Equals and hashcode Approach/ Implementation for Business Objects (Bo)

A common source for bugs while writing code Business Objects for relational database using Object Relation Mapping tools is the implementation of the Equals and Hashcode methods.

If you would like to know more about the Equals and Hashcode importance for an ORM Click here.

To summarize the ORM implementation, There are two types of keys: Technical Keys and Business keys.

Technical keys are the primary key on the for a table to uniquely identify a database row, these numbers are auto generated sequence number (Item Unique IDentification/ IUID).

Business keys are the Business primary (/ composite) keys which uniquely identify the business objects in the database tables.

One of the important factor while writing a equals and hashcode method is to decide on what attributes needs to go into these methods; Some guidelines for deciding the attributes for Equals and hashcode methods.

• It is not necessary to cover all the attributes in Business Objects in equals/ hashcode methods.
• Include the Technical Keys and Business keys in equals and hashcode methods.
• Equals and hashcode methods should take care of the null cases.

Implementation wise, Apache commons-lang has a very good implementation for hashcode and equals method. Here’s an example of equals and hashcode methods using the apache commons-lang.

@Entity
@Table(name = "APP_CONFIGURATION")
@SequenceGenerator(name = "OPS_SEQ", sequenceName = "SQ_CONFIGURATION_CNTR")
public class ConfigurationBo extends AbstractBo {

private static final long serialVersionUID = -5098377177228374794L;

@Column(name = “ITEMNAME”, length = 100)
private String name;

@Column(name = “STRINGVALUE”, length = 100)
private String stringValue;

@Column(name = “INTVALUE”)
private Integer intValue;

@Column(name = “TYPENAME”, length = 20)
private String type;

public Integer getIntValue() {
return intValue;
}

public void setIntValue(Integer intValue) {
this.intValue = intValue;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getStringValue() {
return stringValue;
}

public void setStringValue(String stringValue) {
this.stringValue = stringValue;
}

public String getType() {
return type;
}

public void setType(String type) {
this.type = type;
}

/**
* {@inheritDoc}
*/
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (!(obj.getClass() == this.getClass())) {
return false;
}
ConfigurationBo other = (ConfigurationBo) obj;

return new EqualsBuilder()
.appendSuper(super.equals(obj))
.append(this.name, other.name)
.append(this.type, other.type)
.isEquals();
}

/**
* {@inheritDoc}
*/
@Override
public int hashCode() {
return new HashCodeBuilder()
.appendSuper(super.hashCode())
.append(this.name)
.append(this.type)
.toHashCode();
}

/**
* {@inheritDoc}
*/
@Override
public String toString() {
return super.toString() + “[name=” + name + “, type=” + type + “]”;
}

}

Written by Ravi Nallakukkala on April 15th, 2007 with 4 comments.
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