To Lecture Notes

Some ActiveRecord Examples

• Sometimes you want to display only some of the information in a database.

• Try out the following ActiveRecord method calls in Example 26 (DisplayGradeData Example). Replace the controller line
  

  @a = GradeRecord.all
  

  a line similar to one of the following.
  

  # Find all of the rows in the database.  Long version of previous line:
  @a =GradeRecord.find(:all)
  
  # Find first student in database.  A GradeRecord object is returned.
  @a = GradeRecord.find(:first)
  @a = GradeRecord.first
  
  # Find last student in database.  A GradeRecord object is returned.
  @a = GradeRecord.find(:last)
  @s = GradeRecord.last
  

• Here are some various finds with conditions. You can use :first or :last instead of :all if you wish:
  

  # Find all grade records with credit_hours >= 2.
  @a = GradeRecord.find(:all, :conditions => 'credit_hours >= 2')
  
  # Find the student with stud_id == 3423.
  @a = GradeRecord.find(:all, :condition => 'stud_id = 3423')
  
  # Shortcut for previous statement.
  @a = GradeRecord.where(:stud_id => 3423)
  
  # Previous statement using a dynamic finder.
  @a = GradeRecord.find_all_by_stud_id(3423)
  
  # Sort by grade.
  @a = GradeRecord.find(:all, :order => 'grade')
  
  # Sort by descending grade.
  @a = GradeRecord.find(:all, :order => 'gpa desc')
  
  # Sort by gpa, with secondary sort on student_id.
  # Sorting by student_id only matters when there is a tie for gpa.
  @a = GradeRecord.find(:all, :order => 'stud_id, grade')
  

• You can include both :conditions and :order within the same find statement.
   
• See Example 26 (DisplayGradeData Example).