Spring JPA Entity attribute type converter Attributeconverter

1, Introduction interface attributeconverter<x, y>

This interface is used to convert entity properties, but the id attribute and the Relationship property are not available. It has two methods:

1, y Converttodatabasecolumn (x) Action: The entity attribute x is converted to y stored in the database, that is, the insert and update operations are performed;

2, x Converttoentityattribute (Y) Action: Convert the field y in the database to entity attribute x, which is executed when the query operation

2, the implementation of the demo

Requirements: A status column in a database table, 1 for Enable, 1 for disabled, and 2 for deleted.

Step one: Create Statusenum, listing only some of the key codes

Public enum Statusenum {enable (1, "Enabled"), DISABLE (-1, "disabled"), DELETED (-2, "deleted");        Statusenum (Integer value, String description) {this.value = value;    this.description = description; }}

Step two: Implement Attributeconverter<string, Integer> interface, will represent the number and description of the conversion, where the Status field in the Entity class is a string type

public class statusattributeconverter implements attributeconverter<string,  integer> {     @Override     public Integer  Converttodatabasecolumn (String status)  {        try {             return integer.parseint (status);     //if it is a number, it is returned directly (this can be further verified by traversing the value of Statusenum)          } catch  (numberformatexception e)  {             for  (Statusenum type : statusenum.values ())  {     //if it is not a number, use Statusenum to find a description of the corresponding number                  if  (Status.equals (type.getdescription))  {           &nBsp;         return type.getvalue ();                 }             }        }         throw new runtimeexception ("unknown statusenum: "  +  status);     //If there is no representation number or description in the Statusenum, an exception is thrown     }      @Override     public string converttoentityattribute (Integer value)  {        for  (statusenum type :  Statusenum.values ())  {    //converts a number to a description              if  (Value.equals (type.getvalue))  {             &nbSp;   return type.getdescription ();             }        }         throw new runtimeexception ("unknown database value: "  + value);     }}

Step three: Look at the entity class

@Entity @table (name = "T_demo") public class Demoentity {@Convert (converter = statusattributeconverter.class) Private String status; Status: 1 enabled, 1 disabled,-2 deleted}

3. Advantages

The client does not have to hardcode the background numbers with the corresponding details of the description.

The server provides an interface to get Statusenum, gets to [{"Value": 1, "description": "Enabled"}, {"Value":-1, "description": " Disabled "}, {" Value ": -2,"description":" deleted "}], the client is assembled directly into a drop-down list.

Copyright = {"Author": "Ink Night", "article link": "http://my.oschina.net/letao/blog/524487"}

Spring JPA Entity attribute type converter Attributeconverter