Java and RDBMS. Married with issues. Database constraints

Transcription

1 Java and RDBMS Married with issues Database constraints

2 Speaker Jeroen van Schagen

3 Situation Java Application store retrieve JDBC Relational Database

4 JDBC Java Database Connectivity Data Access API ( java.sql, javax.sql ) JDK 1.1 (1997) Relational Database Many implementations

5 Connection connection = ; Statement statement = connection.createstatement(); String sql = INSERT INTO user (name) VALUES ( Jan ) ; statement.executeupdate(sql);

6 Connection connection = ; Statement statement = connection.createstatement(); String sql = INSERT INTO user (name) VALUES ( Jan ) ; statement.executeupdate(sql);

7 Database Maintain data User Name can only have up to 3 characters name : varchar(3) NOT-NULL, UNIQUE Name is required Name can only occur once

8 Constraint types Not null Check Length Unique key Primary key Type Foreign key

9 User name : varchar(3) NOT-NULL, UNIQUE Connection connection = ; Statement statement = connection.createstatement(); String sql = INSERT INTO user (name) VALUES ( Jan ) ; statement.executeupdate(sql); What happens? Assuming the user table is empty

10 User name : varchar(3) NOT-NULL, UNIQUE Connection connection = ; Statement statement = connection.createstatement(); String sql = INSERT INTO user (name) VALUES ( Jan ) ; statement.executeupdate(sql); 1 row updated

11 User name : varchar(3) NOT-NULL, UNIQUE Connection connection = ; Statement statement = connection.createstatement(); String sql = INSERT INTO user (name) VALUES ( Jan ) ; statement.executeupdate(sql); statement.executeupdate(sql); What will happens? happen?

12 User name : varchar(3) NOT-NULL, UNIQUE Connection connection = ; Statement statement = connection.createstatement(); String sql = INSERT INTO user (name) VALUES ( Jan ) ; statement.executeupdate(sql); statement.executeupdate(sql); SQLIntegrityConstraint What will happen? ViolationException

13 executeupdate(sql) INSERT return 1 Inserted 1 Applicatio n executeupdate(sql) JDBC INSERT Database throw Unique violation SQLIntegrityConstraint ViolationException

14 User name : varchar(3) NOT-NULL, UNIQUE Connection connection = ; Statement statement = connection.createstatement(); String sql = INSERT INTO user (name) VALUES ( Jan ) ; statement.executeupdate(sql); statement.executeupdate(sql);

15 User name : varchar(3) NOT-NULL, UNIQUE Connection connection = ; Statement statement = connection.createstatement(); String sql = INSERT INTO user (name) VALUES ( Jan ) ; try { statement.executeupdate(sql); statement.executeupdate(sql); } catch (SQLIntegrityConstraintViolationException e) { throw new RuntimeException( Name already exists ); }

16 User name : varchar(3) NOT-NULL, UNIQUE Connection connection = ; Statement statement = connection.createstatement(); String sql = INSERT INTO user (name) VALUES (NULL) ; statement.executeupdate(sql); What happens?

17 User name : varchar(3) NOT-NULL, UNIQUE Connection connection = ; Statement statement = connection.createstatement(); String sql = INSERT INTO user (name) VALUES (NULL) ; statement.executeupdate(sql); SQLIntegrityConstraint ViolationException

18 User name : varchar(3) NOT-NULL, UNIQUE Connection connection = ; Statement statement = connection.createstatement(); 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 ); }

19 Unique key violation SQLIntegrityConstraint ViolationException Not null violation

20 Unique key violation SQLIntegrityConstraint ViolationException Not null violation Which was violated?

21 SQLException + getsqlstate() : int + getmessage() : String SQLIntegrityConstraint ViolationException

22 SQLException + getsqlstate() : int + getmessage() : String SQLIntegrityConstraint ViolationException

23 State Name Integrity constraint Restrict violation Not null violation Foreign key violation Unique violation Check violation

24 User name : varchar(3) NOT-NULL, UNIQUE Connection connection = ; Statement statement = connection.createstatement(); 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 ); } }

25 User name : varchar(3) NOT-NULL, UNIQUE Connection connection = ; Statement statement = connection.createstatement(); 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

26 Multiple not-null values User name : varchar(3) NOT-NULL, UNIQUE varchar(30) NOT-NULL, UNIQUE

27 Multiple not-null values Multiple unique values User Which was violated? name : varchar(3) NOT-NULL, UNIQUE varchar(30) NOT-NULL, UNIQUE uk_user_name uk_user_

28 SQLException + getsqlstate() : int + getmessage() : String SQLIntegrityConstraint ViolationException

29 Vendor messages Oracle ORA-00001: unique constraint (GOTO.UK_USER_NAME) violated\n They are all different MySQL Duplicate entry 'Jan' for key 'uk_user_name' 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. H2 Unique index or primary key violation: "UK_USER_NAME_INDEX_1 ON GOTO.USER(NAME)"; SQL statement:\ninsert into user (name) values (?) [ ]

30 Vendor messages Oracle ORA-00001: unique constraint (GOTO.UK_USER_NAME) violated\n The info is there MySQL Duplicate entry 'Jan' for key 'uk_user_name' 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. H2 Unique index or primary key violation: "UK_USER_NAME_INDEX_1 ON GOTO.USER(NAME)"; SQL statement:\ninsert into user (name) values (?) [ ]

31 Extract violation info Message Just too difficult Pattern matching Vendor specific Focus on application logic

32 Concrete exception classes UniqueKeyViolationException NotNullViolationException JDBC needs a better exception API ( for integrity constraints ) Access to constraint info getcolumnname() getconstraintname()

33 Workaround

34 Prevent violations

35 Prevent violations Data integrity checks in application layer.

36 Prevent not-null if (user.getname() == null) { throw new RuntimeException( Name is required ); }

37 Javax validation public class User private String name; } No SQL exception Conveys Less database interaction

38 Less interaction throw new RuntimeException Applicatio n Database

39 Duplication Application User Database private String name name : varchar(3) NOT-NULL, UNIQUE

40 Duplication Application User Database private String name name : varchar(3) NOT-NULL, UNIQUE Kept in sync Unexpected SQL exceptions

41 Prevent unique violation Complicated Depends on other rows

42 id name NULL Testable in isolation

43 id name Jan

44 id name Jan Requires data users id name Piet Jan Henk

45 No SQL exceptions 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); } Extra query Not atomic

46 Problem: Not atomic Thread 1 COUNT WHERE name = Jan return 0 Applicatio n Thread 2 Thread 1 INSERT (name) VALUES ( Jan ) INSERTED 1 INSERT (name) VALUES ( Jan ) Unique key violation Database Uncaught Unexpected Decision on old data

47 Recap Lack proper solution Not null No SQL exceptions Duplication Error prone Unique key No SQL exceptions Extra query Error prone

48 Solution Java Repository Bridge - JaRB

49 Databases are good at maintaining integrity; let them!

50 Prevent exception Testable in isolation Catch exception Not null Type Length Unique key Foreign key Primary key Check

51 Prevent exception Validation Not null Type Length

52 public class private String name; private String ; } User name : varchar(3) NOT-NULL, UNIQUE varchar(100) Retrieve constraints Database as only truth No duplication

53 validate(new User( Henk )); 1. Loop over properties 3. Check name Henk on metadata name = Henk = null Application 2. Get metadata user.name varchar(3) not null Determine column name (Hibernate) Database

54 Name cannot be longer than 3 characters validate(new User( Henk )); 1. Loop over properties 3. Check name Henk on metadata name = Henk = null Application 2. Get metadata user.name varchar(3) not null Database

55 validate(new User( Henk )); validate(new User(null)); 1. Loop over properties name = null = null 3. Check null name on metadata Application 2. Get metadata user.name varchar(3) not null Database

56 Name cannot be null validate(new User( Henk )); validate(new User(null)); 1. Loop over properties name = null = null 3. Check null name on metadata Application 2. Get metadata user.name varchar(3) not null Database

57 validate(new User( Henk )); validate(new User(null)); validate(new User( Jan )); 1. Loop over properties 3. Check name Jan on metadata name = Jan = null Application 2. Get metadata user.name varchar(3) not null Database

58 validate(new User( Henk )); validate(new User(null)); validate(new User( Jan )); 1. Loop over properties 3. Check name Jan on metadata name = Jan = null Application 2. Get metadata user.name varchar(3) not null Database

59 validate(new User( Henk )); validate(new User(null)); validate(new User( Jan )); 1. Loop over properties name = Jan = null 3. Check null on metadata Application 2. Get metadata user. varchar(100) Database

60 validate(new User( Henk )); validate(new User(null)); validate(new User( Jan )); 1. Loop over properties name = Jan = null 3. Check null on metadata Application 2. Get metadata user. varchar(100) Database

61 validate(new User( Henk )); validate(new User(null)); validate(new User( Jan )); 1. Loop over properties name = Jan = null 3. Check null on metadata Application 2. Get metadata user. varchar(100) Database

62 public abstract class BaseEntity { public class User extends BaseEntity { private String name; private String ; }

63 JDBC Custom schema public class User { private String name; private String ; }

64 Catch exception Exception translation Unique key Foreign key Primary key Check

65 Translate the JDBC exception into a proper constraint exception

66 Existing translators

67 Hibernate Object Relation Mapping Extracts constraint name from message

68 Hibernate Access to constraint name ConstraintViolationException getconstraintname() Heavy for plain JDBC Hardcoded names

69 Hardcoded names try { // Insert user } catch (ConstraintViolationException e) { if (e.getconstraintname() == uk_user_name ) { // Handle error } } Too technical Focus on domain

70 Spring Dependency Injection Templates JDBC DAO

71 Spring JDBC JdbcTemplate SQLExceptionTranslator Error codes Register own classes No constraint name

72 Spring Consistent hierarchy Extensible DataAccessException DataIntegrityViolationException

73 Spring DAO ORM (e.g. Hibernate) PersistenceExceptionTranslator Proxy

74 UserRepository Spring$Proxy ConstraintViolation Exception JPASystemException PersistenceExceptionTranslator

75 Hierarchy DataAccessException JPASystemException cause ConstraintViolationException getconstraintname() No constraint name Weaker API

76 Weaker API Unsafe cast try { userrepository.save(user); } catch (JPASystemException e) { ConstraintViolationException ce = (ConstraintViolationException) e.getcause(); if (ce.getconstraintname() == uk_user_name ) { // Handle error } } Why isn t this easier?

77 Recap Best of both worlds Hibernate Spring JaRB Constraint name Hierarchy Extensible

78 JaRB Concrete and domain specific exceptions. Map each constraint to a custom exception.

79 try { userrepository.save(new User( Jan )); } catch (UserNameAlreadyExistsException e) { error( User name already exists. ); }

80 try { userrepository.save(new User( Jan )); } catch (UserNameAlreadyExistsException e) { error( User name already exists. ); } catch (User AlreadyExistsException e) { error( User already exists. ); }

81 Translator SQLIntegrity ConstraintException UserNameAlready ExistsException

82 Resolver Extract all information from exception SQLIntegrity ConstraintException ERROR: duplicate key value violates unique constraint \"uk_user_name\" Detail: Key (name)=(jan) already exists.

83 Resolver Extract all information from exception SQLIntegrity ConstraintException ERROR: duplicate key value violates unique constraint \"uk_user_name\" Detail: Key (name)=(jan) already exists. Constraint name Pattern matching Column name Value Vendor specific Version specific

84 Resolvers Pattern matching (default) PostgreSQL Oracle MySQL HSQL H2 Hibernate: constraint name only

85 Factory Create a concrete exception

86 Default factory InvalidTypeException LengthExceededViolationExceptio n CheckFailedException NotNullViolationException PrimaryKeyViolationException ForeignKeyViolationException UniqueKeyViolationException

87 DatabaseConstraintViolationException Constraint info InvalidTypeException LengthExceededViolationExceptio n CheckFailedException NotNullViolationException PrimaryKeyViolationException ForeignKeyViolationException UniqueKeyViolationException UserNameAlreadyExistsException

88 Custom uk_user_name ) public class UserNameAlreadyExistsException extends UniqueKeyViolationException { } Scanned from class path Registered on constraint

89 Custom exceptions uk_user_name UserNameAlreadyExistsException uk_user_ UniqueKeyViolationException

90 Injectable uk_user_name ) public class UserNameAlreadyExistsException extends UniqueKeyViolationException { UserNameAlreadyExistsException( ) { } } Throwable (cause) DatabaseConstraintViolation ExceptionFactory

91 Less concrete try { userrepository.save(new User( Jan )); } catch (UniqueKeyViolationException e) { error( User name already exists. ); }

92 How?

93 Enable in = org.myproject ) <jarb:enable-constraints base-package= org.myproject /> Enable exception translation Resolve database vendor Register custom exceptions Enable database validation

94 Get source Maven central <dependency> <groupid>org.jarbframework</groupid> <artifactid>jarb-constraints</artifactid> <version>2.1.0</version> </dependency> Github

95 Questions?