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transcript

Java and RDBMSMarried with issues

Database constraints

Speaker

Jeroen van Schagen

Situation

retrieveJava

ApplicationRelational Database

• Java Database Connectivity

• Data Access API ( java.sql, javax.sql )

• JDK 1.1 (1997)

• Relational Database

• Many implementations

Connection connection = …; Statement statement = connection.createStatement();

String sql = “INSERT INTO user (name) VALUES (‘Jan’)”; statement.executeUpdate(sql);

name : varchar(3) NOT-NULL, UNIQUE

Name can only haveup to 3 characters

Name is required

Name can only occur once

Database

Maintain data

Constraint types

Not null

Length

Primary key Foreign key

Unique key

Username : varchar(3) NOT-NULL, UNIQUE

What happens?

Assuming the user table is empty

1 row updated

String sql = “INSERT INTO user (name) VALUES (‘Jan’)”; statement.executeUpdate(sql); statement.executeUpdate(sql);

What will happen?

What happens?

What will happen?

SQLIntegrityConstraintViolationException

Application JDBC Database

executeUpdate(sql) INSERT

return 1 Inserted 1

executeUpdate(sql) INSERT

Unique violationthrowSQLIntegrityConstraint

ViolationException

String sql = “INSERT INTO user (name) VALUES (‘Jan’)”; try { statement.executeUpdate(sql); statement.executeUpdate(sql); } catch (SQLIntegrityConstraintViolationException e) { throw new RuntimeException(“Name already exists”);}

String sql = “INSERT INTO user (name) VALUES (NULL)”; statement.executeUpdate(sql);

What happens?

String sql = “INSERT INTO user (name) VALUES (NULL)”; statement.executeUpdate(sql);

SQLIntegrityConstraintViolationException

String sql = “INSERT INTO user (name) VALUES (NULL)”; try { statement.executeUpdate(sql); } catch (SQLIntegrityConstraintViolationException e) { throw new RuntimeException(“Name is required”); throw new RuntimeException(“Name already exists”);}

Unique key violation

SQLIntegrityConstraint ViolationException

Not null violation

Which was violated?

SQLException

+ getSQLState() : int+ getMessage() : String

SQLException

State Name

23000 Integrity constraint

23001 Restrict violation

23502 Not null violation

23503 Foreign key violation

23505 Unique violation

23514 Check violation

String sql = “INSERT INTO user (name) VALUES (NULL)”; try { statement.executeUpdate(sql); } catch (SQLIntegrityConstraintViolationException e) { if (e.getSQLState() == 23502) { throw new RuntimeException(“Name is required”); } else if (e.getSQLState() == 23505) { throw new RuntimeException(“Name already exists”); } }

Complicated Boilerplate Assumptions

Multiple not-null values

name : varchar(3) NOT-NULL, UNIQUEemail : varchar(30) NOT-NULL, UNIQUE

uk_user_name

uk_user_email

Multiple not-null valuesMultiple unique values

name : varchar(3) NOT-NULL, UNIQUEemail : varchar(30) NOT-NULL, UNIQUE

Which was violated?

SQLException

Vendor messages

HSQL integrity constraint violation: unique constraint or index violation;

UK_USER_NAME table: USER

PostgreSQL ERROR: duplicate key value violates unique constraint \"uk_user_name\"

Detail: Key (name)=(Jan) already exists.

Oracle ORA-00001: unique constraint (GOTO.UK_USER_NAME) violated\n

MySQL Duplicate entry 'Jan' for key 'uk_user_name'

H2 Unique index or primary key violation: "UK_USER_NAME_INDEX_1 ON GOTO.USER(NAME)";

SQL statement:\ninsert into user (name) values (?) [23505-171]

They are all different

Vendor messages

HSQL integrity constraint violation: unique constraint or index violation;

UK_USER_NAME table: USER

PostgreSQL ERROR: duplicate key value violates unique constraint \"uk_user_name\"

Detail: Key (name)=(Jan) already exists.

Oracle ORA-00001: unique constraint (GOTO.UK_USER_NAME) violated\n

MySQL Duplicate entry 'Jan' for key 'uk_user_name'

H2 Unique index or primary key violation: "UK_USER_NAME_INDEX_1 ON GOTO.USER(NAME)";

SQL statement:\ninsert into user (name) values (?) [23505-171]

The info is there

• Message

• Pattern matching

• Vendor specific

Extract violation info

Just too difficult

Focus on application logic

JDBC needs a better exception API ( for integrity constraints )

Concrete exception classes

UniqueKeyViolationException

NotNullViolationException

Access to constraint info

getColumnName()

getConstraintName()

Workaround

Prevent violations

• Data integrity checks in application layer.

Prevent violations

Prevent not-null

if (user.getName() == null) { throw new RuntimeException(“Name is required”); }

Javax validation

public class User { @NotNull private String name; }

Conveys

No SQL exception

Less database interaction

Application

Database

throw new RuntimeException

Less interaction

User@NotNull private String name

Application Database

Duplication

User@NotNull private String name

Kept in sync Unexpected SQL exceptions

Duplication

• Complicated

• Depends on other rows

Prevent unique violation

id name

Testable in isolation

id name

id nameusers

Requires data

No SQL exceptions

Extra query Not atomic

if (countUsersWithName(user.getName()) > 0) { throw new RuntimeException(“Name already exists”);}

private int countUsersWithName(String name) { return jdbcTemplate.queryForObject( “SELECT COUNT(1) FROM user where name = ?”, name, Long.class); }

Problem: Not atomic

INSERT (name) VALUES (‘Jan’)

INSERTED 1

Thread 2

COUNT WHERE name = ‘Jan’return 0

Thread 1

INSERT (name) VALUES (‘Jan’)

Thread 1

Decision onold data

UnexpectedUncaught

No SQL exceptions Error proneDuplication

Not null

Extra query

Unique key

No SQL exceptions Error prone

Lack proper solution

SolutionJava Repository Bridge - JaRB

Databases are good atmaintaining integrity;

let them!

Catch exceptionPrevent exceptionTestable in isolation

Not null

Length

Unique key

Foreign key

Primary key

Prevent exceptionValidation

Not null Type Length

@Entity @DatabaseConstrained public class User { @NotNull @Length(max=3) private String name; private String email; }

Username : varchar(3) NOT-NULL, UNIQUE email : varchar(100)

No duplication

Retrieve constraints

Database as only truth

validate(new User(‘Henk’));

varchar(3) not null

name = ‘Henk’ email = null

1. Loop over properties 3. Check name ‘Henk’ on metadata

Database

Application

2. Get metadata user.name

Determine column name (Hibernate)

Database

Applicationname = ‘Henk’ email = null

varchar(3) not null

1. Loop over properties 3. Check name ‘Henk’ on metadata

“ Name cannot be longer than 3 characters “

name = null email = null

1. Loop over properties 3. Check null name on metadata

validate(new User(null));

varchar(3) not null

Database

Application

Applicationname = null email = null

varchar(3) not null

1. Loop over properties 3. Check null name on metadata

validate(new User(null));

“ Name cannot be null “

Database

name = ‘Jan’ email = null

1. Loop over properties 3. Check name ‘Jan’ on metadata

validate(new User(null));validate(new User(‘Jan’));

Database

Application

varchar(3) not null

Database

Applicationname = ‘Jan’ email = null

varchar(3) not null

1. Loop over properties 3. Check name ‘Jan’ on metadata

name = ‘Jan’ email = null

varchar(100)

1. Loop over properties 3. Check null email on metadata

Database

Application

2. Get metadata user.email

Database

varchar(100)

Database

varchar(100)

Super class@MappedSuperclass @DatabaseConstrained public abstract class BaseEntity { }

@Entity public class User extends BaseEntity { private String name; private String email; }

@DatabaseConstrained public class User { private String name; private String email; }

Custom schema mapper

Catch exceptionException translation

CheckUnique key Foreign key Primary key

Translate the JDBC exception into a proper constraint exception

Existing translators

• Object Relation Mapping

• Extracts constraint name from message

Hibernate

ConstraintViolationExceptiongetConstraintName()

Access to constraint name

Hardcoded namesHeavy for plain JDBC

Hardcoded names

try { // Insert user } catch (ConstraintViolationException e) { if (e.getConstraintName() == “uk_user_name”) { // Handle error } }

Too technical

Focus on domain

• Dependency Injection

• Templates

• JDBC

• DAO

Spring

• JdbcTemplate

• SQLExceptionTranslator

• Error codes

• Register own classes

• No constraint name

Spring JDBC

Spring

DataAccessException

DataIntegrityViolationException

Consistent hierarchy

Extensible

• ORM (e.g. Hibernate)

• PersistenceExceptionTranslator

• Proxy

Spring DAO

Spring$Proxy

PersistenceExceptionTranslator

ConstraintViolation Exception JPASystemException

UserRepository

No constraint name

ConstraintViolationExceptiongetConstraintName()

JPASystemException

DataAccessException

Hierarchy

Weaker API

try { userRepository.save(user); } catch (JPASystemException e) { ConstraintViolationException ce = (ConstraintViolationException) e.getCause(); if (ce.getConstraintName() == “uk_user_name”) { // Handle error } }

Unsafe cast

Why isn’t this easier?

Constraint name

Hierarchy

Extensible

Hibernate Spring JaRB

Best of both worlds

Concrete and domain specific exceptions.

Map each constraint to a custom exception.

try { userRepository.save(new User(“Jan”)); } catch (UserNameAlreadyExistsException e) { error(“User name already exists.”); }

try { userRepository.save(new User(“Jan”)); } catch (UserNameAlreadyExistsException e) { error(“User name already exists.”); } catch (UserEmailAlreadyExistsException e) { error(“User email already exists.”); }

Translator

SQLIntegrity ConstraintException

UserNameAlready ExistsException

Resolver

ERROR: duplicate key value violates unique constraint \"uk_user_name\" Detail: Key (name)=(Jan) already exists.

Extract all information from exception

Resolver

ERROR: duplicate key value violates unique constraint \"uk_user_name\" Detail: Key (name)=(Jan) already exists.

Vendor specific

Pattern matching

Extract all information from exception

Column name Value

Constraint name

Version specific

Resolvers

• Pattern matching (default) • PostgreSQL • Oracle • MySQL • HSQL • H2

• Hibernate: constraint name only

Factory

Create a concrete exception

Default factory

LengthExceededViolationException

PrimaryKeyViolationException

CheckFailedException

InvalidTypeException

ForeignKeyViolationException

DatabaseConstraintViolationException

LengthExceededViolationException

PrimaryKeyViolationException

CheckFailedException

InvalidTypeException

ForeignKeyViolationException

UserNameAlreadyExistsException

Constraint info

Custom exceptions

@NamedConstraint(“uk_user_name”) public class UserNameAlreadyExistsException extends UniqueKeyViolationException { }

Scanned from class path

Registered on constraint

Custom exceptions

uk_user_name UserNameAlreadyExistsException

uk_user_email UniqueKeyViolationException

Injectable arguments

@NamedConstraint(“uk_user_name”) public class UserNameAlreadyExistsException extends UniqueKeyViolationException { UserNameAlreadyExistsException(…) { } }

DatabaseConstraintViolationThrowable (cause)

ExceptionFactory

Less concrete

try { userRepository.save(new User(“Jan”)); } catch (UniqueKeyViolationException e) { error(“User name already exists.”); }

Enable in Spring@EnableDatabaseConstraints(basePackage = “org.myproject”)

Enable exception translation

Enable database validation

Resolve database vendorRegister custom exceptions

<jarb:enable-constraints base-package=“org.myproject”/>

Get source

<dependency> <groupId>org.jarbframework</groupId> <artifactId>jarb-constraints</artifactId> <version>2.1.0</version></dependency>

Maven central

http://www.jarbframework.org

Github

Questions?

Java and RDBMS - gotocon.com · •Java Database Connectivity • Data Access API ( java.sql,...

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