.NET has a large amount of Micro ORMs (Dapper, NPoco, OrmLite, ...) to access databases in a very simple way, while Java is lacking small libraries. SqlMapper is a wrapper over the JDBC ResultSet, and makes it very easy to map between Java Beans and a database table:
Basic Usage
Imagine we want to read a list of Persons from a database, where each Person has a first name, last name and a birthdate.
Database Table
The table in the database could look like this (PostgreSQL):
CREATE TABLE sample.unit_test
(
first_name text,
last_name text,
birth_date date
);
Domain Model
The domain model in the application might look like this:
private class Person {
private String firstName;
private String lastName;
private LocalDate birthDate;
public Person() {}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public LocalDate getBirthDate() {
return birthDate;
}
public void setBirthDate(LocalDate birthDate) {
this.birthDate = birthDate;
}
}
Define the Mapping
All you have implement is the mapping between both, which is done with a ResultSetMapping:
public class PersonMap extends ResultSetMapping<Person>
{
public PersonMap() {
map("first_name", String.class, Person::setFirstName);
map("last_name", String.class, Person::setLastName);
map("birth_date", LocalDate.class, Person::setBirthDate);
}
}
Map ResultSet to an Entity
An SqlMapper is used to perform the actual mapping between a ResultSet and the Entities. It takes
an IObjectCreator and an ResultSetMapping. TheIObjectCreator`` is a functional interface, that is
used to instantiate a target object.
The SqlMapper.toEntity method returns a SqlMappingResult<TEntity>. The SqlMappingResult<TEntity>
holds either the populated target object or an error, which can be checked with the SqlMappingResult<TEntity>.isValid()
method.
If the mapping was successful, the populated entity can be obtained by calling SqlMappingResult<TEntity>.getEntity().
@Test
public void testToEntity() throws Exception {
SqlMapper<Person> sqlMapper = new SqlMapper<>(() -> new Person(), new PersonMap());
Person person0 = new Person();
person0.firstName = "Philipp";
person0.lastName = "Wagner";
person0.birthDate = LocalDate.of(1986, 5, 12);
insert(person0);
ResultSet resultSet = selectAll();
while (resultSet.next() ) {
SqlMappingResult<Person> person = sqlMapper.toEntity(resultSet);
Assert.assertEquals(true, person.isValid());
Assert.assertEquals("Philipp", person.getEntity().get().getFirstName());
Assert.assertEquals("Wagner", person.getEntity().get().getLastName());
Assert.assertEquals(LocalDate.of(1986, 5, 12), person.getEntity().get().getBirthDate());
}
}