Database Connectivity

JDBC

// 1. Import the package
import java.sql.*

// 2a. Load driver (driver for whichever database you are using)
// 2b. Register driver

Class.forName("com.mysql.jdbc.Driver");

// 3. Establish Connection
Connection con = DriverManager.getConnection("URL", "username", "password");

// 4. Create the statement
Statement st = con.createStatement();

// 5. Execute the query
ResultSet rs = st.executeQuery(query);
//OR
int count = st.executeUpdate(query);

// 6. Process Result
rs.next(); 
String s = rs.getString(columnNumber);


// 7. Close
st.close();
con.close();

Use PreparedStatement for user input

Use PreparedStatement instead of Statement to give user input in queries

query - (?,?) // question marks for parameters you want to take as user input in the query

Prepared Statement st = con.prepareStatement(query);
st.setInt(1, input1);
st.setString(2, input2);

JPA

Annotations

Entity and Mapping Annotations

• @Entity: Marks a class as a JPA entity.
• @Id: Primary Key within entity
  • @GeneratedValue: Specified how primary key is generated
    • Strategies: AUTO, IDENTITY, SEQUENCE, TABLE
• Optional Annotations to specify corresponding DB names for accurately mapping the entity. By default, names are directly mapped from the object.
  • @Table: Specifies DB table - default = entity name
  • @Column
• Relationships
  • @JoinColumn: Foreign Key
  • @JoinTable: Defines join table for many-to-many
  • Cardinality
    • @OneToOne
    • @OneToMany
    • @ManyToOne
    • @ManyToMany