The truth first of all, or why the system needs to be designed based on the database device

Code generation

	for (Record2<String, String> record : DSL.using(configuration)
//   ^^^^^^^^^^^^^^^^^^^^^^^      
//     ,    
//   SELECT 
 
       .select(ACTOR.FIRST_NAME, ACTOR.LAST_NAME)
//           vvvvv ^^^^^^^^^^^^  ^^^^^^^^^^^^^^^  
       .from(ACTOR)
       .orderBy(1, 2)) {
    // ...
}

Source code generation

• There is some truth (internal or external) - for example, specification, data model, etc.
• We need a local representation of this truth in our programming language.

Type Providers and Annotation Processing

• You do not see the generated code (perhaps this situation seems to someone not so repulsive?)
• , , , «» . Lombok, “”. , .

?

	@Entity
class Book {
  @Id
  int id;
  String title;
}

	CREATE TABLE book (
  id INTEGER PRIMARY KEY GENERATED ALWAYS AS IDENTITY,
  title VARCHAR(50),
 
  CONSTRAINT pk_book PRIMARY KEY (id)
);
 
CREATE INDEX i_book_title ON book (title);

• Does Hibernate really apply the definition of this named primary key?
• Will Hibernate create an index in TITLE? “I know for sure that we will need him.”
• Does Hibernate exactly make this key identifiable in the Identity Specification?

	@Entity
@Table(name = "book", indexes = {
  @Index(name = "i_book_title", columnList = "title")
})
class Book {
  @Id
  @GeneratedValue(strategy = IDENTITY)
  int id;
  String title;
}

But then you have to pay for it

Database first

• What tablespace is your table in?
• What is its PCTFREE value?
• What is the size of the cache in your sequence (behind the identifier)

What about the client model?

	-- H2, HSQLDB, MySQL, PostgreSQL, SQL Server
SELECT table_schema, table_name
FROM information_schema.tables
 
-- DB2
SELECT tabschema, tabname
FROM syscat.tables
 
-- Oracle
SELECT owner, table_name
FROM all_tables
 
-- SQLite
SELECT name
FROM sqlite_master
 
-- Teradata
SELECT databasename, tablename
FROM dbc.tables

• If you use JDBC or Spring, you can create a set of string constants
• If using JPA, you can generate entities themselves
• If using jOOQ, you can generate the jOOQ meta-model

ALTER TABLE book RENAME COLUMN title TO book_title;

@Entity
@Table(name = "book", indexes = {
 
  //    ?
  @Index(name = "i_book_title", columnList = "book_title")
})
class Book {
  @Id
  @GeneratedValue(strategy = IDENTITY)
  int id;
 
  @Column("book_title")
  String bookTitle;
}

The only truth

• XSD is well understood
• XSD XML
• XSD
• XSD Java XJC

Databases: it's the same thing

Explanation

Exceptions

• When the circuit is unknown, and it must be opened. For example, you are a provider of a tool to help users navigate any scheme. Phew There is no code generation. But still - the database is above all.
• When a circuit should be generated on the fly to solve a certain problem. This example seems like a slightly fanciful version of the entity attribute value pattern , i.e., you really don't have a well-defined schema. In this case, it’s often impossible to be sure at all that an RDBMS is right for you.