
Testing Custom Controllers and Controller Extensions
Validation Rules and Custom Controllers
Using the transient Keyword
Advanced Examples
Overriding Buttons, Links, and Tabs with Visualforce
Using Static Resources
Creating and Using Custom Components
Dynamic Visualforce Bindings
Dynamic Visualforce Components
Integrating Email with Visualforce
Visualforce Charting
Creating Maps with Visualforce
Render Flows with Visualforce
Templating with Visualforce
Developing for Mobile Devices
Adding Visualforce to a Force.com AppExchange App
Using JavaScript in Visualforce Pages
Best Practices
Standard Component Reference
Appendices
Glossary
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Setting Read-Only Mode for an Entire Page

To enable read-only mode for an entire page, set the readOnly attribute on the <apex:page> component to true.

For example, here is a simple page that will be processed in read-only mode:

The controller for this page is also simple, but illustrates how you can calculate summary statistics for display on a page:

Normally, queries for a single Visualforce page request may not retrieve more than 50,000 rows. In read-only mode, this limit is relaxed to allow querying up to 1,000,000 rows.

In addition to querying many more rows, the readOnly attribute also increases the maximum number of items in a collection that can be iterated over using components such as <apex:dataTable>, <apex:dataList>, and <apex:repeat>. This limit increased from 1,000 items to 10,000. Here is a simple controller and page demonstrating this:

While Visualforce pages that use read-only mode for the entire page can’t use data manipulation language (DML) operations, they can call getter, setter, and action methods which affect form and other user interface elements on the page, make additional read-only queries, and so on.