Java developers can use MariaDB Connector/R2DBC to connect to MariaDB database products using the Reactive Relational Database Connectivity (R2DBC) API. R2DBC operations are non-blocking, which makes R2DBC more scalable than Java's standard JDBC API.
DML (Data Manipulation Language) refers to all SQL-data statements in the SQL standard (ISO/IEC 9075-2:2016), for example: , , , , and .
With R2DBC, DML operations are performed with the following classes:
The following example shows how to insert data into the example table created in :
The bind (int index, Object value) method binds non-null values to indexed parameters. The index is an integer that starts at 0, and it should not be null. If the index is invalid, the method throws an IllegalArgumentException, which is handled in the catch block.
Alternatively, the bind (String name, Object value) method could be used to bind a non-null value to a named parameter.
The execute() method executes the statement and returns the results as a Publisher<? extends Result> instance.
Result instances must be fully consumed to ensure full execution of the corresponding Statement instance.
Confirm the data was properly inserted by using MariaDB Client to execute a SELECT statement:
SELECT is a DML (Data Manipulation Language) operation that reads the data from a table. The following example shows how to select data from the example table created in :
The Flux must be fully consumed to retrieve results, for which the method call sequence Flux.from(stmnt.execute()).flatMap(...) is used.
Results can be consumed only once by either consuming getRowsUpdated() or map(BiFunction) method in the Result class.
Result object maintains a consumption state that may be backed by a cursor pointing to its current row of data. A Result allows read-only and forward-only consumption of statement results. Thus, you can consume either getRowsUpdated()
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map(BiFunction)The sample application makes use of the map(BiFunction<Row, RowMetadata, ? extends T> mappingFunction) method.
The map method returns a mapping of the rows that are the results of a query against a database. It may be empty if the query did not return any rows. A Row can be only considered valid within a BiFunction mapping function callback. The mapping Function BiFunction maps a Row and RowMetadata to a value. It throws an IllegalArgumentException if mappingFunction is null, and throws IllegalStateException if the result was consumed.
In a Row object, which represents a row returned from a database query, values from columns can be retrieved either by specifying a column name using the get(String name) method, or by specifying the column index using the get(int index) method. The sample application retrieves data by column index. Columns are numbered from 0.
A row is invalidated after consumption in the Result.map(BiFunction) mapping function.
The number, type, and characteristics of columns are described through RowMetadata.
Use the Flux.toIterable() method to transform the Flux object into a lazy Iterable blocking on Iterator.next() calls.
io.r2dbc.spi.Statement
Creates a statement to execute on the server.
io.r2dbc.spi.Result
Contains the result-set from the server.
io.r2dbc.spi.Row
Contains a single row.
io.r2dbc.spi.RowMetadata
Contains metadata for a row.
//Module Imports
import org.mariadb.r2dbc.MariadbConnectionConfiguration;
import org.mariadb.r2dbc.MariadbConnectionFactory;
import io.r2dbc.spi.Connection;
import io.r2dbc.spi.Statement;
import reactor.core.publisher.Mono;
// Main Application Class
public class App {
// Connection Configuration
private static MariadbConnectionConfiguration conf;
private static MariadbConnectionFactory connFactory;
private static Connection conn;
// Main Process
public static void main(String[] args) {
//Initialize Connection Factory
initConnectionFactory();
// Insert a contact
insertContact("John", "Smith", "js@example.com");
}
public static void initConnectionFactory() {
try {
// Configure the Connection
conf = MariadbConnectionConfiguration.builder()
.host("192.0.2.1").port(3306)
.username("db_user").password("db_user_password")
.database("test").build();
// Instantiate a Connection Factory
connFactory = new MariadbConnectionFactory(conf);
}
catch (java.lang.IllegalArgumentException e) {
System.err.println("Issue encountered while getting connection");
e.printStackTrace();
}
}
public static void insertContact(String first_name, String last_name, String email) {
try {
//Initialize a Connection
conn = connFactory.create().block();
// Initialize Statement
Statement stmnt = conn.createStatement(
"INSERT INTO test.contact (first_name, last_name, email) VALUES (?, ?, ?)");
// Bind Values to Statement
stmnt.bind(0, first_name);
stmnt.bind(1, last_name);
stmnt.bind(2, email);
// Execute Statement
Mono.from(stmnt.execute()).subscribe();
}
// Catch Exception
catch (java.lang.IllegalArgumentException e) {
System.err.println("Issue encountered while adding contact");
e.printStackTrace();
} finally {
// Close Connection
conn.close();
}
}
}SELECT * FROM test.contact;+----+------------+-----------+----------------+
| id | first_name | last_name | email |
+----+------------+-----------+----------------+
| 1 | John | Smith | js@example.com |
+----+------------+-----------+----------------+//Module Imports
import org.mariadb.r2dbc.MariadbConnectionConfiguration;
import org.mariadb.r2dbc.MariadbConnectionFactory;
import io.r2dbc.spi.Connection;
import io.r2dbc.spi.Statement;
import io.r2dbc.spi.Result;
import io.r2dbc.spi.Row;
import io.r2dbc.spi.RowMetadata;
import reactor.core.publisher.Flux;
public class App {
// Connection Configuration
private static MariadbConnectionConfiguration conf;
private static MariadbConnectionFactory connFactory;
private static Connection conn;
public static void main(String[] argv) {
//Initialize Connection Factory
initConnectionFactory();
// Print contacts
printContactList();
}
public static void initConnectionFactory() {
try {
// Configure the Connection
conf = MariadbConnectionConfiguration.builder()
.host("192.0.2.1").port(3306)
.username("db_user").password("db_user_password")
.database("test").build();
// Instantiate a Connection Factory
connFactory = new MariadbConnectionFactory(conf);
}
catch (java.lang.IllegalArgumentException e) {
System.err.println("Issue encountered while getting connection");
e.printStackTrace();
} finally {
}
}
public static void printContactList() {
try {
//Initialize a Connection
conn = connFactory.create().block();
// Initialize Statement
Statement stmnt = conn.createStatement(
"SELECT first_name, last_name, email FROM test.contact");
// Execute Statement and Iterate over the Result-set
for (String contact_entry : Flux.from(stmnt.execute()).flatMap( res ->
res.map( (row, metadata) -> {
return String.format( "- %s %s <%s>",
// Get First Name
row.get(0, String.class),
// Get Last Name
row.get(1, String.class),
//Get Email
row.get(2, String.class));
})).toIterable()) {
System.out.println(contact_entry);
}
}
// Catch Exception
catch (java.lang.IllegalArgumentException e) {
System.err.println("Encountered issue querying contact list");
e.printStackTrace();
} finally {
// Close Connection
conn.close();
}
}
}John Smith <js@example.com>