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JdbcMapper is an ORM (Object Relational Mapper) that enables you to write normal SQL queries and use them to select POJOs (Plain Old Java Objects) from the database in different types of collections quickly and easily. Type safety is enforced throughout so neither casting nor ignoring warnings is required.
There are 2 different approaches to accomplish this. JdbcMapper generates code at compile time, QueryMapper does everything at runtime. Currently there are different packages for java6 and java8+, these are built from the same source with a bit of sed-like magic, when the documentation refers to classes only available in java8+ just know these are obviously unavailable if you use the java6 version.
Why
The java.sql API is horrible, ResultSet.wasNull() ?, enough said. Hibernate is black magic that generates some truly awful SQL queries. Everything in between insists on writing your queries and/or forcing you to fully annotate all your POJOs with information on how to map them from SQL, making them some combination of too verbose, too slow, or too much unknown magic.
Goals
- Write as little code as possible
- Have it run as fast as possible
- Have it check and error out on everything it possibly can at compile time
- Be runnable and testable inside or outside of containers easily
- No surprises, as little magic as possible
Column to Object Mapping
All decisions as to which ResultSet method(s) to call are based on the Java type being mapped to, because we have no knowledge of any database schema. These mappings rarely if ever need changed, they can be overridden with QueryMapper but not currently at compile-time with JdbcMapper.
If you are thinking 'shut up and show me the code already' refer to ResultSetUtil.java which contains the implementations actually called.
For the purposes of this mapping, consider 'rs' an instance of ResultSet, and 'index' an int index of a ResultSet column.
numeric primitives
if the SQL value is NULL, 0 is returned for these, and no exception is thrown
byte
return rs.getByte(index);
short
return rs.getShort(index);
int
return rs.getInt(index);
long
return rs.getLong(index);
float
return rs.getFloat(index);
double
return rs.getDouble(index);
numeric objects
these wrapper types are retrieved using the same function returning their primitives above, except null is returned if the SQL value is NULL instead of 0
x ret = rs.getX(index);
return rs.wasNull() ? null : ret;
java.math.BigDecimal
return rs.getBigDecimal(index);
boolean
in all cases of SQL NULL being returned, if primitive boolean is requested an SQLException is thrown, if Object Boolean is requested then null is returned.
boolean has special handling due to many popular databases not actually having a boolean type (hi Oracle!), forcing application level workarounds.
0/1 numeric types convert to boolean using the standard ResultSet API, but many systems use char/varchar of Y/N or T/F, which we default to Y/N but can be set via system properties:
ResultSetUtil.TRUE=Y ResultSetUtil.FALSE=N
First the standard ResultSet API is attempted:
return rs.getBoolean(index);
If this does not throw an SQLException, it is returned directly If SQLException is thrown, then we try to compare as a String:
String bool = rs.getString(index);
boolean ret = ResultSetUtil.TRUE.equals(bool);
if (!ret && !ResultSetUtil.FALSE.equals(bool))
throw new SQLException(String.format("Implicit conversion of database string to boolean failed on column '%d'. Returned string needs to be '%s' or '%s' and was instead '%s'.", index, ResultSetUtil.TRUE, ResultSetUtil.FALSE, bool));
return ret;
The returned string MUST be either TRUE or FALSE (or null, for Object Boolean) or an exception will be thrown
Misc Objects
For all of these, when SQL NULL is returned, it maps to null
String
return rs.getString(index);
byte[]
return rs.getBytes(index);
java.sql.Ref
return rs.getRef(index);
java.sql.Blob
return rs.getBlob(index);
java.sql.Clob
return rs.getClob(index);
java.sql.Array
return rs.getArray(index);
java.sql.Struct
return rs.getObject(index);
*
If nothing else fits, we call getObject and cross our fingers with QueryMapper at runtime, this is a compile-time error with JdbcMapper. todo: is this actually a compile-time error? it should be, check...
return rs.getObject(index);
todo: finish documenting this
Row to Object Mapping
todo: explain how rows are mapped to POJOs
JdbcMapper
Write an interface or abstract class with methods that make sense for accessing your database, annotate the methods with SQL, and on compilation an annotation processor will generate the required java.sql API code to execute your query and return what you wanted. This code is guaranteed to be the fastest code possible because hand written code would look the same, just more error prone and harder to maintain. The annotation processor also checks that the SQL queries are valid, have all the right bind parameters, and can bind the result columns to all the correct fields on the result object. If anything is wrong it's a compile error pointing you to the exact problem.
Example:
@JdbcMapper.Mapper(jndiName = "java:/comp/env/jdbc/testPool") // omit jndiName and you must send in a java.sql.Connection
public interface PersonDAO extends Closeable { // Closeable is optional but must have a 'void close()' method to use cachePreparedStatements or jndiName
@JdbcMapper.SQL("CREATE TABLE person (person_no NUMERIC, first_name VARCHAR(40), last_name VARCHAR(40), birth_date TIMESTAMP)")
void createTablePerson();
@JdbcMapper.SQL("INSERT INTO person (person_no, birth_date, last_name, first_name) VALUES ({personNo}, {birthDate}, {firstName}, {lastName})")
int insertPerson(long personNo, Date birthDate, String firstName, String lastName);
@JdbcMapper.SQL("UPDATE person SET first_name = {firstName} WHERE person_no = {personNo}")
int setFirstName(String firstName, long personNo); // returning int will return number of rows modified, can also return void
@JdbcMapper.SQL("SELECT first_name FROM person WHERE person_no = {personNo}")
String getFirstName(long personNo) throws SQLException; // can map directly to simple types
@JdbcMapper.SQL("SELECT person_no, first_name, last_name, birth_date FROM person WHERE person_no = {personNo}")
Person getPerson(long personNo) throws SQLException; // or multiple fields, set methods, or constructor parameters on a POJO
@JdbcMapper.SQL("SELECT person_no, first_name, last_name, birth_date FROM person WHERE last_name = {lastName}")
List<Person> getPeople(String lastName) throws SQLException; // all rows in any Collection<T> (like Set<T>, LinkedList<T> etc), T[], ResultSetIterable<T> or Stream<T> (java8+) works too
}
// code:
try(PersonDAO personDao = JdbcMapperFactory.create(PersonDAO.class)) {
personDao.createTablePerson();
System.out.println(personDao.insertPerson(0, null, "First", "Person")); // 1
System.out.println(personDao.insertPerson(1, null, "First", "Person")); // 1
System.out.println(personDao.setFirstName("Second", 1)); // 1
System.out.println(personDao.getFirstName(0)); // First
System.out.println(personDao.getFirstName(1)); // Second
System.out.println(personDao.getPerson(0)); // Person{personNo=0,birthDate=null,firstName=First,lastName=Person}
System.out.println(personDao.getPerson(1)); // Person{personNo=1,birthDate=null,firstName=Second,lastName=Person}
System.out.println(personDao.getPeople("Person")); // [Person{personNo=0,birthDate=null,firstName=First,lastName=Person}, Person{personNo=1,birthDate=null,firstName=Second,lastName=Person}]
}
QueryMapper
Need to generate SQL dynamically or just execute some queries quickly and easily? Mapping is done using reflection in ResultSetMapper or code is dynamically generated, compiled, instantiated, and cached at runtime to do the mapping using CompilingResultSetMapper.
Example:
// CompilingResultSetMapper is an alternative to ResultSetMapper, default is ResultSetMapper
try(QueryMapper qm = new QueryMapper("java:/comp/env/jdbc/testPool", new ResultSetMapper())) { // or send in java.sql.Connection
// executeUpdate returns int
qm.executeUpdate("CREATE TABLE person (person_no NUMERIC, first_name VARCHAR(40), last_name VARCHAR(40), birth_date TIMESTAMP)");
System.out.println(qm.executeUpdate("INSERT INTO person (person_no, birth_date, last_name, first_name) VALUES (?, ?, ?, ?)", 0, null, "First", "Person")); // 1
System.out.println(qm.executeUpdate("INSERT INTO person (person_no, birth_date, last_name, first_name) VALUES (?, ?, ?, ?)", 1, null, "First", "Person")); // 1
System.out.println(qm.executeUpdate("UPDATE person SET first_name = ? WHERE person_no = ?", "Second", 1)); // 1
// can map directly to simple types
System.out.println(qm.toObject("SELECT first_name FROM person WHERE person_no = ?", String.class, 0)); // First
System.out.println(qm.toObject("SELECT first_name FROM person WHERE person_no = ?", String.class, 1)); // Second
// or multiple fields, set methods, or constructor parameters on a POJO
System.out.println(qm.toObject("SELECT person_no, first_name, last_name, birth_date FROM person WHERE person_no = ?", String.class, 0)); // Person{personNo=0,birthDate=null,firstName=First,lastName=Person}
System.out.println(qm.toObject("SELECT person_no, first_name, last_name, birth_date FROM person WHERE person_no = ?", String.class, 1)); // Person{personNo=1,birthDate=null,firstName=Second,lastName=Person}
// instead of toCollection can use toList, toArray, toResultSetIterable, toStream (java8+)
System.out.println(qm.toCollection("SELECT person_no, first_name, last_name, birth_date FROM person WHERE last_name = ?", new ArrayList<String>(), String.class, "Person")); // [Person{personNo=0,birthDate=null,firstName=First,lastName=Person}, Person{personNo=1,birthDate=null,firstName=Second,lastName=Person}]
}
TODO
- DOCUMENTATION!!!!!
- sql other than select return boolean, int > 0 ?
- @RunInTransaction void support
- QueryMapper mapping errors should be clearer, especially if a .finish(ResultSet) throws an error