Custom mapping tutorial
This tutorial shows you examples of greater control over the mapping process
Here we use a large set of annotations to show some of the possibilities offered by the mapping process.
@TableName("Three")
public class Three {
@ColumnName("id") @PrimaryKey
public int theKey;
@Unique
public String name;
@Ignored
public String notMadePersistent;
@Indexed
public String lookup;
@Required
public String required;
@MaxLength(10)
public String code;
@OrderBy(true)
public short order;
}The TableName and ColumnName are explained in the reverse mapping tutorial, all the other annotations should be self explanatory, see below for the effect they have on the schema.
We then create a simple program to access these records,
DBDataMapper dbm = new DBDataMapper();
dbm.checkApplication(Three.class);
dbm.createSchema();
Three three = new Three();
three.required = "somestring";
three.code = "1234";
three.name = "name1";
three.order = 1;
IOHelper.insert(three);
three.name = "name2";
three.code = "0001";
three.order = 0;
IOHelper.insert(three);
//Read all of them:
for (Three t : IOHelper.readAll(Three.class)) {
System.out.println(t.code+" "+t.name+" "+t.order+" "+t.theKey);
}
//Read one by name
Three name1 = IOHelper.readObject(Three.class, "name", "name2");
System.out.println(name1.code+" "+name1.name+" "+name1.order+" "+name1.theKey);
dbm.dropSchema();
Running this program produces the following output (sanitized):
CREATE TABLE Three (
id INT NOT NULL PRIMARY KEY ,
name VARCHAR(255) UNIQUE,
lookup VARCHAR(255),
required VARCHAR(255) NOT NULL,
code VARCHAR(10),
D_order INT,
INDEX (lookup))
SELECT MAX(id) FROM Three;
INSERT INTO Three(id,name,lookup,required,code,D_order) VALUES (?,?,?,?,?,?)
INSERT INTO Three(id,name,lookup,required,code,D_order) VALUES (?,?,?,?,?,?)
SELECT id,name,lookup,required,code,D_order FROM Three ORDER BY D_order ASC
0001 name2 0 2
1234 name1 1 1
SELECT id,name,lookup,required,code,D_order FROM Three WHERE name=? ORDER BY D_order ASC
0001 name2 0 2
ALTER TABLE Three DROP INDEX lookup
DROP TABLE Three- Because the primary key is a number, the engine defines a sequence generator to ensure each record is allocate its own ID on insert
- The order column is named "d_order" as ORDER is a keyword known to the MySQL engine used here.
