SlimDbSync

SlimDbSync is a lightweight and simple-to-use library for updating database according to current entity model. No update scripts (Java, XML, JSon) are necessary - this is different from other change management systems like Liquibase. 2 lines of Java code is enough to configure and execute syncing.

Basic Usage

Establish database link:

Database db = new Database("org.postgresql.Driver", "jdbc:postgresql://localhost:5432/demoDB", "demouser", "password");
new SchemaGenerator(db).sync(Employee.class, EmployeeDetails.class);

Dependencies

Add SlimDbSync dependency into build.gradle:

dependencies {
    implementation 'eu.miltema:slim-db-sync:1.0.2'
}

or alternatively, if using Maven, then into pom.xml:

<dependencies>
  <dependency>
    <groupId>eu.miltema</groupId>
    <artifactId>slim-db-sync</artifactId>
    <version>x.y.z</version>
  </dependency>
</dependencies>

In addition, build.gradle or pom.xml must refer to database driver. For example, when using PostgreSQL, build.gradle contains:

dependencies {
    implementation 'eu.miltema:slim-db-sync:x.y.z'
    runtime 'org.postgresql:postgresql:42.2.5'
}

SlimDbSync itself depends on eu.miltema.slimorm and javax.persistence. These are resolved by build system automatically.

Annotations

SlimDbSync supports these javax.persistence annotations (listed with supported attributes) when declaring entities:

• @Table (name, uniqueConstraints) - without this annotation, SlimDbSync uses snake-case class name as table name. For example, class EmployeeDetails would be stored into table employee_details
• @Column (name, nullable, unique) - without this annotation, SlimDbSync uses snake-case field name as column name. For example, field dateOfBirth would be stored into column date_of_birth
• @Transient - annotation @Transient and Java modifier transient have the same effect: SlimDbSync will not create a column for this field in the database
• @Id - declares a primary key field. Only single-field primary keys are supported - composite primary keys are not. SlimDbSync generates a corresponding primary key
• @GeneratedValue - indicates that a sequence or identity is used as a default value for this column
• @ManyToOne - indicates that this is a foreign key field. Field type must be elementary type to store key value, not target entity class.
• @JSon - declares that this field will be stored as a JSon object. This is not a javax.persistence annotation, but SlimDbSync annotation
• @Indexes - this SlimDbSync annotation declares the indexes for this table. Several indexes can be declared, for example @Indexes({@Index("id"), @Index({"dateOfBirth", "name"})})

For example:

@Table(name="employees")
@Indexes(@Index("name"))
public class Employee {
	@Id
	@GeneratedValue
	int id;

	String name;

	@Column(name = "dob")
	LocalDate dateOfBirth;

	@Transient
	boolean isDirty;

	transient boolean isDirty2;

	@JSon Contract[] contracts;

	@ManyToOne
	Department department;
}

NB! Since most database designs have an auto-generated primary key with name id, then SlimDbSync has a special shorthand: a field with name id and without @Id is still treated as if both annotations were present. If this is not what You need, declare Your primary key with a different name or add @Id annotation to a different field.

SQL Dialects

By default, SlimDbSync uses PostgreSQL dialect.

Data Types

SlimDbSync supports these Java types: String, byte, Byte, short, Short, int, Integer, long, Long, float, Float, double, Double, BigDecimal, byte[], Timestamp, Instant, Date, LocalDate, LocalDateTime, ZonedDateTime, enum.

Be aware that PostgreSQL does not store timezone id into record (even when data type is with time zone). Therefore, all time-related columns store correct instant in time, but have lost the original timezone id.

Logging

To keep the amount of dependencies low, SlimDbSync is not logging automatically. To add logging (System.out, log4j, slf etc), add custom logger:

new DatabaseSync(db).
	setLogger(message -> System.out.println(message)).
	sync(entityClasses);