Object Relational Mapping/Code Generation

The rest of this article will show you how to generate criteria class and how to use it with examples.

Generating Criteria Class

1. Let's assume you have the following class diagram:

• 

2. Synchronize the class diagram to ERD and generate code by using the Database Code Generation dialog box. On the Database Code Generation dialog box, check the Generate Criteria option as follow:

• 

An extra source file MemberCriteria.java is generated.

Using Criteria Class

Usage

A property will be generated in criteria class corresponding to each simple property in ORM Persistable class. To use the criteria class, first create an instance of criteria class, then apply restriction to properties, finally get a single or array of result.

To apply restriction to property, simply call:

•  criteria.prop.expression(param);
  

  where criteria is the criteria instance, prop is the property to be restricted, expression is the expression to apply, and param is the parameter for the expression.
  
  

The following table is a list of available expression: (Note: Some expression applies to particular data types only)

• Expression	Description
  eq(value)	Property equal to value
  ne(value)	Property not equal to value
  gt(value)	Property greater than value
  ge(value)	Property greater than or equal to value
  lt(value)	Property less than value
  le(value)	Property less than or equal to value
  isEmpty()	Property is empty
  isNotEmpty()	Property is not empty
  isNull()	Property is NULL
  isNotNull()	Property is not NULL
  in(values)	Property contains in values array
  between(value1, value2)	Property value is between value1 and value2
  like(value)	String property like value, use '%' in value for wildcard
  ilike(value)	Case-insensitive like

A special method order(ascending) is used to sort the property in ascending (ascending = true) or descending (ascending = false) order. All these restrictions and orders can be applied to the same criteria instance.

The following methods limit the range of result to be retrieved:

• Method	Description
  setFirstResult(i)	Set the first result to be retrieved
  setMaxResults(i)	Limit the number of result to be retrieved

Two methods are available to execute the query and return the result(s):

• Method	Description
  uniqueClass()	Return a single result, will throw exception if result count <> 1
  listClass()	Return an array of result

  where Class is the name of the ORM Persistable Class.
  

Examples

Assuming you have the following data in your database:

• ID	name	gender	dob	type
  1	Henry Chan	M	1967-06-23	1
  2	Amy Wong	F	1983-01-03	2
  3	Louie Kwan	M	1977-04-18	3

• Select a single member with name = "Amy Wong"

  MemberCriteria criteria = new MemberCriteria();
  criteria.name.eq("Amy Wong");
  Member member = criteria.uniqueMember();
  System.out.println(member);
  

  System Output (Assuming you selected override toString() method with all properties option)
  Member[ ID=2 Name=Amy Wong Gender=F Dob=1983-01-03 Type=2 ]
  
  

• Select all members whose DOB is between 1960-01-01 and 1980-01-01:

  MemberCriteria criteria = new MemberCriteria();
  criteria.dob.between(new GregorianCalendar(1960, 1, 1).getTime(), new GregorianCalendar(1980, 1, 1).getTime());
  Member[] members = criteria.listMember();
  for (int i = 0; i < members.length; i++) {
    System.out.println(members[i]);
  } 
  

  System Output
  Member[ ID=1 Name=Henry Chan Gender=M Dob=1967-06-23 Type=1 ]
  Member[ ID=3 Name=Louie Kwan Gender=M Dob=1977-04-18 Type=3 ]
  
  

• Select all golden and silver members:

  MemberCriteria criteria = new MemberCriteria();
  criteria.type.in(new int[] {Member.TYPE_GOLDEN, Member.TYPE_SILVER});
  Member[] members = criteria.listMember();
  for (int i = 0; i < members.length; i++) {
    System.out.println(members[i]);
  } 
  

  System Output
  Member[ ID=1 Name=Henry Chan Gender=M Dob=1967-06-23 Type=1 ]
  Member[ ID=2 Name=Amy Wong Gender=F Dob=1983-01-03 Type=2 ]
  
  

• Select all members with gender='M', type is not silver; and sort the retrieved records by DOB in ascending order:

  MemberCriteria criteria = new MemberCriteria();
  criteria.gender.eq('M');
  criteria.type.ne(Member.TYPE_SILVER);
  criteria.dob.order(true);
  Member[] members = criteria.listMember();
  for (int i = 0; i < members.length; i++) {
    System.out.println(members[i]);
  } 
  

  System Output
  Member[ ID=1 Name=Henry Chan Gender=M Dob=1967-06-23 Type=1 ]
  Member[ ID=3 Name=Louie Kwan Gender=M Dob=1977-04-18 Type=3 ]
  
  

Related Articles

• Learn how to use the generated Java persistence class to manipulate the database by static method persistent API
  Using Java Persistence Class with Static Method Persistent API
  
  

• Learn how to use the generated Java persistence class to manipulate the database by factory class persistent API
  Using Java Persistence Class with Factory Class Persistent API
  
  

• Learn how to use the generated Java persistence class to manipulate the database by POJO persistent API
  Using Java Persistence Class with POJO Persistent API
  
  

• Learn how to use the generated Java persistence class to manipulate the database by DAO persistent API
  Using Java Persistence Class wtih DAO Persistent API
  

Resources

• Know more about DB Visual ARCHITECT - Java Persistent Code Generator for Relational Database
  http://www.visual-paradigm.com/product/dbva/
  
  

• Look at the features of DB Visual ARCHITECT
  http://www.visual-paradigm.com/product/dbva/features/
  
  

• Get the Free 30 Days Trial of DB Visual ARCHITECT
  http://www.visual-paradigm.com/download/
  
  

• Browse the DB Visual ARCHITECT's online documentation
  http://www.visual-paradigm.com/documentation/dbvauserguide.jsp
  

  • Chapter 7 Implementation - This chapter shows you how to generate the persistent code and describes how the POJO Model maps to ORM-Persistent Class
    
    

  • Chapter 8 Manipulating Persistent Data - This chapter shows how to use the generated persistent code for inserting, retrieving, updating and deleting persistent data and demonstrates how to run the generated sample code.
    
    

• View DB Visual ARCHITECT's Interactive Tutorials
  http://www.visual-paradigm.com/product/dbva/tutorials/